Testbed for Quantitative Thermoacoustic Tomography

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DESCRIPTION (provided by applicant): We propose to develop a testbed for quantifying thermoacoustic computerized tomography (TCT) signal strength as a function of electromagnetic (EM) illumination pulse parameters. TCT images a completely new contrast mechanism: conversion of EM to acoustic pressures via thermal expansion. TCT pressures are measured by ultrasound transducers located outside of the imaging field of view (FOV) but are generated by thermal expansion inside the FOV caused by the short burst of EM illumination propagated into the FOV. TCT pressures can be reconstructed to provide an image related to the tissue's specific absorption rate (SAR) of EM energy. SAR is a function of both applied electric field strength, |E|, and intrinsic tissue properties. The goal of quantitative TCT is to recover intrinsic tissue properties independent of |E| applied by the TCT system. The goal of this proposal is to quantify TCT signal strength as a function of |E| to ensure strong TCT signal can be generated robustly in vivo. Many encouraging photoacoustic tomography (PAT) studies show good results within 2-3 cm of the skin surface and intravascularly, but only one clinical trial of TCT with deeply penetrating radiofrequency (RF) illumination has been reported. We will use both software and hardware "testbeds" designed to generate TCT pressure signals under a controlled EM environment to achieve the following specific aims: 1. Quantify TCT acoustic signal strength in Pascals (Pa) vs. RF illumination parameters: peak power, carrier frequency, polarization and pulse width for simple test phantoms and animal tissue specimens. Analytical calculations for geometrically simple phantoms from the software testbed will be compared to measurements from the hardware testbed. 2. Quantify effect of contrast agents on TCT contrast and S/N. We will focus on microbubbles used in ultrasound and nanoparticles as used in PAT. 3. Modify the testbed to become a benchtop TCT tomography system for ex vivo imaging. This testbed will rotate and translate specimens, providing cylindrical measurement surfaces for tomographic reconstruction. PUBLIC HEALTH RELEVANCE: We will validate a completely new contrast mechanism for diagnostic medical imaging in soft tissues. Thermoacoustics may be a boon to applications for which current imaging techniques are woefully inadequate, such as prostate cancer imaging.