Interstitial photoacoustic spectral analysis: instrumentation and validation.

Photoacoustic (PA) spectral analysis (PASA) is a recently developed approach for quantifying molecular components and microscopic architectures in tissue. The PASA relies on signals with sufficient temporal length and narrow dynamic range for statistics based analysis. However, the optical and acoustic attenuation within the biological tissue make it difficult to acquire desirable signals from deep locations in biological tissue for PASA. This study proposes an interstitial PASA approach. By combining a fiber optics diffuser and a small aperture needle hydrophone, a fine needle PA probe facilitates PASA in deep tissue. A prototype probe has been fabricated and tested in quantifying the prostate cancer cell concentrations in vitro and lipid infiltrated hepatocyte in liver ex vivo. Experiment results show that the needle probe could potentially provide pathologic information of the tissues.