Photoacoustic imaging using a frequency domain synthetic aperture focusing technique

This paper describes the application of a frequency domain synthetic aperture focusing technique to photoacoustic imaging. The photoacoustic probe consisted of a laser delivery fibre-optic (diameter of 600μm, plastic coated silica) combined with a polymer (PVDF) transducer for ultrasonic detection. This system had a broadband frequency response in the MHz region. Such an integral probe was designed to optically transmit and receive near on-axis ultrasonic transients simultaneously, in under water applications. A frequency domain synthetic aperture method was successfully applied using phantom samples to produce 2D images from A-scan signals received from the probe. A range of samples were examined, including black nylon with 1 mm circular holes at a depth of 5.9 mm from the surface. A comparison was made with conventional B-scan images and with time domain synthetic aperture images. Results showed that synthetic focussing apertures, in time or frequency domains, offer better signal-to-noise ratios with improved capabilities in lateral resolution.