Analytical and Computational Tools for Long-Pulse Photoacoustics

点击翻译按钮获取中文摘要

Photoacoustic signal generation is a technique which has demonstrated great potential for non-invasive medical tomography. With this technique, a short-pulse of laser energy is used on a sample. The absorbed energy produces a small temperature rise, which in turn induces a change in pressure inside the sample due to thermal expansion. This pressure acts as a source of ultrasound waves which can be detected by ultrasound detectors positioned outside the sample. Since there is a large difference between how blood and surrounding tissue absorb the light energy, this provides a way to look for anomalies in the tissue. This approach is thus suitable for imaging of the micro-vascular system, tumour detection or tissue characterization. The general field of biomedical photoacoustics has largely been based on using very short laser pulses. The short-pulse approach offers computational advantages but also many difficulties with instrumentation and radiation exposure limits. To overcome these difficulties, a methodology has emerged that uses linearly frequency modulated waves of light instead of short pulses to generate the ultrasound wave. This technique is referred to as frequency domain photoacoustics. With this approach that uses longer pulses, many of the modelling and computation approaches on which pulsed photoacoustics is based must be re-examined. More recently, pulse compression techniques of radar have been implemented with frequency domain photoacoustics, whereby the acquired acoustic signal is cross-correlated with the generating light signal. This methodology has been successfully demonstrated experimentally, however many analytical and computational questions remain as pulse-compression radar has not been analyzed or optimized for a photoacoustic application. The questions that the proposed research will address are: Which modelling and computation approaches of pulsed photoacoustics can be retained for frequency domain photoacoustics? How can pulse-compression radar approaches be used effectively to produce images based on frequency domain photoacoustic measurements? Can probing (input) waveforms be designed to achieve (i) a better signal-to-noise ratio (ii) more information (iii) information that is useful for the reconstruction of image? The goal of this research is the development of photoacoustic radar imaging modelling and computational methodologies which hold the promise for sensitive diagnostics of cancerous lesions in, for example, a human breast. Improved modelling and computational approaches, in addition to better waveform design are required to achieve these diagnostic and imaging objectives, and as such form the goals of the proposed research.