Measurement of photoacoustic detector sensitivity distribution by robotic source placement

摘要

Many photoacoustic imaging systems use back projection-based image reconstruction algorithms to estimate photoacoustic source locations from the time-of-flight pressure information collected by either a scanned single transducer or an array of stationary transducer elements. Accurate image reconstruction requires that the transducer(s) locations relative to the imaged volume and the transducer(s) sensitivity distribution within the imaged volume be accurately known. The objective of this work was to develop a method for estimation of the sensitivity distribution of a transducer array. Our approach was to capture for each transducer element the response to a photoacoustic point source that was robotically scanned throughout the imaging volume. The temporally resolved photoacoustic signal was then processed to obtain the relative transducer sensitivity at the source location. We performed a scan over a transducer array fabricated in our laboratory that consisted of twelve 3 mm elements in a 30 mm annular ring arrangement. We measured both the sensitivity distribution of single elements, from which the spatial and angular sensitivity profiles were extracted, as well as the simultaneous response of all transducer elements, which allowed us to locate the effective position of each element, but also highlighted the non-uniformity between transducers' response of up to 20%. We present these and other measured parameters, and discuss their significance as well as their effect on our image reconstruction algorithm.