Study of Photoacoustic Imaging based on all-optical Detection

Photoacoustic imaging is attracting increasing interests in biomedical imaging. The comparing between the traditional piezoelectric detections and optical detections is described. Three kinds of all-optical detection photoacoustic imaging systems, including system based on optical reflectance at a glass-liquid interface, system based on FP polymer film and the system based on POISe, are introduced and compared in this paper. Because these methods are difficult to realize measuring the photoacoustic signal on a 2D plane with the backward detection mode, a new kind of photoacoustic imaging system based on Electronic Speckle Pattern Interferometry (ESPI) is proposed. An ESPI outside displacement measurement system is adopted to detect the surface displacement of sample. Since the exposure time of a standard CCD which is of the order of tens of milliseconds, the temporal resolution to sample an acoustic field at MHz frequencies is achieved by interrogating the sensor with a short laser pulse whose bandwidth is about 20ns. After measuring and disposing the displacement data of the sample at a series detecting time, the photoacoustic image will be reconstructed by a delay and sum beam-forming algorithm or by a reconstruction algorithm based on the decomposition. In principle, the system will realize noncontact and backward-mode inspection and smaller element sizes of the receiver in the photoacoustic imaging application.