Relationship of Images of Acoustic Refractive Index and Attenuation to Tissue Types within Excised Female Breast

Abstract

Two-dimensional images of the distribution of values of acoustic attenuation (A) and velocity (V) in coronal planes of excised human female breasts were obtained using computer assisted tomography (CAT) techniques. Projection profiles of amplitude attenuation and of propagation delay of acoustic pulses were obtained by rectilinear transverse scanning of the tissue under study. Over 200 equispaced pulses were obtained along a 15 cm scan for each of about 35 angles of view separated by 5.4°. Focusing acoustic lenses were used to insonify as small a volume as possible in order to minimize the probability of receiving pulses from multiple pathways. The received pulses were digitized at one 8-bit sample every 10 nanoseconds for up to 1,024 samples. Edge detection algorithms were used to determine the arrival time of the pulse within the digitized signal. The amplitude of the arriving pulse was determined by measuring the peak or the area of the earliest arriving pulse.