EP1898794A2

EP1898794A2 - Method and apparatus for use with doppler measurements in medical applications

Info

Publication number: EP1898794A2
Application number: EP06745145A
Authority: EP
Inventors: Dan Manor; Eli Levi; Adi Yosef
Original assignee: Viasys Ireland Ltd
Current assignee: Viasys Ireland Ltd
Priority date: 2005-06-14
Filing date: 2006-06-14
Publication date: 2008-03-19
Also published as: WO2006134595A2; CN101277649A; KR20080057216A; WO2006134595A3; KR101247520B1; JP2008543415A; EP1898794A4

Abstract

A novel method and apparatus are presented for use in analyzing and presenting Doppler data in a Doppler ultrasound system. At least one distance range from an ultrasound transducer along an ultrasound beam is controlled. This at least one distance range includes a plurality of successive locations between a first distance along the ultrasound beam and a second distance along the ultrasound beam. A Doppler signal spectrum representative of the plurality of locations within said at least one distance range is displayed in at least one display window, respectively.

Description

METHOD AND APPARATUS FOR USE WITH DOPPLER MEASUREMENTS

IN MEDICAL APPLICATIONS

FIELD OF THE INVENTION

The invention is generally in the field of medical techniques related to measurements of blood flow velocities, and relates to a method and apparatus for optimizing measurements and monitoring of Doppler signals.

BACKGROUND OF THE INVENTION

Application of the Doppler effect for measurements of physiological signals in medical applications has been used for many years. In particular, the Doppler effect has been used to measure blood flow velocities in cardiovascular circulation for assessment and diagnosis of a patient's condition. In general, application of Doppler technology for blood flow velocities is based on transmitting a beam with a special transducer, normally an ultrasound beam, into a patient's body and in a general direction towards the target blood vessel. The beam is typically with a constant carrier frequency. The beam is reflected by any moving particles that are along its path, and is returned to a receiver located in the transducer, with a frequency shift that is proportional to the component of the velocity of the moving particles in the direction of the beam. In applications that are related to velocity measurements in flowing blood, the reflecting particles are typically the blood cells. Medical Doppler devices are able to perform the required filtering and frequency transforms on the received signals, and display the resulting velocities or Doppler shift frequencies in a graphical manner whereby the X axis relates to time (typically in units of seconds), and the Y axis displays either the Doppler shift frequency (typically in units of Kilo Hertz) or the velocity (typically in units of centimeters per second). When the full range of velocities or frequencies is displayed for a given time, the resulting display is called a spectrum analysis.

In most medical examinations for blood flow velocity measurements, and particularly during most non-invasive medical procedures, the blood vessel is not visible to an examiner. Hence, the examiner is required to aim the transducer and the transmitted beam towards a general direction of the assumed location of the blood vessel within the patient's body. The vessel is typically identified when Doppler signals are received and a velocity or a Doppler shift frequency signal or spectrum is displayed.

Two common operation modes are known in the application of the Doppler method for blood flow measurements. The first mode is known as Continuous Wave Doppler (CW) and the second mode is known as Pulse Wave Doppler (PW).

With CW mode, a transducer normally houses two transmitting/receiving elements, whereby the first element (the transmitting element) continuously transmits a beam, and the second element functions as a receiver (the receiving element) and continuously receives reflected signals. Thus, the received Doppler signals in CW mode reflect movement of particles from all sites along the path of the transmitted beam. The main advantage of CW mode is the ability to receive Doppler signals rather quickly. However, the main limitation of this mode is that with CW operation the examiner cannot discriminate between different blood vessels since the Doppler signals are received from all the blood vessels and other physiological movements that are along the path of the beam, and there is no specificity for a distance from the transducer. In addition, due to the continuous beam transmission into the body tissues, the beam amplitude is normally required to be small in order to minimize the potential hazardous effects of tissue insonation, and therefore medical applications that require high beam penetration energy, such as penetration of the skull for transcranial velocity measurements, are very difficult.

The PW mode is an alternative Doppler solution to overcome the limitations of CW Doppler. With PW mode, the transducer typically houses only a single transmitting/receiving element. The transmitter sends bursts of waves, the bursts being composed of a several waveforms (a train of waveforms) with a given carrier frequency, and are repeated at another given frequency, the Pulse Repetition Frequency (PRF). After the transmitted burst the transducer element acts as a receiver to receive the reflected Doppler signals. By measuring the time from the beginning of the transmitted burst, Doppler signals can be received from a defined distance from the transducer face, while the duration (or length) of the transmitted burst defines the size of the region along the beam from which signals are acquired (sample volume). Thus, PW allows distance discrimination along the path of the transmitted beam. This feature is particularly advantageous when the examiner wants to discriminate between different blood vessels that cross the path of the transmitted beam, or to discriminate between various locations along a single vessel that lies in the direction of the beam, such as the Middle Cerebral Artery during a transcranial Doppler examination from a temporal approach. In addition, since the beam transmission is relatively short in duration relative to the Pulse Repetition Interval (PRI), the transmitted wave amplitude is normally allowed to be larger than that of the CW mode, thus allowing penetration of difficult regions such as the temporal bone. The main limitation of PW mode, though, is that the measurement procedure becomes rather difficult, since the user is now required not only to aim the transducer towards the assumed position of the blood vessel, but also to set a specific distance from the transducer face from which the Doppler signals are received from the sample volume. Thus, it is possible that the transducer direction is correct, but the set distance is incorrect and the examiner will not be able to appreciate this information.

To overcome this last limitation, as well as to address some other applications, several Doppler systems offer the multigating option, which allows the examiner to simultaneously view several graphical displays of velocity spectrums, whereby each display shows the velocity spectrum obtained at a specific distance from the transducer's face.

SUMMARY OF THE INVENTION

The use of multigating Doppler and multiple graphical displays, although assisting in faster signal identification and transducer orientation during measuring procedure, is still limited in that it displays velocity spectrums as a function of sample volume size at several specific user-defined distances.

The present invention provides a new method and apparatus for providing and displaying Doppler measurements to an examiner during a Doppler measurement procedure. This is particularly useful for measurements of blood flow velocities in blood vessels. A novel Doppler examination mode according to the invention utilizes the advantages of both the CW and PW modes in a single examination of blood flow velocities. According to this novel examination mode, Doppler signal information from a plurality of successive locations or distances along a carrier beam, typically ultrasound, are integrated together and analyzed to present a Doppler signal from the respective distance range. For comparison, the pulse wave Doppler mode allows presentation of a Doppler signal from a single location along the beam, while the continuous wave Doppler mode presents Doppler data that is obtained from the face of the transducer and on to infinity.

Also, the present invention provides various presentation modes, including a

Doppler display from a plurality of distance ranges, and a main window display for a corresponding optimal signal obtained in one of these distance ranges.

In the present invention, a transducer is typically used in a PW Doppler mode, thus using a single element transducer. The receiver is continuously open in between the transmitted wave bursts, receiving Doppler signals along the beam path, starting from practically the transducer face and until the maximal distance that is allowed by the active PRF. The Doppler signals are acquired from multiple locations along the beam and until the maximal distance. In typical PW mode, one of these multiple locations is analyzed and graphically displayed as a velocity or Doppler shift spectrum.

The term location, as used herein, defines a specific distance from the face of the transducer, from which Doppler data is being acquired and analyzed. This data is displayed as a Doppler velocity spectrum that represents this specific distance. The term distance range, as used herein, defines a plurality of locations starting at one specific distance from the face of the transducer, and ending at a second specific distance from the face of the transducer. A set distance range is used to describe a user defined distance range. The minimal first specific distance allowed according to the present invention is the face of the transducer, whereas the maximal second specific distance is typically limited according to the active PRF.

The present invention allows for the user to selectively set one or more distance ranges of interest. Different sizes of ranges of interest can be defined, and even ranges that overlap each other. For comparison, the multigating option is unable to display Doppler velocity spectrum in a single graphical display from a set distance range, but rather can display Doppler velocity spectrum only from a given single specific location.

For each of the set distance ranges, a graphical display of the velocity or Doppler shift spectrum is generated, that is composed of the integrated signals that are received from the plurality of locations that correspond to set distance range. Thus, if for example the selected range is set by the examiner to be the maximal allowed distance range, a Doppler signal that is similar in nature to the CW Doppler mode is obtained while working with basically the PW mode.

This invention allows use of one-element transducers, insonating higher energy PW Doppler bursts that can penetrate difficult locations, and have the potential to selectively discriminate signals from various locations along the beam, yet maintain the ability to view a graphical velocity spectrum display in a manner similar to that of the CW mode.

This invention is particularly advantageous during an insonation into a patient's body, whereby the user selects to start with a set distance range that is maximally open in order to quickly identify the location of the target blood vessel, and after optimizing the direction of the transducer towards the body viewing graphical spectrum displays of smaller, more specific distance ranges of interest along the beam.

The invention can be further advantageous when the examiner subdivides the selected maximal distance range into a selected number of graphical displays, each providing a spectrum display from a different selected distance range. During an examination, all of the graphical displays can show simultaneously the integrated velocity spectrums within each of these selected distance ranges, thus allowing the examiner to quickly identify and focus on the preferred range of interest.

By means of example, during a transcranial Doppler examination from a temporal approach, the selected set distance ranges maybe such that in one or more ranges the Middle Cerebral Artery Doppler velocity spectrum is shown, and in a further distance range the bifurcation of the Middle and Anterior Cerebral Arteries is shown, and in an even further distance range the Doppler velocity spectrum typical to the Anterior Cerebral Artery is shown. The examiner can thus quickly focus on the preferred range of interest and/or identify pathologies which may have been otherwise overseen with normal PW operation.

Further advantages of the present invention relate to the simultaneous display of the graphical spectrum displays in accordance with the selected distance ranges, and in parallel displaying in a central display area, as is customary with PW or CW displays, the Doppler velocity spectrum from a specific location from the transducer face that lies within one of the selected distance ranges. Furthermore, a controller may be added to relate the selected distance range

Doppler velocity spectrum display and the main Doppler velocity spectrum display of either a set range or a specific location. Such a controller may be in the form, but not limited to, a touch screen, whereby touching the range display of interest or clicking on it with a mouse or using a remote control results in an update of the main spectrum display to show the optimal velocity spectrum that corresponds to one of the distances that are included in the selected range of interest. In addition, a pointer may be included to highlight the graphical spectrum display that correlates to the display presently shown in the main spectrum display.

Thus, according to one broad aspect of the invention, there is provided an apparatus for use in analyzing and presenting Doppler data in a Doppler ultrasound system, the apparatus comprising: a controller configured to control at least one distance range from an ultrasound transducer along an ultrasound beam, said at least one distance range including a plurality of successive locations between a first distance along the ultrasound beam and a second distance along the ultrasound beam; and a display unit configured for displaying a Doppler signal spectrum representative of said plurality of locations within said at least one distance range in at least one display window, respectively.

The apparatus is preferably configured for defining a plurality of the distance ranges and simultaneously displaying the Doppler signal spectra within said distance ranges in a plurality of the display windows, respectively. At least some of the distance ranges may overlap. At least some of the distance ranges may be continuous along the ultrasound beam.

The display unit may be configured for displaying a characteristic Doppler signal spectrum corresponding to a single location within said at least one distance range. This characteristic Doppler signal spectrum is displayed in at least one separate graphical display. The characteristic Doppler signal spectrum may correspond to the single location within the plurality of distance ranges. According to another broad aspect of the invention, there is provided a method for use in analyzing and presenting Doppler data in a Doppler ultrasound system, the method comprising: controlling at least one distance range from an ultrasound transducer along an ultrasound beam, said at least one distance range including a plurality of successive locations between a first distance along the ultrasound beam and a second distance along the ultrasound beam; ' and displaying a Doppler signal spectrum representative of said plurality of locations within said at least one distance range in at least one display window, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows the matrix of Doppler data that is obtained from a plurality of locations as a function of time;

Fig. 2 shows an example of an integrated Doppler velocity spectrum display within a set range of distances Dl to D2;

Fig. 3 depicts one possible display mode of the velocity spectrums within set range distances in accordance with an embodiment of the invention; and

Fig. 4 is a representation of a second possible display mode, whereby a main graphical display window of the velocity spectrum that correlates to the distance within one of the set ranges as displayed in Figure 2 is shown. DETAILED DESCRIPTION OF THE INVENTION

The following description describes a novel method and apparatus for providing and displaying Doppler measurements to an examiner during a Doppler measurement procedure that typically measures blood flow velocities in a patient's blood vessel. In order to avoid unnecessary information that may deter the reader from the invention, particular details that are clear to people skilled in the art such as electrical circuits and drawings, control units, general Doppler algorithms and software controls have been avoided in this description.

Fig. 1 is a schematic representation of the Doppler data that is acquired during Doppler measurements. In general, for each transmitted burst i, a plurality of signals is received from a plurality of locations j. Thus, a signal, generally at 101, received from the first transmitted burst and at the first location is A_y, the signal received from the second location is Ay₊i, and so on until the maximal location n, corresponding to signal Ai_j+n- The signal that is received from the second transmitted burst and at the first location is A{₊i_j, at the second location is _^4_/+i^₊i, and so on until location n. This process is repeated for each transmitted burst in a new row. Each row, generally at 120, is a data vector that represents signals that are received from a specific single burst for all locations along the path of the beam. Each column 121 represents signals that are received for one specific location as a function of time. Together, the data points described in Fig. 1 form the Doppler matrix.

Typical data processing in the PW mode in order to display the Doppler velocity spectrum at one specific location requires mathematical operations on the received signals that are included in the data column 121 for said specific location. Such mathematical operations may include data filtering and application of transformation methods to convert the data from the time domain to the frequency domain, with the output typically being a graphical representation of the Doppler velocity spectrum for said one location. In the present invention, the set distance range is first defined between location Dl (108) and location D2 (105). A new integration data column is generated, whereby each data point in the column that corresponds to a given burst represents the summation of data points between Dl and D2 for that specific burst. The generation of this integration column can be performed at any stage of the mathematical operations. Thus, the integration column can be generated before or after the filtering process, and before or after the time to frequency domain transformation. The mathematical operations are continued in order on the integration column, with a resulting typically graphical display of the Doppler velocity spectrum for said set distance range.

Fig. 2 is a graphical display of the basic concept in accordance with the embodiment of the present invention. A Doppler velocity waveform or spectrum 104 is displayed in a graphical window 102, and represents an integration of the Doppler signal that is acquired from a plurality of locations within the set distance range between locations Dl 108 and D2 105. Dl and D2 are measured from the face of the transducer and along the transmitted beam as previously described. The beam used in many medical applications is typically an ultrasound beam. A similar display in the CW mode would be equivalent to Dl=O, and D2 being equal to infinity. A similar display in the PW mode would require that D1=D2. It should be clear that the waveform shown in Fig. 2 is by way of example only, and can represent a full velocity or Doppler shift spectrum analysis as is typical with many Doppler systems.

Fig. 3 represents an extension of the display in Fig. 2, and depicts another possible display that may be typical for the representation of Doppler signals in accordance with the present invention. A plurality of set distance ranges Dl 108 to D6 109 is shown. A plurality of graphical display windows 102 is shown, each displaying the Doppler velocity spectrum that is generated based on the integration of the Doppler signals from a plurality of locations within the respective set distance range described above. Each window 102 corresponds to the respective set distance ranges Dl to D6, such that the first graphical window displays the integrated Doppler signal that is obtained from locations Dl 108 to D2 105, and so on until the maximal displayed distance D6 109. An accompanying bar 106 or tic marks, or generally any other graphical form of display, can accompany the display in order to show the respective distance ranges for each graphical window 102. The Doppler velocity waveform or spectrum 104 is typically different in magnitude and shape for each graphical window. The selection of five graphical windows in the figure between Dl and D6 is by means of example only. Dl is typically the distance that is the closest to the transducer face, while D6 is typically the distance that is farthest from the transducer face and along the beam path. In this specific example, the set distance ranges are continuous. However, the invention allows an overlap in the selected distance ranges, or some discontinuity in the set distance ranges.

Fig. 4 represents an even further extension of the display in Figs. 2 and 3, and depicts another possible display that may be typical for the representation of Doppler signals in accordance with the present invention. This display may be most useful to an examiner that wishes to focus on a specific location as in the PW mode, yet aim the transducer and make examination decisions as in the CW mode and in accordance with the present invention. A main graphical display window 110 is included in the display. This main window will typically be larger in size relative to the range display windows 102 since it typically displays Doppler velocity waveform or spectrum 112 measurements from the target location. While the display 110 could possibly display the integrated Doppler signals from a set distance range, for instance the distance between D4 and D5 in the example given here, the more common embodiment will be of a Doppler velocity or spectrum signal from a specific location as is common during the PW mode. In the present example, the specific location lies between D4 and D5, and its respective location is further depicted by an arrow or marker 113. Alternatively or in addition to this preferred embodiment, a specific indicator of the location (depth xx) 115 can be related to the main window 110.

It will be appreciated that while specific embodiments of the invention have been described for purposes of illustration, various modifications may be made without deviating from the scope of this invention.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for use in analyzing and presenting Doppler data in a Doppler ultrasound system, the apparatus comprising: a controller configured to control at least one distance range from an ultrasound transducer along an ultrasound beam, said at least one distance range including a plurality of successive locations between a first distance along the ultrasound beam and a second distance along the ultrasound beam; and a display unit configured for displaying a Doppler signal spectrum representative of said plurality of locations within said at least one distance range in at least one display window, respectively.

2. The apparatus of Claim 1, configured for defining a plurality of the distance ranges and simultaneously displaying the Doppler signal spectra within said distance ranges in a plurality of the display windows, respectively.

3. The apparatus of Claim 1, wherein the display unit is configured for displaying, in at least one separate graphical display, a characteristic Doppler signal spectrum corresponding to a single location within said at least one distance range.

4. The apparatus of Claim 2, wherein the display unit is configured for displaying, in at least one separate graphical display, a characteristic Doppler signal spectrum corresponding to a single location within at least one of said distance ranges.

5. The apparatus of Claim 2, wherein at least some of said plurality of distance ranges overlap.

6. The apparatus of Claim 4, wherein at least some of said plurality of distance ranges overlap.

7. The apparatus of Claim 2, wherein at least some of said plurality of distance ranges are continuous along the ultrasound beam.

8. The apparatus of Claim 4, wherein at least some of said plurality of distance ranges are continuous along the ultrasound beam.

9. The apparatus of Claim 4, wherein said characteristic Doppler signal spectrum corresponds to the single location within the plurality of distance ranges.

10. A method for use in analyzing and presenting Doppler data in a Doppler ultrasound system, the method comprising: controlling at least one distance range from an ultrasound transducer along an ultrasound beam, said at least one distance range including a plurality of successive locations between a first distance along the ultrasound beam and a second distance along the ultrasound beam; and displaying a Doppler signal spectrum representative of said plurality of locations within said at least one distance range in at least one display window, respectively.

11. The method of Claim 10, comprising defining a plurality of the distance ranges and simultaneously displaying the Doppler signal spectra within said distance ranges in a plurality of the display windows, respectively.

12. The method of Claim 10, comprising displaying, in at least one separate graphical display, a characteristic Doppler signal spectrum corresponding to a single location within said at least one distance range.

13. The method of Claim 11, comprising displaying, in at least one separate graphical display, a characteristic Doppler signal spectrum corresponding to a single location within at least one of said distance ranges.

14. The method of Claim 11, wherein at least some of said plurality of distance ranges overlap.

15. The method of Claim 13, wherein at least some of said plurality of distance ranges overlap.

16. The method of Claim 11, wherein at least some of said plurality of distance ranges are continuous along the ultrasound beam.

17. The method of Claim 13, wherein at least some of said plurality of distance ranges are continuous along the ultrasound beam.

18. The method of Claim 13, wherein said characteristic Doppler signal spectrum corresponds to the single location within the plurality of distance ranges.