EP3801281A1 - Method and system for determining the speed of sound in a fluid in the region of an implanted vascular support system - Google Patents

Method and system for determining the speed of sound in a fluid in the region of an implanted vascular support system

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Publication number
EP3801281A1
EP3801281A1 EP19729271.7A EP19729271A EP3801281A1 EP 3801281 A1 EP3801281 A1 EP 3801281A1 EP 19729271 A EP19729271 A EP 19729271A EP 3801281 A1 EP3801281 A1 EP 3801281A1
Authority
EP
European Patent Office
Prior art keywords
sound
reflector
fluid
speed
support system
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19729271.7A
Other languages
German (de)
French (fr)
Inventor
Thomas Alexander SCHLEBUSCH
Tobias Schmid
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kardion GmbH
Original Assignee
Kardion GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kardion GmbH filed Critical Kardion GmbH
Publication of EP3801281A1 publication Critical patent/EP3801281A1/en
Pending legal-status Critical Current

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M60/00—Blood pumps; Devices for mechanical circulatory actuation; Balloon pumps for circulatory assistance
    • A61M60/50—Details relating to control
    • A61M60/508—Electronic control means, e.g. for feedback regulation
    • A61M60/538—Regulation using real-time blood pump operational parameter data, e.g. motor current
    • A61M60/546—Regulation using real-time blood pump operational parameter data, e.g. motor current of blood flow, e.g. by adapting rotor speed
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/12—Diagnosis using ultrasonic, sonic or infrasonic waves in body cavities or body tracts, e.g. by using catheters
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/48—Diagnostic techniques
    • A61B8/488—Diagnostic techniques involving Doppler signals
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/52—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/5215—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of medical diagnostic data
    • A61B8/5223—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of medical diagnostic data for extracting a diagnostic or physiological parameter from medical diagnostic data
    • G—PHYSICS
    • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
    • G16H—HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA
    • G16H50/00—ICT specially adapted for medical diagnosis, medical simulation or medical data mining; ICT specially adapted for detecting, monitoring or modelling epidemics or pandemics
    • G16H50/30—ICT specially adapted for medical diagnosis, medical simulation or medical data mining; ICT specially adapted for detecting, monitoring or modelling epidemics or pandemics for calculating health indices; for individual health risk assessment
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/08—Clinical applications
    • A61B8/0883—Clinical applications for diagnosis of the heart
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M2205/00—General characteristics of the apparatus
    • A61M2205/33—Controlling, regulating or measuring
    • A61M2205/3375—Acoustical, e.g. ultrasonic, measuring means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M2205/00—General characteristics of the apparatus
    • A61M2205/70—General characteristics of the apparatus with testing or calibration facilities
    • A61M2205/702—General characteristics of the apparatus with testing or calibration facilities automatically during use

Definitions

  • the invention relates to a method for determining the speed of sound in a fluid in the region of an implanted vascular support system, a system for determining the speed of sound in a fluid in the region of an implanted vascular support system and an implantable, vascular support system.
  • the invention finds particular application in (fully) implanted left heart assist systems (LVAD).
  • LVAD left heart assist systems
  • An ultrasound Doppler measurement is suitable as a measuring method in which only a single ultrasound transducer is required as a transmitting and receiving element, which saves above all space in the implant.
  • the flow velocity can be calculated by the frequency shift through the Doppler effect:
  • the object of the invention is to specify a method and to provide a system with which the speed of sound in a fluid, in particular the speed of sound of blood in the region of an implanted, vascular support system can be determined.
  • a method for determining the speed of sound in a fluid in the region of an implanted, vascular support system comprising the following steps:
  • the vascular support system is preferably a cardiac support system, more preferably a ventricular assist system. Regularly, the support system serves to aid in the delivery of blood in the bloodstream of a human, and possibly patient.
  • the Support system may be at least partially arranged in a blood vessel.
  • the blood vessel is, for example, the aorta, in particular a left heart support system, or the common trunk (trunk pulmonalis) in the two pulmonary arteries, in particular in a right heart support system, preferably around the aorta.
  • the support system is preferably located at the exit of the left ventricle of the heart or left ventricle. Particularly preferably, the support system is arranged in aortic valve position.
  • the method is preferably for measuring the speed of sound in blood by means of ultrasound in a cardiac assist system.
  • the method may be for determining a fluid flow rate and / or a fluid volume flow from a ventricle of a heart, in particular from a (left) ventricle of a heart to the aorta in the region of a (fully) implanted (left) ventricular (heart -) support system.
  • the fluid is usually blood.
  • the sound velocity is preferably determined in a fluid flow or fluid volume flow which flows through the support system.
  • the method advantageously makes it possible to determine the speed of sound in the blood required for a (Doppler) measurement of the blood flow or flow rate, even outside the surgical scenario, with high quality, in particular by the implanted support system self.
  • FMCW (frequency modulated approach) -based analysis algorithm allows the explicit determination of the speed of sound so that the accuracy of the Doppler-based blood flow measurement is not affected by any uncertainty in the speed of sound.
  • the solution presented here is based, in particular, on supplementing a cardiac support system integrated Doppler volume flow sensor by one or more reflectors in a defined distance to the ultrasonic element, so that from the geometrically defined and known distance between the ultrasonic element and reflector and the measured pulse duration and / or beat frequency (so-called beat frequency) on the Sound velocity can be closed.
  • an ultrasound signal is emitted by means of an ultrasound sensor.
  • the ultrasound sensor preferably has an ultrasound element which, for example due to its oscillation, is designed to be able to emit one or more ultrasound signals.
  • the ultrasonic element is a piezoelectric element.
  • the ultrasonic sensor is preferably oriented so that an angle between the ultrasonic sound path and the main flow direction of the fluid is less than 5 °. It is also advantageous if the ultrasonic sensor is embodied in the manner of an ultrasound transducer which is set up both for transmitting and for receiving ultrasound signals, for example in that an ultrasound element can function as a transmitting and receiving element.
  • the emitted ultrasonic signal can also be referred to as a transmission signal and generally has a specific frequency and / or amplitude.
  • the transmission signal can also be pulsed or have at least one (in) pulse (in the pulse transit time approach).
  • the transmission signal can be influenced by frequency modulation, in particular for the determination of beat frequencies (in the FMCW approach).
  • the ultrasound signal is reflected on at least one sound reflector, which is in the field of view of the ultrasound sensor and at a (pre-) defined distance to the ultrasound sensor and / or to another sound (also arranged in the field of vision of the ultrasound sensor).
  • Reflector is arranged.
  • the field of view of the ultrasonic sensor is usually determined or clamped by its emission characteristic.
  • the Sound reflector arranged circumferentially along an inner circumference of a flow channel of the support system.
  • the at least one sound reflector projects at least partially into a flow path of the fluid or flow channel for the fluid through the support system. This flow path or channel can run, for example, through an (inlet) cannula or be formed by it.
  • the at least one sound reflector rotates along an (inner) surface of the cannula.
  • This defined distance between the ultrasonic sensor and the acoustic reflector is preferably in the range from 5 to 35 mm, in particular from 5 to 30 mm.
  • the at least one sound reflector may have at least one air-filled cavity.
  • the at least one sound reflector is preferably designed and / or aligned in such a way that it effects (only) a reflection or (only) reflection in the direction of the ultrasound sensor.
  • the at least one sound reflector is set up and / or aligned in such a way that it reflects incident ultrasonic waves or signals, in particular directly and / or only towards the ultrasonic sensor.
  • the at least one sound reflector is aligned so that a surface of the reflector is parallel to the incident ultrasonic wavefront.
  • the at least one sound reflector is a separate component to the further components (eg channel inner wall) of the support system which come into contact with the fluid.
  • the at least one sound reflector is attached or attached to a channel inner wall of the support system.
  • the reflected ultrasound signal is received.
  • the reflected ultrasound signal is received by means of the ultrasound sensor.
  • the received ultrasound signal can also be referred to as receive signal.
  • several reflected ultrasonic signals can also be received in step c).
  • the speed of sound in the fluid is determined using the reflected ultrasound signal.
  • the ultrasound signal can be evaluated or analyzed, for example, by means of an evaluation unit of the assistance system, in particular of the ultrasound sensor. In this case, a (pulse) runtime-based approach and / or a so-called FMCW-based approach can be exercised.
  • the ultrasound signal is reflected at at least two sound reflectors, which are arranged at different distances from the ultrasound sensor.
  • the two sound reflectors have a (pre-) defined distance from one another. This distance is preferably in the range of 1 to 10 mm.
  • the use of at least two reflectors at different distances advantageously makes it possible to further increase the accuracy, in particular since this makes it possible to compensate for uncertainties in the speed of sound of the impedance matching layer of the ultrasound transducer as well as tissue deposits possibly present thereon.
  • the at least one sound reflector has an acoustic impedance that is greater than the largest acoustic impedance of the fluid or less than the smallest acoustic impedance of the fluid.
  • the at least one sound reflector has an acoustic impedance that differs from the acoustic impedance of the fluid by at least 5 MRayl. If several sound reflectors are provided, they may have the same acoustic impedance or different acoustic impedances from each other.
  • the at least one sound reflector should have an acoustic impedance that is greater than the largest acoustic impedance of the fluid or less than the smallest acoustic impedance of the fluid.
  • the at least one sound reflector preferably has an acoustic impedance in the range from 2 to 80 MRayl. Further preferred is the at least one acoustic reflector with one or more of the following materials formed: titanium, medical grade stainless steel z. MP35N, platinum-iridium, NiTiNol.
  • the at least one sound reflector preferably has a reflection factor which is greater than the largest reflection factor of the fluid.
  • a reflection factor of the sound reflector is understood in particular to be the reflection factor of the boundary layer between the material of the sound reflector and the fluid.
  • a reflection factor of the fluid is understood to mean, in particular, the reflection factor of the boundary layer between blood cells and blood serum. If several sound reflectors are provided, they may have the same reflection factor or different reflection factors from each other. However, all existing sound reflectors should have a reflection factor that is greater than the largest reflection factor of the fluid.
  • the reflection factor of the at least one sound reflector is in the range of 0.3 to 0.99.
  • the at least one sound reflector is embedded in an embedding material.
  • the potting material preferably has an acoustic impedance that substantially corresponds to the acoustic impedance of the fluid.
  • a silicone may be used as the embedding material.
  • the embedding material preferably surrounds at least partially, preferably completely, the surface of the acoustic reflector facing towards the fluid.
  • the at least one sound reflector (by means of the embedding material) is embedded in a flat and / or smooth surface.
  • the at least one sound reflector is embedded (by means of the embedding material) in a surface whose maximum pitch is smaller than the maximum pitch of the outer surface of the sound reflector.
  • the sound velocity using a (pulse) runtime-based Evaluation algorithm is determined.
  • the speed of sound is preferably determined as a function of the defined distance at least between the ultrasonic sensor and the sound reflector or between two sound reflectors and at least one (measured) signal propagation time.
  • a cross-correlation in particular of the transmission pulse (pulse of the transmitted ultrasound signal) with the reception pulses (pulses of the received, reflected pulses reflected at the sound reflectors) delayed by the transit time (s), is particularly preferred. reflected ultrasound signals).
  • the sound velocity is determined using an FMCW-based evaluation algorithm.
  • FMCW stands for frequency-modulated continuous wave.
  • the sound velocity is preferably determined as a function of the defined distance at least between the ultrasonic sensor and the sound reflector or between two sound reflectors, a change in a frequency of an ultrasonic signal and at least one (resulting) beat frequency.
  • the speed of sound is determined as a function of the defined distance between the ultrasonic sensor and the sound reflector and / or between two sound reflectors, the slope of a frequency ramp and at least one (resulting) beat frequency.
  • a beat frequency is determined in the case of or for the FMCW-based evaluation algorithm.
  • the beat frequency can also be referred to as difference frequency and / or beat frequency.
  • the beat frequency from a superposition of the of the Ultrasonic sensor emitted ultrasonic signal (transmission signal) with the received from the ultrasonic sensor reflected ultrasonic signal (received signal) determines.
  • the number of dominant beat frequencies to be determined or determined corresponds to the number of (ultra) sound reflectors.
  • a discrete Fourier transformation (DFT) or fast Fourier transformation (FFT) can be used to determine the beat frequency.
  • a system for determining sound velocity in a fluid in the region of an implanted vascular support system comprising:
  • At least one sound reflector which is arranged in the field of view of the ultrasound sensor and at a defined distance at least to the ultrasound sensor or to another sound reflector.
  • At least two sound reflectors are arranged at different distances from the ultrasonic sensor. Furthermore, it is also preferred in the system when the at least one sound reflector is embedded in an embedding material.
  • an evaluation unit in which a pulse duration-based evaluation algorithm is stored.
  • an evaluation unit can be provided, in which an FMCW-based evaluation algorithm is stored.
  • the evaluation unit is preferably part of the support system, in particular of the ultrasonic sensor. Further preferably, the evaluation unit is set up to carry out a method proposed here.
  • the evaluation unit can have a memory in which the pulse duration-based evaluation algorithm and / or the FMCW-based evaluation algorithm is / are stored.
  • the evaluation unit a Microprocessor, which can access the memory.
  • the processing unit preferably receives data from an ultrasound element of the ultrasound sensor.
  • an implantable vascular support system comprising a system for determining the speed of sound proposed herein.
  • the support system is preferably a left ventricular cardiac assist system (LVAD) or a percutaneous, minimally invasive left ventricular assist system.
  • LVAD left ventricular cardiac assist system
  • this is preferably fully implantable.
  • the support system is located completely in the body of the patient and remains there.
  • the support system is set up or suitable for being able to be arranged at least partially in a ventricle, preferably the left ventricle of a heart and / or an aorta, in particular in the aortic valve position.
  • the support system comprises a cannula, in particular inlet cannula and a turbomachine, such as a pump.
  • the support system may further comprise an electric motor, which is regularly a part of the turbomachine.
  • the (inlet) cannula is preferably arranged so that it can lead fluid in the implanted state from a (left) ventricle of a heart to the flow machine.
  • the support system is preferably elongate and / or tubular.
  • the inlet cannula and the turbomachine are arranged in the region of opposite ends of the support system.
  • FIG. 2a is a detailed view of an implantable vascular support system
  • FIG. 2b is a detailed view of another implantable vascular support system
  • FIG. 4 shows an illustration of a system presented here
  • FIG. 5 shows an illustration of a pulse transit time-based approach that can be used here
  • FIG. 5 shows an illustration of a pulse transit time-based approach that can be used here
  • Fig. 6 is an illustration of an FMCW-based one usable here
  • FIG. 7 shows exemplary courses of real parts of impedances
  • Fig. 8a is a detail view of a system presented here
  • Fig. 8b is a detail view of another system presented here.
  • Fig. 1 shows schematically a flow of a method presented here in a regular operation.
  • the illustrated sequence of method steps a), b), c) and d) with the blocks 110, 120, 130 and 140 is merely exemplary.
  • an ultrasound signal is emitted by means of an ultrasound sensor.
  • the ultrasound signal is reflected on at least one sound reflector, which is arranged in the field of view of the ultrashort sensor and at a defined distance from the ultrasound sensor.
  • the reflected ultrasound signal is received.
  • the speed of sound in the fluid is determined using the reflected ultrasound signal.
  • the method steps a), b), and c) can also run at least partially in parallel or at the same time.
  • 2a schematically shows a detailed view of an implantable vascular support system 2.
  • FIG. 2b schematically shows a detailed view of another implantable vascular support system 2.
  • FIGS. 2a and 2b will be explained together below. The reference numbers are used uniformly.
  • FIG. 2 a shows the integration into a left ventricular microaxial pump in the aortic valve position and, in FIG. 2 b, the integration into an apically placed radial support system 2.
  • the flow direction of the fluid 1 is entered in Figures 2a and 2b by arrows.
  • an ultrasonic sensor 4 is provided, which is arranged in or on the support system 2.
  • the ultrasonic sensors 4 are exemplified in FIGS. 2a and 2b as ultrasonic transducers.
  • circumferential sound reflectors 5 are provided, which are arranged in the field of view 6 of the ultrasonic sensor 4 and each at a defined distance 7 to the ultrasonic sensor 4.
  • the flow channel can be formed in the interior of a (inlet) cannula (not shown here) of the support system 2.
  • the detailed view according to FIG. 2 a shows a tip of a support system 2 accommodating the ultrasonic sensor 4 with a micro-axial pump (not shown here).
  • a flow guide body 10 is placed here by way of example. This is not spaced apart from the ultrasound sensor 4 and is permeable to ultrasound signals.
  • the fluid 1 flows here in the direction of the pump.
  • the tip of the support system 2 shown in the detailed view according to FIG. 2 a can protrude into a ventricle (not shown here) of a heart in a preferred arrangement with the end shown here on the left, the pump at least partially in the aorta (not here) can be arranged). In this arrangement, the support system thus penetrates an aortic valve (not shown here).
  • FIG. 2b The detailed view of Fig. 2b relates to a support system 2, which is also referred to as apical radial pump.
  • the support system 2 has a turbomachine 1 1 (here pump), which discharges the fluid 1 in the radial direction as shown.
  • FIG. 3 shows schematically a radiation characteristic 12 of an ultrasonic element (not shown here).
  • FIG. 3 illustrates the field of view 6 of the ultrasound sensor (not shown here).
  • a field of view width 13 and along the abscissa (x-axis) a field of view length 14 can be measured.
  • the system comprises an ultrasound sensor 4 and two sound reflectors 5, which are arranged at different (defined) distance 7 from the ultrasound sensor 4.
  • the reflectors 5 protrude into the fluid 1 by way of example.
  • Each boundary layer between two acoustic impedances has a reflection factor at which a part of the sound energy is reflected in accordance with the quantity G.
  • the slightly different acoustic impedance of red blood cells and blood serum provides the reflected signal, which is usually used to calculate the Doppler frequency shift, from which the flow rate of the blood can be determined.
  • An (additional) reflector proposed here should preferably have the highest possible reflec- tion factor, which can be achieved in particular by an impedance mismatch with the blood, ie the acoustic impedance of the reflector should differ as clearly as possible from blood, for example by the reflector from an air-filled reflector Cavity or a metal is executed.
  • the method with only one reflector 5 can be faulty as soon as there is more than one unknown medium between the ultrasonic sensor 4 and the reflector 5.
  • the acoustic impedance (formula symbol: Zwi) and thus the speed of sound (symbol: Ci) of the matching layers 15 could change over the years due to water diffusion or it could lead to deposits 16 of cell layers (with their own acoustic impedance Zw 2 and sonic velocity C 2 ) on the ultrasonic sensor 4, so that an additional material layer of unknown thickness and / or unknown speed of sound is formed, as is illustrated in more detail in FIG. 4.
  • the differing sound velocities of the various media are entered by way of example in FIG. 4, namely the speed of sound Ci of the adaptation layers 15, the speed of sound C 2 of the deposits 16 and the speed of sound C3 of the fluid 1 (here: blood).
  • FIG. 5 schematically shows an illustration of a pulse duration-based approach that can be used here.
  • the pulse transit time-based approach reference will also be made to the depiction of the system according to FIG. 4.
  • the pulse transit time of the ultrasonic sensor 4 to the reflector 5 and back to the ultrasonic sensor 4 calculate. Since the mechanical structure of the (cardiac) support system 2 and thus the (defined) distance 7 between the ultrasound sensor 4 and the reflector 5 are known, it is possible according to the formula with the known (defined) distance 7 between the ultrasonic sensor 4 and the reflector 5 and t of the measured signal propagation time, the sought sound velocity c can be determined.
  • the sound velocity C 3 can be determined independently of the influence of additional layers between the ultrasonic sensor 4 and the reflector 5.
  • One possibility for determining the transit times t Ri and t R2 or t Ri -t R2 is the calculation of the cross-correlation 17 of the transmit pulse 3 (pulse of the transmitted ultrasound signal 3) with the delays delayed by the transit times t Ri or t R2 , at the ultrasonic reflectors 5 reflected receiving pulses 8 (pulses of the received, reflected ultrasonic signals 8).
  • the time-discrete cross-correlation 17 can be calculated for energy signal as follows: With R xy [n] the discrete cross-correlation at time n, the operator "star” as shorthand for the cross-correlation, x * [m] the conjugate complex transmission signal over all time shifts m and y [m + n] the received signal at time n all time shifts m.
  • FIG. 5 shows by way of example the result of this calculation.
  • the pulse of the emitted ultrasonic signal 3 the pulses of the received, reflected ultrasonic signals 8 and the (time-discrete) cross-correlation 17 are plotted against time 18. From the distance between z. B. the two peaks (peaks) in the cross-correlation signal 17 can - after the recalculation of the discrete time steps - the time interval t Ri - t R2 are determined.
  • Fig. 6 shows schematically an illustration of an FMCW-based approach which can be used here. In order to explain the illustration according to FIG. 6 or the FMCW-based approach, reference is also made to the illustration of the system according to FIG. 4.
  • the (ultra) sound reflectors 5 represent, in particular because of their high reflection factor, the dominant targets in the emission area of the ultrasonic sensor 4. Therefore, their beat frequencies (so-called beat frequencies) can be clearly recognized in the calculated spectrum. Since the mechanical structure of the (cardiac) support system and thus the distance between the ultrasound sensor 4 and the reflector 5 (symbol x) is known, the formula
  • the resulting beat frequency (beating frequency) in the baseband, the desired Schalgeschwindig- speed c are determined.
  • the reflectors 5 are fixed in place, the resulting beat frequency is influenced only by their distance from the ultrasound sensor 4 and the corresponding transit time of the frequency ramp in the fluid (here: blood) and, in particular, contains no speed-dependent component.
  • the beat frequency f beat.Ri is accordingly the frequency ramp reflected at the first reflector and the beat frequency fbeat, R2 of the frequency ramp reflected at the second reflector with S1 the thickness of the matching layers 15, S2 the thickness of the deposits 16, S3 the distance between deposits 16 and the first (left) reflector 5 and s 4 the distance between the first (left) reflector 5 and second (right) reflector fifth and with Ci the speed of sound in the matching layers 15, C2 the speed of sound in the deposits 16, C3 the speed of sound in the fluid 1 (here: blood).
  • the speed of sound C3 can be determined independently of the influence of additional layers between the ultrasonic sensor 4 and the reflector 5.
  • the ultrasonic frequency f o is hereby influenced by frequency modulation as an example. Sinusoidal, sawtooth, triangular or rectangular modulation types can be used. It is particularly preferable if the ultrasonic sensor or the ultrasonic element of the sensor provides a broadband resonance and that the ramp duration (symbol: T) much larger than the running time (so-called "time of flight") of the frequency ramps from the ultrasonic sensor 4 (ultrasonic transducer or transducer) to the (ultra) sound reflectors 5 and back again. The echoes of the successively transmitted, modulated ultrasonic frequency ramps reflected at the reflectors 5 are mixed down (superimposed) with the instantaneous transmission frequency ramp. The baseband signal thus generated contains the beat frequencies to be determined. These are transformed by the transformation into the frequency range z. As determined by discrete Fourier transform (DFT) or fast Fourier transformation (FFT).
  • DFT discrete Fourier transform
  • FFT fast Fourier transformation
  • FIG. 6 a possible implementation of the above-described FMCW-based approach by means of sawtooth modulation is shown.
  • the course of the frequency 19 over the time 18 is plotted.
  • both the ultrasound signal 3 (transmission signal) emitted by the ultrasound sensor and the reflected ultrasound signals 8 (reception signals) received by the ultrasound sensor are shaped in the manner of a sawtooth.
  • three are applied to the transmission signal 3 and mutually shifted reception signals 8, which would be the case, for example, if three ultrasound reflectors arranged at different distances from the ultrasound sensor were used.
  • the FMCW approach regularly uses a periodic frequency modulation, here periodic sawtooth modulation, which should be as linear as possible in order to achieve a high degree of accuracy in the measurement.
  • the modulation is usually carried out cyclically.
  • Such a passage from the lowest to the highest frequency is also called a burst (so-called burst).
  • the duration of a corresponding passage is entered in the upper diagram of FIG. 6 as a so-called chirp duration (chirp duration) 22.
  • chirp duration 23 is marked.
  • the ultrasonic sensor transmits here by way of example a linearly frequency-modulated signal with a sawtooth-shaped change of the transmission frequency 3. The same signal is received by the ultrasonic sensor after reflection on one of the ultrasonic reflectors.
  • the received signal 8 differs once in time, wherein the time difference 21 between the frequency jumps is usually proportional to the distance of the reflecting ultrasonic I-reflector from the ultrasonic sensor.
  • the difference frequency 20 between the transmission signal 3 and the reception signal 8 is the same at every point in time and is therefore also a measure of the distance of the reflecting ultrasonic reflector. This frequency difference can be evaluated in particular in the frequency domain.
  • a frequency spectrum 25 is generated here, for example, by Fieruntermixing / multiplication with the instantaneous transmission signal and by means of downstream fast Fourier transformation 24, in which the difference frequencies 20 are entered in addition to the background noise 26 are.
  • this is a multiplication of the received signal with the instantaneous transmission signal and subsequent Fourier transformation of the baseband time signal, from which the difference frequencies 20 result, which are also referred to here as beat frequencies or beat frequencies.
  • the particularly advantageous linearity can be achieved over the desired frequency band.
  • real parts 27 of the impedances of 8 MFIz piezo elements are plotted as an example over the stimulation frequency 28.
  • FIG. 8a shows schematically a detail view of a system presented here.
  • Fig. 8b shows schematically a detailed view of another system presented here.
  • FIGS. 8a and 8b will be explained together below.
  • the reference numerals are used uniformly.
  • the surface of the reflector should be parallel to the incident ultrasonic wavefront. Since uneven surfaces such as applied reflectors can cause turbulence in the flow (disadvantageous for the Doppler ultrasound measurement), the formation of thrombi as well as by occurring shear forces to additional blood damage (flaemolysis), it is expedient, the reflectors 5 with to embed an embedding material 9, as exemplified in Figures 8a and 8b.
  • the embedding material 9 is used here by way of example to provide a surface which is smoother in comparison to the reflector surface or a surface without corners and / or edges. It is particularly preferred, the to embed at least one reflector 5, in particular by means of the embedding material 9 in a flat surface.
  • the embedding material 9 should have an acoustic impedance that is as similar as possible to the fluid 1 (here: blood) and should be as thin as possible, so that no additional reflections or diffractions of the sound impulse occur, unless this additional diffraction is desired.
  • the or each reflector 5 with acoustic impedance C 4 can be embedded in a silicone with acoustic impedance C 3 ' , where C 3' is similar to the acoustic impedance C 3 of blood.
  • the solution presented here enables one or more of the following advantages:
  • the speed of sound can be determined from the resulting pulse transit time and / or ramp runtime by the reflector.

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Abstract

The invention relates to a method for determining the speed of sound in a fluid (1) in the region of an implanted vascular support system (2), comprising the following steps: a) emitting an ultrasonic signal (3) by means of an ultrasonic sensor (4); b) reflecting the ultrasonic signal (3) on at least one sound reflector (5), which is arranged in the field of vision (6) of the ultrasonic sensor (4) and at a defined distance at least from the ultrasonic sensor (4) or from a further sound reflector (5); c) receiving the reflected ultrasonic signal (8); determining the speed of sound in the fluid using the reflected ultrasonic signal (8).

Description

Verfahren und System zum Ermitteln der Schallgeschwindigkeit in einem Fluid im Bereich eines implantierten, vaskulären Unterstützungssystems  Method and system for determining the velocity of sound in a fluid in the region of an implanted vascular support system
Beschreibung description
Die Erfindung betrifft ein Verfahren zum Ermitteln der Schallgeschwindigkeit in einem Fluid im Bereich eines implantierten, vaskulären Unterstützungssys- tems, ein System zum Ermitteln der Schallgeschwindigkeit in einem Fluid im Bereich eines implantierten, vaskulären Unterstützungssystems sowie ein im- plantierbares, vaskuläres Unterstützungssystem. Die Erfindung findet insbe- sondere Anwendung bei (voll-)implantierten Linksherz-Unterstützungssyste- men (LVAD). The invention relates to a method for determining the speed of sound in a fluid in the region of an implanted vascular support system, a system for determining the speed of sound in a fluid in the region of an implanted vascular support system and an implantable, vascular support system. The invention finds particular application in (fully) implanted left heart assist systems (LVAD).
Die Kenntnis über das tatsächlich geförderte Blutvolumen eines Flerzunterstüt- zungssystems bzw. kardialen Unterstützungssystems ist medizinisch von gro- ßer Bedeutung, insbesondere zur Regelung des (implantierten) Unterstüt- zungssystems. The knowledge about the actually promoted blood volume of a vascular support system or cardiac support system is medically of great importance, in particular for the regulation of the (implanted) support system.
Daher wird an der Integration ultraschallbasierter Volumenstrom-Messtechnik in die Unterstützungssysteme gearbeitet. Als Messverfahren bietet sich eine Ultraschall-Doppler-Messung an, bei der lediglich ein einzelner Ultraschall- wandler als Sende- und Empfangselement erforderlich ist, was vor allem Bau- raum im Implantat spart. Die Flussgeschwindigkeit kann über die Frequenz- verschiebung durch den Doppler-Effekt berechnet werden: Therefore, the integration of ultrasound-based volume flow measurement technology into the support systems is being worked on. An ultrasound Doppler measurement is suitable as a measuring method in which only a single ultrasound transducer is required as a transmitting and receiving element, which saves above all space in the implant. The flow velocity can be calculated by the frequency shift through the Doppler effect:
Mit Af der resultierenden Doppler-Frequenzverschiebung, fo der Frequenz des ausgesendeten Ultraschall-Impulses, v der Flussgeschwindigkeit des Medi- ums, c der Schallgeschwindigkeit im Medium und a dem Winkel zwischen Ult- raschall-Schallpfad und Flauptströmungsrichtung. Bei einem (Herz-)Unterstützungssystem ist v gesucht, a in der Regel bekannt und fo bekannt. Die Schallgeschwindigkeit c ist nur näherungsweise bekannt und von Zusammensetzung und Eigenschaften des Blutes abhängig. Für eine hohe Messqualität ist es daher erforderlich, die Schallgeschwindigkeit c im Blut explizit durch Messung zu ermitteln. With Af the resulting Doppler frequency shift, f o the frequency of the emitted ultrasonic pulse, v the flow velocity of the medium, c the speed of sound in the medium and a the angle between ultrasound sound path and main flow direction. In a (cardiac) support system, v is searched, a usually known and known. The speed of sound c is only approximately known and depends on the composition and properties of the blood. For a high quality of measurement, it is therefore necessary to determine the speed of sound c in the blood explicitly by measurement.
Aufgabe der Erfindung ist es, ein Verfahren anzugeben und System bereitzu- stellen, mit dem die Schallgeschwindigkeit in einem Fluid, insbesondere die Schallgeschwindigkeit von Blut im Bereich eines implantierten, vaskulären Un- terstützungssystems bestimmt werden kann. The object of the invention is to specify a method and to provide a system with which the speed of sound in a fluid, in particular the speed of sound of blood in the region of an implanted, vascular support system can be determined.
Diese Aufgabe wird durch das in Anspruch 1 angegebene Verfahren und das in Anspruch 8 angegebene System gelöst. Vorteilhafte Ausführungsformen der Erfindung sind in den abhängigen Ansprüchen angegeben. This object is achieved by the method specified in claim 1 and the system specified in claim 8. Advantageous embodiments of the invention are indicated in the dependent claims.
Hier vorgeschlagen wird gemäß Anspruch 1 ein Verfahren zum Ermitteln der Schallgeschwindigkeit in einem Fluid im Bereich eines implantierten, vaskulä- ren Unterstützungssystems, umfassend folgende Schritte: According to claim 1, a method is proposed for determining the speed of sound in a fluid in the region of an implanted, vascular support system, comprising the following steps:
a) Aussenden eines Ultraschallsignals mittels eines Ultraschallsensors, b) Reflektieren des Ultraschallsignals an mindestens einem Schall-Reflek- tor, der im Sichtfeld des Ultraschallsensors und in einem definierten Ab- stand zumindest zum Ultraschallsensor oder zu einem weiteren Schall- Reflektor angeordnet ist, a) emitting an ultrasound signal by means of an ultrasound sensor, b) reflecting the ultrasound signal at at least one sound reflector, which is arranged in the field of view of the ultrasound sensor and at a defined distance at least to the ultrasound sensor or to another sound reflector;
c) Empfangen des reflektierten Ultraschallsignals, c) receiving the reflected ultrasound signal,
d) Ermitteln der Schallgeschwindigkeit in dem Fluid unter Verwendung des reflektierten Ultraschallsignals. d) determining the speed of sound in the fluid using the reflected ultrasound signal.
Das vaskuläre Unterstützungssystem ist bevorzugt ein kardiales Unterstüt- zungssystem, besonders bevorzugt ein ventrikuläres Unterstützungssystem. Regelmäßig dient das Unterstützungssystem zur Unterstützung der Förderung von Blut im Blutkreislauf eines Menschen, ggf. Patienten. Das Unterstützungssystem kann zumindest teilweise in einem Blutgefäß angeord- net sein. Bei dem Blutgefäß handelt es sich beispielsweise um die Aorta, ins- besondere bei einem Linksherz-Unterstützungssystem, oder um den gemein- samen Stamm (Truncus pulmonalis) in die beiden Lungenarterien, insbeson- dere bei einem Rechtsherz-Unterstützungssystem, bevorzugt um die Aorta. Das Unterstützungssystem ist bevorzugt am Ausgang des linken Ventrikels des Herzens bzw. der linken Herzkammer angeordnet. Besonders bevorzugt ist das Unterstützungssystem in Aortenklappenposition angeordnet. The vascular support system is preferably a cardiac support system, more preferably a ventricular assist system. Regularly, the support system serves to aid in the delivery of blood in the bloodstream of a human, and possibly patient. The Support system may be at least partially arranged in a blood vessel. The blood vessel is, for example, the aorta, in particular a left heart support system, or the common trunk (trunk pulmonalis) in the two pulmonary arteries, in particular in a right heart support system, preferably around the aorta. The support system is preferably located at the exit of the left ventricle of the heart or left ventricle. Particularly preferably, the support system is arranged in aortic valve position.
Das Verfahren dient vorzugsweise zur Messung der Schallgeschwindigkeit in Blut mittels Ultraschall in einem Herzunterstützungssystem. Das Verfahren kann zur Bestimmung einer Fluid-Strömungsgeschwindigkeit und/oder eines Fluid-Volumenstroms aus einem Ventrikel eines Herzens, insbesondere von einem (linken) Ventrikel eines Herzens hin zur Aorta im Bereich eines (voll- )implantierten, (links-)ventrikulären (Herz-)Unterstützungssystems beitragen. Bei dem Fluid handelt es sich regelmäßig um Blut. Bevorzugt wird die Schall geschwindigkeit in einem Fluidstrom bzw. Fluid-Volumenstrom bestimmt, der durch das Unterstützungssystem hindurch strömt. Das Verfahren ermöglich in vorteilhafter Weise, dass die für eine (Doppler-)Messung der Blut-Fluss- bzw. Strömungsgeschwindigkeit benötigte Schallgeschwindigkeit im Blut auch au- ßerhalb des OP-Szenarios mit hoher Qualität bestimmt werden kann, insbe- sondere durch das implantierte Unterstützungssystem selbst. The method is preferably for measuring the speed of sound in blood by means of ultrasound in a cardiac assist system. The method may be for determining a fluid flow rate and / or a fluid volume flow from a ventricle of a heart, in particular from a (left) ventricle of a heart to the aorta in the region of a (fully) implanted (left) ventricular (heart -) support system. The fluid is usually blood. The sound velocity is preferably determined in a fluid flow or fluid volume flow which flows through the support system. The method advantageously makes it possible to determine the speed of sound in the blood required for a (Doppler) measurement of the blood flow or flow rate, even outside the surgical scenario, with high quality, in particular by the implanted support system self.
Insbesondere durch die Integration eines oder mehrerer Schall-Reflektoren im Sichtfeld eines Doppler-Ultraschallsensors eines Herzunterstützungs-Sys- tems, insbesondere in Kombination mit der Ergänzung eines zusätzlichen Aus- wertealgorithmus, insbesondere eines zusätzlichenIn particular, by the integration of one or more sound reflectors in the field of view of a Doppler ultrasound sensor of a cardiac assist system, in particular in combination with the addition of an additional evaluation algorithm, in particular an additional one
FMCW(Frequenzmodulierter Ansatz)-basierten Auswertealgorithmus wird die explizite Bestimmung der Schallgeschwindigkeit ermöglicht, sodass die Ge- nauigkeit der Doppler-basierten Blutflussmessung nicht durch Unsicherheiten in der Schallgeschwindigkeit beeinflusst wird. Die hier vorgestellte Lösung fußt insbesondere auf einer Ergänzung eines Herzunterstützungssystems mit integriertem Doppler-Volumenstromsensor um ein oder mehrere Reflektoren in definiertem Abstand zum Ultraschall-Element, sodass aus der geometrisch definierten und bekannten Wegstrecke zwischen Ultraschall-Element und Re- flektor sowie der gemessenen Pulslaufzeit und/oder Schwebungsfrequenz (sog. Beat-Frequenz) auf die Schallgeschwindigkeit geschlossen werden kann. FMCW (frequency modulated approach) -based analysis algorithm allows the explicit determination of the speed of sound so that the accuracy of the Doppler-based blood flow measurement is not affected by any uncertainty in the speed of sound. The solution presented here is based, in particular, on supplementing a cardiac support system integrated Doppler volume flow sensor by one or more reflectors in a defined distance to the ultrasonic element, so that from the geometrically defined and known distance between the ultrasonic element and reflector and the measured pulse duration and / or beat frequency (so-called beat frequency) on the Sound velocity can be closed.
In Schritt a) erfolgt ein Aussenden eines Ultraschallsignals mittels eines Ultra- schallsensors. Hierzu weist der Ultraschallsensor vorzugsweise ein Ultra- schall-Element auf, das beispielsweise aufgrund seiner Schwingung dazu ein- gerichtet ist, ein oder mehrere Ultraschallsignale aussenden zu können. Be- sonders bevorzugt ist für das Ultraschall-Element ein Piezo-Element. Weiter- hin bevorzugt ist der Ultraschallsensor so ausgerichtet, dass ein Winkel zwi- schen Ultraschall-Schallpfad und Hauptströmungsrichtung des Fluids kleiner als 5° ist. Es ist auch vorteilhaft, wenn der Ultraschallsensor in der Art eines Ultraschallwandlers ausgeführt ist, der sowohl zum Senden als auch zum Empfangen von Ultraschallsignalen eingerichtet ist, beispielsweise dadurch, dass ein Ultraschall-Element als Sende- und Empfangselement fungieren kann. Das ausgesendete Ultraschallsignal kann auch als Sendesignal be- zeichnet werden und weist in der Regel eine bestimmte Frequenz und/oder Amplitude auf. Darüber hinaus kann das Sendesignal auch gepulst sein bzw. mindestens einen (Im-)Puls aufweisen (beim Pulslaufzeit-Ansatz). Weiterhin bevorzugt kann das Sendesignal durch Frequenzmodulation beeinflusst wer- den, insbesondere zur Bestimmung von Beat-Frequenzen (beim FMCW- Ansatz). In step a), an ultrasound signal is emitted by means of an ultrasound sensor. For this purpose, the ultrasound sensor preferably has an ultrasound element which, for example due to its oscillation, is designed to be able to emit one or more ultrasound signals. Particularly preferred for the ultrasonic element is a piezoelectric element. Furthermore, the ultrasonic sensor is preferably oriented so that an angle between the ultrasonic sound path and the main flow direction of the fluid is less than 5 °. It is also advantageous if the ultrasonic sensor is embodied in the manner of an ultrasound transducer which is set up both for transmitting and for receiving ultrasound signals, for example in that an ultrasound element can function as a transmitting and receiving element. The emitted ultrasonic signal can also be referred to as a transmission signal and generally has a specific frequency and / or amplitude. In addition, the transmission signal can also be pulsed or have at least one (in) pulse (in the pulse transit time approach). Further preferably, the transmission signal can be influenced by frequency modulation, in particular for the determination of beat frequencies (in the FMCW approach).
In Schritt b) erfolgt ein Reflektieren des Ultraschallsignals an mindestens ei- nem Schall-Reflektor, der im Sichtfeld des Ultraschallsensors und in einem (vor-)definierten Abstand zum Ultraschallsensor und/oder zu einem weiteren (ebenfalls im Sichtfeld des Ultraschallsensors angeordneten) Schall -Reflektor angeordnet ist. Das Sichtfeld des Ultraschallsensors wird üblicherweise durch dessen Abstrahlcharakteristik bestimmt bzw. aufgespannt. Bevorzugt ist der Schall-Reflektor entlang eines Innenumfangs eines Strömungskanals des Un- terstützungssystems umlaufend angeordnet. Bevorzugt ragt der mindestens eine Schall-Reflektor zumindest teilweise in einen durch das Unterstützungs- system hindurch verlaufenden Strömungsweg des Fluids bzw. Strömungska- nal für das Fluid hinein. Dieser Strömungsweg bzw. -kanal kann beispiels- weise durch eine (Einlauf-)Kanüle verlaufen bzw. durch diese gebildet sein. Hierbei ist es besonders bevorzugt, wenn der mindestens eine Schall-Reflek- tor entlang einer (Innen-)Oberfläche der Kanüle umläuft. Dieser definierte Ab- stand zwischen Ultraschallsensor und Schall-Reflektor liegt vorzugsweise im Bereich von 5 bis 35 mm, insbesondere von 5 bis 30 mm. In step b), the ultrasound signal is reflected on at least one sound reflector, which is in the field of view of the ultrasound sensor and at a (pre-) defined distance to the ultrasound sensor and / or to another sound (also arranged in the field of vision of the ultrasound sensor). Reflector is arranged. The field of view of the ultrasonic sensor is usually determined or clamped by its emission characteristic. Preferably, the Sound reflector arranged circumferentially along an inner circumference of a flow channel of the support system. Preferably, the at least one sound reflector projects at least partially into a flow path of the fluid or flow channel for the fluid through the support system. This flow path or channel can run, for example, through an (inlet) cannula or be formed by it. In this case, it is particularly preferred if the at least one sound reflector rotates along an (inner) surface of the cannula. This defined distance between the ultrasonic sensor and the acoustic reflector is preferably in the range from 5 to 35 mm, in particular from 5 to 30 mm.
Der mindestens eine Schall-Reflektor kann mindestens eine luftgefüllte Kavität aufweisen. Vorzugsweise ist der mindestens eine Schall-Reflektor so eingeri- chet und/oder ausgerichtet, dass er (nur) eine Reflexion bzw. (nur) Reflexio- nen in Richtung des Ultraschall-Sensors bewirkt. Mit anderen Worten ausge- drückt, ist der mindestens eine Schall-Reflektor so eingerichtet und/oder aus- gerichtet, dass er einfallende Ultraschall-Wellen bzw. -Signale insbesondere unmittelbar und/oder nur hin zu dem Ultraschall-Sensor reflektiert. Weiterhin bevorzugt ist der mindestens eine Schall-Reflektor so ausgerichtet, dass eine Oberfläche des Reflektors parallel zur einfallenden Ultraschall-Wellenfront liegt. Vorzugsweise ist der mindestens eine Schall-Reflektor ein zu den weite- ren mit dem Fluid in Kontakt kommenden Komponenten (z. B. Kanalinnen- wand) des Unterstützungssystems separates Bauteil. Bevorzugt ist der min- destens eine Schall-Reflektor an einer Kanalinnenwand des Unterstützungs- systems angebracht bzw. befestigt. The at least one sound reflector may have at least one air-filled cavity. The at least one sound reflector is preferably designed and / or aligned in such a way that it effects (only) a reflection or (only) reflection in the direction of the ultrasound sensor. In other words, the at least one sound reflector is set up and / or aligned in such a way that it reflects incident ultrasonic waves or signals, in particular directly and / or only towards the ultrasonic sensor. Further preferably, the at least one sound reflector is aligned so that a surface of the reflector is parallel to the incident ultrasonic wavefront. Preferably, the at least one sound reflector is a separate component to the further components (eg channel inner wall) of the support system which come into contact with the fluid. Preferably, the at least one sound reflector is attached or attached to a channel inner wall of the support system.
In Schritt c) erfolgt ein Empfangen des reflektierten Ultraschallsignals. Vor- zugsweise wird das reflektierte Ultraschallsignal mittels des Ultraschall-Sen- sors empfangen. Das empfangene Ultraschallsignal kann auch als Empfangs- signal bezeichnet werden. Insbesondere wenn mehrere Schall-Reflektoren vorgesehen sind, können in Schritt c) auch mehrere reflektierte Ultraschallsig- nale empfangen werden. In Schritt d) erfolgt ein Ermitteln der Schallgeschwindigkeit in dem Fluid unter Verwendung des reflektierten Ultraschallsignals. Hierzu kann das Ultraschall signal beispielsweise mittels einer Auswerteeinheit des Unterstützungssys- tems, insbesondere des Ultraschall-Sensors ausgewertet bzw. analysiert wer- den. Hierbei kann ein (Puls-)Laufzeit-basierter Ansatz und/oder ein sog. FMCW-basierter Ansatz ausgeübt werden. In step c), the reflected ultrasound signal is received. Preferably, the reflected ultrasound signal is received by means of the ultrasound sensor. The received ultrasound signal can also be referred to as receive signal. In particular, if a plurality of sound reflectors are provided, several reflected ultrasonic signals can also be received in step c). In step d), the speed of sound in the fluid is determined using the reflected ultrasound signal. For this purpose, the ultrasound signal can be evaluated or analyzed, for example, by means of an evaluation unit of the assistance system, in particular of the ultrasound sensor. In this case, a (pulse) runtime-based approach and / or a so-called FMCW-based approach can be exercised.
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass das Ultra- schallsignal an mindestens zwei Schall-Reflektoren reflektiert wird, die in un- terschiedlichem Abstand zum Ultraschallsensor angeordnet sind. In der Regel weisen die zwei Schall-Reflektoren einen (vor-)definierten Abstand zueinander auf. Dieser Abstand liegt bevorzugt im Bereich von 1 bis 10 mm. Die Verwen- dung von mindestens zwei Reflektoren in unterschiedlichem Abstand ermög- licht in vorteilhafter Weise, dass die Genauigkeit weiter gesteigert werden kann, insbesondere da dadurch Unsicherheiten in der Schallgeschwindigkeit der Impedanz-Anpassschicht des Ultraschallwandlers sowie möglicherweise darauf vorhandenen Gewebeablagerungen kompensiert werden können. Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass der mindes- tens eine Schall-Reflektor eine akustische Impedanz aufweist, die größer ist als die größte akustische Impedanz des Fluids oder kleiner ist als die kleinste akustische Impedanz des Fluids. Vorzugsweise weist der mindestens eine Schall-Reflektor eine akustische Impedanz auf, die sich um mindestens 5 MRayl von der akustischen Impedanz des Fluids unterscheidet. Wenn meh- rere Schall-Reflektoren vorgesehen sind, können diese dieselbe akustische Impedanz oder voneinander verschiedene akustische Impedanzen haben. Da- bei sollten jedoch alle vorhandenen Schall-Reflektoren eine akustische Impe- danz aufweisen, die jeweils größer ist als die größte akustische Impedanz des Fluids oder kleiner ist als die kleinste akustische Impedanz des Fluids. Weiter- hin bevorzugt weist der mindestens eine Schall-Reflektor eine akustische Im- pedanz im Bereich von 2 bis 80 MRayl auf. Weiterhin bevorzugt wird der mindestens eine Schall-Reflektor mit einem oder mehreren der folgenden Ma- terialien gebildet: Titan, medizinischer Edelstahl z. B. MP35N, Platin-Iridium, NiTiNol. According to an advantageous embodiment, it is proposed that the ultrasound signal is reflected at at least two sound reflectors, which are arranged at different distances from the ultrasound sensor. As a rule, the two sound reflectors have a (pre-) defined distance from one another. This distance is preferably in the range of 1 to 10 mm. The use of at least two reflectors at different distances advantageously makes it possible to further increase the accuracy, in particular since this makes it possible to compensate for uncertainties in the speed of sound of the impedance matching layer of the ultrasound transducer as well as tissue deposits possibly present thereon. According to an advantageous embodiment, it is proposed that the at least one sound reflector has an acoustic impedance that is greater than the largest acoustic impedance of the fluid or less than the smallest acoustic impedance of the fluid. Preferably, the at least one sound reflector has an acoustic impedance that differs from the acoustic impedance of the fluid by at least 5 MRayl. If several sound reflectors are provided, they may have the same acoustic impedance or different acoustic impedances from each other. However, all existing sound reflectors should have an acoustic impedance that is greater than the largest acoustic impedance of the fluid or less than the smallest acoustic impedance of the fluid. Furthermore, the at least one sound reflector preferably has an acoustic impedance in the range from 2 to 80 MRayl. Further preferred is the at least one acoustic reflector with one or more of the following materials formed: titanium, medical grade stainless steel z. MP35N, platinum-iridium, NiTiNol.
Weiterhin bevorzugt weist der mindestens eine Schall-Reflektor einen Reflexi- onsfaktor auf, der größer ist als der größte Reflexionsfaktor des Fluids. Unter einem Reflexionsfaktor des Schall-Reflektors wird hier insbesondere der Re- flexionsfaktor der Grenzschicht zwischen dem Material des Schall-Reflektors und dem Fluid verstanden. Unter einem Reflexionsfaktor des Fluids wird hier insbesondere der Reflexionsfaktor der Grenzschicht zwischen Blutkörperchen und Blutserum verstanden. Wenn mehrere Schall-Reflektoren vorgesehen sind, können diese denselben Reflexionsfaktor oder voneinander verschie- dene Reflexionsfaktoren haben. Dabei sollten jedoch alle vorhandenen Schall- Reflektoren einen Reflexionsfaktor aufweisen, der jeweils größer ist als der größte Reflexionsfaktor des Fluids. Vorzugsweise liegt der Reflexionsfaktor des mindestens einen Schall -Reflektors im Bereich von 0,3 bis 0,99. Furthermore, the at least one sound reflector preferably has a reflection factor which is greater than the largest reflection factor of the fluid. In this case, a reflection factor of the sound reflector is understood in particular to be the reflection factor of the boundary layer between the material of the sound reflector and the fluid. A reflection factor of the fluid is understood to mean, in particular, the reflection factor of the boundary layer between blood cells and blood serum. If several sound reflectors are provided, they may have the same reflection factor or different reflection factors from each other. However, all existing sound reflectors should have a reflection factor that is greater than the largest reflection factor of the fluid. Preferably, the reflection factor of the at least one sound reflector is in the range of 0.3 to 0.99.
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass der mindes- tens eine Schall-Reflektor in einem Einbettungsmaterial eingebettet ist. Das Einbettungsmaterial hat vorzugsweise eine akustische Impedanz, die im We- sentlichen der akustischen Impedanz des Fluids entspricht. Beispielsweise kann als Einbettungsmaterial ein Silikon verwendet werden. Weiterhin bevor- zugt umgibt das Einbettungsmaterial die hin zu dem Fluid weisende Oberflä- che des Schall-Reflektors zumindest teilweise, bevorzugt vollständig. Beson- ders bevorzugt ist der mindestens eine Schall-Reflektor (mittels des Einbet- tungsmaterials) in eine ebene und/oder glatte Oberfläche eingebettet. Vor- zugsweise ist der mindestens eine Schall-Reflektor (mittels des Einbettungs- materials) in eine Oberfläche eingebettet, deren maximale Steigung kleiner ist als die maximale Steigung der Außenoberfläche des Schall -Reflektors. According to an advantageous embodiment, it is proposed that the at least one sound reflector is embedded in an embedding material. The potting material preferably has an acoustic impedance that substantially corresponds to the acoustic impedance of the fluid. For example, a silicone may be used as the embedding material. Furthermore, the embedding material preferably surrounds at least partially, preferably completely, the surface of the acoustic reflector facing towards the fluid. Particularly preferably, the at least one sound reflector (by means of the embedding material) is embedded in a flat and / or smooth surface. Preferably, the at least one sound reflector is embedded (by means of the embedding material) in a surface whose maximum pitch is smaller than the maximum pitch of the outer surface of the sound reflector.
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass die Schall geschwindigkeit unter Verwendung eines (Puls-)Laufzeit-basierten Auswertealgorithmus ermittelt wird. Dies bedeutet mit anderen Worten insbe- sondere, dass zur Bestimmung der Schallgeschwindigkeit ein (Puls-)Laufzeit -basierter Auswertealgorithmus verwendet wird. Bevorzugt wird bei dem Puls- laufzeit-basierten Auswertealgorithmus die Schallgeschwindigkeit in Abhän- gigkeit des definierten Abstands zumindest zwischen Ultraschallsensor und Schall-Reflektor oder zwischen zwei Schall-Reflektoren und mindestens einer (gemessenen) Signallaufzeit bestimmt. Besonders bevorzugt wird zur Bestim- mung der Signallaufzeit(en) eine Kreuzkorrelation, insbesondere des Sende- pulses (Puls des ausgesendeten Ultraschallsignals) mit den durch die Lauf- zeit(en) verzögerten, an den Schall-Reflektoren reflektierten Empfangspulsen (Pulse der empfangenen, reflektierten Ultraschallsignale) verwendet. According to an advantageous embodiment, it is proposed that the sound velocity using a (pulse) runtime-based Evaluation algorithm is determined. In other words, this means in particular that a (pulse) transit time-based evaluation algorithm is used to determine the speed of sound. In the pulse transit time-based evaluation algorithm, the speed of sound is preferably determined as a function of the defined distance at least between the ultrasonic sensor and the sound reflector or between two sound reflectors and at least one (measured) signal propagation time. In order to determine the signal propagation time (s), a cross-correlation, in particular of the transmission pulse (pulse of the transmitted ultrasound signal) with the reception pulses (pulses of the received, reflected pulses reflected at the sound reflectors) delayed by the transit time (s), is particularly preferred. reflected ultrasound signals).
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass die Schall geschwindigkeit unter Verwendung eines FMCW-basierten Auswertealgorith- mus ermittelt wird. Dies bedeutet mit anderen Worten insbesondere, dass zur Bestimmung der Schallgeschwindigkeit ein FMCW-basierter Auswertealgo- rithmus verwendet wird. FMCW steht hierbei für frequenzmodulierter Dauer- strich (engl frequency modulated continuous wave). According to an advantageous embodiment, it is proposed that the sound velocity is determined using an FMCW-based evaluation algorithm. In other words, this means in particular that an FMCW-based evaluation algorithm is used to determine the speed of sound. FMCW stands for frequency-modulated continuous wave.
Bevorzugt wird bei dem FMCW-basierten Auswertealgorithmus die Schallge- schwindigkeit in Abhängigkeit des definierten Abstands zumindest zwischen Ultraschallsensor und Schall-Reflektor oder zwischen zwei Schall-Reflektoren, einer Änderung einer Frequenz eines Ultraschallsignals und mindestens einer (resultierenden) Schwebungsfrequenz bestimmt. Besonders bevorzugt wird die Schallgeschwindigkeit in Abhängigkeit des definierten Abstands zwischen Ultraschallsensor und Schall-Reflektor und/oder zwischen zwei Schall-Reflek- toren, der Steigung einer Frequenzrampe und mindestens einer (resultieren- den) Schwebungsfrequenz bestimmt.  In the FMCW-based evaluation algorithm, the sound velocity is preferably determined as a function of the defined distance at least between the ultrasonic sensor and the sound reflector or between two sound reflectors, a change in a frequency of an ultrasonic signal and at least one (resulting) beat frequency. Particularly preferably, the speed of sound is determined as a function of the defined distance between the ultrasonic sensor and the sound reflector and / or between two sound reflectors, the slope of a frequency ramp and at least one (resulting) beat frequency.
Bevorzugt wird bei dem bzw. für den FMCW-basierten Auswertealgorithmus eine Schwebungsfrequenz bestimmt. Die Schwebungsfrequenz kann auch als Differenzfrequenz und/oder Beat-Frequenz bezeichnet werden. Vorteilhafter- weise wird die Schwebungsfrequenz aus einer Überlagerung des von dem Ultraschallsensor ausgesendeten Ultraschallsignals (Sendesignals) mit dem von dem Ultraschallsensor empfangenen reflektierten Ultraschallsignal (Emp- fangssignal) bestimmt. In der Regel entspricht die Anzahl der zu bestimmen- den bzw. bestimmten, dominanten Schwebungsfrequenzen der Anzahl der (Ultra-)Schall-Reflektoren. Weiterhin bevorzugt kann zur Bestimmung der Schwebungsfrequenz eine Diskrete Fourier-Transformation (DFT) oder schnelle Fourier-Transformation (FFT) verwendet werden. Preferably, a beat frequency is determined in the case of or for the FMCW-based evaluation algorithm. The beat frequency can also be referred to as difference frequency and / or beat frequency. Advantageously, the beat frequency from a superposition of the of the Ultrasonic sensor emitted ultrasonic signal (transmission signal) with the received from the ultrasonic sensor reflected ultrasonic signal (received signal) determines. As a rule, the number of dominant beat frequencies to be determined or determined corresponds to the number of (ultra) sound reflectors. Furthermore, a discrete Fourier transformation (DFT) or fast Fourier transformation (FFT) can be used to determine the beat frequency.
Nach einem weiteren Aspekt wird ein System zum Ermitteln der Schallge- schwindigkeit in einem Fluid im Bereich eines implantierten, vaskulären Unter- stützungssystems vorgeschlagen, umfassend: In another aspect, a system for determining sound velocity in a fluid in the region of an implanted vascular support system is proposed, comprising:
einen Ultraschallsensor, der in oder an dem Unterstützungssystem an- geordnet ist,  an ultrasonic sensor disposed in or on the support system,
mindestens einen Schall-Reflektor, der im Sichtfeld des Ultra- schallsensors und in einem definierten Abstand zumindest zum Ultra schallsensor oder zu einem weiteren Schall -Reflektor angeordnet ist.  at least one sound reflector, which is arranged in the field of view of the ultrasound sensor and at a defined distance at least to the ultrasound sensor or to another sound reflector.
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass mindestens zwei Schall-Reflektoren in unterschiedlichem Abstand zum Ultraschallsensor angeordnet sind. Weiterhin ist es auch bei dem System bevorzugt, wenn der mindestens eine Schall-Reflektor in einem Einbettungsmaterial eingebettet ist. According to an advantageous embodiment, it is proposed that at least two sound reflectors are arranged at different distances from the ultrasonic sensor. Furthermore, it is also preferred in the system when the at least one sound reflector is embedded in an embedding material.
Nach einer vorteilhaften Ausgestaltung wird vorgeschlagen, dass eine Aus- werteeinheit vorgesehen ist, in der ein Pulslaufzeit-basierter Auswertealgorith- mus hinterlegt ist. Alternativ oder kumulativ kann eine Auswerteeinheit vorge- sehen sein, in der ein FMCW-basierter Auswertealgorithmus hinterlegt ist. Die Auswerteeinheit ist bevorzugt Bestandteil des Unterstützungssystems, insbe- sondere des Ultraschallsensors. Weiterhin bevorzugt ist die Auswerteeinheit eingerichtet zur Durchführung eines hier vorgeschlagenen Verfahrens. Die Auswerteeinheit kann einen Speicher aufweisen, in dem der Pulslaufzeit-ba- sierte Auswertealgorithmus und/oder der FMCW-basierte Auswertealgorith- mus hinterlegt ist bzw. sind. Darüber hinaus kann die Auswerteeinheit einen Mikroprozessor umfassen, der auf den Speicher zugreifen kann. Die Verarbei- tungseinheit empfängt vorzugsweise Daten von einem Ultraschallelement des Ultraschallsensors. According to an advantageous embodiment, it is proposed that an evaluation unit is provided in which a pulse duration-based evaluation algorithm is stored. Alternatively or cumulatively, an evaluation unit can be provided, in which an FMCW-based evaluation algorithm is stored. The evaluation unit is preferably part of the support system, in particular of the ultrasonic sensor. Further preferably, the evaluation unit is set up to carry out a method proposed here. The evaluation unit can have a memory in which the pulse duration-based evaluation algorithm and / or the FMCW-based evaluation algorithm is / are stored. In addition, the evaluation unit a Microprocessor, which can access the memory. The processing unit preferably receives data from an ultrasound element of the ultrasound sensor.
Nach einem weiteren Aspekt wird ein implantierbares, vaskuläres Unterstüt- zungssystem vorgeschlagen, umfassend ein hier vorgeschlagenes System zum Ermitteln der Schallgeschwindigkeit. Bei dem Unterstützungssystem han- delt es sich vorzugsweise um ein linksventrikuläres Herzunterstützungssystem (LVAD) bzw. ein perkutanes, minimalinvasives Linksherz-Unterstützungssys- tem. Weiterhin bevorzugt ist dieses voll-implantierbar. Das bedeutet mit ande- ren Worten insbesondere, dass das Unterstützungssystem sich vollständig im Körper des Patienten befindet und dort verbleibt. Besonders bevorzugt ist das Unterstützungssystem so eingerichtet bzw. dazu geeignet, dass es zumindest teilweise in einem Ventrikel, bevorzugt dem linken Ventrikel eines Herzens und/oder einer Aorta, insbesondere in Aortenklappenposition angeordnet wer- den kann. In another aspect, an implantable vascular support system is proposed, comprising a system for determining the speed of sound proposed herein. The support system is preferably a left ventricular cardiac assist system (LVAD) or a percutaneous, minimally invasive left ventricular assist system. Furthermore, this is preferably fully implantable. In other words, this means in particular that the support system is located completely in the body of the patient and remains there. Particularly preferably, the support system is set up or suitable for being able to be arranged at least partially in a ventricle, preferably the left ventricle of a heart and / or an aorta, in particular in the aortic valve position.
Weiterhin bevorzugt umfasst das Unterstützungssystem eine Kanüle, insbe- sondere Einlaufkanüle und eine Strömungsmaschine, wie etwa eine Pumpe. Das Unterstützungssystem kenn weiterhin einen Elektromotor aufweisen, der dabei regelmäßig ein Bestandteil der Strömungsmaschine ist. Die (Einlauf- )Kanüle ist vorzugsweise so eingerichtet, dass sie im implantierten Zustand Fluid aus einem (linken) Ventrikel eines Herzens hin zu der Strömungsma- schine führen kann. Das Unterstützungssystem ist vorzugsweise länglich und/oder schlauchartig gebildet. Bevorzugt sind die Einlaufkanüle und die Strömungsmaschine im Bereich einander gegenüberliegender Enden des Un- terstützungssystems angeordnet. Further preferably, the support system comprises a cannula, in particular inlet cannula and a turbomachine, such as a pump. The support system may further comprise an electric motor, which is regularly a part of the turbomachine. The (inlet) cannula is preferably arranged so that it can lead fluid in the implanted state from a (left) ventricle of a heart to the flow machine. The support system is preferably elongate and / or tubular. Preferably, the inlet cannula and the turbomachine are arranged in the region of opposite ends of the support system.
Die im Zusammenhang mit dem Verfahren erörterten Details, Merkmale und vorteilhaften Ausgestaltungen können entsprechend auch bei dem hier vorge- stellten System und/oder dem Unterstützungssystem auftreten und umgekehrt. Insoweit wird auf die dortigen Ausführungen zur näheren Charak- terisierung der Merkmale vollumfänglich Bezug genommen. The details, features and advantageous embodiments discussed in connection with the method can accordingly also occur in the system presented here and / or the support system, and vice versa. In that regard, reference is made in full to the statements there concerning the closer characterization of the features.
Die hier vorgestellte Lösung sowie deren technisches Umfeld werden nachfol- gend anhand der Figuren näher erläutert. Es ist darauf hinzuweisen, dass die Erfindung durch die gezeigten Ausführungsbeispiele nicht beschränkt werden soll. Insbesondere ist es, soweit nicht explizit anders dargestellt, auch möglich, Teilaspekte der in den Figuren erläuterten Sachverhalte zu extrahieren und mit anderen Bestandteilen und/oder Erkenntnissen aus anderen Figuren und/oder der vorliegenden Beschreibung zu kombinieren. Es zeigen schema- tisch: The solution presented here and its technical environment are explained in more detail below with reference to the figures. It should be noted that the invention should not be limited by the embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and / or findings from other figures and / or the present description. It shows schematically:
Fig. 1 einen Ablauf eines hier vorgestellten Verfahrens bei einem regulä- ren Betriebsablauf, 1 shows a sequence of a method presented here in a regular operating sequence,
Fig. 2a eine Detailansicht eines implantierbaren, vaskulären Unterstüt- zungssystems, 2a is a detailed view of an implantable vascular support system,
Fig. 2b eine Detailansicht eines weiteren implantierbaren, vaskulären Un- terstützungssystems, 2b is a detailed view of another implantable vascular support system,
Fig. 3 eine Abstrahlcharakteristik eines Ultraschallelements, Fig. 4 eine Veranschaulichung eines hier vorgestellten Systems, Fig. 5 eine Veranschaulichung eines hier verwendbaren Pulslaufzeit-ba- sierten Ansatzes, 4 shows an illustration of a system presented here, FIG. 5 shows an illustration of a pulse transit time-based approach that can be used here, FIG.
Fig. 6 eine Veranschaulichung eines hier verwendbaren FMCW-basierten Fig. 6 is an illustration of an FMCW-based one usable here
Ansatzes,  approach,
Fig. 7 beispielhafte Verläufe von Realteilen von Impedanzen, Fig. 8a eine Detailansicht eines hier vorgestellten Systems, und 7 shows exemplary courses of real parts of impedances, Fig. 8a is a detail view of a system presented here, and
Fig. 8b eine Detailansicht eines weiteren hier vorgestellten Systems. Fig. 8b is a detail view of another system presented here.
Fig. 1 zeigt schematisch einen Ablauf eines hier vorgestellten Verfahrens bei einem regulären Betriebsablauf. Die dargestellte Reihenfolge der Verfahrens- schritte a), b), c) und d) mit den Blöcken 110, 120, 130 und 140 ist lediglich beispielhaft. In Block 110 erfolgt ein Aussenden eines Ultraschallsignals mit- tels eines Ultraschallsensors. In Block 120 erfolgt ein Reflektieren des Ultra- schallsignals an mindestens einem Schall-Reflektor, der im Sichtfeld des Ult- raschallsensors und in einem definierten Abstand zum Ultraschallsensor an- geordnet ist. In Block 130 erfolgt ein Empfangen des reflektierten Ultraschall- signals. In Block 140 erfolgt ein Ermitteln der Schallgeschwindigkeit in dem Fluid unter Verwendung des reflektierten Ultraschallsignals. Fig. 1 shows schematically a flow of a method presented here in a regular operation. The illustrated sequence of method steps a), b), c) and d) with the blocks 110, 120, 130 and 140 is merely exemplary. In block 110, an ultrasound signal is emitted by means of an ultrasound sensor. In block 120, the ultrasound signal is reflected on at least one sound reflector, which is arranged in the field of view of the ultrashort sensor and at a defined distance from the ultrasound sensor. In block 130, the reflected ultrasound signal is received. In block 140, the speed of sound in the fluid is determined using the reflected ultrasound signal.
Insbesondere die Verfahrensschritte a), b), und c) können auch zumindest teil- weise parallel oder zeitgleich ablaufen. Fig. 2a zeigt schematisch eine Detailansicht eines implantierbaren, vaskulären Unterstützungssystems 2. Fig. 2b zeigt schematisch eine Detailansicht eines weiteren implantierbaren, vaskulären Unterstützungssystems 2. Die Figuren 2a und 2b werden nachfolgend gemeinsam erläutert. Die Bezugszeichen wer- den einheitlich verwendet. In particular, the method steps a), b), and c) can also run at least partially in parallel or at the same time. 2a schematically shows a detailed view of an implantable vascular support system 2. FIG. 2b schematically shows a detailed view of another implantable vascular support system 2. FIGS. 2a and 2b will be explained together below. The reference numbers are used uniformly.
Das hier vorgestellte Verfahren ist prinzipiell in alle Bauformen von Flerzunter- stützungssystemen integrierbar. Beispielhaft soll hier in Fig. 2a die Integration in eine linksventrikuläre Mikroaxialpumpe in Aortenklappenposition sowie in Fig. 2b die Integration in ein apikal platziertes radiales Unterstützungssystem 2 gezeigt werden. Die Strömungsrichtung des Fluids 1 ist in den Figuren 2a und 2b durch Pfeile eingetragen. Es ist jeweils ein Ultraschallsensor 4 vorgesehen, der in oder an dem Unterstützungssystem 2 angeordnet ist. Die Ultraschallsensoren 4 sind in den Figuren 2a und 2b beispielhaft als Ultraschall-Wandler ausgeführt. Zu dem sind jeweils zwei entlang eines Innenumfangs eines Strömungskanals des Unterstützungssystems 2 umlaufende Schall-Reflektoren 5 vorgesehen, die im Sichtfeld 6 des Ultraschallsensors 4 und jeweils in einem definierten Abstand 7 zum Ultraschallsensor 4 angeordnet sind. Der Strömungskanal kann insbesondere bei der Ausführungsform nach Fig. 2a im Innern einer (Ein- lauf-)Kanüle (hier nicht dargestellt) des Unterstützungssystems 2 gebildet sein. The method presented here can in principle be integrated into all types of Flerzunterstützungssystemen. By way of example, FIG. 2 a shows the integration into a left ventricular microaxial pump in the aortic valve position and, in FIG. 2 b, the integration into an apically placed radial support system 2. The flow direction of the fluid 1 is entered in Figures 2a and 2b by arrows. In each case, an ultrasonic sensor 4 is provided, which is arranged in or on the support system 2. The ultrasonic sensors 4 are exemplified in FIGS. 2a and 2b as ultrasonic transducers. To each of the two along an inner periphery of a flow channel of the support system 2 circumferential sound reflectors 5 are provided, which are arranged in the field of view 6 of the ultrasonic sensor 4 and each at a defined distance 7 to the ultrasonic sensor 4. In particular in the embodiment according to FIG. 2 a, the flow channel can be formed in the interior of a (inlet) cannula (not shown here) of the support system 2.
Die Detailansicht nach Fig. 2a zeigt eine den Ultraschallsensor 4 aufneh- mende Spitze eines Unterstützungssystems 2 mit einer Mikroaxialpumpe (hier nicht dargestellt). Unmittelbar vor dem Ultraschallsensor 4 ist hier beispielhaft ein Strömungs-Leitkörper 10 platziert. Dieser ist nicht zu dem Ultra- schallsensor 4 beabstandet und durchlässig für Ultraschallsignale. Das Fluid 1 strömt hier in Richtung der Pumpe. Die in der Detailansicht nach Fig. 2a gezeigte Spitze des Unterstützungssystems 2 kann in einer bevorzugten An- ordnung mit dem hier links dargestellten Ende in einen Ventrikel (hier nicht dargestellt) eines Herzens hinein ragen, wobei die Pumpe zumindest teilweise in der Aorta (hier nicht dargestellt) angeordnet sein kann. Bei dieser Anord- nung durchdringt das Unterstützungssystem somit eine Aortenklappe (hier nicht dargestellt). The detailed view according to FIG. 2 a shows a tip of a support system 2 accommodating the ultrasonic sensor 4 with a micro-axial pump (not shown here). Immediately before the ultrasonic sensor 4, a flow guide body 10 is placed here by way of example. This is not spaced apart from the ultrasound sensor 4 and is permeable to ultrasound signals. The fluid 1 flows here in the direction of the pump. The tip of the support system 2 shown in the detailed view according to FIG. 2 a can protrude into a ventricle (not shown here) of a heart in a preferred arrangement with the end shown here on the left, the pump at least partially in the aorta (not here) can be arranged). In this arrangement, the support system thus penetrates an aortic valve (not shown here).
Die Detailansicht nach Fig. 2b betrifft ein Unterstützungssystem 2, das auch als apikale Radialpumpe bezeichnet wird. Das Unterstützungssystem 2 weist eine Strömungsmaschine 1 1 (hier Pumpe) auf, die das Fluid 1 wie gezeigt in radialer Richtung austrägt. The detailed view of Fig. 2b relates to a support system 2, which is also referred to as apical radial pump. The support system 2 has a turbomachine 1 1 (here pump), which discharges the fluid 1 in the radial direction as shown.
In beiden exemplarischen Pumpenvarianten wird der Ultraschallsensor 4, ins- besondere ein Ultraschall-Element des Ultraschallsensors 4 üblicherweise derart platziert, dass der Winkel zur Strömung a = 0° (Null Grad) beträgt und somit eine bestmögliche Dopplerverschiebung realisiert werden kann. In both exemplary pump variants, the ultrasonic sensor 4, in particular an ultrasonic element of the ultrasonic sensor 4, is customary placed so that the angle to the flow a = 0 ° (zero degrees) and thus an optimum Doppler shift can be realized.
Fig. 3 zeigt schematisch eine Abstrahlcharakteristik 12 eines Ultraschallele- ments (hier nicht dargestellt). Die Abstrahlcharakteristik 12 eines Ultra- schallsensors bzw. eines Ultraschallelements des Ultraschallsensors ist in der Regel keulenförmig mit einer geradeaus gerichteten Hauptstrahlrichtung. Dies ist in Fig. 3 exemplarisch für einen Kreisscheiben-Ultraschall-Wandler(Trans- ducer) von 3 mm Durchmesser bei fo = 4 MHz gezeigt. Mit anderen Worten veranschaulicht Fig. 3 das Sichtfeld 6 des Ultraschallsensors (hier nicht dar- gestellt). Entlang der Ordinate (y-Achse) kann eine Sichtfeldbreite 13 und ent- lang der Abszisse (x-Achse) kann eine Sichtfeldlänge 14 gemessen werden. FIG. 3 shows schematically a radiation characteristic 12 of an ultrasonic element (not shown here). The emission characteristic 12 of an ultrasonic sensor or an ultrasound element of the ultrasonic sensor is generally club-shaped with a straight-line main radiation direction. This is shown in FIG. 3 by way of example for a circular disk ultrasound transducer (transducer) of 3 mm diameter at fo = 4 MHz. In other words, FIG. 3 illustrates the field of view 6 of the ultrasound sensor (not shown here). Along the ordinate (y-axis), a field of view width 13 and along the abscissa (x-axis) a field of view length 14 can be measured.
Fig. 4 zeigt schematisch eine Veranschaulichung eines hier vorgestellten Sys- tems. Das System umfasst einen Ultraschallsensor 4 und zwei Schall-Reflek- toren 5, die in unterschiedlichem (definierten) Abstand 7 zum Ultra- schallsensor 4 angeordnet sind. Die Reflektoren 5 ragen beispielhaft in das Fluid 1 hinein. 4 shows schematically an illustration of a system presented here. The system comprises an ultrasound sensor 4 and two sound reflectors 5, which are arranged at different (defined) distance 7 from the ultrasound sensor 4. The reflectors 5 protrude into the fluid 1 by way of example.
Jede Grenzschicht zwischen zwei akustischen Impedanzen weist einen Refle- xionsfaktor auf, an dem entsprechend der Größe G ein Teil der Schallenergie reflektiert wird. Each boundary layer between two acoustic impedances has a reflection factor at which a part of the sound energy is reflected in accordance with the quantity G.
Dabei ist Zwi die Wellenimpedanz vor der Sprungstelle sowie ZW2 die Wellen- impedanz nach der Sprungstelle. It is the wave impedance Z wi before the jump point, and Z W 2, the characteristic impedance after the jump point.
Die geringfügig unterschiedliche akustische Impedanz von roten Blutkörper- chen und Blutserum sorgt beispielsweise für das reflektierte Signal, das in der Regel zur Berechnung der Doppler-Frequenzverschiebung herangezogen wird, woraus die Strömungsgeschwindigkeit des Bluts ermittelt werden kann. Ein hier vorgeschlagener (zusätzlicher) Reflektor sollte vorzugsweise einen möglichst hohen Reflesionsfaktor aufweisen, was insbesondere durch eine Im- pedanzfehlanpassung zum Blut erreicht werden kann, das heißt die akustische Impedanz des Reflektors sollte sich möglichst deutlich von Blut unterscheiden, beispielsweise indem der Reflektor aus einer luftgefüllten Kavität oder einem Metall ausgeführt ist. The slightly different acoustic impedance of red blood cells and blood serum, for example, provides the reflected signal, which is usually used to calculate the Doppler frequency shift, from which the flow rate of the blood can be determined. An (additional) reflector proposed here should preferably have the highest possible reflec- tion factor, which can be achieved in particular by an impedance mismatch with the blood, ie the acoustic impedance of the reflector should differ as clearly as possible from blood, for example by the reflector from an air-filled reflector Cavity or a metal is executed.
Das Verfahren mit nur einem Reflektor 5 kann fehlerbehaftet sein, sobald sich zwischen Ultraschallsensor 4 und Reflektor 5 mehr als ein unbekanntes Me- dium befindet. Beispielsweise könnte sich die akustische Impedanz (Formel- zeichen: Zwi) und damit die Schallgeschwindigkeit (Formelzeichen: Ci) der Anpassschichten 15 durch Wasser-Diffusion über die Jahre ändern oder es könnte zu Ablagerungen 16 von Zellschichten (mit eigener akustischer Impe- danz Zw 2 und Schallgeschwindigkeit C2) auf dem Ultraschallsensor 4 kommen, sodass eine zusätzliche Materialschicht unbekannter Dicke und/oder unbe- kannter Schallgeschwindigkeit entsteht, wie dies in Fig. 4 näher veranschau- licht ist. In diesem Zusammenhang sind in Fig. 4 die sich unterscheidenden Schallgeschwindigkeiten der verschiedenen Medien beispielhaft eingetragen, nämlich die Schallgeschwindigkeit Ci der Anpassschichten 15, die Schallge- schwindigkeit C2 der Ablagerungen 16 sowie die Schallgeschwindigkeit C3 des Fluids 1 (hier: Blut). The method with only one reflector 5 can be faulty as soon as there is more than one unknown medium between the ultrasonic sensor 4 and the reflector 5. For example, the acoustic impedance (formula symbol: Zwi) and thus the speed of sound (symbol: Ci) of the matching layers 15 could change over the years due to water diffusion or it could lead to deposits 16 of cell layers (with their own acoustic impedance Zw 2 and sonic velocity C 2 ) on the ultrasonic sensor 4, so that an additional material layer of unknown thickness and / or unknown speed of sound is formed, as is illustrated in more detail in FIG. 4. In this context, the differing sound velocities of the various media are entered by way of example in FIG. 4, namely the speed of sound Ci of the adaptation layers 15, the speed of sound C 2 of the deposits 16 and the speed of sound C3 of the fluid 1 (here: blood).
Fig. 5 zeigt schematisch eine Veranschaulichung eines hier verwendbaren Pulslaufzeit-basierten Ansatzes. Zur Erläuterung der Darstellung nach Fig. 5 bzw. des Pulslaufzeit-basierten Ansatzes wird weiterhin auch auf die Veran- schaulichung des Systems gemäß Fig. 4 Bezug genommen. 5 schematically shows an illustration of a pulse duration-based approach that can be used here. In order to explain the illustration according to FIG. 5 or the pulse transit time-based approach, reference will also be made to the depiction of the system according to FIG. 4.
Zusätzlich zur kontinuierlich an jedem Streuteilchen des Fluids 1 (hier: Bluts; insbesondere am jeweiligen Übergang von Blutserum zu Blutkörperchen) re- flektierten Ultraschall-Leistung kommt es an den Reflektoren 5 zu deutlichen Echos, die in den empfangenen Amplituden-Zeit-Daten identifiziert werden können. Darüber hinaus lässt sich die Impulslaufzeit vom Ultraschallsensor 4 zum Reflektor 5 und zurück zum Ultraschallsensor 4 berechnen. Da der me- chanische Aufbau des (Herz-)Unterstützungssystems 2 und damit der (defi- nierte) Abstand 7 zwischen Ultraschallsensor 4 und Reflektor 5 bekannt ist, kann nach der Formel mit s dem bekannten (definierten) Abstand 7 zwischen Ultraschallsensor 4 und Reflektor 5 und t der gemessenen Signallaufzeit, die gesuchte Schallge- schwindigkeit c bestimmt werden. In addition to the ultrasound power continuously reflected at each scattering particle of the fluid 1 (here: blood, in particular at the respective transition from blood serum to blood corpuscles), clear reflections occur at the reflectors 5, which are identified in the received amplitude-time data can. In addition, the pulse transit time of the ultrasonic sensor 4 to the reflector 5 and back to the ultrasonic sensor 4 calculate. Since the mechanical structure of the (cardiac) support system 2 and thus the (defined) distance 7 between the ultrasound sensor 4 and the reflector 5 are known, it is possible according to the formula with the known (defined) distance 7 between the ultrasonic sensor 4 and the reflector 5 and t of the measured signal propagation time, the sought sound velocity c can be determined.
Bei Verwendung von zwei Reflektoren 5 mit unterschiedlichem Abstand 7, wie dies in Fig. 4 gezeigt ist, beträgt demnach die Laufzeit tRi des am ersten Re- flektor 5 gestreuten Impulses When using two reflectors 5 with different spacing 7, as shown in FIG. 4, the transit time t Ri of the pulse scattered at the first reflector 5 is accordingly
Und die Laufzeit tR2 des am zweiten Reflektor 5 gestreuten Impulses mit si der Dicke der Anpassschichten 15, S2 der Dicke der Ablagerungen 16, S3 dem Abstand zwischen Ablagerungen 16 und dem ersten (linken) Reflektor 5 und s4 dem Abstand zwischen erstem (linkem) Reflektor 5 und zweiten (rech- tem) Reflektor 5 sowie mit Ci der Schallgeschwindigkeit in den Anpassschich- ten 15, C2 der Schallgeschwindigkeit in den Ablagerungen 16, C3 der Schallge- schwindigkeit im Fluid 1 (hier: Blut). And the transit time t R 2 of the second reflector 5 scattered pulse with the thickness of the matching layers 15, S2 the thickness of the deposits 16, S3 the distance between deposits 16 and the first (left) reflector 5 and s 4 the distance between the first (left) reflector 5 and second (right) reflector fifth and with Ci the speed of sound in the matching layers 15, C2 the speed of sound in the deposits 16, C3 the speed of sound in the fluid 1 (here: blood).
Da die Anpassschichten 15 mit der Schallgeschwindigkeit Ci und die Ablage- rungen 16 mit der Schallgeschwindigkeit C2 gleichermaßen auf beide Impulse wirken, enthält die Differenz der Signallaufzeiten tR2 - tRi nur Komponenten im gesuchten bzw. hier relevanten (Fluid-)Bereich mit der (gesuchten) Schallge- schwindigkeit C3: Since the matching layers 15 with the speed of sound Ci and the deposits 16 with the speed of sound C2 equally on both pulses act, contains the difference of the signal delay t R2 - t Ri only components in the sought or relevant here (fluid) range with the (sought) sound velocity C3:
Da der Abstand s4 der beiden Reflektoren 5 zueinander bekannt ist, kann un- abhängig vom Einfluss von zusätzlichen Schichten zwischen Ultraschallsensor 4 und Reflektor 5 die Schallgeschwindigkeit C3 bestimmt werden. Since the distance s 4 of the two reflectors 5 is known to one another, the sound velocity C 3 can be determined independently of the influence of additional layers between the ultrasonic sensor 4 and the reflector 5.
Eine Möglichkeit zur Bestimmung der Laufzeiten tRi und tR2 bzw. tRi - tR2 ist die Berechnung der Kreuzkorrelation 17 des Sendepulses 3 (Puls des ausgesen- deten Ultraschallsignals 3) mit den durch die Laufzeiten tRi oder tR2 verzöger- ten, an den Ultraschall-Reflektoren 5 reflektierten Empfangspulsen 8 (Pulse der empfangenen, reflektierten Ultraschallsignale 8). Die zeitdiskrete Kreuz- korrelation 17 kann für Energiesignal wie folgt berechnet werden: Mit Rxy [ n ] der diskreten Kreuzkorrelation zum Zeitpunkt n, dem Operator „Stern“ als Kurzschreibweise für die Kreuzkorrelation, x* [ m ] dem konjugiert komplexen Sendesignal über alle Zeitverschiebungen m und y[m+n] dem Empfangssignal zum Zeitpunkt n über alle Zeitverschiebungen m . One possibility for determining the transit times t Ri and t R2 or t Ri -t R2 is the calculation of the cross-correlation 17 of the transmit pulse 3 (pulse of the transmitted ultrasound signal 3) with the delays delayed by the transit times t Ri or t R2 , at the ultrasonic reflectors 5 reflected receiving pulses 8 (pulses of the received, reflected ultrasonic signals 8). The time-discrete cross-correlation 17 can be calculated for energy signal as follows: With R xy [n] the discrete cross-correlation at time n, the operator "star" as shorthand for the cross-correlation, x * [m] the conjugate complex transmission signal over all time shifts m and y [m + n] the received signal at time n all time shifts m.
Die Darstellung nach Fig. 5 zeigt exemplarisch das Ergebnis dieser Berech- nung. In Fig. 5 sind der Puls des ausgesendeten Ultraschallsignals 3, die Pulse der empfangenen, reflektierten Ultraschallsignale 8 sowie die (zeitdiskrete) Kreuzkorrelation 17 über der Zeit 18 aufgetragen. Aus dem Abstand zwischen z. B. den beiden Spitzen (Peaks) im Kreuzkorrelationssignal 17 kann - nach der Rückrechnung der diskreten Zeitschritte - der zeitliche Abstand tRi - tR2 ermittelt werden. Fig. 6 zeigt schematisch eine Veranschaulichung eines hier verwendbaren FMCW-basierten Ansatzes. Zur Erläuterung der Darstellung nach Fig. 6 bzw. des FMCW-basierten Ansatzes wird weiterhin auch auf die Veranschaulichung des Systems gemäß Fig. 4 Bezug genommen. The illustration according to FIG. 5 shows by way of example the result of this calculation. In FIG. 5, the pulse of the emitted ultrasonic signal 3, the pulses of the received, reflected ultrasonic signals 8 and the (time-discrete) cross-correlation 17 are plotted against time 18. From the distance between z. B. the two peaks (peaks) in the cross-correlation signal 17 can - after the recalculation of the discrete time steps - the time interval t Ri - t R2 are determined. Fig. 6 shows schematically an illustration of an FMCW-based approach which can be used here. In order to explain the illustration according to FIG. 6 or the FMCW-based approach, reference is also made to the illustration of the system according to FIG. 4.
Die (Ultra-)Schall-Reflektoren 5 stellen insbesondere aufgrund ihres hohen Reflexionsfaktors die dominanten Ziele im Abstrahlbereich des Ultra- schallsensors 4 dar. Deshalb sind deren Schwebungsfrequenzen (sog. Beat- Frequenzen) deutlich im berechneten Spektrum zu erkennen. Da der mecha- nische Aufbau des (Herz-)Unterstützungssystems und damit der Abstand zwi- schen dem Ultraschall-Sensor 4 und dem Reflektor 5 (Formelzeichen x) be- kannt ist, kann nach der Formel The (ultra) sound reflectors 5 represent, in particular because of their high reflection factor, the dominant targets in the emission area of the ultrasonic sensor 4. Therefore, their beat frequencies (so-called beat frequencies) can be clearly recognized in the calculated spectrum. Since the mechanical structure of the (cardiac) support system and thus the distance between the ultrasound sensor 4 and the reflector 5 (symbol x) is known, the formula
mit sx dem bekannten Abstand zwischen Ultraschallsensor und Reflektor x, bw/T der Steigung der Frequenzrampe und fbeat.x der resultierenden Beat-Fre- quenz (Schwebungsfrequenz) im Basisband, die gesuchte Schalgeschwindig- keit c bestimmt werden. Insbesondere da die Reflektoren 5 ortsfest verbaut sind, wird die resultierende Beat-Frequenz nur von deren Abstand zum Ultra- schallsensor 4 und der entsprechenden Laufzeit der Frequenzrampe im Fluid (hier: Blut) beeinflusst und enthält insbesondere keinen geschwindigkeitsab- hängigen Anteil. with s x the known distance between the ultrasonic sensor and reflector x, bw / T of the slope of the frequency ramp and fbeat.x the resulting beat frequency (beating frequency) in the baseband, the desired Schalgeschwindig- speed c are determined. In particular, since the reflectors 5 are fixed in place, the resulting beat frequency is influenced only by their distance from the ultrasound sensor 4 and the corresponding transit time of the frequency ramp in the fluid (here: blood) and, in particular, contains no speed-dependent component.
Bei Verwendung von zwei Reflektoren 5 mit unterschiedlichem Abstand 7, wie dies in Fig. 4 gezeigt ist, beträgt demnach die Beat-Frequenz fbeat.Ri der am ersten Reflektor reflektierten Frequenzrampe und die Beat-Frequenz fbeat,R2 der am zweiten Reflektor reflektierten Frequenz- rampe mit S1 der Dicke der Anpassschichten 15, S2 der Dicke der Ablagerungen 16, S3 dem Abstand zwischen Ablagerungen 16 und dem ersten (linken) Reflektor 5 und s4 dem Abstand zwischen erstem (linkem) Reflektor 5 und zweiten (rech- tem) Reflektor 5 sowie mit Ci der Schallgeschwindigkeit in den Anpassschich- ten 15, C2 der Schallgeschwindigkeit in den Ablagerungen 16, C3 der Schallge- schwindigkeit im Fluid 1 (hier: Blut). When using two reflectors 5 with different spacing 7, as shown in FIG. 4, the beat frequency f beat.Ri is accordingly the frequency ramp reflected at the first reflector and the beat frequency fbeat, R2 of the frequency ramp reflected at the second reflector with S1 the thickness of the matching layers 15, S2 the thickness of the deposits 16, S3 the distance between deposits 16 and the first (left) reflector 5 and s 4 the distance between the first (left) reflector 5 and second (right) reflector fifth and with Ci the speed of sound in the matching layers 15, C2 the speed of sound in the deposits 16, C3 the speed of sound in the fluid 1 (here: blood).
Da die Anpassschichten 15 mit der Schallgeschwindigkeit Ci und die Ablage- rungen 16 mit der Schallgeschwindigkeit C2 gleichermaßen auf beide Fre- quenzrampen wirken, enthält die Differenz der Beat-Frequenzen fbeat,R2 - fbeat.Ri nur Komponenten im gesuchten bzw. hier relevanten (Fluid-)Bereich mit der (gesuchten) Schallgeschwindigkeit C3: Since the matching layers 15 with the speed of sound Ci and the deposits 16 with the speed of sound C2 act equally on both frequency ramps, the difference of the beat frequencies fbeat, R2-fbeat.Ri contains only components in the sought or relevant (fluid -) Range with the (sought) speed of sound C3:
Da der Abstand s4 der beiden Reflektoren 5 zueinander bekannt ist, kann un- abhängig vom Einfluss von zusätzlichen Schichten zwischen Ultraschallsensor 4 und Reflektor 5 die Schallgeschwindigkeit C3 bestimmt werden. Since the distance s 4 of the two reflectors 5 is known to one another, the speed of sound C3 can be determined independently of the influence of additional layers between the ultrasonic sensor 4 and the reflector 5.
Zur Bestimmung der Beat-Frequenzen wird hier beispielhaft die Ultraschallfre- quenz fo durch Frequenzmodulation beeinflusst. Es können unter anderem si- nusförmige, sägezahnförmige, dreieckförmige oder rechteckförmige Modulati- onsarten verwendet werden. Besonders zu bevorzugen ist es dabei, wenn der Ultraschallsensor bzw. das Ultraschall-Element des Sensors eine breitbandige Resonanz zur Verfügung stellt und dass die Rampendauer (Formelzeichen: T) sehr viel größer als die Laufzeit (sog.„Time of Flight“) der Frequenzrampen vom Ultraschallsensor 4 (Ultraschall-Wandler bzw. Transducer) zu den (Ultra- )Schall-Reflektoren 5 und wieder zurück ist. Die an den Reflektoren 5 reflek- tierten Echos der sukzessiv ausgesendeten, modulierten Ultraschallfrequenz- rampen werden mit der instantanen Sendefrequenzrampe heruntergemischt (überlagert). Das so erzeugte Basisbandsignal enthält die zu ermittelnden Beat-Frequenzen. Diese werden durch die Transformation in den Frequenz- bereich z. B. durch Diskrete Fourier-Transformation (DFT) oder schnelle Fou- rier-Transformation (FFT) bestimmt. To determine the beat frequencies, the ultrasonic frequency f o is hereby influenced by frequency modulation as an example. Sinusoidal, sawtooth, triangular or rectangular modulation types can be used. It is particularly preferable if the ultrasonic sensor or the ultrasonic element of the sensor provides a broadband resonance and that the ramp duration (symbol: T) much larger than the running time (so-called "time of flight") of the frequency ramps from the ultrasonic sensor 4 (ultrasonic transducer or transducer) to the (ultra) sound reflectors 5 and back again. The echoes of the successively transmitted, modulated ultrasonic frequency ramps reflected at the reflectors 5 are mixed down (superimposed) with the instantaneous transmission frequency ramp. The baseband signal thus generated contains the beat frequencies to be determined. These are transformed by the transformation into the frequency range z. As determined by discrete Fourier transform (DFT) or fast Fourier transformation (FFT).
In der Darstellung nach Fig. 6 ist eine mögliche Realisierung des vorangehend beschriebenen FMCW-basierten Ansatzes mittels einer Sägezahnmodulation gezeigt. In dem oberen Diagramm der Fig. 6 ist der Verlauf der Frequenz 19 über der Zeit 18 aufgetragen. Es ist zu erkennen, dass sowohl das von dem Ultraschallsensor ausgesendete Ultraschallsignal 3 (Sendesignal), als auch die (hier beispielhaft drei) von dem Ultraschallsensor empfangenen reflektier- ten Ultraschallsignale 8 (Empfangssignale) in der Art eines Sägezahns ge- formt sind. Hier sind beispielhaft drei zu dem Sendesignal 3 und zueinander verschobene Empfangssignale 8 aufgetragen, was beispielsweise der Fall wäre, wenn drei mit unterschiedlichem Abstand zum Ultraschall-Sensor ange- ordnete Ultraschall-Reflektoren zu Einsatz kämen. In the illustration according to FIG. 6, a possible implementation of the above-described FMCW-based approach by means of sawtooth modulation is shown. In the upper diagram of FIG. 6, the course of the frequency 19 over the time 18 is plotted. It can be seen that both the ultrasound signal 3 (transmission signal) emitted by the ultrasound sensor and the reflected ultrasound signals 8 (reception signals) received by the ultrasound sensor (here three by way of example) are shaped in the manner of a sawtooth. Here, by way of example, three are applied to the transmission signal 3 and mutually shifted reception signals 8, which would be the case, for example, if three ultrasound reflectors arranged at different distances from the ultrasound sensor were used.
Der FMCW-Ansatz arbeitet regelmäßig mit einer periodischen Frequenzmo- dulation, hier periodischen Sägezahnmodulation, die für einen hohen An- spruch an eine Genauigkeit der Messung möglichst zeitlinear sein sollte. Die Modulation wird üblicherweise zyklisch vorgenommen. Ein solcher Durchgang von der tiefsten bis zur höchsten Frequenz wird auch als Signalfolge (sog. Burst) bezeichnet. Die Dauer eines entsprechenden Durchgangs ist in dem oberen Diagramm der Fig. 6 als sog. Zirpen-Dauer (Chirp-Dauer) 22 eingetra- gen. Zudem ist eine nutzbare Zirpen-Dauer 23 markiert. Der Ultraschell-Sensor sendet hier beispielhaft ein linear frequenzmoduliertes Signal mit einer sägezahnförmigen Änderung der Sendefrequenz 3 aus. Das gleiche Signal wird nach einer Reflexion an einem der Ultraschall-Reflektoren vom Ultraschall-Sensor empfangen. Das empfangene Signal 8 unterscheidet sich einmal in der Zeit, wobei die Zeitdifferenz 21 zwischen den Frequenz- sprüngen in der Regel proportional zur Entfernung des reflektierenden Ultra- schal I-Reflektors vom Ultraschall-Sensor ist. Gleichzeitig ist (lineare Fre- quenzänderung vorausgesetzt) zu jedem Zeitpunkt die Differenzfrequenz 20 zwischen Sendesignal 3 und Empfangssignal 8 gleich und ist so ebenfalls ein Maß für die Entfernung des reflektierenden Ultraschall-Reflektors. Dieser Fre- quenzunterschied kann insbesondere im Frequenzbereich ausgewertet wer- den. The FMCW approach regularly uses a periodic frequency modulation, here periodic sawtooth modulation, which should be as linear as possible in order to achieve a high degree of accuracy in the measurement. The modulation is usually carried out cyclically. Such a passage from the lowest to the highest frequency is also called a burst (so-called burst). The duration of a corresponding passage is entered in the upper diagram of FIG. 6 as a so-called chirp duration (chirp duration) 22. In addition, a usable chirp duration 23 is marked. The ultrasonic sensor transmits here by way of example a linearly frequency-modulated signal with a sawtooth-shaped change of the transmission frequency 3. The same signal is received by the ultrasonic sensor after reflection on one of the ultrasonic reflectors. The received signal 8 differs once in time, wherein the time difference 21 between the frequency jumps is usually proportional to the distance of the reflecting ultrasonic I-reflector from the ultrasonic sensor. At the same time (assuming a linear frequency change), the difference frequency 20 between the transmission signal 3 and the reception signal 8 is the same at every point in time and is therefore also a measure of the distance of the reflecting ultrasonic reflector. This frequency difference can be evaluated in particular in the frequency domain.
Aus den Frequenzverläufen des oberen Diagramms in Fig. 6 wird hier beispiel- haft durch Fieruntermischen / Multiplikation mit dem instantanen Sendesignal und mittels nachgelagerter schnellen Fourier-Transformation 24 ein Frequenz- spektrum 25 generiert, in dem neben dem Grundrauschen 26 die Differenzfre- quenzen 20 eingetragen sind. Dabei erfolgt vereinfacht ausgedrückt eine Mul- tiplikation das Empfangssignals mit dem instantanen Sendesignal und an- schließender Fourier-Transformation des Basisband Zeitsignals, aus der die Differenzfrequenzen 20 resultieren, die hier auch als Schwebungsfrequenzen bzw. Beat-Frequenzen bezeichnet werden. From the frequency profiles of the upper diagram in FIG. 6, a frequency spectrum 25 is generated here, for example, by Fieruntermixing / multiplication with the instantaneous transmission signal and by means of downstream fast Fourier transformation 24, in which the difference frequencies 20 are entered in addition to the background noise 26 are. In simplified terms, this is a multiplication of the received signal with the instantaneous transmission signal and subsequent Fourier transformation of the baseband time signal, from which the difference frequencies 20 result, which are also referred to here as beat frequencies or beat frequencies.
Die minimale Abstandstrennbarkeit von FMCW-Systemen ist durch definiert. Dementsprechend kann bei einer Platzierung von zwei Ultraschall- Reflektoren 5, z. B. im Abstand von Ar = s4 = 6 mm zueinander, bei einer (zu erwartenden) Schallgeschwindigkeit im Blut c von etwa 1540 m/s (verwendet zur Bestimmung der ungefähr benötigten bzw. besonders vorteilhaften Band- breite) mit einer Bandbreite bw « 128 kFIz < 150 kFIz gearbeitet werden. Durch die zusätzliche Verwendung von Techniken wie z. B. das sog. Zero Pad- ding (Anhängen bzw. Auffüllen von Nullen) oder leistungsstarken (High-Per- formance) Frequenzschätzverfahren, kann jedoch eine wesentlich höhere Ab- standsgenauigkeit erreicht werden. Dies führt kann einer wesentlich genaue- ren Bestimmbarkeit der Schallgeschwindigkeit c in Blut beitragen. Die erreich- bare Genauigkeit hängt insbesondere vom Frequenzschätzverfahren und/o- der vom Signal zu Rausch Verhältnis ab. The minimum distance separability of FMCW systems is through Are defined. Accordingly, in a placement of two ultrasonic reflectors 5, z. At a distance of Ar = s 4 = 6 mm from each other, at an (expected) speed of sound in the blood c of about 1540 m / s (used to determine the required or particularly advantageous band width) with a bandwidth bw « 128 kFIz <150 kFIz are worked. Due to the additional use of techniques such. However, for example, so-called zero padding (appending or filling in zeros) or high-performance frequency estimation methods, a significantly higher distance accuracy can be achieved. This can contribute to a much more accurate determination of the speed of sound c in blood. The achievable accuracy depends in particular on the frequency estimation method and / or on the signal-to-noise ratio.
Insbesondere bei der Verwendung von Piezo-Elementen (als Ultraschall-Ele- mente), vorzugsweise mit durch sog. Backing (Verstärkung) reduzierter Güte der Resonanz (breitbandige Resonanz), kann die besonders vorteilhafte Line- arität über das gewünschte Frequenzband erreicht werden. In der Darstellung nach Fig. 7 sind beispielhaft Realteile 27 der Impedanzen von 8 MFIz Piezo- Elementen über der Stimulationsfrequenz 28 aufgetragen. Im gezeigten Fall könnte im in grau hinterlegten Frequenzband 29 eine Frequenzrampe mit der beispielhaft verwendeten Bandbreite bw = 150 kFIz platziert werden. Particularly when using piezoelectric elements (as ultrasonic elements), preferably with a reduced quality of the resonance (broadband resonance) due to so-called backing, the particularly advantageous linearity can be achieved over the desired frequency band. In the illustration according to FIG. 7, real parts 27 of the impedances of 8 MFIz piezo elements are plotted as an example over the stimulation frequency 28. In the case shown, a frequency ramp with the bandwidth bw = 150 kFIz used by way of example could be placed in the frequency band 29 deposited in gray.
Fig. 8a zeigt schematisch eine Detailansicht eines hier vorgestellten Systems. Fig. 8b zeigt schematisch eine Detailansicht eines weiteren hier vorgestellten Systems. Die Figuren 8a und 8b werden nachfolgend gemeinsam erläutert. Die Bezugszeichen werden einheitlich verwendet. Fig. 8a shows schematically a detail view of a system presented here. Fig. 8b shows schematically a detailed view of another system presented here. FIGS. 8a and 8b will be explained together below. The reference numerals are used uniformly.
Zur bestmöglichen Reflexion sollte die Oberfläche des Reflektors parallel zur einfallenden Ultraschall-Wellenfront liegen. Da unebene Oberflächen wie auf- gesetzte Reflektoren zu Verwirbelungen in der Strömung (nachteilig für die Doppler-Ultraschallmessung), zur Bildung von Thromben sowie durch auftre- tende Scherkräfte zu einer zusätzlichen Blutschädigung (Flaemolyse) führen können, ist es zweckmäßig, die Reflektoren 5 mit einem Einbettungsmaterial 9 einzubetten, wie dies in den Figuren 8a und 8b beispielhaft veranschaulicht ist. Das Einbettungsmaterial 9 ist hier beispielhaft dazu genutzt, eine im Ver- gleich zu der Reflektoroberfläche glattere Oberfläche bzw. eine Oberfläche ohne Ecken und/oder Kanten bereitzustellen. Besonders bevorzugt ist es, den mindestens einen Reflektor 5, insbesondere mittels des Einbettungsmaterials 9 in eine ebene Oberfläche einzubetten. Das Einbettungsmaterial 9 sollte da- bei eine dem Fluid 1 (hier: Blut) möglichst gleiche akustische Impedanz auf- weisen und möglichst dünn sein, sodass es nicht zu zusätzlichen Reflexionen oder Beugungen des Schallimpulses kommt, außer diese zusätzliche Beu- gung ist gewünscht. Beispielsweise kann der bzw. jeder Reflektor 5 mit akus- tischer Impedanz C4 in ein Silikon mit akustischer Impedanz C3' eingebettet sein, wobei C3' der akustischen Impedanz C3 von Blut ähnelt. Die hier vorgestellte Lösung ermöglich insbesondere einen oder mehrere der nachfolgenden Vorteile: For best reflection, the surface of the reflector should be parallel to the incident ultrasonic wavefront. Since uneven surfaces such as applied reflectors can cause turbulence in the flow (disadvantageous for the Doppler ultrasound measurement), the formation of thrombi as well as by occurring shear forces to additional blood damage (flaemolysis), it is expedient, the reflectors 5 with to embed an embedding material 9, as exemplified in Figures 8a and 8b. The embedding material 9 is used here by way of example to provide a surface which is smoother in comparison to the reflector surface or a surface without corners and / or edges. It is particularly preferred, the to embed at least one reflector 5, in particular by means of the embedding material 9 in a flat surface. The embedding material 9 should have an acoustic impedance that is as similar as possible to the fluid 1 (here: blood) and should be as thin as possible, so that no additional reflections or diffractions of the sound impulse occur, unless this additional diffraction is desired. For example, the or each reflector 5 with acoustic impedance C 4 can be embedded in a silicone with acoustic impedance C 3 ' , where C 3' is similar to the acoustic impedance C 3 of blood. In particular, the solution presented here enables one or more of the following advantages:
• Durch Ergänzung von mindestens einem Ultraschallreflektor im Abstrahl- bereich des Ultraschallsystems kann aus der resultierenden Pulslaufzeit und/oder Rampenlaufzeit vom Reflektor die Schallgeschwindigkeit ermit- telt werden.  • By supplementing at least one ultrasonic reflector in the emission area of the ultrasound system, the speed of sound can be determined from the resulting pulse transit time and / or ramp runtime by the reflector.
• Bekannte Schallgeschwindigkeit erhöht die Messgenauigkeit der Fluss- messung.  • Known speed of sound increases the measuring accuracy of the flow measurement.
• Schallgeschwindigkeit ist von der Zusammensetzung des Blutes abhän- gig und kann hier direkt ermittelt und eingesetzt werden.  • Speed of sound depends on the composition of the blood and can be determined and used directly here.
· Bei dem FMCW-Ansatz muss keine sehr genaue Zeitdifferenz gemessen werden, sondern es kann ein äquivalenter Frequenzunterschied be- stimmt werden, was den technischen Aufwand erheblich reduziert. · With the FMCW approach, it is not necessary to measure a very precise time difference, but an equivalent frequency difference can be determined, which considerably reduces the technical complexity.

Claims

Patentansprüche claims
1 . Verfahren zum Ermitteln der Schallgeschwindigkeit in einem Fluid (1 ) im Bereich eines implantierten, vaskulären Unterstützungssystems (2), um- fassend folgende Schritte: 1 . Method for determining the speed of sound in a fluid (1) in the region of an implanted vascular support system (2), comprising the following steps:
a) Aussenden eines Ultraschallsignals (3) mittels eines Ultra- schallsensors (4),  a) emitting an ultrasound signal (3) by means of an ultrasound sensor (4),
b) Reflektieren des Ultraschallsignals (3) an mindestens einem Schall- Reflektor (5), der im Sichtfeld (6) des Ultraschallsensors (4) und in einem definierten Abstand zumindest zum Ultraschallsensor (4) o- der zu einem weiteren Schall-Reflektor (5) angeordnet ist, c) Empfangen des reflektierten Ultraschallsignals (8),  b) reflecting the ultrasound signal (3) on at least one sound reflector (5) in the field of view (6) of the ultrasound sensor (4) and at a defined distance at least to the ultrasound sensor (4) or to another sound reflector ( 5), c) receiving the reflected ultrasonic signal (8),
d) Ermitteln der Schallgeschwindigkeit in dem Fluid unter Verwendung des reflektierten Ultraschallsignals (8).  d) determining the speed of sound in the fluid using the reflected ultrasound signal (8).
2. Verfahren nach Anspruch 1 , wobei das Ultraschallsignal (3) an mindes- tens zwei Schall-Reflektoren (5) reflektiert wird, die in unterschiedlichem Abstand (7) zum Ultraschallsensor (4) angeordnet sind. 2. The method of claim 1, wherein the ultrasonic signal (3) at least two sound reflectors (5) is reflected, which are arranged at different distances (7) to the ultrasonic sensor (4).
3. Verfahren nach Anspruch 1 oder 2, wobei der mindestens eine Schall- Reflektor (5) eine akustische Impedanz aufweist, die größer ist als die größte akustische Impedanz des Fluids (1 ) oder kleiner ist als die kleinste akustische Impedanz des Fluids (1 ). 3. The method of claim 1 or 2, wherein the at least one acoustic reflector (5) has an acoustic impedance that is greater than the largest acoustic impedance of the fluid (1) or less than the smallest acoustic impedance of the fluid (1). ,
4. Verfahren nach einem der vorhergehenden Ansprüche, wobei der min- destens eine Schall-Reflektor (5) in einem Einbettungsmaterial (9) einge- bettet ist. 4. Method according to one of the preceding claims, wherein the at least one sound reflector (5) is embedded in an embedding material (9).
5. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Schall geschwindigkeit unter Verwendung eines Pulslaufzeit-basierten Auswer- tealgorithmus ermittelt wird. 5. The method according to any one of the preceding claims, wherein the sound velocity using a pulse duration-based evaluation algorithm is determined.
6. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Schall geschwindigkeit unter Verwendung eines FMCW-basierten Auswerteal- gorithmus ermittelt wird. 6. The method according to any one of the preceding claims, wherein the sound velocity is determined using an FMCW-based Auswerteal- ergorithmus.
7. Verfahren nach Anspruch 6, wobei eine Schwebungsfrequenz bestimmt wird. 7. The method of claim 6, wherein a beat frequency is determined.
8. System zum Ermitteln der Schallgeschwindigkeit in einem Fluid (1 ) im Bereich eines implantierten, vaskulären Unterstützungssystems (2), um- fassend: 8. System for determining the speed of sound in a fluid (1) in the region of an implanted vascular support system (2), comprising:
einen Ultraschallsensor (4), der in oder an dem Unterstützungssys- tem (2) angeordnet ist,  an ultrasonic sensor (4) arranged in or on the support system (2),
mindestens einen Schall-Reflektor (5), der im Sichtfeld (6) des Ult- raschallsensors (4) und in einem definierten Abstand zumindest zum Ultraschallsensor (4) oder zu einem weiteren Schall -Reflektor (5) angeordnet ist.  at least one sound reflector (5) which is arranged in the field of view (6) of the ultrasonic sensor (4) and at a defined distance at least to the ultrasonic sensor (4) or to a further sound reflector (5).
9. System nach Anspruch 8, wobei mindestens zwei Schall-Reflektoren (5) in unterschiedlichem Abstand (7) zum Ultraschallsensor (4) angeordnet sind. 9. System according to claim 8, wherein at least two sound reflectors (5) at different distances (7) to the ultrasonic sensor (4) are arranged.
10. System nach Anspruch 8 oder 9, wobei der mindestens eine Schall-Re- flektor (5) in einem Einbettungsmaterial (9) eingebettet ist. 10. System according to claim 8 or 9, wherein the at least one sound reflector (5) is embedded in an embedding material (9).
11. System nach einem der Ansprüche 8 bis 10, wobei eine Auswerteeinheit vorgesehen ist, in der ein Pulslaufzeit-basierter Auswertealgorithmus hin terlegt ist. 11. System according to one of claims 8 to 10, wherein an evaluation unit is provided in which a pulse duration-based evaluation algorithm is put down.
12. System nach einem der Ansprüche 8 bis 11 , wobei eine Auswerteeinheit vorgesehen ist, in der ein FMCW-basierter Auswertealgorithmus hinter- legt ist. 12. System according to any one of claims 8 to 11, wherein an evaluation unit is provided, in which an FMCW-based evaluation algorithm is deposited.
13. Implantierbares, vaskuläres Unterstützungssystem (2), umfassend ein System zum Ermitteln der Schallgeschwindigkeit nach einem der An- sprüche 8 bis 12. 13. An implantable vascular support system (2) comprising a system for determining the speed of sound according to any one of claims 8 to 12.
EP19729271.7A 2018-06-06 2019-06-06 Method and system for determining the speed of sound in a fluid in the region of an implanted vascular support system Pending EP3801281A1 (en)

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US12311160B2 (en) 2025-05-27
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