Computational Study of Microwave-induced Thermo-acoustic Tomography by Time-domain Finite Element Method

Abstract

This work presents a time-domain finite element method (TDFEM) for simulation of thermo-acoustic (TA) signal generation in biological tissue for the application of microwave-induced thermo-acoustic tomography (MITAT). This time-domain numerical technique is useful in the analysis of time-varying electric and pressure field generation while a non-conventional microwave pulse excitation in non-homogeneous medium of complex biological tissue structure is applied in this application. In this work, an intensity-modulated chirp pulse at microwave frequency is first applied as an alternative microwave pulse excitation for MITAT. The results of applying the modulated chirp pulse show that the peak-power of microwave pulse can be reduced compared with that of using the conventional modulated Gaussian pulse excitation. In this work, two configurations of acoustic detector array for TA signal detection are considered: concave and convex array, which is a suitable configuration for the application of breast cancer and prostate cancer detection, respectively. The detected TA signal by the array of acoustic detector is processed using a cross-correlation detection in which the propagation (delay) time characteristic of captured TA signal is extracted. This delay time characteristic carries information of the electromagnetic absorption distribution of the tissue in which the back-projection is applied for an image reconstruction. The numerical results of induced TA signal from conventional and modulated chirp pulse are shown. The reconstructed images are compared on the different cases of microwave pulses, detector arrays, tissue properties and geometries.