Algebraic Reconstruction of Spatial Distributions of Acoustic Velocities in Tissue from Their Time-of-Flight Profiles

Abstract

Two-dimensional distributions of acoustic velocities were measured in transverse sections through intact isolated organs, using reconstruction techniques. Profiles of time-of-flight (TOF) of 10 MHz pulses through the specimen were obtained by rectilinearly scanning two opposing transducers along either side of the specimen in the plane of interest. The received pulses were digitized at a rate of one 8-bit sample-per-10 nanosec, for 512 samples and were analyzed with a computer algorithm which calculated the TOF of the pulse to within ± 10 nanosec. Typically, 256 measurements of TOF were made in each profile scan for each of 37 angles of view separated by 5°, TOF’s through tissue, normalized by TOF through water, were used to calculate velocity within the specimen, using an algebraic reconstruction technique (ART), Images obtained represented acoustic velocities in individual cross sections within the tissue specimen with a resolution of 64 by 64 elements (< 2 mm square), The disadvantage of TOF reconstruction is that transmission scanning is required. Advantages over B- and C-scan imaging are: 1) dynamic changes in gain of receiver are not required, 2) attenuation occurs on only one traversal through tissue, and 3) the absolute value of an important acoustic parameter (velocity) is determined, which may have significant diagnostic value.