2 D line-scan photoacoustic imaging of absorbers in a scattering tissue

A photoacoustic imaging system has been evaluated by mapping the temporal distribution of photoacoustic signals generated in a tissue phantom. The phantom comprised an Intralipid scattering solution (μs’=1mm -1 and μa=0.01mm ) containing two regions of enhanced absorption; a 1.5mm thick layer (μa=1mm ) and a 75μm layer (μa=40mm ). These were located 1cm beneath the surface of the Intralipid which was irradiated with 7ns Q switched laser pulses of fluence 0.05 J/cm. A Fabry Perot polymer film ultrasound sensing interferometer was used for the detection of the photoacoustic signals. A 1D ultrasound array was simulated by illuminating the sensing interferometer with a large diameter laser beam and line scanning a photodiode across the reflected output beam. The detection sensitivity of the system was 3kPA over a 25MHz measurement bandwidth, the 3dB acoustic bandwidth was 17.5MHz, the sensitive azimuthal “array” aperture and element size were 12mm and 0.8mm respectively. Greyscale images of the timeresolved photoacoustic signals enabled both absorbers to be clearly identified with an axial spatial resolution of less than 100μm. It is envisaged that this approach could form the basis of a practical photoacoustic tissue imaging system.