Passive acoustic thermotomography—Correlation and noncorrelation variants

Abstract

Passive thermoacoustic tomography is a method for reconstructing temperature, 2D and 3D distributions inside objects, using the intensity of ultrasonic thermal acoustic radiation emitted from within the object. This radiation can be measured by piezotransducers (PT) both in noncorrelation and correlation mode. For noncorrelation mode, a priori information about ultrasound absorption coefficient distribution is needed for reconstruction. In this case, the methods for the reconstruction of temperature distributions were analyzed by computer simulation. The standard error of reconstruction did not exceed 0.25 K (for about 300 measurements and fluctuation error of every measurement, 0.1 K). The physical experiments confirmed the predictions of the theory. In correlation mode, two spatial distributions—of the temperature and of the absorption coefficient—could be potentially reconstructed. The spatial correlation function of sound pressure from a source of thermal acoustic radiation was measured experimentally by a two-probe acoustic interferometer. The acoustic blackbody made from a narrow strip of a material with a large absorption coefficient served as the source of radiation. The spatial correlation function was computed; this function turned to be in good agreement with experimental data. [Work supported by Russian Basic Research Foundation Grant No. 98-01-00100.]