Advancing Photoacoustic Imaging as a Tool for Disease Diagnosis

Abstract

Photoacoustics is an imaging modality that uses short pulses of laser light to probe tissue for physical properties that have diagnostic value. Applications have been developed widely, including for improved diagnostic of primary and metastatic tumors, atherosclerosis, and arthritis. In this dissertation, photoacoustic imaging as a diagnostic tool is advanced in two ways. Methods for improving light penetration and determining light distribution are improved. A set of simulations of light propagation is used to optimize the geometry of photoacoustic imaging setups for light penetration. Optimal geometries are suggested for researchers depending on the tissue type, wavelength, and imaging species of their application. It was found that several times more light will be delivered in mice than humans, which has implications for the clinical translation of imaging techniques developed in mice across the field of photoacoustics. Next, a new technique is introduced that could be used to compensate for the decrease in fluence deep in tissue. A set of simulations are used to show the viability of the technique, and to show its effectiveness in a simulated phantom. The safety of intravascular photoacoustics is also investigated. Intravascular photoacoustics is a catheter-based imaging modality meant to improve identification of atherosclerotic plaques. A set of in vitro experiments indicated that the light dosage damage threshold may be low enough to limit the imaging protocols that can be used safely. Next, experiments were conducted in vivo to test for damage to the wall of the carotid artery in swine at multiple clinically relevant dosages. Damage was found at the highest dosages. However, no vessel wall damage was found at dosages that have been used successfully to image plaque in recent in vivo studies. This indicates that intravascular photoacoustic imaging can be used to identify lipid plaque without damaging the artery wall, although future studies to corroborate this result are needed.