WO2019192970A1 - Imagerie ultrasonore par ondes de cisaillement présentant une précision et une fiabilité améliorées - Google Patents

Imagerie ultrasonore par ondes de cisaillement présentant une précision et une fiabilité améliorées Download PDF

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Publication number
WO2019192970A1
WO2019192970A1 PCT/EP2019/058211 EP2019058211W WO2019192970A1 WO 2019192970 A1 WO2019192970 A1 WO 2019192970A1 EP 2019058211 W EP2019058211 W EP 2019058211W WO 2019192970 A1 WO2019192970 A1 WO 2019192970A1
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shear wave
processor
confidence
stiffness
imaging system
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PCT/EP2019/058211
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English (en)
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James Robertson JAGO
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Koninklijke Philips N.V.
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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
    • A61B8/48—Diagnostic techniques
    • A61B8/485—Diagnostic techniques involving measuring strain or elastic properties
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/46—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient
    • A61B8/461—Displaying means of special interest
    • A61B8/463—Displaying means of special interest characterised by displaying multiple images or images and diagnostic data on one display
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
    • G01S15/8909—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration
    • G01S15/8915—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration using a transducer array
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52019—Details of transmitters
    • G01S7/5202—Details of transmitters for pulse systems
    • G01S7/52022—Details of transmitters for pulse systems using a sequence of pulses, at least one pulse manipulating the transmissivity or reflexivity of the medium
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52023—Details of receivers
    • G01S7/52036—Details of receivers using analysis of echo signal for target characterisation
    • G01S7/52042—Details of receivers using analysis of echo signal for target characterisation determining elastic properties of the propagation medium or of the reflective target
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52053—Display arrangements
    • G01S7/52057—Cathode ray tube displays
    • G01S7/52071—Multicolour displays; using colour coding; Optimising colour or information content in displays, e.g. parametric imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52053—Display arrangements
    • G01S7/52057—Cathode ray tube displays
    • G01S7/52073—Production of cursor lines, markers or indicia by electronic means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/46—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient
    • A61B8/461—Displaying means of special interest
    • A61B8/466—Displaying means of special interest adapted to display 3D data
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/46—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient
    • A61B8/467—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient characterised by special input means
    • A61B8/469—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient characterised by special input means for selection of a region of interest
    • 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
    • A61B8/483—Diagnostic techniques involving the acquisition of a 3D volume of data
    • 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
    • A61B8/5207—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of raw data to produce diagnostic data, e.g. for generating an image
    • 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
    • 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
    • A61B8/5238—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of medical diagnostic data for combining image data of patient, e.g. merging several images from different acquisition modes into one image
    • A61B8/5246—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of medical diagnostic data for combining image data of patient, e.g. merging several images from different acquisition modes into one image combining images from the same or different imaging techniques, e.g. color Doppler and B-mode

Definitions

  • This invention relates to medical ultrasound imaging systems and, in particular, to ultrasound systems which perform measurements of tissue
  • An advantage of ultrasound imaging and other imaging modalities is that, in addition to depicting the structure of tissue and pathology in the body, it is also possible to anatomically visualize
  • tissue or pathology being imaged. This is done by acquiring two images of the anatomy, one structural and another which is parametric. The two images are then
  • a basic parametric image in ultrasound is a colorflow image, whereby a B mode image of tissue structure is overlaid with a color image representing the
  • the structure of blood vessel walls frames the blood flow information, showing the clinician parameters of the blood flow at the locations where it is occurring.
  • the clinician can diagnose blood flow functionality at specific locations in the body by observing parameters of the flow such as its velocity and direction at anatomical locations defined by the surrounding tissue.
  • Other parametric imaging procedures are also well known in ultrasound, such as tissue motion imaging, contrast imaging of tissue perfusion, and strain imaging of tissue elasticity.
  • shear wave imaging is an orthogonal orthogonal orthogonal ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇
  • stiffer tissue regions of the breast or liver might be malignant or scarred, whereas softer and more compliant areas are more likely to be benign and healthy. Since the stiffness of a region is known to correlate with malignancy or benignity, and scarred or healthy cells, elastography provides the clinician with another piece of evidence to aid in diagnosis and determination of a treatment regimen.
  • shear wave measurements are made throughout a region of interest.
  • the physiological phenomena behind an ultrasonic shear wave measurement are as follows. When a point on the body is compressed, then released, the
  • a shear wave is the response in the surrounding tissue to the shear wave
  • the force needed to push the tissue downward can be produced by radiation pressure from an ultrasound pulse, and ultrasound reception can be used to sense and measure the tissue motion induced by the shear waves.
  • Shear wave velocity is determined by local tissue mechanical properties.
  • the shear wave will travel at one velocity through soft tissue, and at another, higher velocity through stiffer tissue.
  • the positioning of the tracking pulses can also be moved laterally to follow the propagation of the shear wave.
  • the data from the repetitively sampled tracking pulse vectors is processed to find the times at which the shear wave causes a peak displacement at each point of the tracking pulse vector, preferably by cross-correlation, curve fitting or interpolating successive displacement measurements. Analysis of the times at which points on adjacent sampling vectors experience peak
  • shear wave displacement produces a measurement corresponding to the velocity of the shear wave at particular vector locations, with velocity variations indicating tissues of different stiffness or elasticity. Since the shear waves attenuate rapidly, it is generally not possible to acquire shear wave data from an entire image field with a single push pulse vector. Thus, the process is repeated at other locations in the tissue to acquire shear wave velocity
  • the process is repeated until shear wave data has been acquired over the desired image field.
  • the velocity information is then presented as a two- or three- dimensional overlay of the structural B mode image of the tissue, color-coded by the shear wave velocity data or corresponding stiffness values at points in the image.
  • the shear wave velocity or stiffness values are reviewed as an image.
  • ROI regions of interest
  • displacements are at best about 10 ym, and under more common, less favorable circumstances are closer to 1 ym.
  • the precision of displacement estimates for accurate shear wave measurements should be at least on the order of 100 nm.
  • shear wave measurements will be excluded from the ultrasound image and shear wave computations, including for example the calculation of average shear wave speed or stiffness values within or across ROIs.
  • the clinician may decide that only shear wave measurements with a confidence factor above 50% should be used in the image and for the calculation of average values. The 50% percentage is selected and measurements with confidence factors below 50% are excluded from calculations of stiffness in the ultrasound image. The clinician thus has a greater confidence in the accuracy and reliability of the stiffness measurements depicted in his diagnostic shear wave image and related computations such as average values.
  • One clinician can use a 50% confidence factor cutoff, while another clinician favors a 70% cutoff.
  • the different selections can yield different stiffness measurements for the same patient, which consequently will result in different values for average stiffness for that patient.
  • a clinician can select different confidence factors for different patients or even for the same patient on different days, depending for instance upon the technical difficulty of the exam that day. Shear wave measurements and images with these differing results may thus not be suitable for serial studies or clinical decision-making. Accordingly, it is desirable to make shear wave measurements and form shear wave images which are consistent in terms of accuracy and reliability and that are less operator dependent .
  • the present disclosure generally relates to an ultrasonic imaging system for shear wave analysis.
  • the system includes an ultrasonic array configured to transmit a push pulse along a predetermined vector to generate a shear wave and to receive echo signals indicative of shear wave tissue displacement in a region of interest.
  • the ultrasound array is typically included in a probe, such as a handle-held probe.
  • One or more processors are in communication with the array and at least memory comprising instructions that when read by the processor cause the processor to execute one or more steps.
  • the processor is
  • tissue stiffness or shearwave velocity values for points of the region of interest
  • confidence or reliability values for the points of the region of interest
  • the at least one processor configured to execute one or more steps may be one processor or a combination of processors.
  • processors may be particularized to carry out one or more actions.
  • the present disclosure describes several processors, including a shear wave processor, confidence factor processor, weighting processor, etc., and these processors may be the same or different.
  • the present disclosure includes ultrasonic imaging systems for shear wave analysis.
  • An ultrasound system of the present disclosure can include an ultrasonic array probe configured to transmit a push pulse along a predetermined vector to generate a shear wave, and to receive echo signals indicative of shear wave tissue displacement in a region of interest, a shear wave processor that is responsive to the received echo signals and is configured to determine tissue stiffness or shearwave velocity values for points of the region of interest, a confidence factor processor adapted to produce confidence or reliability values for the points of the region of interest, and a stiffness/velocity weighting processor that is adapted to produce a weighted average tissue stiffness or weighted average velocity value for the region of interest based at least in part on the confidence or reliability values.
  • the present disclosure includes methods for shear wave analysis.
  • a method of the present disclosure can include generating a shear wave, receiving echo signals indicative of shear wave tissue displacement in a region of
  • tissue stiffness or shearwave velocity values for points of the region of interest, producing confidence or reliability values for the points of the region of interest, producing a
  • weighted average tissue stiffness or weighted average velocity value for the region of interest based at least in part on the confidence or reliability values.
  • the stiffness/velocity is the stiffness/velocity
  • weighting processor is further adapted to produce a plurality of weighted average tissue stiffness or weighted average velocity values for a plurality of regions of interest.
  • the system can include an image processor that is adapted to produce a shear wave stiffness or velocity image.
  • the image processor can be further adapted to overlay the shear wave
  • the confidence factor processor can be further
  • the confidence factor processor can be further adapted to produce confidence or reliability values based on at least one of tissue motion and blood flow location in the region of interest.
  • the stiffness/velocity weighting processor can be further adapted to produce confidence or reliability values with a weight of zero for blood flow locations in the region of
  • the system can include a confidence map memory adapted to store a map of confidence or reliability values.
  • An image processor can be coupled to the confidence map memory and adapted to produce a confidence map image for display.
  • the image processor can be further adapted to display both the confidence map image and a shear wave image.
  • the system can further include a multiline receive beamformer.
  • the shear wave processor can include a shear wavefront peak detector, an A-line r.f. cross correlator, and/or an A-line memory.
  • stiffness/velocity weighting processor can be
  • S aV erage is the weighted average tissue stiffness or the weighted average shear wave velocity value
  • S n is the measured tissue stiffness or shear wave velocity value for a point n in a region of interest
  • C n is the confidence value for the point n .
  • FIGURE 1 illustrates in block diagram form an ultrasonic imaging system in accordance with the principles of the present invention.
  • FIGURE 2 spatially illustrates a sequence of pulses along a push pulse vector, the resultant shear wavefront, and a series of tracking pulse vectors.
  • FIGURE 3 illustrates four laterally adjacent groups of 4x multiline tracking pulse vectors.
  • FIGURE 4 illustrates the transmission and reception of a 4x multiline pulse for the production of four adjacent multiline tracking pulse vectors in a region of interest.
  • FIGURE 5 illustrates shear wave displacement curves at two locations as it progresses through tissue .
  • FIGURE 6 illustrates an example embodiment for calculating a weighted average velocity or stiffness value according to the present invention.
  • an ultrasonic shear wave imaging system which improves the accuracy and reliability of shear wave measurements.
  • a confidence map is formed representing confidence factors for shear wave velocity or stiffness
  • the velocity or stiffness values are thereby compensated for variability in measurement confidence without the inconsistency arising from differences in user input. This is particularly significant for single stiffness or velocity
  • An ultrasound system constructed for the measurement of shear waves is shown in block diagram form.
  • An ultrasound probe 10 has an array 12 of transducer elements for
  • the array can be a one dimensional or a two-dimensional array of transducer elements. Either type of array can scan a 2D plane and a two-dimensional array can be used to scan a volumetric region in front of the array.
  • the array elements are coupled to a transmit beamformer 18 and a multiline receive beamformer 20 by a transmit/receive (T/R) switch 14. Coordination of transmission and reception by the beamformers is controlled by a beamformer controller 16.
  • multiline receive beamformer produces multiple, spatially distinct receive lines (A-lines) of echo signals during a single transmit-receive interval.
  • the echo signals are processed by filtering, noise reduction, and the like by a signal processor 22, then processed by a shear wave processor comprising the following components.
  • the received A-lines are stored in an A-line memory 24. Temporally distinct A-line samples relating to the same spatial vector location are associated with each other in an
  • the r.f. echo signals of successive A-line sampling of the same spatial vector are cross- correlated by an A-line r.f. cross-correlator 26 to produce a sequence of samples of tissue displacement for each sampling point on the vector.
  • the A-lines of a spatial vector can be Doppler
  • a wavefront peak detector 28 is responsive to detection of the shear wave displacement along the A-line vector to detect the peak of the shear wave displacement at each sampling point on the A-line.
  • this is done by curve-fitting, although cross-correlation and other interpolative techniques can also be employed if desired.
  • the time at which the peak of the shear wave displacement occurs on an A-line is noted in relation to the times of the same event at other A-line locations, all to a common time reference, and this information is
  • a completed map indicates the tissue stiffness or velocity of the shear wave at spatially different points in a 2D or 3D image field scanned by push pulse transmission and shearwave acquisition by the probe 10.
  • the stiffness or velocity display map is coupled to an image
  • processor 34 which processes the map for display, typically overlaying the velocity map on an
  • the image is anatomical (B mode) ultrasound image of the tissue for display on an image display 36.
  • processor can also compute aggregate shear wave measurement values for display, such as the average stiffness of a region of interest of an image, using the stiffness values of a region of interest, e.g., pixel values .
  • FIGURE 2 is an illustration of the use of four push pulses to create a composite shear wavefront.
  • the four push pulses are transmitted along vectors 44, 54, 64 and 74 which are seen to be aligned along a single vectorial direction in FIGURE 2.
  • the shallowest push pulse of vector 44 is transmitted first, followed by successively deeper push pulses 54, 64, and 74, the shear wavefronts of the respective push pulses will have propagated as indicated by waves 46, 56, 66, and 76 by a time shortly after the last push pulse (vector 74) has been transmitted.
  • the shear waves 46, 56, 66, and 76 travel outward from the push pulse vector, they are interrogated by tracking pulses 80 shown in spatial sequence along the top of the drawing. Tracking pulses can occur between as well as after push pulses.
  • the velocity of the laterally traveling shear wave is detected by sensing the tissue displacement caused by the shear wave as it proceeds through the tissue. This is done with time-interleaved sampling pulses transmitted adjacent to the push pulse vector as shown in FIGURE 3.
  • the push pulse (s) 40 is transmitted along push pulse vector 44 to cause a laterally traveling shear wave.
  • A-line vectors adjacent to the push pulse vector 40 are sampled by sampling pulses Tl, T2, T3, T4, and T5 transmitted along each vector in a time-interleaved sequence.
  • the first vector location A1 is sampled by a first pulse Tl, then the second vector location A2 by the next pulse T2, then A3, A4, and A5.
  • PRF pulse repetition frequency
  • the pulse repetition interval PRI
  • each of the five vector locations is sampled once in every five sampling pulses in this example.
  • every vector location is pulsed fifty-five times for a total tracking time of 27.5 msec.
  • Each pulse results in echoes returning from along the vector which are sampled by a high speed A/D converter.
  • the typical ensemble length at each echo location on a sampling vector is 40-100 samples.
  • the sampling rate will be chosen in consideration of the frequency content of the shear wave displacement being detected so as to satisfy the Nyquist criterion for sampling. Since the purpose of the sampling is to sense and track the displacement effect of the shear wave as it
  • the vector locations may be located closer together for slowly moving shear waves and further apart for more rapidly moving shear waves. Other sequences of time-interleaving the vector sampling may also be employed. For example,
  • odd-numbered vectors could be sampled in sequence, followed by sampling of the even-numbered vectors.
  • vector locations A1-A3 could be sampled in a time-interleaved manner, then vector locations A2-A4, then vector locations A3-A5 to track the shear wave displacement as it progresses.
  • Other sequences may also be employed based upon the exigencies of the situation.
  • the ensembles of time- interleaved samples at each point along each sampling vector are then processed to find the time of peak tissue displacement at each point of each vector.
  • multiline transmission and reception is employed so that a single tracking pulse can simultaneously sample a plurality of adjacent, tightly spaced, A-line
  • FIGURE 4 one technique for multiline transmission and reception is shown.
  • a single A-line tracking pulse with a beam profile 82a, 82b is transmitted as indicated by the wide arrow A#.
  • the broad beam profile insonifies multiple receive line locations as shown in the drawing.
  • the tracking pulse is a so- called "fat pulse” as described in US Pat. 4,644,795 (Augustine), for example.
  • four receive line locations Al-1, Al-2, Al-3 and Al-4 are insonified. Echoes from the four receive lines (4x multiline) are received in response to the single transmit pulse and are appropriately delayed and summed to produce coherent echo signals along each of the receive line locations.
  • beamformers are typically used to decrease the acquisition time and thereby increase the frame rate of live ultrasound images, which is particularly useful when imaging the beating heart and blood flow in real time echocardiography. They are also useful in 3D ultrasound imaging so that real time frame rates of display can be attained. See, in this regard, US Pat. 6,494,838 (Cooley et al . )
  • the benefit of multiline acquisition is two-fold: it enables a closely-spaced sampling line density and rapid acquisition of a short duration shear wave which only travels a short distance through tissue before being dissipated by attenuation.
  • FIGURE 3 illustrates the use of 4x multiline reception for transmission and reception along each sampling vector A1-A5.
  • a first tracking pulse Ti is transmitted close to the push pulse vector 44, insonifying four receive line locations Al-1 to Al-4 and four multiline A-lines are received in response from the lateral region Al .
  • the four multilines are centered with respect to the transmitted tracking pulse, echoes from two A-lines are received on each side of the center of the tracking pulse beam center, shown by Al-1 and Al-2 to the left of center and Al-3 and Al-4 to the right of center.
  • the A-lines are spaced 0.5mm apart from each other.
  • Shear waves generally move at a speed of 1-10 meters per second, and consequently tracking pulses are repetitively transmitted down regions Al- A5 in a time-interleaved manner and A-line samples received from the A-line locations during the time intervals between push pulses (when there are such intervals), and for 20 msec after the last push pulse, after which the shear wave has propagated out of the one centimeter A1-A5 sampling window.
  • shear waves can have frequency components in the range of about 100Hz to about 1000Hz, sampling theory dictates that each A-line should have a sampling rate of 2kHz. This results in a set (ensemble) of fifty-five A-line samplings of each sampling point on each multiline A- line .
  • a typical sampling pulse is a short pulse, usually only one or two cycles, at a frequency suitable for penetrating the depth being studied, such as 7-8 MHz.
  • Each tracking pulse is offset by 2mm from its adjacent neighbors, resulting in twenty A-lines spaced 0.5mm apart with 4x multiline over a total distance of one centimeter.
  • sampling of the near window can be terminated and the sampling time can be devoted to the remaining sampling windows through which the shear wave is still propagating. Sampling continues until the shear wave has propagated out of the one cm. sampling region, by which time the shear wave has usually attenuated below a detectable level. Shear waves on average have a relaxation time of 10 msec.
  • sampling times of the tracking A-line positions be related to a common time base when the tracking pulses are time-interleaved so that the results can be used to make a continuous measurement of time, and hence velocity, across the one cm. sampling region. For example, since the sampling pulses for sampling window A2 do not occur until 50 microseconds following the corresponding sampling pulses for window Al, a 50 microsecond time offset exists between the sampling times of the two adjacent windows. This time difference must be taken into account when comparing the peak times of
  • FIGURES 2-5 Since a diagnostic region-of-interest (ROI) is generally greater than one centimeter in width, the procedure of FIGURES 2-5 is repeated with push pulses transmitted at different lateral locations across the image field. An image field is thereby interrogated in one-centimeter wide regions, and the results of the interrogations are displayed adjacent to each other in anatomical relationship to present an image of the full ROI . A four centimeter wide image field can be interrogated in four adjacent or overlapping one cm. regions, which are then displayed side-by- side or wholly or partially overlaid on the display.
  • ROI diagnostic region-of-interest
  • FIGURE 5 illustrates a sequence of displacement values for two laterally adjacent points of tissue on two adjacent A-lines such as Al-3 and Al-4 in FIGURE 3.
  • Curve 100 represents the displacement over time caused by passage of a shear wave through a point on A-line Al-3, and curve 120 the displacement at an adjacent point of A-line Al-4.
  • Points 102-118 of tissue displacement values are calculated from local cross correlations of r.f. data (e.g., 10-30 r.f. samples in depth) acquired around a sampling point depth on Al-3 over time to yield the local
  • the points 102-118 of displacement values detected at successive times (y-axis) when plotted as a function of time, are joined to form the first displacement curve 100.
  • the succession 122-136 of displacement values produced by local cross correlation can be joined to form a second displacement curve 120. Since the shear wave is traveling from left to right in this example, the second curve 120 for the right-most A-line is shifted to the right (in time) of the first displacement curve 100.
  • a precise time reference of the passage of the wavefront from one point to the next is measured by the detected peak or inflection point of each displacement curve, indicated at 200 and 220 in this example.
  • Various techniques can be used to find the curve peak. In one implementation the
  • the velocity of shear wave travel can be calculated from one image point to another across the entire region of interest.
  • This two- or three- dimensional matrix of velocity values is color-coded or otherwise coded with corresponding stiffness estimates to form a velocity or stiffness display map which is overlaid and in spatial alignment with a B mode image of the region of interest for display on image display 36.
  • the ultrasound system of FIGURE 1 has a B mode image processor 48.
  • the B mode processor receives echo signals acquired in response to image pulse transmission and performs amplitude detection of the echoes for production of B mode images of tissue.
  • B mode processing also includes logarithmic compression of the amplitude values to produce a more diagnostic range of
  • the ultrasound system of FIGURE 1 further comprises a confidence factor processor 40 which produces confidence or reliability values.
  • the confidence or reliability values can be stored in a confidence map memory 42 for a confidence value map of the anatomy spatially associated with a stiffness or shear wave velocity map.
  • the confidence factor processor 40 operates by combining several types of information which bear upon the reliability of the shear wave measurements. For example, the confidence factor processor receives A-line values from the A- line memory 24, which indicate the amplitudes of the tissue displacements detected by the tracking pulses. These values indicate the strength of the shear waves detected at points in the measurement field. Strong shear wave signals are generally more reliable than weaker shear wave signals.
  • the confidence factor processor also receives B mode images which provide two other types of information.
  • Successive B mode images are compared or correlated to determine whether local or global tissue motion has occurred during shear wave measurement, either due to motion of the tissue or of the probe.
  • This motion can be determined by correlation of pixel values at the same location in successive images, or by block matching of pixel areas as is known in the art.
  • the presence of tissue motion indicates that shear wave tissue displacement estimates are contaminated by motion from other sources.
  • the B mode images can also reveal the locations of blood vessels in the image field, which appear as dark areas in B mode images. Since the shear wave measurements interrogate tissue, signals from vessel lumens should be omitted from shear wave measurement computation.
  • color Doppler, power Doppler, or contrast detection can be used to identify regions of blood flow.
  • the confidence factor processor can calculate a confidence factor using the expression
  • the confidence factor (CF) for an image point is the sum of the shear wave amplitude (Ampl s hear) plus one-half of the tissue motion value (TM) plus the B mode image pixel value, where vessel lumens have a value of zero and tissue pixels a value of one.
  • the raw values of these three variables may be used, or they may be normalized if desired. For instance, if the shear wave amplitude varies between zero and eight pm, this range can be converted to a range of zero to one or 0% to 100%. The converted range can be linear, or nonlinear to emphasize (or de-emphasize) one or both range extremes.
  • the confidence factor processor produces a confidence factor value for each location in the stiffness or velocity display map.
  • the raw confidence factor values can be used, or the values can be converted to a range of 0% to 100% by use of a conversion look-up table. As before, the conversion can be either linear or nonlinear to emphasize or de-emphasize different parts of the range .
  • confidence factor values for each location in the shear wave display map are stored as a map of confidence factors in confidence map memory 52.
  • the confidence map is continually updated for each newly acquired stiffness or shear wave velocity map.
  • the confidence map values can be further processed by a stiffness/velocity weighting processor 50 where they are used to weight the spatially corresponding values of the stiffness or shear wave velocity display map when calculating a weighted average value of stiffness or shear wave velocity within an ROI or weighted average values of stiffness or shear wave velocity within multiple ROIs.
  • the user can in certain embodiments engage this use of the confidence factors by actuating a control of the user interface, or the system can automatically engage the use of the confidence factors.
  • the stiffness/velocity weighting processor can produce one or more weighted average tissue stiffness or weighted average velocity values using the confidence or reliability values.
  • S average ( Si*Ci+S2*C2+...+S n *C n ) / (Ci+C2+...C n ) , where S aVerage is the weighted average tissue stiffness or the weighted average shear wave velocity value, S n is the measured tissue stiffness or shear wave
  • the sum of the confidence values of all points in the region of interest being averaged are used in the denominator to reduce or remove bias in the calculated weighted average tissue stiffness or the weighted average shear wave velocity value.
  • This weighting process can advantageously produce an image in which questionable stiffness and velocity values are only dimly perceived while more reliable values are brightly displayed, and questionable stiffness and velocity values play a lesser role in regional stiffness computations.
  • the user can choose to display the weighted shear wave image alone, or together with a confidence map from the confidence map memory 52.
  • FIGURE 6 shows a visual example of an embodiment of the present disclosure.
  • a display 90 shows an ultrasound image 92, which can include B- mode image information.
  • a stiffness or shear wave velocity map bounded by a region of interest 94 can be overlaid on the ultrasound image 92.
  • confidence or reliability values can be calculated for points 96 in the map.
  • each gray block in FIGURE 6 represents a point for which a measured stiffness or shear wave velocity value S n can be calculated.
  • a confidence or reliability value C n can be calculated for each point.
  • a weighted average value of stiffness or shear wave velocity can be calculated for more than one region. For example, four different regions can be positioned or drawn in different areas of a tissue of interest, e.g., a liver. A weighted average a weighted average value of stiffness or shear wave velocity can be calculated for each, and the ultrasound system can further calculate additional information from the weighted average values of stiffness or shear wave velocity.
  • tissue stiffness and/or shear wave velocity measurements will be more consistent from one
  • weighting process is automatic and involves no user-selected variable. This means that serial studies of a patient over a period of time will be more consistent and reliable.
  • a second advantage is that weighted average stiffness or velocity
  • a third advantage is that there is no need to carefully trace around blood vessels in an image when drawing a region of interest. Since clinicians know that stiffness measurements should only come from tissue and not blood flow, past practice has been for a clinician to carefully outline a region of interest that includes only tissue and excludes blood vessel segments from the region.
  • the use of the confidence factor computation described above where regions of blood revealed in a B mode or motion image are given a weight of zero in the weighting process, automatically excludes these regions from stiffness and velocity computations through zero weighting, sparing the clinician from this tedious tracing task and its inherent user variability.
  • the system of the present invention is well suited to clinicians such as hepatologists who generally prefer to spend less time adjusting
  • the confidence factor weighting techniques of the present invention are applicable to ultrasound, and to other diagnostic modalities which measure tissue stiffness noninvasively .
  • the techniques of the present invention are also applicable to ultrasound, and to other diagnostic modalities which measure tissue stiffness noninvasively .
  • the techniques of the present invention are also present.
  • ultrasound system of FIGURE 1 which measures shear wave speed and derived measurements of stiffness may be implemented in hardware, software or a combination thereof.
  • the various embodiments and/or components of an ultrasound system of FIGURE 1 which measures shear wave speed and derived measurements of stiffness may be implemented in hardware, software or a combination thereof.
  • ultrasound system for example, the modules, or components and controllers therein, also may be implemented as part of one or more computers or microprocessors.
  • the computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet.
  • the computer or processor may include a microprocessor.
  • the microprocessor may be connected to a communication bus, for example, to access a PACS system.
  • the computer or processor may also include a memory.
  • the memory devices such as the A-line memory 24 and the confidence map memory 52 may include Random Access Memory (RAM) and Read Only Memory (ROM) .
  • the computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as a floppy disk drive, optical disk drive, solid-state thumb drive, and the like.
  • the storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.
  • the term "computer” or “module” or “processor” as used in describing the B mode image processor 48, the confidence factor processor 40, and the stiffness/velocity weighting processor 50 may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC) , ASICs, logic circuits, and any other circuit or processor capable of executing the functions described herein.
  • RISC reduced instruction set computers
  • ASICs application specific integrated circuits
  • logic circuits any other circuit or processor capable of executing the functions described herein.
  • the computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data.
  • storage elements may also store data or other
  • element may be in the form of an information source or a physical memory element within a processing machine .
  • the set of instructions of an ultrasound system may include various commands that instruct a computer or processor as a processing machine to perform specific operations such as the methods, computations, and processes of the various embodiments of the invention.
  • the set of instructions may be in the form of a software program.
  • the software may be in various forms such as system software or application software and which may be embodied as a tangible and non-transitory computer readable medium. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. For example, the expressions calculated by the confidence factor and
  • stiffness/velocity weighting processors may be executed by software modules calculating the
  • the software also may include modular programming in the form of object-oriented
  • the processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine.

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Abstract

La présente invention concerne un système d'imagerie ultrasonore permettant d'analyser des caractéristiques d'ondes de cisaillement qui comprend un processeur de facteurs de confiance produisant des facteurs de confiance correspondant aux points d'une carte d'affichage de rigidité ou de vitesse. Un processeur de pondération de rigidité/vitesse génère une valeur moyenne pondérée de rigidité ou de vitesse sur la base des valeurs des facteurs de confiance pour les mesures de rigidité ou de vitesse dans une région d'intérêt.
PCT/EP2019/058211 2018-04-02 2019-04-01 Imagerie ultrasonore par ondes de cisaillement présentant une précision et une fiabilité améliorées WO2019192970A1 (fr)

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EP3977938A1 (fr) * 2020-10-05 2022-04-06 Esaote S.p.A. Procédé et système à ultrasons pour imagerie d'élasticité d'ondes de cisaillement

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