Adjunctive ultrasound processing and display for breast cancer screening

Abstract

An adjunctive ultrasound mammography system and associated methods are described comprising an adjunctive ultrasound display configured for quick, intuitive, interactive viewing of data derived from volumetric ultrasound scans, the data being displayed near a conventional x-ray mammogram display. Preferred embodiments for navigating among a thick-slice image array, a selected enlarged thick-slice image, and planar ultrasound views are described, including a preferred embodiment in which the planar ultrasound views are updated in real time as a cursor is moved across an active thick-slice image. In one preferred embodiment the thick-slice images are inverted prior to display, with non-breast areas of the image preferably segmented out and reset to dark. The inverted thick-slice images are of more familiar significance to radiologists having years of expertise in analyzing conventional x-ray mammograms. For example, the inverted thick-slice images allow benign features to be more easily dismissed as compared to non-inverted thick-slice images. Preferred embodiments for computing thick-slice image values from the volumetric scan data are also described that emphasize larger mass lesions in the resulting thick-slice images, and that compensate for mass lesions that straddle thick-slice region borders.

1 . A method for facilitating breast cancer screening, comprising:
 acquiring raw ultrasound slices representing sonographic properties of a breast;   forming a volumetric representation of said sonographic properties from said raw ultrasound slices;   computing a two-dimensional thick-slice ultrasound image from said volumetric representation, said thick-slice ultrasound image representing said sonographic properties within a slab-like subvolume of the breast having a thickness greater than about 2 mm and less than about 20 mm;   displaying said thick-slice ultrasound image to a user during a viewing session;   computing a planar ultrasound image from said volumetric representation, said planar ultrasound image representing said sonographic properties along a substantially planar portion of the breast substantially nonparallel to said slab-like volume; and   electronically displaying said planar ultrasound image to the user during the viewing session.   
   
   
       2 . The method of  claim 1 , wherein said thick-slice ultrasound image and said planar ultrasound image are simultaneously displayed to the user near each other to facilitate back-and-forth viewing therebetween. 
   
   
       3 . The method of  claim 2 , wherein said slab-like subvolume is substantially parallel to a standard x-ray mammogram view plane. 
   
   
       4 . The method of  claim 1 , said slab-like subvolume being substantially parallel to a standard x-ray mammogram view plane, further comprising displaying an x-ray mammogram image of the breast taken along said standard x-ray mammogram view plane to said user during the viewing session. 
   
   
       5 . The method of  claim 4 , wherein said thick-slice ultrasound image, said planar ultrasound image, and said x-ray mammogram image are simultaneously displayed to the user near each other to facilitate back-and-forth viewing thereamong. 
   
   
       6 . The method of  claim 5 , wherein said x-ray mammogram is displayed as an x-ray film on a backlit display. 
   
   
       7 . The method of  claim 6 , wherein said thick-slice ultrasound image is electronically displayed. 
   
   
       8 . The method of  claim 7 , wherein said planar ultrasound image is displayed on a high-brightness CRT monitor positioned adjacent to said thick-slice ultrasound image. 
   
   
       9 . The method of  claim 8 , wherein said thick-slice ultrasound image is displayed on an LCD monitor. 
   
   
       10 . The method of  claim 9 , wherein said thick-slice ultrasound image is enlarged or reduced to have the same spatial dimensions as the x-ray mammogram image. 
   
   
       11 . The method of  claim 1 , said raw ultrasound slices comprising values according to a conventional ultrasound display convention in which higher reflection readings are displayed as brighter and lower reflection readings displayed as darker, further comprising inverting said thick-slice image to an inverted ultrasound display convention in which higher reflection readings are displayed as darker and lower reflection readings displayed as brighter. 
   
   
       12 . The method of  claim 11 , further comprising:
 segmenting said thick-slice image into a first region lying inside the breast and a second region lying outside the breast, said second region having bright pixels directly after said inverting; and   resetting said second region pixels to dark values, the resulting thick-slice image thereby being more reminiscent of a conventional x-ray mammogram image in said second region.   
   
   
       13 . A method for computing a two-dimensional thick-slice ultrasound image from a volumetric ultrasound representation of a breast, said volumetric ultrasound representation comprising voxels, said thick-slice ultrasound image comprising pixels and corresponding to a first slab-like subvolume of the breast lying between a first border plane and a second border plane thereof, comprising:
 identifying for each pixel location in the thick-slice ultrasound image a first voxel set corresponding to a voxel column in said volumetric ultrasound representation passing through that pixel location and extending from the first border plane to the second border plane;   computing one or more statistical properties of said first voxel set; and   computing an output value for that pixel location using said one or more statistical properties of said first voxel set.   
   
   
       14 . The method of  claim 13 , said one or more statistical properties of said first voxel set incurring changes across different pixel locations in mass localities that are more significant for masses greater than a preselected size of interest and that are less significant for masses smaller than said preselected size of interest, mass lesions greater than said preselected size of interest being emphasized and mass lesions smaller than said preselected size of interest being de-emphasized in said thick-slice image. 
   
   
       15 . The method of  claim 14 , said computing an output value comprising:
 computing a histogram of values of said first voxel set;   computing at least a portion of a cumulative distribution function from said histogram;   determining a first pixel level for which said cumulative distribution function is equal to a threshold, said threshold being a function of said preselected size of interest;   and   setting said output value equal to said first pixel level.   
   
   
       16 . The method of  claim 15 , said threshold being a fixed value equal to a preselected constant K times a ratio of (i) said preselected size of interest, to (ii) a distance between said first and second border planes. 
   
   
       17 . The method of  claim 16 , wherein K is between about 0.20 and about 0.45. 
   
   
       18 . The method of  claim 15 , said threshold being variable for different pixel locations in said thick-slice ultrasound image, said threshold being equal to a variable multiplier K times a ratio of (i) said preselected size of interest, to (ii) a distance between said first and second border planes. 
   
   
       19 . The method of  claim 18 , wherein values of K are maintained within a range of about 0.20 to about 0.45. 
   
   
       20 . The method of  claim 13 , the breast further having a second slab-like subvolume immediately adjacent to the first slab-like volume, further comprising:
 identifying for each pixel location in the thick-slice ultrasound image a second voxel set corresponding to said voxel column extending from a first intermediate elevation in said first slab-like volume to a second intermediate location is said second slab-like volume, said first and second voxel sets having about the same number of voxels;   computing said one or more statistical properties of said second voxel set;   computing an alternative result for that pixel location using said one or more statistical properties of said second voxel set; and   if said alternative result indicates an ultrasound echo intensity less than that indicated by said output value, resetting said output value to said alternative result.   
   
   
       21 . The method of  claim 20 , said volumetric ultrasound representation being formed from scans taken during a sweep of an ultrasound probe across the breast, wherein said second slab-like volume is closer to a locus of said ultrasound probe sweep than said first slab-like volume. 
   
   
       22 - 28 . (canceled)