Design and Development of a Novel Photoacoustic Imaging System for Detection of Intracranial Hemorrhages

Abstract

Photoacoustic (PA) imaging has the potential to overcome disadvantages of optical and ultrasonic imaging techniques by combining the two imaging modalities. This allows for exploitation of endogenous contrasts (variants of hemoglobin) to generate energy with light, and provides enhanced resolution by probing for resulting acoustic signals. The resulting platform has widespread applications ranging from structural (vasculature-based) to functional (oxygenation-based) point-of-care clinical imaging. This thesis has been aimed towards the development of a PA system for detection of intracranial hemorrhages. Simulations have been performed using a photon tracking Monte Carlo program and ultrasound wave propagation modeling software, k-wave to simulate light absorption and resultant acoustic signals in tissue. Furthermore, development of a PA imaging setup utilizes a 6-ns pulsed laser operating at 532-nm with a pulse repetition frequency of 28-Hz as the light source. Ultrasonic transducers with centre frequencies ranging from 1- to 5-MHz are used to receive acoustic signals produced from the object illuminated. The system is designed in a handheld, probe-like configuration to enable point-of-care detection and/or imaging. Acoustic signals are amplified and collected through a data acquisition system and processed through software to form an image. Simulations have shown sufficient penetration through superficial tissue, and absorption of light by blood at relevant wavelengths (near-infrared range). Black plastic resin phantoms have been used to characterize point-source PA signals, and complex geometries of phantoms have successfully been imaged and reconstructed with the PA system. Phantom geometries have also been imaged through gelatin and bone. The PA system has been successfully shown to image PA absorbers in different surrounding media, providing a promising first-step towards further development of the PA system for the detection of intracranial hemorrhages. This research has shown that photoacoustic detection of intracranial hemorrhages may be possible for adult human patients with brain injuries, and that the PA system design presented should be further developed to meet this goal.