Ultrasound-transmission parameter imaging in a photoacoustic imager

We present a 'hybrid' imaging system, which can image both optical absorption properties and acoustic transmission properties of an object in a two-dimensional slice using a computed tomography photoacoustic imager. The ultrasound transmission measurement method uses a strong absorber of light which is placed in the path of the light illuminating the sample. This acts as a source of ultrasound, whose interaction with the sample can be measured at the far-end of the sample using the same ultrasound detector used for photoacoustics. Such measurements are made at various angles around the sample in a computerized tomography approach. The ultrasound transients at the multi-element detector at all projections are analyzed for both times-of-arrival and amplitude. Using a fan-beam projection reconstruction algorithm we obtain hybrid images of optical absorption, speed-of-sound and acoustic attenuation. We validate the method on an appropriate phantom