An optical detection system for biomedical photoacoustic imaging

An all-optical system for the detection of photoacoustic transients is under development for photoacoustic imaging applications. The sensing mechanism is based upon the detection of acoustically-induced variations in the optical thickness of a Fabry Perot polymer film interferometer and provides an alternative to piezoelectric based detection methods. A key advantage is that the sensing geometry is defined by the area of the polymer sensing film that is optically addressed. This offers the prospect of obtaining sufficiently small element sizes and interelement spacing to employ the synthetic focussing techniques of phased arrays for image reconstruction. The optical nature of detection also allows for a transparent sensor head through which the excitation laser pulses can be transmitted for backward-mode photoacoustic imaging. Preliminary work has shown that the detection sensitivity (<10kPa - without signal averaging) and bandwidth (30MHz) are comparable to wideband piezoelectric PVDF ultrasound transducers with the prospect of achieving substantially smaller element sizes (<35 mu m).