Photoacoustic tomography of rat brain in vivo using multibandwidth ultrasonic detection

Photoacoustic tomography employs short laser pulses to generate acoustic waves. The photoacoustic image of a test sample can be reconstructed using the detected acoustic signals. The reconstructed image is characterized by the convolution of the sample structure in optical absorption, the laser pulse, and the impulse response of the ultrasonic transducer used for detection. Although laser-induced ultrasonic waves cover a wide spectral range, a single transducer can receive only part of the spectrum because of its limited bandwidth. To systematically analyze this problem, we constructed a photoacoustic tomographic system that uses multiple ultrasonic transducers, each at a different central frequency, to simultaneously receive the induced acoustic waves. The photoacoustic images associated with the different transducers were compared and analyzed. The system was used to detect the vascular system of the rat brain. The vascular vessels in the brain cortex were revealed by all of the transducers, but the image resolutions differed. The higher frequency detectors with wider bandwidths provided better image resolution.