WO2013014647A1 - Ultrasound probe, method and device for acquiring a blood flow signal of an artery and system for measuring systolic blood pressure - Google Patents

Ultrasound probe, method and device for acquiring a blood flow signal of an artery and system for measuring systolic blood pressure Download PDF

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Publication number
WO2013014647A1
WO2013014647A1 PCT/IB2012/053852 IB2012053852W WO2013014647A1 WO 2013014647 A1 WO2013014647 A1 WO 2013014647A1 IB 2012053852 W IB2012053852 W IB 2012053852W WO 2013014647 A1 WO2013014647 A1 WO 2013014647A1
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WIPO (PCT)
Prior art keywords
signal
artery
doppler
blood flow
ultrasound
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PCT/IB2012/053852
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French (fr)
Inventor
Jianyi Zhong
Ajay Anand
John Petruzzello
Yinan Chen
Weijia Lu
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Koninklijke Philips Electronics N.V.
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Publication of WO2013014647A1 publication Critical patent/WO2013014647A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/04—Measuring blood pressure
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/48—Other medical applications
    • A61B5/4887—Locating particular structures in or on the body
    • A61B5/489—Blood vessels
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/06—Measuring blood flow
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/44—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device
    • A61B8/4477—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device using several separate ultrasound transducers or probes
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/44—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device
    • A61B8/4483—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device characterised by features of the ultrasound transducer
    • 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
    • A61B8/42—Details of probe positioning or probe attachment to the patient
    • A61B8/4209—Details of probe positioning or probe attachment to the patient by using holders, e.g. positioning frames
    • A61B8/4236—Details of probe positioning or probe attachment to the patient by using holders, e.g. positioning frames characterised by adhesive patches

Definitions

  • the invention relates to non-invasive blood pressure measurement, in particular to an ultrasound probe, a method and device for acquiring a blood flow signal of an artery and a system for measuring systolic blood pressure (SBP).
  • SBP systolic blood pressure
  • non-invasive blood pressure measurement is an indirect method of measuring the blood pressure in an artery of the human body.
  • a predominant method of clinical measurement is the so-called auscultatory method.
  • an inflatable cuff of a sphygmomanometer is used to apply a changing pressure to an artery to restrict blood flow in the artery.
  • the cuff is first inflated until the artery is completely occluded and then deflated until the artery is open again.
  • the pressure values at the moment of occlusion and at the moment of re-opening of the artery are commonly called SBP-I (SBP in inflation) and SBP-D (SBP in deflation), respectively.
  • clinicians should accurately localize the artery to be measured through manual adjustment.
  • the clinician uses a Doppler ultrasound probe
  • the clinician has to place the Doppler ultrasound probe at an appropriate location such that an ultrasound transducer in the Doppler ultrasound probe is above the artery, which requires not only anatomical knowledge but also experience in ultrasound.
  • an ultrasound probe comprises a plurality of ultrasound transducers, and each of the plurality of ultrasound transducers is configured to obtain an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal.
  • the basic idea is to use a plurality of ultrasound transducers. Subject to the condition that the artery lays within the footprint of the plurality of ultrasound transducers, at least one of the obtained echo signals indicates information about the blood flow in the artery. By comparison, accurately placing a single transducer with respect to the artery is much more difficult than attaching the ultrasound probe in such a way that the artery lies within the footprint of a plurality of ultrasound transducers. Thus, the need to accurately place an ultrasound transducer above the artery through manual adjustment is eliminated.
  • the plurality of ultrasound transducers are arranged into one or more rows, and each row comprises multiple ultrasound transducers.
  • the ultrasound transducers in two adjacent rows of a plurality of rows are arranged in a way such that the ultrasound transducers in one row are offset with respect to the ultrasound transducers in the other row. In other words, the ultrasound transducers in one row are not aligned with those in the other
  • the plurality of ultrasound transducers are of the same width, the ultrasound transducers in each of the plurality of rows are equally spaced with a predefined spacing, and the offset is set to half of the sum of the width and the predefined spacing.
  • the ultrasound probe further comprises a fixture configured to hold the plurality of ultrasound transducers.
  • a surface of the fixture is intended to be attached to the exterior of a body, and the plurality of ultrasound transducers are configured in a way such that the angle between the surface and the transmitting/receiving direction of the ultrasonic wave is in a predefined range.
  • a device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body comprises:
  • an ultrasound probe as described above the ultrasound probe being intended to be attached to the exterior of the body;
  • a first deriving unit configured to derive, from each obtained echo signal, at least one Doppler signal, the at least one Doppler signal being associated with the ultrasound transducer obtaining the echo signal and being indicative of information about Doppler shift of the echo signal;
  • a selecting unit configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
  • the predefined condition includes that:
  • the selected Doppler signal is periodic over time
  • the power of the selected Doppler signal is greater than a threshold.
  • the blood flow is periodic and the periodicity of the blood flow is synchronous with heart beats. Accordingly, characteristics of the blood flow, such as the quantity, the velocity and the like are also periodic. Consequently, when a Doppler signal is related to the blood flow, namely that Doppler shifts indicated by the Doppler signal are mainly caused by the blood flow (e.g. the moving red blood cells therein), the Doppler signal is also periodic. Moreover, since an arterial blood flow has many more red blood cells than other blood flows, such as capillary blood flows, the power of the Doppler signal related to the blood flow in the artery is accordingly higher. Thus, when making a selection among the obtained Doppler signals according to the above predefined condition, the selected Doppler signal is related to the blood flow and is indicative of at least one characteristic of the blood flow in the artery.
  • the predefined condition further includes that: the power of the selected Doppler signal is the highest.
  • the strongest Doppler signal is selected.
  • each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and indicates information about Doppler shift caused at the predefined distance.
  • the blood flow signal can be acquired more accurately.
  • the selected Doppler signal indicates Doppler shifts caused by the blood flow in the artery, it can be determined that the artery is located at the predefined distance associated with the selected Doppler signal.
  • the device further comprises a first determining unit configured to determine the location of the artery on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
  • a method of acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body comprises:
  • each one of the plurality of echo signals being obtained by one of a plurality of ultrasound transducers attached to the exterior of the body;
  • the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
  • an ultrasound transducer obtains an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal.
  • the plurality of ultrasound transducers are arranged into multiple rows of ultrasound transducers, and each row comprises multiple ultrasound transducers.
  • the predefined condition comprises:
  • the selected Doppler signal is periodic over time
  • the power of the selected Doppler signal is greater than a threshold.
  • each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and indicates information about Doppler shift caused at the predefined distance.
  • a system for measuring the systolic blood pressure of an artery of a body comprises: a first device configured to apply a changing pressure on the artery, the first device being attachable to the exterior of the body;
  • a pressure sensor configured to obtain a plurality of pressure values of the changing pressure at a plurality of time points
  • a second device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in the artery under the changing pressure as described in the above; a third device configured to determine the systolic blood pressure on the basis of the acquired blood flow signal.
  • the systolic blood pressure of an artery can be measured automatically.
  • the third device comprises:
  • a second deriving unit configured to derive, from the acquired blood flow signal, at least one of a first variable indicative of the magnitude of the blood flow and a second variable indicative of the periodicity of the blood flow;
  • a detecting unit configured to detect an occluded and/or reopened artery caused by the changing pressure on the basis of the at least one variable
  • a second determining unit configured to determine the systolic blood pressure from at least one of a first pressure value of the changing pressure at a time point corresponding to the detected occlusion of the artery, and a second pressure value of the changing pressure at a time point corresponding to the detected reopening of the artery.
  • the measurement result is more predictable and repeatable, and is therefore more accurate. Furthermore, since the measuring procedure is automated, it is more convenient to measure systolic blood pressure.
  • first pressure value and the second pressure value correspond to the SBP-I and the SBP-D, respectively, and the systolic blood pressure is determined from either SBP-I or SBP-D or both.
  • Fig.l depicts a schematic diagram of a device for acquiring a blood flow signal in accordance with an embodiment of the present invention
  • Fig.2 depicts a schematic view of an ultrasound probe attached to an upper limb in accordance with an embodiment of the present invention
  • Fig.3a depicts a schematic view of the arrangement of ultrasound transducers in an ultrasound probe in accordance with an embodiment of the present invention
  • Fig.3b depicts a schematic side view of an ultrasound probe with a fixture in accordance with an embodiment of the present invention
  • Fig.4 depicts a flow chart of a method of acquiring a blood flow signal in accordance with an embodiment of the present invention
  • Fig.5 depicts a schematic diagram of a system for measuring thesystolic blood pressure of an artery in accordance with an embodiment of the present invention
  • Fig.6 depicts a schematic diagram of a device for determining the systolic blood pressure in accordance with an embodiment of the present invention.
  • Fig.7 depicts a diagram of a changing pressure in accordance with an embodiment of the present invention.
  • Fig.l depicts a schematic diagram of a device for acquiring a blood flow signal in accordance with an embodiment of the present invention.
  • the blood flow signal is indicative of at least one characteristic of a blood flow in a target artery of a body.
  • the device comprises an ultrasound probe 101, a first deriving unit 102 and a selecting unit 103.
  • the ultrasound probe 101 is intended to be attached to the exterior of the body.
  • the ultrasound probe 101 can be attached to a different part of the body to acquire a blood flow signal related to a different artery.
  • an ultrasound probe 201 is provided at an upper limb of the body 1 when the target artery is a posterior tibial artery of the body.
  • the ultrasound probe 101 comprises a plurality of ultrasound transducers, each of which obtains an echo signal.
  • an ultrasound transducer is driven to transmit an ultrasonic wave, namely high frequency sound waves, into a part of the body, receive the scattered-back ultrasonic wave and transform the scattered-back ultrasonic wave into an electrical signal, called echo signal.
  • Doppler shifts of the echo signal indicate the relative velocities between the transducer and the scatterers such as the moving red blood cells in the part of the body.
  • the ultrasound transducers 101 can be in the form of a continuous wave ultrasound transducer or a pulsed wave ultrasound transducer.
  • the plurality of ultrasound transducers of the ultrasound probe 101 can be arranged in different ways.
  • Fig.3a depicts a schematic view of the arrangement of ultrasound transducers in an ultrasound probe in accordance with an embodiment of the present invention.
  • the plurality of ultrasound transducers 301 comprises 6 transducers placed in 2 rows.
  • each ultrasound transducer has a width of about 5mm, and the ultrasound transducers in each row are equally spaced with a small, predefined spacing.
  • the ultrasound transducers in one row have an offset, as indicated by arrow A, with respect to the ultrasound transducers in the other row.
  • the offset is, for example, set to half of the sum of the width of the transducer and the predefined spacing. In this way, an ultrasound transducer in one row is aligned with a spacing between two ultrasound transducers in the other row.
  • the second and third ultrasound transducers in the second row are aligned with the spacing between the first and second ultrasound transducers in the first row and with the spacing between the second and third ultrasound transducers in the first row, respectively.
  • the target artery happens to be not right below any transducer in one row, e.g. below the spacing between two transducers in one row, it can lie right below a transducer in the other row.
  • Fig.3b depicts a schematic side view of an ultrasound probe with a fixture in accordance with an embodiment of the present invention.
  • the ultrasound probe further comprises a fixture 302 for holding the plurality of ultrasound transducers 301.
  • the fixture 302 has a surface 303 intended to be attached to the exterior of the body.
  • the surface 303 can be configured to be attachable to the exterior of the body in a stable manner.
  • the angle between the surface 303 and the transmitting/receiving direction (as indicated by arrows) of the ultrasonic waves of the ultrasound transducers is in a predefined range. According to an embodiment, the angle is set to be approximately 60°.
  • the first deriving unit 102 is configured to derive, from each obtained echo signal, at least one Doppler signal, wherein the at least one Doppler signal is associated with the ultrasound transducer obtaining the echo signal and is indicative of information about the Doppler shift of the echo signal.
  • a Doppler signal can be any signal indicative of information about the Doppler shift of the echo signal obtained by the ultrasound transducer.
  • the Doppler signal refers to the so-called raw acoustic signal obtained using the ultrasound transducer.
  • the so-called raw acoustic signal represents a plurality of Doppler shifts of the echo signal, wherein each frequency component is associated with a particular Doppler shift and the amplitude of each frequency component is associated with the amount of scatterers moving at a velocity corresponding to the particular Doppler shift.
  • the at least one Doppler signal comprises a single Doppler signal.
  • the single Doppler signal can indicate information about the Doppler shift caused at all distances from the ultrasound probe. That is to say, the scatterers encountered by the ultrasound wave, and thereby causing the Doppler shifts, are located at all distances.
  • the single Doppler signal can indicate information about the Doppler shift caused at a predefined distance from the ultrasound probe. That is to say, the scatterers encountered by the ultrasound wave, and thereby causing the Doppler shifts, are all located at the predefined distance from the ultrasound probe.
  • the predefined distance corresponds to the distance from the ultrasound probe to the target artery, which can be estimated by other means.
  • the at least one Doppler signal comprises a plurality of Doppler signals, and each of the Doppler signals is associated with a predefined distance from the ultrasound probe and indicates information about the Doppler shift caused at the predefined distance from the ultrasound probe.
  • the predefined distances associated with the plurality of Doppler signals span a predefined range with a predefined granularity.
  • the predefined range can be determined based on anatomical knowledge, such that the target artery is located within the predefined distance range from the exterior of the body.
  • the predefined granularity can be determined based on the size of the target artery.
  • the predefined granularity is 2-4 mm.
  • the selecting unit 103 is configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
  • the predefined condition comprises:
  • the selected Doppler signal is periodic over time
  • the power of the selected Doppler signal is greater than a threshold.
  • the selecting unit 103 determines, for each of the obtained Doppler signals, whether the Doppler signal satisfies the predefined condition, which can be implemented using a variety of signal processing techniques. An approach based on time-frequency analysis is described below.
  • a spectrogram of the Doppler signal is calculated.
  • a spectrogram is a time- varying spectral representation that shows how the spectral density of a signal varies with time, also known as sonagram.
  • the spectrogram is a graph with a time axis, a frequency axis and a third axis indicating the amplitude at a particular frequency and a particular time.
  • a short-term Fourier transform STFT
  • the spectrogram can be also calculated using other known methods such as wavelet transform.
  • the spectrogram is accumulated within a predefined frequency range to obtain a signal as a function of time, referred to as Doppler power signal hereinafter.
  • the predefined frequency range can be from 100 Hz to 3000 Hz.
  • the Doppler power signal can be obtained from the spectrogram by extracting the frequency corresponding to the maximum amplitude value along the frequency axis, i.e. the value of the Doppler power signal at a time point is the frequency corresponding to the maximum amplitude value of the spectrogram among all frequencies at the time point.
  • the selecting unit 103 determines whether the cross-correlation signal is periodic. When the cross-correlation signal is periodic, the corresponding Doppler signal is determined as being periodic. This is based on the signal processing theory, which states that the cross- correlation of a periodic signal will contain peaks equal in magnitude separated by the period.
  • the selecting unit 103 determines whether the peak value of the cross-correlation signal is greater than the threshold.
  • the predefined condition further comprises:
  • the Doppler signal with the highest power is selected.
  • the device further comprises a first determining unit 104.
  • the first determining unit 104 is configured to determine the location of the target artery.
  • the location of the target artery can be determined on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
  • the first deriving unit 102, the selecting unit 103 and the first determining unit can be embodied as a processor.
  • the processor can be configured in different ways.
  • the processor can be a single processing unit connected to the ultrasound probe 101.
  • the processor can comprise multiple separate components, and certain components can be part of the ultrasound probe 101, e.g. placed inside the fixture thereof.
  • Fig.4 depicts a flowchart of a method of acquiring a blood flow signal in accordance with an embodiment of the present invention.
  • the blood flow signal is indicative of at least one characteristic of a blood flow in an artery of a body.
  • the method comprises a step S410 of obtaining a plurality of echo signals, wherein each of the plurality of echo signals is obtained by one of a plurality of ultrasound transducers attached to an exterior of the body.
  • the method further comprises a step S420 of deriving, from each echo signal, at least one Doppler signal indicative of information about the Doppler shift of the echo signal.
  • the method further comprises a step S430 of selecting a Doppler signal from the obtained
  • Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
  • the method can further comprise a step S440 of determining a location of the artery on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
  • Fig.5 depicts a schematic diagram of a system for measuring the systolic blood pressure of an artery in accordance with an embodiment of the present invention.
  • the system comprises a first device 501, a pressure sensor 502, a second device 503 and a third device 504.
  • the first device 501 is intended to be attached to the exterior of a body 1 to apply a changing pressure on an artery of the body 1.
  • the first device 510 can be an inflatable cuff.
  • the inflatable cuff can be wrapped around an upper limb of the body to apply the changing pressure on the brachial artery.
  • the inflatable cuff can be wrapped around a lower limb of the body to apply the changing pressure on the posterior tibial artery and/or dorsalis pedis artery.
  • the pressure sensor 502 is configured to obtain values of the changing pressure applied by the first device 501. In particular, the pressure sensor 502 obtains a plurality of values of the changing pressure at a plurality of time points.
  • the second device 503 is a device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in the artery, such as the device shown in Fig.1.
  • the third device 504 is configured to determine the systolic blood pressure on the basis of the acquired blood flow signal.
  • the system operates as follows.
  • the first device 501 does not apply any changing pressure on a target artery of the body 1, and the second device 503 acquires a blood flow signal related to the blood flow in the target artery by performing a selection among the obtained Doppler signals according to a predefined condition.
  • the first device 501 applies the changing pressure on the target artery of the body 1, the second device 503 continuously provides the blood flow signal, namely the selected Doppler signal, to the third device 504, and the third device 504 determines the systolic blood pressure on the basis of the blood flow signal.
  • Fig.6 depicts a schematic diagram of a device for determining the systolic blood pressure in accordance with an embodiment of the present invention.
  • the device of Fig.6 can, for example, serve as the third device 504 of Fig.5.
  • the device for determining the systolic blood pressure comprises a second deriving unit 601.
  • the second deriving unit 601 is configured to derive, from the blood flow signal related to the blood flow in the artery, at least one of a first variable and a second variable.
  • the first variable indicates the magnitude of the blood flow
  • the second variable indicates the periodicity of the blood flow.
  • the device for determining the systolic blood pressure further comprises a detecting unit 602.
  • the detecting unit 602 is configured to detect an occluded and/or reopened artery of the body by means of the changing pressure applied on the artery on the basis of the at least one variable.
  • the artery is occluded when the applied pressure is sufficiently high, and the artery is reopened when the applied pressure decreases below a certain value. Accordingly, during the increase of the changing pressure, the detecting unit 602 detects when the occlusion occurs; and during the decrease of the changing pressure, the detecting unit 602 detects when the artery is reopened.
  • the second deriving unit 601 and the detecting 602 will be further described below.
  • the device for determining the systolic blood pressure further comprises a second determining unit 603.
  • the second determining unit 603 is configured to determine the systolic blood pressure from at least one of a first pressure value of the changing pressure at a time point corresponding to the detected occlusion of the artery, and a second pressure value of the changing pressure at a time point corresponding to the detected reopening of the artery.
  • the systolic blood pressure comprises SBP-I and SBP-D, wherein SBP-I is the value of the changing pressure at a time when the artery is occluded during the increase of the changing pressure, and SBP-D is the value of the changing pressure when the artery is reopened during the decrease of the changing pressure.
  • SBP-I is the value of the changing pressure at a time when the artery is occluded during the increase of the changing pressure
  • SBP-D is the value of the changing pressure when the artery is reopened during the decrease of the changing pressure.
  • the first pressure value and the second pressure value are the SBP-I value and the SBP-D value, respectively.
  • the systolic blood pressure is determined of the available one.
  • the second determining unit 603 can determine the systolic blood pressure in different ways. For example, the systolic blood pressure can be determined as one of the first pressure value and the second pressure value. For another example, the systolic blood pressure can be determined as the higher one of the first pressure value and the second pressure value.
  • the second determining unit 603 can obtain at least one of the first and the second pressure values in different ways.
  • the pressure sensor 102 provides a plurality of pressure values at the plurality of time points to the detecting unit 602, and then the detecting unit 602 provides at least one of the first and the second pressure values corresponding respectively to the detected occlusion and reopening of the artery to the second determining unit 603.
  • the pressure sensor 102 provides a plurality of pressure values at the plurality of time points to the second determining unit 603; the detecting unit 602 provides at least one of two time points corresponding to the detected occlusion and reopening of the artery to the second determining unit 603, and then the second determining unit 603 selects at least one of the first and the second pressure values among the plurality of pressure values from the pressure sensor 102 according to at least one of two time points from the detecting unit 602.
  • Fig.7 depicts a diagram of a changing pressure in accordance with an embodiment of the present invention.
  • Fig.7 depicts a change of the changing pressure versus time.
  • the changing pressure increases gradually to a maximum pressure value that is sufficiently high for the artery to become occluded, and then starts to decrease to enable the artery to reopen.
  • the pressure values corresponding respectively to the occlusion and the reopening of the artery are denoted as SBP-I and SBP-D.
  • the maximum pressure value can be set in different ways.
  • the maximum pressure value can be predefined.
  • different maximum pressure values can be individually set for different persons.
  • the maximum pressure value is set to be relatively high for a patient with hypertension.
  • the maximum pressure value can be adaptively defined according to the detected occlusion.
  • the maximum pressure value is set to be in a range of 20 mmHg to 30 mmHg above the SBP-I value.
  • the maximum pressure value is set to, for example, 220 mmHg, and the changing pressure starts to decrease when it reaches the maximum pressure at about second 15.
  • the third device 502 can provide a real-time feedback to the first device 501, such that the first device 501 can start to decrease the changing pressure according to the detected occlusion of the artery. In this way, the inflatable cuff is controlled automatically and precisely.
  • the second deriving unit 601 derives, from the blood flow signal, at least one variable of a first variable and a second variable.
  • the blood flow signal comprises a Doppler signal.
  • the first variable indicates the magnitude of the blood flow
  • the second variable indicates the periodicity of the blood flow.
  • a predefined time window slides along the time axis, and a value of each of the first and the second variable is calculated for each time window.
  • the time window can be defined so as to have a width of 3 seconds and slide for 1 second each time, and accordingly, the value of each of the first and the second variable is calculated every second.
  • the values of the first and the second variable for a given time window can be calculated in different ways. An approach based on time-frequency analysis is described below.
  • the spectrogram of the Doppler signal in the given time window is calculated.
  • the spectrogram is filtered to remove spectrum components in predefined frequency ranges.
  • the predefined frequency ranges comprises 0-100 Hz and above 3000 Hz.
  • the amplitude of the filtered spectrogram is accumulated along the frequency axis to obtain a waveform as a function of time, referred to as blood flow waveform hereinafter.
  • the blood flow waveform can be obtained from the filtered spectrogram by extracting the frequency corresponding to the maximum amplitude value along the frequency axis, namely the value of the blood flow waveform at a time point is the frequency corresponding to the maximum amplitude value of the filtered spectrogram among all frequencies at said time point.
  • the values of the first and the second variable for the given time window are derived from the obtained blood waveform.
  • the value of the first variable is associated with the peak amplitude of the blood waveform, and, for example, it can be the maximum or average value of the peak values in the blood waveform.
  • the value of the second variable is associated with the periodicity of the blood waveform, and for example, it can be the number of peaks per second. Various methods are known to determine the peak values and the number of peaks and will not be further discussed herein.
  • the values of the first and the second variable for a given time window are calculated from the blood flow signal in the given time window.
  • the detecting unit 602 detects the occlusion and/or reopening of the artery on the basis of at least one variable of the first variable and the second variable.
  • the artery is detected as being occluded in the given time window, when the calculated value of the first variable for the given time window is less than the first threshold and/or the calculated value of the second variable for the given time window is outside the first range.
  • the first threshold and the first range can be determined in different ways. Each of the first threshold and the first range can be constant and predetermined according to statistical data. Alternatively, each of the first threshold and the first range can be determined from the blood flow signal and can therefore vary. For example, the first threshold can be related to noise in the blood flow signal, and the noise can be calculated from the filtered spectrogram. Alternatively, the first threshold can be related to the average peak value in the blood waveform, and for example, be set to 10% to 20% of the average peak value. For example, the first range can be determined according to the mean and the standard deviation of the second variable in the previous time windows. Denoting the mean and the standard deviation by ⁇ and ⁇ , the first range can, for example, be determined as a range [ ⁇ - ⁇ , ⁇ + ⁇ ].
  • the artery is detected as being reopened in the given time window, when the calculated value of the first variable for the given time window is greater than a second threshold and/or the calculated value of the second variable for the given time window is within a second range.
  • the second threshold and the second range can, respectively, be identical to the first threshold and the first range. This is the case, for example, when the first threshold and the first range are not constant, but are updated in each time window till the occlusion of the artery, the second threshold and the second range can be set to the latest values of the first threshold and the first range, respectively.
  • the time of reopening can be further determined as occurring at a moment corresponding to the first peak that is greater than the second threshold.
  • the reopening is detected.
  • the predefined time period is sufficiently long to contain at least five cycles of the blood flow.
  • the current time window is marked. Then, in a predefined number of subsequent time windows, it is determined whether, for each of the subsequent time windows, the calculated value of the first variable is greater than the second threshold and/or the calculated value of the second variable for the current time window is within the second range. If yes, it indicates that the blood flow is stable, and the artery is determined as being actually reopened in the marked time window. In this way, the possibility of false detection due to the so-called Gap phenomenon can be reduced, and the detected reopening of the artery is therefore more reliable.

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Abstract

This invention provides an ultrasound probe, a device and method for acquiring a blood flow signal of an artery and a system for measuring systolic blood pressure. The ultrasound probe comprises a plurality of ultrasound transducers, wherein each of the plurality of ultrasound transducers is configured to obtain an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal. The device for acquiring a blood flow signal of an artery comprises the ultrasound probe, wherein the ultrasound probe is intended to be attached to the exterior of the body. The device further comprises: a first deriving unit configured to derive, from each obtained echo signal, at least one Doppler signal, the at least one Doppler signal being associated with the ultrasound transducer obtaining the echo signal and being indicative of information about Doppler shift of the echo signal; a selecting unit configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body. In this way, the need for accurate localization of the artery by means of manual adjustment is eliminated on the proviso that the ultrasound probe is attached in such a way that the artery lies within the footprint of the ultrasound probe.

Description

Ultrasound Probe, Method And Device For Acquiring A Blood Flow Signal Of An Artery And System For Measuring Systolic Blood Pressure FIELD OF THE INVENTION
The invention relates to non-invasive blood pressure measurement, in particular to an ultrasound probe, a method and device for acquiring a blood flow signal of an artery and a system for measuring systolic blood pressure (SBP).
BACKGROUND OF THE INVENTION
Unlike invasive blood pressure measurement, non-invasive blood pressure measurement is an indirect method of measuring the blood pressure in an artery of the human body. A predominant method of clinical measurement is the so-called auscultatory method. According to the auscultatory method, an inflatable cuff of a sphygmomanometer is used to apply a changing pressure to an artery to restrict blood flow in the artery. The cuff is first inflated until the artery is completely occluded and then deflated until the artery is open again. The pressure values at the moment of occlusion and at the moment of re-opening of the artery are commonly called SBP-I (SBP in inflation) and SBP-D (SBP in deflation), respectively.
Clinicians manually detect the moment of occlusion and the moment of reopening of the artery by listening with a stethoscope or a Doppler ultrasound probe and read the SBP values from the sphygmomanometer. The clinicians should have no hearing deficit and are required to highly focus on the devices during the whole measuring procedure. Consequently, when using the auscultatory method to measure SBP, clinicians might easily start to feel tired, as a result of which the accuracy of the detected moments of occlusion and reopening of the artery is impacted accordingly.
Moreover, clinicians should accurately localize the artery to be measured through manual adjustment. For example, in the case that the clinician uses a Doppler ultrasound probe, the clinician has to place the Doppler ultrasound probe at an appropriate location such that an ultrasound transducer in the Doppler ultrasound probe is above the artery, which requires not only anatomical knowledge but also experience in ultrasound.
SUMMARY OF THE INVENTION
Based on the understanding of the technical problems and prior art described above, it would be desirable to acquire information related to blood flow in an artery without the need of accurate localization of the artery through manual adjustment. It would also be desirable to automatically measure SBP while still achieving good measurement accuracy.
To better address one or more of the above concerns, according to an embodiment of an aspect of the present invention, an ultrasound probe is provided. The ultrasound probe comprises a plurality of ultrasound transducers, and each of the plurality of ultrasound transducers is configured to obtain an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal.
The basic idea is to use a plurality of ultrasound transducers. Subject to the condition that the artery lays within the footprint of the plurality of ultrasound transducers, at least one of the obtained echo signals indicates information about the blood flow in the artery. By comparison, accurately placing a single transducer with respect to the artery is much more difficult than attaching the ultrasound probe in such a way that the artery lies within the footprint of a plurality of ultrasound transducers. Thus, the need to accurately place an ultrasound transducer above the artery through manual adjustment is eliminated.
In another embodiment, the plurality of ultrasound transducers are arranged into one or more rows, and each row comprises multiple ultrasound transducers.
Preferably, the ultrasound transducers in two adjacent rows of a plurality of rows are arranged in a way such that the ultrasound transducers in one row are offset with respect to the ultrasound transducers in the other row. In other words, the ultrasound transducers in one row are not aligned with those in the other
In this way, when attaching the ultrasound probe to the body, even if the artery is not right below any transducer in a given row, e.g. right below a spacing between two transducers in a given row, it could lie right below a transducer in the other row, enabling the artery to be more accurately localized.
In another embodiment, the plurality of ultrasound transducers are of the same width, the ultrasound transducers in each of the plurality of rows are equally spaced with a predefined spacing, and the offset is set to half of the sum of the width and the predefined spacing.
In another embodiment, the ultrasound probe further comprises a fixture configured to hold the plurality of ultrasound transducers. Preferably, a surface of the fixture is intended to be attached to the exterior of a body, and the plurality of ultrasound transducers are configured in a way such that the angle between the surface and the transmitting/receiving direction of the ultrasonic wave is in a predefined range.
In this way, there is no need to manually tilt the ultrasound probe to an appropriate angle to enhance the quality of the acquired blood flow signal.
According to an embodiment of another aspect of the present invention, a device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body is provided. The device comprises:
an ultrasound probe as described above, the ultrasound probe being intended to be attached to the exterior of the body;
a first deriving unit configured to derive, from each obtained echo signal, at least one Doppler signal, the at least one Doppler signal being associated with the ultrasound transducer obtaining the echo signal and being indicative of information about Doppler shift of the echo signal;
a selecting unit configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
In another embodiment, the predefined condition includes that:
- the selected Doppler signal is periodic over time; and
- the power of the selected Doppler signal is greater than a threshold.
As is well-known, the blood flow is periodic and the periodicity of the blood flow is synchronous with heart beats. Accordingly, characteristics of the blood flow, such as the quantity, the velocity and the like are also periodic. Consequently, when a Doppler signal is related to the blood flow, namely that Doppler shifts indicated by the Doppler signal are mainly caused by the blood flow (e.g. the moving red blood cells therein), the Doppler signal is also periodic. Moreover, since an arterial blood flow has many more red blood cells than other blood flows, such as capillary blood flows, the power of the Doppler signal related to the blood flow in the artery is accordingly higher. Thus, when making a selection among the obtained Doppler signals according to the above predefined condition, the selected Doppler signal is related to the blood flow and is indicative of at least one characteristic of the blood flow in the artery.
In another embodiment, the predefined condition further includes that: the power of the selected Doppler signal is the highest.
In this way, when more than one Doppler signal is determined to be related to the blood flow, the strongest Doppler signal is selected.
In another embodiment, each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and indicates information about Doppler shift caused at the predefined distance.
In this way, information about Doppler shift caused at different distances can be separated. Thus, the blood flow signal can be acquired more accurately. Moreover, since the selected Doppler signal indicates Doppler shifts caused by the blood flow in the artery, it can be determined that the artery is located at the predefined distance associated with the selected Doppler signal.
In another embodiment, the device further comprises a first determining unit configured to determine the location of the artery on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
Since the selected Doppler signal is related to the blood flow in the artery, the location of the artery can be determined accordingly. In particular, it can be determined that the artery is located right below the ultrasound transducer associated with the selected Doppler signal and the distance from the ultrasound probe to the artery is equal to the predefined distance associated with the selected Doppler signal. According to an embodiment of another aspect of the present invention, a method of acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body is provided. The method comprises:
- obtaining a plurality of echo signals, each one of the plurality of echo signals being obtained by one of a plurality of ultrasound transducers attached to the exterior of the body;
- deriving, from each echo signal, at least one Doppler signal indicative of information about the Doppler shift of the echo signal;
- selecting a Doppler signal from the obtained Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
As is well-known, an ultrasound transducer obtains an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal.
Preferably, the plurality of ultrasound transducers are arranged into multiple rows of ultrasound transducers, and each row comprises multiple ultrasound transducers.
Preferably, the predefined condition comprises:
- the selected Doppler signal is periodic over time; and
- the power of the selected Doppler signal is greater than a threshold.
Preferably, each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and indicates information about Doppler shift caused at the predefined distance.
According to an embodiment of another aspect of the present invention, a system for measuring the systolic blood pressure of an artery of a body is provided. The system comprises: a first device configured to apply a changing pressure on the artery, the first device being attachable to the exterior of the body;
a pressure sensor configured to obtain a plurality of pressure values of the changing pressure at a plurality of time points;
a second device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in the artery under the changing pressure as described in the above; a third device configured to determine the systolic blood pressure on the basis of the acquired blood flow signal.
By means of such a system, the systolic blood pressure of an artery can be measured automatically.
Preferably, the third device comprises:
- a second deriving unit configured to derive, from the acquired blood flow signal, at least one of a first variable indicative of the magnitude of the blood flow and a second variable indicative of the periodicity of the blood flow;
- a detecting unit configured to detect an occluded and/or reopened artery caused by the changing pressure on the basis of the at least one variable;
- a second determining unit configured to determine the systolic blood pressure from at least one of a first pressure value of the changing pressure at a time point corresponding to the detected occlusion of the artery, and a second pressure value of the changing pressure at a time point corresponding to the detected reopening of the artery.
Since the need to manually detect the occlusion and reopening of the artery by listening with a stethoscope or a Doppler ultrasound probe is eliminated and the need to manually read the pressure value at the time of occlusion and/or reopening of the artery is also eliminated, the measurement result is more predictable and repeatable, and is therefore more accurate. Furthermore, since the measuring procedure is automated, it is more convenient to measure systolic blood pressure.
Further, the first pressure value and the second pressure value correspond to the SBP-I and the SBP-D, respectively, and the systolic blood pressure is determined from either SBP-I or SBP-D or both.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which:
Fig.l depicts a schematic diagram of a device for acquiring a blood flow signal in accordance with an embodiment of the present invention;
Fig.2 depicts a schematic view of an ultrasound probe attached to an upper limb in accordance with an embodiment of the present invention;
Fig.3a depicts a schematic view of the arrangement of ultrasound transducers in an ultrasound probe in accordance with an embodiment of the present invention; Fig.3b depicts a schematic side view of an ultrasound probe with a fixture in accordance with an embodiment of the present invention;
Fig.4 depicts a flow chart of a method of acquiring a blood flow signal in accordance with an embodiment of the present invention;
Fig.5 depicts a schematic diagram of a system for measuring thesystolic blood pressure of an artery in accordance with an embodiment of the present invention;
Fig.6 depicts a schematic diagram of a device for determining the systolic blood pressure in accordance with an embodiment of the present invention; and
Fig.7 depicts a diagram of a changing pressure in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION A detailed description of the present invention is given below in connection with the accompanying drawings.
Fig.l depicts a schematic diagram of a device for acquiring a blood flow signal in accordance with an embodiment of the present invention. The blood flow signal is indicative of at least one characteristic of a blood flow in a target artery of a body. Referring to Fig.l, the device comprises an ultrasound probe 101, a first deriving unit 102 and a selecting unit 103.
The ultrasound probe 101 is intended to be attached to the exterior of the body. In particular, the ultrasound probe 101 can be attached to a different part of the body to acquire a blood flow signal related to a different artery. For example, as shown in Fig.2, an ultrasound probe 201 is provided at an upper limb of the body 1 when the target artery is a posterior tibial artery of the body.
The ultrasound probe 101 comprises a plurality of ultrasound transducers, each of which obtains an echo signal. As is well-known, an ultrasound transducer is driven to transmit an ultrasonic wave, namely high frequency sound waves, into a part of the body, receive the scattered-back ultrasonic wave and transform the scattered-back ultrasonic wave into an electrical signal, called echo signal. Moreover, Doppler shifts of the echo signal indicate the relative velocities between the transducer and the scatterers such as the moving red blood cells in the part of the body. The ultrasound transducers 101 can be in the form of a continuous wave ultrasound transducer or a pulsed wave ultrasound transducer.
The plurality of ultrasound transducers of the ultrasound probe 101 can be arranged in different ways.
Fig.3a depicts a schematic view of the arrangement of ultrasound transducers in an ultrasound probe in accordance with an embodiment of the present invention.
Referring to Fig.3a, the plurality of ultrasound transducers 301 comprises 6 transducers placed in 2 rows. In an embodiment, each ultrasound transducer has a width of about 5mm, and the ultrasound transducers in each row are equally spaced with a small, predefined spacing. The ultrasound transducers in one row have an offset, as indicated by arrow A, with respect to the ultrasound transducers in the other row. The offset is, for example, set to half of the sum of the width of the transducer and the predefined spacing. In this way, an ultrasound transducer in one row is aligned with a spacing between two ultrasound transducers in the other row. For example, the second and third ultrasound transducers in the second row are aligned with the spacing between the first and second ultrasound transducers in the first row and with the spacing between the second and third ultrasound transducers in the first row, respectively. In this way, when attaching the ultrasound probe to the body, even if the target artery happens to be not right below any transducer in one row, e.g. below the spacing between two transducers in one row, it can lie right below a transducer in the other row.
Fig.3b depicts a schematic side view of an ultrasound probe with a fixture in accordance with an embodiment of the present invention.
Referring to Fig.3b, the ultrasound probe further comprises a fixture 302 for holding the plurality of ultrasound transducers 301. The fixture 302 has a surface 303 intended to be attached to the exterior of the body. The surface 303 can be configured to be attachable to the exterior of the body in a stable manner. Preferably, the angle between the surface 303 and the transmitting/receiving direction (as indicated by arrows) of the ultrasonic waves of the ultrasound transducers is in a predefined range. According to an embodiment, the angle is set to be approximately 60°.
Referring again to Fig.l, the first deriving unit 102 is configured to derive, from each obtained echo signal, at least one Doppler signal, wherein the at least one Doppler signal is associated with the ultrasound transducer obtaining the echo signal and is indicative of information about the Doppler shift of the echo signal.
A Doppler signal can be any signal indicative of information about the Doppler shift of the echo signal obtained by the ultrasound transducer. In an embodiment, the Doppler signal refers to the so-called raw acoustic signal obtained using the ultrasound transducer. The so-called raw acoustic signal represents a plurality of Doppler shifts of the echo signal, wherein each frequency component is associated with a particular Doppler shift and the amplitude of each frequency component is associated with the amount of scatterers moving at a velocity corresponding to the particular Doppler shift.
In an embodiment, the at least one Doppler signal comprises a single Doppler signal. The single Doppler signal can indicate information about the Doppler shift caused at all distances from the ultrasound probe. That is to say, the scatterers encountered by the ultrasound wave, and thereby causing the Doppler shifts, are located at all distances. Alternatively, the single Doppler signal can indicate information about the Doppler shift caused at a predefined distance from the ultrasound probe. That is to say, the scatterers encountered by the ultrasound wave, and thereby causing the Doppler shifts, are all located at the predefined distance from the ultrasound probe. The predefined distance corresponds to the distance from the ultrasound probe to the target artery, which can be estimated by other means.
In another embodiment, the at least one Doppler signal comprises a plurality of Doppler signals, and each of the Doppler signals is associated with a predefined distance from the ultrasound probe and indicates information about the Doppler shift caused at the predefined distance from the ultrasound probe. Preferably, the predefined distances associated with the plurality of Doppler signals span a predefined range with a predefined granularity. The predefined range can be determined based on anatomical knowledge, such that the target artery is located within the predefined distance range from the exterior of the body. Furthermore, the predefined granularity can be determined based on the size of the target artery. Typically, the predefined granularity is 2-4 mm.
Further referring to Fig.l, the selecting unit 103 is configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
According to an embodiment, the predefined condition comprises:
a) the selected Doppler signal is periodic over time; and
b) the power of the selected Doppler signal is greater than a threshold.
Accordingly, the selecting unit 103 determines, for each of the obtained Doppler signals, whether the Doppler signal satisfies the predefined condition, which can be implemented using a variety of signal processing techniques. An approach based on time-frequency analysis is described below.
First, a spectrogram of the Doppler signal is calculated. A spectrogram is a time- varying spectral representation that shows how the spectral density of a signal varies with time, also known as sonagram. Generally, the spectrogram is a graph with a time axis, a frequency axis and a third axis indicating the amplitude at a particular frequency and a particular time. In an embodiment, a short-term Fourier transform (STFT) is performed on the raw acoustic signal, and the magnitude squared of the STFT yields the spectrogram. Alternatively, the spectrogram can be also calculated using other known methods such as wavelet transform.
Next, the spectrogram is accumulated within a predefined frequency range to obtain a signal as a function of time, referred to as Doppler power signal hereinafter. In an embodiment, the predefined frequency range can be from 100 Hz to 3000 Hz. Alternatively, after the removal of noise from the spectrogram, the Doppler power signal can be obtained from the spectrogram by extracting the frequency corresponding to the maximum amplitude value along the frequency axis, i.e. the value of the Doppler power signal at a time point is the frequency corresponding to the maximum amplitude value of the spectrogram among all frequencies at the time point.
Next, the cross-correlation signal of the Doppler power signal is computed.
The selecting unit 103 then determines whether the cross-correlation signal is periodic. When the cross-correlation signal is periodic, the corresponding Doppler signal is determined as being periodic. This is based on the signal processing theory, which states that the cross- correlation of a periodic signal will contain peaks equal in magnitude separated by the period.
Further, since the peak value of the cross-correlation signal indicates the power of the Doppler signal, the selecting unit 103 determines whether the peak value of the cross-correlation signal is greater than the threshold.
According to another embodiment, the predefined condition further comprises:
c) the power of the selected Doppler signal is the highest.
As a result, when there is more than one Doppler signal satisfying the above conditions a) and b), the Doppler signal with the highest power is selected.
Further referring to Fig.l, the device further comprises a first determining unit 104. The first determining unit 104 is configured to determine the location of the target artery. When a Doppler signal is selected from the obtained Doppler signals according to the predefined condition, the location of the target artery can be determined on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal. In particular, it can be determined that the artery is located right below the ultrasound transducer associated with the selected Doppler signal and the distance from the ultrasound probe to the artery is equal to the predefined distance associated with the selected Doppler signal..
Additionally, when no Doppler signal satisfies the condition a) and b) and thus no Doppler signal is selected, an alert signal can be generated to indicate that no blood flow is detected. In an embodiment, the first deriving unit 102, the selecting unit 103 and the first determining unit can be embodied as a processor. Moreover, the processor can be configured in different ways. For example, the processor can be a single processing unit connected to the ultrasound probe 101. For another example, the processor can comprise multiple separate components, and certain components can be part of the ultrasound probe 101, e.g. placed inside the fixture thereof.
Fig.4 depicts a flowchart of a method of acquiring a blood flow signal in accordance with an embodiment of the present invention. The blood flow signal is indicative of at least one characteristic of a blood flow in an artery of a body.
Referring to Fig.4, the method comprises a step S410 of obtaining a plurality of echo signals, wherein each of the plurality of echo signals is obtained by one of a plurality of ultrasound transducers attached to an exterior of the body.
The method further comprises a step S420 of deriving, from each echo signal, at least one Doppler signal indicative of information about the Doppler shift of the echo signal.
The method further comprises a step S430 of selecting a Doppler signal from the obtained
Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
Additionally, the method can further comprise a step S440 of determining a location of the artery on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
Fig.5 depicts a schematic diagram of a system for measuring the systolic blood pressure of an artery in accordance with an embodiment of the present invention.
Referring to Fig.5, the system comprises a first device 501, a pressure sensor 502, a second device 503 and a third device 504.
The first device 501 is intended to be attached to the exterior of a body 1 to apply a changing pressure on an artery of the body 1. In an embodiment, the first device 510 can be an inflatable cuff. For example, the inflatable cuff can be wrapped around an upper limb of the body to apply the changing pressure on the brachial artery. For another example, the inflatable cuff can be wrapped around a lower limb of the body to apply the changing pressure on the posterior tibial artery and/or dorsalis pedis artery. The pressure sensor 502 is configured to obtain values of the changing pressure applied by the first device 501. In particular, the pressure sensor 502 obtains a plurality of values of the changing pressure at a plurality of time points.
The second device 503 is a device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in the artery, such as the device shown in Fig.1.
The third device 504 is configured to determine the systolic blood pressure on the basis of the acquired blood flow signal.
The system operates as follows. In the initialization stage, the first device 501 does not apply any changing pressure on a target artery of the body 1, and the second device 503 acquires a blood flow signal related to the blood flow in the target artery by performing a selection among the obtained Doppler signals according to a predefined condition. Then, in the measuring stage, the first device 501 applies the changing pressure on the target artery of the body 1, the second device 503 continuously provides the blood flow signal, namely the selected Doppler signal, to the third device 504, and the third device 504 determines the systolic blood pressure on the basis of the blood flow signal.
Fig.6 depicts a schematic diagram of a device for determining the systolic blood pressure in accordance with an embodiment of the present invention. The device of Fig.6 can, for example, serve as the third device 504 of Fig.5.
Referring to Fig.6, the device for determining the systolic blood pressure comprises a second deriving unit 601. The second deriving unit 601 is configured to derive, from the blood flow signal related to the blood flow in the artery, at least one of a first variable and a second variable. The first variable indicates the magnitude of the blood flow, and the second variable indicates the periodicity of the blood flow.
Referring to Fig.6, the device for determining the systolic blood pressure further comprises a detecting unit 602. The detecting unit 602 is configured to detect an occluded and/or reopened artery of the body by means of the changing pressure applied on the artery on the basis of the at least one variable. As is well-known, the artery is occluded when the applied pressure is sufficiently high, and the artery is reopened when the applied pressure decreases below a certain value. Accordingly, during the increase of the changing pressure, the detecting unit 602 detects when the occlusion occurs; and during the decrease of the changing pressure, the detecting unit 602 detects when the artery is reopened.
The second deriving unit 601 and the detecting 602 will be further described below.
Referring to Fig.6, the device for determining the systolic blood pressure further comprises a second determining unit 603. The second determining unit 603 is configured to determine the systolic blood pressure from at least one of a first pressure value of the changing pressure at a time point corresponding to the detected occlusion of the artery, and a second pressure value of the changing pressure at a time point corresponding to the detected reopening of the artery.
As is well-known, the systolic blood pressure (SBP) comprises SBP-I and SBP-D, wherein SBP-I is the value of the changing pressure at a time when the artery is occluded during the increase of the changing pressure, and SBP-D is the value of the changing pressure when the artery is reopened during the decrease of the changing pressure. Thus, the first pressure value and the second pressure value are the SBP-I value and the SBP-D value, respectively.
When only one of the first and the second pressure values is available, the systolic blood pressure is determined of the available one. When both the first and the second pressure values are available, the second determining unit 603 can determine the systolic blood pressure in different ways. For example, the systolic blood pressure can be determined as one of the first pressure value and the second pressure value. For another example, the systolic blood pressure can be determined as the higher one of the first pressure value and the second pressure value.
The second determining unit 603 can obtain at least one of the first and the second pressure values in different ways. In an embodiment, the pressure sensor 102 provides a plurality of pressure values at the plurality of time points to the detecting unit 602, and then the detecting unit 602 provides at least one of the first and the second pressure values corresponding respectively to the detected occlusion and reopening of the artery to the second determining unit 603. In another embodiment, the pressure sensor 102 provides a plurality of pressure values at the plurality of time points to the second determining unit 603; the detecting unit 602 provides at least one of two time points corresponding to the detected occlusion and reopening of the artery to the second determining unit 603, and then the second determining unit 603 selects at least one of the first and the second pressure values among the plurality of pressure values from the pressure sensor 102 according to at least one of two time points from the detecting unit 602.
Fig.7 depicts a diagram of a changing pressure in accordance with an embodiment of the present invention. Fig.7 depicts a change of the changing pressure versus time.
Referring to Fig.7, according to an embodiment of the present invention, the changing pressure increases gradually to a maximum pressure value that is sufficiently high for the artery to become occluded, and then starts to decrease to enable the artery to reopen. The pressure values corresponding respectively to the occlusion and the reopening of the artery are denoted as SBP-I and SBP-D.
The maximum pressure value can be set in different ways.
In an embodiment, the maximum pressure value can be predefined. Alternatively, different maximum pressure values can be individually set for different persons. For example, the maximum pressure value is set to be relatively high for a patient with hypertension.
In another embodiment, when the occlusion of the artery is detected in real-time, the maximum pressure value can be adaptively defined according to the detected occlusion. For example, the maximum pressure value is set to be in a range of 20 mmHg to 30 mmHg above the SBP-I value. As shown in Fig.7, as the changing pressure increases, the occlusion is detected to occur at about second 13 and the corresponding SBP-I is 190 mmHg. Accordingly, the maximum pressure value is set to, for example, 220 mmHg, and the changing pressure starts to decrease when it reaches the maximum pressure at about second 15. Referring to Fig.5, the third device 502 can provide a real-time feedback to the first device 501, such that the first device 501 can start to decrease the changing pressure according to the detected occlusion of the artery. In this way, the inflatable cuff is controlled automatically and precisely.
Referring back to Fig.6, the second deriving unit 601 and the detecting 602 will be described hereinbelow.
The second deriving unit 601 derives, from the blood flow signal, at least one variable of a first variable and a second variable. The blood flow signal comprises a Doppler signal. The first variable indicates the magnitude of the blood flow, and the second variable indicates the periodicity of the blood flow. According to an embodiment, a predefined time window slides along the time axis, and a value of each of the first and the second variable is calculated for each time window. For example, the time window can be defined so as to have a width of 3 seconds and slide for 1 second each time, and accordingly, the value of each of the first and the second variable is calculated every second.
The values of the first and the second variable for a given time window can be calculated in different ways. An approach based on time-frequency analysis is described below.
First, the spectrogram of the Doppler signal in the given time window is calculated.
Next, the spectrogram is filtered to remove spectrum components in predefined frequency ranges. For example, the predefined frequency ranges comprises 0-100 Hz and above 3000 Hz.
Next, the amplitude of the filtered spectrogram is accumulated along the frequency axis to obtain a waveform as a function of time, referred to as blood flow waveform hereinafter. Alternatively, after noise has been removed from the filtered spectrogram, the blood flow waveform can be obtained from the filtered spectrogram by extracting the frequency corresponding to the maximum amplitude value along the frequency axis, namely the value of the blood flow waveform at a time point is the frequency corresponding to the maximum amplitude value of the filtered spectrogram among all frequencies at said time point.
Next, the values of the first and the second variable for the given time window are derived from the obtained blood waveform. The value of the first variable is associated with the peak amplitude of the blood waveform, and, for example, it can be the maximum or average value of the peak values in the blood waveform. The value of the second variable is associated with the periodicity of the blood waveform, and for example, it can be the number of peaks per second. Various methods are known to determine the peak values and the number of peaks and will not be further discussed herein.
Consequently, the values of the first and the second variable for a given time window are calculated from the blood flow signal in the given time window.
The detecting unit 602 detects the occlusion and/or reopening of the artery on the basis of at least one variable of the first variable and the second variable.
In an embodiment, for a given time window, the artery is detected as being occluded in the given time window, when the calculated value of the first variable for the given time window is less than the first threshold and/or the calculated value of the second variable for the given time window is outside the first range.
The first threshold and the first range can be determined in different ways. Each of the first threshold and the first range can be constant and predetermined according to statistical data. Alternatively, each of the first threshold and the first range can be determined from the blood flow signal and can therefore vary. For example, the first threshold can be related to noise in the blood flow signal, and the noise can be calculated from the filtered spectrogram. Alternatively, the first threshold can be related to the average peak value in the blood waveform, and for example, be set to 10% to 20% of the average peak value. For example, the first range can be determined according to the mean and the standard deviation of the second variable in the previous time windows. Denoting the mean and the standard deviation by μ and σ, the first range can, for example, be determined as a range [μ-σ, μ+σ].
Further, for a given time window, the artery is detected as being reopened in the given time window, when the calculated value of the first variable for the given time window is greater than a second threshold and/or the calculated value of the second variable for the given time window is within a second range. The second threshold and the second range can, respectively, be identical to the first threshold and the first range. This is the case, for example, when the first threshold and the first range are not constant, but are updated in each time window till the occlusion of the artery, the second threshold and the second range can be set to the latest values of the first threshold and the first range, respectively.
Additionally, when the artery is detected as being reopened in the given time window, the time of reopening can be further determined as occurring at a moment corresponding to the first peak that is greater than the second threshold.
In another embodiment, when the first variable is greater than a second threshold and/or the second variable is within a second range for a predefined time period, the reopening is detected. Preferably, the predefined time period is sufficiently long to contain at least five cycles of the blood flow.
In particular, when the calculated value of the first variable for the current time window is greater than the second threshold and/or the calculated value of the second variable for the current time window is within the second range, the current time window is marked. Then, in a predefined number of subsequent time windows, it is determined whether, for each of the subsequent time windows, the calculated value of the first variable is greater than the second threshold and/or the calculated value of the second variable for the current time window is within the second range. If yes, it indicates that the blood flow is stable, and the artery is determined as being actually reopened in the marked time window. In this way, the possibility of false detection due to the so-called Gap phenomenon can be reduced, and the detected reopening of the artery is therefore more reliable.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. The embodiments are illustrative rather than restrictive. It is intended that the invention include all modifications and variations to the illustrated and described embodiments within the scope and spirit of the invention. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or in the description. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the device claims enumerating several units, several of these units can be embodied by one and the same item of hardware or software. The usage of the words first, second and third, et cetera, does not indicate any ordering. These words are to be interpreted as names.

Claims

CLAIMS:
1. An ultrasound probe comprising:
a plurality of ultrasound transducers (301), each one of the plurality of ultrasound transducers being configured to obtain an echo signal by transmitting an ultrasonic wave, receiving an ultrasonic wave and transforming the received ultrasonic wave into the echo signal.
2. An ultrasound probe as claimed in claim 1 , wherein the plurality of ultrasound transducers (301) are arranged into one or more rows, and each row comprises multiple ultrasound transducers.
3. An ultrasound probe as claimed in claim 2, wherein the ultrasound transducers in two adjacent rows of the plurality of rows are arranged in a way such that the ultrasound transducers in one row have an offset (A) with respect to the ultrasound transducers in the other row.
4. An ultrasound probe as claimed in claim 3, wherein the plurality of ultrasound transducers are of the same width, the ultrasound transducers in each of the plurality of rows are equally spaced with a predefined spacing, and the offset (A) is set to half of the sum of the width and the predefined spacing.
5. An ultrasound probe as claimed in claim 1 , further comprising:
a fixture (302) configured to hold the plurality of ultrasound transducers (301), a surface (303) of the fixture (302) being intended to be attached to the exterior of a body; wherein the plurality of ultrasound transducers (301) are configured in a way such that the angle between the surface (303) and the transmitting/receiving direction of the ultrasonic wave is in a predefined range.
6. A device for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body, comprising:
an ultrasound probe (101) according to any one of claims 1 to 5, the ultrasound probe being intended to be attached to the exterior of the body;
a first deriving unit (102) configured to derive, from each obtained echo signal, at least one Doppler signal, the at least one Doppler signal being associated with the ultrasound transducer obtaining the echo signal and being indicative of information about Doppler shift of the echo signal;
a selecting unit (103) configured to select a Doppler signal from the derived Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
7. A device as claimed in claim 6, wherein the predefined condition includes that:
- the selected Doppler signal is periodic over time; and
- the power of the selected Doppler signal is greater than a threshold.
8. A device as claimed in claim 7, wherein the predefined condition further includes that:
- the power of the selected Doppler signal is the highest.
9. A device as claimed in claim 6, wherein each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and provides information about Doppler shift caused at the predefined distance.
10. A device as claimed in claim 9, further comprising:
a first determining unit (104) configured to determine the location of the artery on the basis of the location of the ultrasound transducer associated with the selected Doppler signal and the predefined distance associated with the selected Doppler signal.
11. A method of acquiring a blood flow signal indicative of at least one characteristic of a blood flow in an artery of a body, comprising the following steps :
obtaining (S410) a plurality of echo signals, each of the plurality of echo signals being obtained by one of a plurality of ultrasound transducers attached to the exterior of the body;
deriving (S420), from each echo signal, at least one Doppler signal indicative of information about Doppler shift of the echo signal;
selecting (S430) a Doppler signal from the obtained Doppler signals according to a predefined condition, the selected Doppler signal being indicative of the at least one characteristic of the blood flow in the artery of the body.
12. A method as claimed in claim 11, wherein the plurality of ultrasound transducers are arranged into multiple rows of ultrasound transducers, and each row comprises multiple ultrasound transducers.
13. A method as claimed in claim 11, wherein the predefined condition includes that:
- the selected Doppler signal is periodic over time; and
- the power of the selected Doppler signal is greater than a threshold.
14. A method as claimed in claim 11 , wherein each of the at least one Doppler signal is associated with a predefined distance from the ultrasound probe, and indicates information about Doppler shift caused at the predefined distance.
15. A system for measuring the systolic blood pressure of an artery of a body, comprising: a first device (501) configured to apply a changing pressure on the artery, the first device being attachable to the exterior of the body;
a pressure sensor (502) configured to obtain a plurality of pressure values of the changing pressure at a plurality of time points;
a second device (503) for acquiring a blood flow signal indicative of at least one characteristic of a blood flow in the artery under the changing pressure according to any one of claims 6 to 10;
a third device (504) configured to determine the systolic blood pressure on the basis of the acquired blood flow signal.
PCT/IB2012/053852 2011-07-28 2012-07-27 Ultrasound probe, method and device for acquiring a blood flow signal of an artery and system for measuring systolic blood pressure WO2013014647A1 (en)

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