Fundamental Investigations On Two-dimensional Photoacoustic Imaging For Biomedicinal Applications

Photoacoustic imaging, which maps the distribution of the optical absorption within biological tissues by use of time-resolved laser-induced ultrasonic signals, is attracting increasing interests in biomedical imaging. As a hybrid imaging technique, it takes the advantages of both optical and ultrasonic techniques in that the reconstrcued image has the optical contrast similar to the optical techniques while enjoying the high spatial resolution comparable to the ultrasound. In theories, this novel modality can image the objects embedded several centimeters deep within targets with a resolution of several tens of microns.In this dissertation, the theoretical analysis, computer simulation, and phantom experiments are performed to investigate and resolve the practical problems in PA (Photoacoustic) imaging based on the propagation mechanism of PA signals. The corresponding PA imaging system is also designed and realized. In addition, the PA image reconstruction of phantom and in-vitro biological tissue is studied, and the image of the in-vivo cerebral blood vessel of mices was also successfully achieved. These studies have built necessary theoretical and experimental bases for further investigations of the early stage diagnosis of breast tumors and the cerebral functional imaging of small animals. The tasks are summarized as follows:1. By conducting the theoretical analysis of PA imaging, we employed a normalized mean square distance (NMSD) as the index for the evaluation of the effect of the number of measurement position (NMP) and the signal-to-noise ratio (SNR) of PA signals on the imaging quality. It was found that the quality of PA images is improved exponentially with the increase of the NMP and the SNR of PA signals. Furthermore, the assessment curve for imaging quality exhibits an turning point, whose position is determined by the actual object and measurement conditions. The imaging quality will be hardly improved when the NMP or the SNR of PA signals exceeds this turning point. On the other hand, the imaging quality will decline significantly when the NMP or the SNR of PA signals is below the turning point. This conclusion gives an important guidance to determine the actual system setup.2. The influence of the tissue optical parameters on PA signals is investigated...