Enabling Biomedical Imaging Diagnostics using Optical Methods

This thesis work applies optical schemes to existing biomedical imaging techniques to improve the performance of present state-of-the-art biomedical imagers, and is in two parts. In the first part, a fast and simple optical time-gate scheme for counting single photons is presented. The gate is useful for measuring the temporal point spread functions of biological tissues during imaging. Its construction consists of a silicon photodiode connected in series with a 50-ohm resistor, and operates in the photoconductive mode. The compactness, simplicity and ease of construction of the gating scheme make it low-cost and widely accessible to a whole range of applications. Additionally, the scheme may be easily integrated into current medical imaging techniques to reduce cost and size. In the second part of the thesis, a novel hybrid photoacoustic and diffuse optical tomography hand-held probe is constructed for improving the accuracy of diffuse optical imaging. The probe design incorporates photoacoustic technology into the standard diffuse optical imaging systems. The photoacoustic tomography is first used to reconstruct, at ultrasound resolution, the qualitative optical absorption distribution that reveals optical contrast. The location information of the imaged target is then used as a-priori information for the image reconstruction in diffuse optical tomography. Diffuse optical tomography systems have the ability to provide quantitative absorption coefficient values of tumors that is indicative or a malignant or benign tumor. Unfortunately, they have rather low resolution. Therefore, by incorporating photoacoustic imaging to provide depth information, the accuracy of the absorption coefficient reconstruction is improved.