Backscatter and Attenuation Imaging from Ultrasonic Scanning in Medicine
by E. J. Farrell
Images of backscatter, attenuation, and frequency dependence of attenuation are obtained based on a three-parameter model and computation techniques described in this paper. There are several critical sources of error: backscatter speckle, beamwidth distortion, and cross-coupling artifacts between attenuation and backscatter. An iterative method of imaging and filtering is developed which effectively reduces these errors. Stability of the numerical solution involving the large number of unknowns is obtained by image iteration as opposed to parameter iteration along individual transmitter rays. This method incorporates three basic functional aspects: (1) multiple scans to reduce speckle, beamwidth distortions, and certain cross-coupling artifacts, (2) pre-image filtering to decrease beam distortions and post-image filtering to reduce cross-coupling artifacts, and (3) proper sequencing of image reconstruction and filtering. Backscatter images formed by this image iteration method are significantly superior to standard B-scan images. Further, the image iteration method yields three images of the same scan field. The present investigation is based on simulated echo data from cyst-like and complex targets.