| dc.description.abstract | This dissertation focuses on laser-based noninvasive photoacoustic microscopy of subsurface structures in vivo. Photoacoustic microscopy is a hybrid imaging modality that combines the high-resolution advantage of ultrasonic imaging in deep tissue with the high-contrast advantage of optical imaging. It detects the short-pulsed laser-induced photoacoustic waves, whose amplitudes reflect the localized laser energy absorption, to image the internal optical absorption distributions. The spatial resolution is determined by the ultrasonic focal ability and the ultrasonic bandwidth. The imaging depth is primarily limited by the acoustic attenuation within the reach of diffuse photons. The ratio of maximum imaging depth to axial resolution in photoacoustic microscopy is greater than 100, which is comparable to that of modern high-resolution optical imaging modalities, such as confocal microscopy, two-photon microscopy, and optical coherence tomography. However, the maximum imaging depth has been much enlarged by taking advantages of absorbed diffuse photons. Based on the intrinsic optical contrast, we have achieved in vivo volumetric imaging of subcutaneous microvasculature, skin melanoma, and acute thermal injuries in high spatial resolution. We have imaged physiological parameters in subcutaneous microvessels, such as total hemoglobin concentration and hemoglobin oxygen saturation, on a single vessel basis in small animals in vivo. We have also monitored changes of hemoglobin oxygen concentration between different systemic physiological states on a vessel-by-vessel basis. Moreover, we have demonstrated the feasibility of human imaging using photoacoustic microscopy by imaging finger tips and subcutaneous palm vessels. | en |
