Quantitative assessment of photoacoustic tomography systems integrating clinical ultrasound transducers using novel tissue-simulating phantoms

Abstract

Photoacoustic Tomography (PAT) systems based on commercial ultrasound instruments have the benefit of dualmodality imaging, which increases their appeal from a clinical standpoint. However, factors that influence PAT system performance have not been thoroughly investigated and standardized test methods have not been established for image quality evaluation. To address these issues we have adapted phantom-based approaches from ultrasound imaging standards and implemented them to assess a PAT system developed for vascular imaging. Our system comprises a tunable near-infrared pulsed laser and a commercial ultrasound imaging system, including four interchangeable linear array clinical ultrasound transducers with varying center frequencies, acoustic bandwidths and geometries. Phantoms consisted of a customized polyvinyl chloride (PVC) plastisol gel that simulates both optical and acoustic properties of breast tissue. One phantom incorporates a sub-resolution filament array suitable for bimodal ultrasound-photoacoustic imaging, while another contains an array of hemoglobin-filled cylindrical inclusions at various depths. Key performance characteristics were evaluated, including spatial resolution, signal uniformity, contrast, and penetration depth. These characteristics were evaluated at 750 nm at radiant exposures below ANSI safety limits. Effects of transducer properties on imaging performance were evaluated. Axial and lateral resolution ranged from 0.27-0.83 mm and 0.28-1.8 mm, respectively, and penetration depths from 1.9-4.2 cm were achieved. These results demonstrate variation in PAT system performance based on clinical transducer selection, as well as the utility of realistic phantom-based test methods in performing benchtop evaluations of system performance.