Noncontact full-field measurements of photoacoustic wave and acoustic wave backpropagation for tomography reconstruction

Abstract

A system for Full Field Photoacoustic Tomography (FF-PAT) has been implemented. Photoacoustic tomography (PAT) has been studied as a powerful biomedical imaging modality for several decades. Because it can use scattered light for photoacoustic excitation, deep tissue imaging becomes possible. However, in a conventional PAT system, the excited acoustic wave is detected by a transducer, which limits the application of PAT. In general, acoustic transducer asks physical contact with the specimen. To overcome the contact problem, optical interferometer has been studied as a non-contact point detector. Basically, the optical detection is better than the mechanical contact-based transducer detection in sensitivity. However, the point detection needs transverse scan to get a volume image. In this study, we propose a full field scheme of PAT, called FF-PAT. The 2D variation of the surface of a specimen, caused by photoacoustic waves, is obtained by utilizing the digital holography. To capture the fast motion of the photoacoustic wave, the full field image is captured with a pulsed probe beam. The propagation of the wave is monitored by adjusting the time delay between the excitation and the probe pulses. By making backpropagation of the measured wave, the original distribution of the target is reconstructed.