Energy Transform and Initial Acoustic Pressure Distribution in Microwave-induced Thermoacoustic Tomography

Abstract

A study of Microwave-induced Thermoacoustic Tomography is presented in this paper. Microwaves illuminate biological tissues to generate acoustic waves by thermoelastic expansion when electromagnetic energy was absorbed by human tissues. The generated acoustic waves carry information about different electromagnetic properties of different tissues which will be collected and processed to reconstruct human cross section image. In this paper, digital electromagnetic human body model with 1cm resolution was founded according to algorithm requirements. Firstly we analyzed the transform and interrelation among electromagnetic energy, heat energy and acoustic energy. On the basis of established human model: (1) we calculated initial acoustic pressure distribution in cross section image under plane microwave radiation with different frequency. It shows that microwave absorption properties and initial acoustic pressure were different with the change of frequency; (2) using single pulse to illuminate human model, initial acoustic pressure maps of thorax cross section at different time steps were analyzed. These results provided a research basis for further study and calculation of acoustic pressure in microwave-induced thermoacoustic tomography.

Thermoacoustic contrast of prostate cancer due to heating by very high frequency irradiation

“…EM frequency affects the source term in many ways including depth penetration and uniformity of EM deposition. Optical depth penetration is only 5.7 mm (Wang and Wu 2007), whereas microwave depth penetration extends to a few cm (Yan et al 2005, Tao et al 2006, Wang et al 2012. Optical fluence decreases smoothly with distance from the laser source, whereas microwaves suffer diffraction and develop standing waves which can cause signal drop-out in microwave induced TCT systems (Li et al 2008).…”