ABSTRACT
This chapter analyzes the effects of acoustic heterogeneities on thermoacoustic tomography (TAT) images. It shows that the distortion and blurring effects of acoustic heterogeneities on TAT can be reduced by using the acoustic speed distribution. The chapter considers ultrasonic transmission tomography (UTT) to quantitatively measure the acoustic speed distribution in tissue. UTT is implemented by time-of-flight measurements and is compatible with TAT. The image quality of UTT alone is often insufficient for early stage tumor detection, since UTT only reveals mechanical contrast. By using a combined TAT/UTT system, the ability of TAT to image small targets in weakly refractive tissues is improved. The chapter presents a numerical method based on the acoustic speed distribution measured by UTT to compensate for the distortion and blurring. It explains a numerical reconstruction algorithm by incorporating the acoustic speed distribution into the reconstruction algorithm.
