Imaging methods and apparatuses for performing shear wave elastography imaging

Abstract

A method for performing shear wave elastography imaging of an observation field in a medium includes shear wave imaging operations to acquire sets of shear wave propagation parameters, and determining a reliability indicator of the shear wave elastography imaging of the observation field.

1 . A method for performing shear wave elastography imaging of an observation field in a medium, the method comprising:
 acquiring a plurality of sets of shear wave propagation parameters in a plurality of shear wave imaging operations corresponding to respective shear waves, the propagation parameters being one of a shear modulus, Young’s modulus, a propagation speed of shear waves, and shear elasticity; and   determining a reliability indicator of the shear wave elastography imaging operations of the observation field, the reliability indicator being a function of a motion indicator.   
     
     
         2 . The method according to  claim 1 , wherein the determining the reliability indicator comprises determining the motion indicator based on at least two sets of data, and
 said two sets of data being two successive B-mode images of the observation field or two successive phase sensitive acquisitions of the observation field.   
     
     
         3 . The method according to  claim 1 , further comprising comparing the motion indicator with at least one threshold value. 
     
     
         4 . The method according to  claim 1 , further comprising comparing the reliability indicator with a threshold value, and an iteration of the plurality of shear wave imaging operations are stopped when the reliability indicator reaches the threshold value. 
     
     
         5 . The method according to  claim 1 , wherein the reliability indicator is a function of a stability indicator, and
 the determining the reliability indicator comprises determining a stability indicator based on at least two sets of shear wave propagation parameters.   
     
     
         6 . The method according to  claim 5 , wherein the stability indicator is a function of a similarity between at least two sets of data, said two sets of data being two successive sets of shear wave propagation parameters or two histograms respectively associated with two successive sets of shear wave propagation parameters. 
     
     
         7 . The method according to  claim 6 , wherein the similarity between the two sets of data is determined by computing a metric for each set of data and comparing said metrics, said metrics being selected in from one of a means square, a correlation, a normalized correlation, a pattern intensity, and mutual information. 
     
     
         8 . The method according to according to  claim 5 , wherein the stability indicator is a function of a statistical dispersion of the plurality of sets of shear wave propagation parameters. 
     
     
         9 . The method according to  claim 8 , wherein the statistical dispersion of the plurality of sets of shear wave propagation parameters is determined by computing a statistical indicator selected from one of an interquartile range, an interdecile range, a standard deviation, a median absolute deviation, an average absolute deviation, and a distance standard deviation. 
     
     
         10 . The method according to  claim 9 , wherein the statistical dispersion is determined by further normalizing the computed statistical indicator by a statistical measure of central tendency of the plurality of sets of shear wave propagation parameters. 
     
     
         11 . The method according to  claim 1 , wherein the acquiring comprises:
 generating a shear wave inside the medium by causing an array of transducers to emit at least one ultrasound wave into the medium,   observing the shear wave at a plurality of points in an observation field of the medium, by
 causing the array of transducers to emit into the medium a succession of ultrasound waves with spatial coverage and timing adapted so that said ultrasound waves exhibit at least partial spatial and temporal overlap with the propagating shear wave in the observation field, and 
 causing sound signals received from said observation field to be detected in real time by said array of transducers, said sound signals comprising echoes generated by the ultrasound waves interacting with scatterers in the medium; and 
   determining the set of shear wave propagation parameters in the observation field, said set of shear wave propagation parameters being associated with a plurality of points in the observation field.   
     
     
         12 . The method according to  claim 1 , wherein the motion indicator is a function of a local or global displacement between two successive B-mode images determined by computing an optical flow from said two successive B-mode images. 
     
     
         13 . The method according to  claim 1 , wherein the motion indicator is a function of a local or global displacement between two successive phase sensitive acquisitions computed from phase values measurements of said two successive phase sensitive acquisitions. 
     
     
         14 . The method according to  claim 1 , wherein the reliability indicator is a function of an image quality indicator,
 the reliability indicator determining comprising determining an image quality indicator based on at least one B-mode-image of the observation field.   
     
     
         15 . The method according to  claim 14 , wherein the image quality indicator is determined by computing a statistical property of at least one B-mode-image, and comparing said statistical property with a threshold value. 
     
     
         16 . The method according to  claim 15 , wherein the statistical property of the at least one B-mode-image is a B-mode 1 st  order statistic, a B-mode 2 nd  order statistic or a combination of B-mode 1 st  order and 2 nd  order statistics, of the at least one B-mode-image. 
     
     
         17 . The method according to  claim 14 , wherein the image quality indicator is determined based on at least two B-mode-images of the observation field, and
 wherein the image quality indicator is a function of a similarity between said at least two B-mode-images,   said similarity being determined by computing a metric for each of said B-mode images and comparing said metrics, said metrics being selected from one of a means square, a correlation, a normalized correlation, a pattern intensity, and mutual information.   
     
     
         18 . The method according to  claim 1 , further comprising conducting at least one B-mode imaging operation. 
     
     
         19 . The method according to  claim 18 , further comprising conducting a plurality of phase sensitive acquisitions. 
     
     
         20 . The method according to  claim 18 , wherein one or more of at least one B-mode imaging operation and the phase sensitive acquisition operations are performed before the acquiring the plurality of sets of shear wave propagation parameters. 
     
     
         21 . The method according to  claim 1 , further comprising comparing one or more of the reliability indicator, a stability indicator, the motion indicator and an image quality indicator with at least one threshold value. 
     
     
         22 . The method according to  claim 1 , further comprising displaying the reliability indicator to an operator. 
     
     
         23 . The method according to  claim 22 , wherein the displaying to the operator the reliability indicator comprises displaying one or more of a stability indicator, the motion indicator, and an image quality indicator. 
     
     
         24 . The method according to  claim 22 , wherein the displaying to the operator the reliability indicator comprises one of displaying a numerical value of the reliability indicator, and displaying a graphical representation of the reliability indicator. 
     
     
         25 . The method according to  claim 1 , further comprising displaying to an operator a synthetic indicator function of one or more of the motion indicator and an image quality indicator,
 said displaying the synthetic indicator being performed prior to the acquiring.   
     
     
         26 . The method according to  claim 1 , wherein a plurality of reliability indicators, associated to a plurality of points in the observation field, are determined, and
 the method further comprises displaying a map of reliability indicators to an operator.   
     
     
         27 . The method according to  claim 26 , wherein said map of reliability indicators comprises one or more of a map of stability indicators, a map of motion indicators, a map of image quality indicators, and a map of synthetic indicators. 
     
     
         28 . The method according to  claim 26 , further comprising:
 determining a composite image based on at least two maps comprising
 a map of the shear wave propagation parameters in the observation field, and 
 the map of reliability indicators, 
   said determining the composite image comprising one of varying a color component of one of said at least two maps in function of another of said at least two maps, alpha blending said at least two maps, and determining a set of lines or icons from one of said at least two maps to be layered on top of another of said at least two maps, and   displaying to an operator said composite image.   
     
     
         29 . The method according to  claim 22 , wherein the displaying is reiterated a plurality of times. 
     
     
         30 . An imaging apparatus for shear wave elastography imaging of an observation field in a medium, the apparatus comprising:
 at least one electronic central controller; and   an array of transducers that are controlled independently of one another by the at least one electronic central controller configured to:
 acquire a plurality of sets of shear wave propagation parameters in a plurality of shear wave imaging operations corresponding to respective shear waves, the propagation parameters being one of a shear modulus, Young’s modulus, a propagation speed of the shear waves, and a shear elasticity, by:
 causing at least one ultrasound wave to be emitted into the medium by the array of transducers to generate an elastic shear wave inside the medium, 
 observing simultaneously at a plurality of points in an observation field the propagation of said shear wave, by: 
 causing the array of transducers to emit into the medium a succession of ultrasound waves with spatial coverage and timing adapted so that said ultrasound waves exhibit at least partial spatial and temporal overlap with the propagating shear wave in the observation field, and 
 causing sound signals received from said observation field to be detected in real time by said array of transducers, said sound signals comprising echoes generated by the ultrasound waves interacting with scatterers in the medium, and 
 
 determine the plurality of sets of shear wave propagation parameters in the observation field, said sets of shear wave propagation parameters being associated with the plurality of points in the observation field, and 
 determine a reliability indicator of the shear wave elastography imaging operations of the observation field, 
   wherein the reliability indicator is a function of a motion indicator.