Ultrasound shear wave vibro-elastography of the abdomen

Patent metadata

Field	Value
Publication number	US-2019192119-A1
Application number	US-201816226401-A
Country	US
Kind code	A1
Filing date	Dec 19, 2018
Priority date	Jun 30, 2016
Publication date	Jun 27, 2019
Grant date	—

Abstract

A system useful for performing ultrasound elastography of organs such as the liver allows efficient and robust data acquisition. The system may be applied to perform real-time, non-invasive ultrasound imaging of the liver in humans. Steady-state, shear wave absolute elastography is used to measure the Young's modulus of the liver tissue. This method involves the use of an external exciter or vibrator to shake the tissue and generate a shear wave. Accurate placement of an ultrasound transducer facilitates measurement of the tissue motion due to the shear wave. The stiffness of tissues in the region being imaged may be computed from the measured tissue motions. The following innovations address both vibrator and transducer placement, as well as some specific methods to ensure adequate wave propagation, in order to obtain accurate and consistent measurements.

First claim

1 . (canceled)

2 . Apparatus for ultrasound elastography, the apparatus comprising:
an external vibrator comprising a generally flat, stiff, patient-contacting member dimensioned to support at least a portion of the back of a patient and at least one exciter, the at least one exciter comprising a mass that is movable to apply inertial forces to the patient-contacting member whereby net inertial forces from the at least one exciter cause motions of the patient-contacting member that generate shear waves in a patient lying on the patient-contacting member; the external vibrator placed on a bed mattress that supports the external vibrator while allowing the motions of the patient-contacting member; an ultrasound imaging system comprising an ultrasound transducer, driving circuits operative to drive the ultrasound transducer to transmit ultrasound pulses and to receive ultrasound echo signals; controller configured to process the ultrasound echo signals to detect and measure motions corresponding to shear waves generated by the external vibrator.

3 . The apparatus according to claim 2 wherein the patient-contacting member is generally rectangular and has dimensions in the range of 40 to 60 cm in a direction transverse to the mattress and 10 to 20 cm in a direction along the mattress.

4 . The apparatus according to claim 3 wherein the patient-contacting member comprises a honeycomb core reinforced on top and bottom faces with sheets of a fiber reinforced plastic material.

5 . The apparatus according to claim 3 wherein the patient-contacting member comprises a honeycomb core reinforced on top and bottom faces with sheets of a fiber reinforced plastic material.

6 . The apparatus according to claim 3 wherein the patient-contacting member is formed with a curvature

7 . The apparatus according to claim 3 wherein the patient-contacting member comprises adjustable bolsters or supports that project on a top side of the patient-contacting member and are engageable against opposed sides of the ribcage of a patient lying on the patient-contacting member.

8 . The apparatus according to claim 3 wherein the patient-contacting member comprises one or more accelerometers operable to quantify the acceleration or velocity or displacement of the patient-contacting member.

9 . The apparatus according to claim 2 wherein the at least one exciter is configured to generate the inertial forces by moving a counterweight linearly or rotationally.

10 . The apparatus according to claim 2 wherein the ultrasound transducer is supported by a remote centre of rotation mechanism that allows rotation of an imaging plane of the ultrasound transducer without changing a point of contact of the ultrasound transducer with the patient.

11 . The apparatus according to claim 2 wherein timing of operation of the ultrasound imaging system is synchronized to vibrations of the external vibrator.

12 . The apparatus according to claim 2 wherein the at least one exciter comprises first and second exciters that generate inertial forces directed in different directions and a phase of the motion of a first mass of the first exciter relative to the phase of the motion of a second mass of the second exciter is adjustable to cause a direction of the net inertial force on the patient-contacting member to change.

13 . The apparatus according to claim 2 wherein the net inertial force comprises plural frequencies in the range of 45 to 70 Hz.

14 . The apparatus according to claim 2 wherein the controller is connected to deliver driving signals to the one or more exciters and to adjust the driving signals in a closed-loop in response to feedback received at least in part by way of the ultrasound imaging system, the controller configured to compute a quality measure of tissue displacements and/or a measurement wavelength of shear waves in a plane of ultrasound imaging in real-time and to adjust operation of the one or more exciters to move or eliminate low displacement nodes and/or optimize the shear wave direction and amplitude.

15 . The apparatus according to claim 14 wherein the quality measure comprises a signal to noise ratio.

16 . The apparatus according to claim 14 wherein the quality measure comprises an indication of whether the magnitude of a phasor representing the shear waves is outside of a range between a minimum magnitude and a maximum magnitude.

17 . The apparatus according to claim 2 wherein the controller is configured to optimize shear wave direction relative to a plane of imaging by the ultrasound transducer by:
processing the ultrasound echo data to determine an apparent wavelength of shear waves and adjusting one of more operating parameters of the external vibrator in a manner that causes the apparent wavelength of the shear waves to be reduced. wherein the one or more operating parameters of the external vibrator comprise one or more of: a frequency of operation of one or more exciters of the at least one exciter, a relative phase of operation of first and second exciters of the at least one exciter, an amplitude of operation of one or more exciters of the at least one exciter, and a direction of vibration of one or more exciters of the at least one exciter.

18 . The apparatus according to claim 17 wherein the controller is configured to control the one or more operating parameters of the external vibrator in real time as the orientation of the ultrasound transducer is changed to minimize the apparent wavelength of the shear waves for each orientation of the ultrasound transducer.

19 . The apparatus according to claim 2 wherein the at least one exciter comprises a plurality of exciters and the controller is connected to drive the plurality of exciters and to adjust shear wave direction in a target volume of tissue to be imaged by monitoring ultrasound images of the target volume to determine an apparent wavelength of the shear waves and adjusting phases of the plurality of exciters to minimize the apparent wavelength of the shear waves.

20 . The apparatus according to claim 2 wherein the controller is configured to process a sequence of ultrasound images of the target volume to identify any regions of tissue displacements by the shear waves that are below a threshold displacement level and, If such regions are found, automatically adjust the frequency(ies) and/or phases and/or amplitudes of driving signals being delivered to one or more of the exciters to determine if a set of frequency(ies) and/or phases and/or amplitudes of the driving signals can be found in which the possible nodes are gone or moved to another location.

21 . The apparatus according to claim 2 wherein the controller is configured to process the echo signals to identify shear wave nodes located in a volume of interest and to control one or more operating parameters of the external vibrator in a manner that causes the nodes to move or disappear wherein the one or more operating parameters of the external vibrator comprise one or more of: a frequency of operation of one or more exciters of the at least one exciter, a relative phase of operation of first and second exciters of the at least one exciter; and an amplitude of operation of one or more exciters of the at least one exciter, and a direction of vibration of one or more exciters of the at least one exciter.

22 . The apparatus according to claim 2 wherein the controller is configured to generate colour elastography images which indicate areas in which imaged tissues

Assignees

• Univ British Columbia

Inventors

• Salcudean Septimiu
• Rohling Robert
• Honarvar Mohammad
• Lobo Julio Raul
• Schneider Caitlin Marie

Classifications

• A61B8/4209

  by using holders, e.g. positioning frames · CPC title

• A61B8/483

  involving the acquisition of a 3D volume of data · CPC title

• A61B8/4245

  involving determining the position of the probe, e.g. with respect to an external reference frame or to the patient · CPC title

• A61B8/085

  for locating body or organic structures, e.g. tumours, calculi, blood vessels, nodules · CPC title

• A61B8/485 Primary

  involving measuring strain or elastic properties · CPC title