Microwave thermoelastic tissue imaging - System design

Abstract

A microwave-induced thermoelastic tissue imaging system is proposed as a new and promising imaging modality. lt possesses unique features that permit noninvasive imaging of tissue characteristics which are not identifiable by otber techniques. It uses nonionizing radiation and relies on a beam of impinging microwave energy to launch an acoustic wavefront into tissue. This thermoelastic wave of pressure propagates through the tissue and is detected by a two-dimensional array of piezoelectric transducers positioned on the body surface to give an image of the intervening tissue structure. Signals from the output of this transducer array are amplified and band-limited. A computer-controlled data acquisition system samples and converts them to digital form for further processing. A hybrid paralleljserial design for dividing the array into segments and collecting data from each segment sequentially is used. The area image sensor offers inherent geometric stability essential for reliable measurement. Error in scan position is not a conctrn, since mechanical scanning is not involved. The gray Ievel resolution is 256 after digitization, and the spatial resolution is 5 x 5 mm. These resolutions, along with a calculated signal-to-noise ratio (SNR) greater than 2500, are sufficient to provide structural information needed to render microwave-induced thermoelastic imaging a useful, noninvasive method for imaging biological tissues.