Copyright 2004-2011, University of Rochester
Three Dimensional (3D) Sonoelastography
3D sonoelastography refers to the display of information related to the relative stiffness (hardness or softness) of a volume of tissue. The technique is based on vibration sonoelastography, where low amplitude, low frequency shear waves (less than 0.1 mm displacement and 1 KHz frequency) are propagated through deep organs, while real-time Doppler techniques are used to image the resulting vibration pattern. A discrete hard inhomogeneity, such as a tumor, will produce a localized disturbance in the vibration pattern, forming the basis for tumor detection. 3D imaging, produced by acquiring sequential tomographic slices with Doppler/vibration information, enables the reconstruction and quantification of tumor volumes, even if the tumor is isoechoic on conventional B-scan display. Crawling waves are interference patterns generated by two opposing shear waves. These produce beautiful patterns which are imaged by Doppler scanners and can be analyzed to produce quantitative measures of the biomechanical properties of tissues.
A representative first generation image of vibration sonoelastography, circa 1990. Doppler spectral variance is employed as an estimator of vibration in the 1-10 micron range and displayed over the B-scan images. No color implies low vibrations below threshold. Shown is the fill-in of vibration within a whole prostate, with a growing cancerous region indicated by the deficit of color within the peripheral zone. Courtesy of Dr. R. M. Lerner.
Prostate B-scan, sonelastography and corresponding pathology. Blue circles on the pathology slides indicate BPH, black outline indicates cancer. The sono image shows a lower contrast deficit from the BPH (red arrow) and a higher contrast deficit, or dark region, from the cancer on the right border.
3D prostate imaging protocol. Courtesy of Prof. B. Castaneda.
Crawling waves in the prostate. Fig. (a), left: B-scan of whole excised prostate; Fig. (a), right: crawling waves frame; Fig. (b), right: pathology with labels: black=cancer and blue=BPH; Fig. (b), left: quantitative estimates of shear velocity from crawling waves analysis, indicating the hard region as a red area (corresponding to the region with cancer). Estimates from an average of 3 frequencies are shown. All images are co-registered.
Four Dimensional (4D) Sonoelastography
4D sonoelastography takes three-dimensional ultrasound images and adds the 4th element - time. The result is developmental images of changes within organs. For more information about 4D Imaging, visit VirtualScopics.