Enlarged acceptance angle of a finite size detector in photoacoustic imaging using acoustic lenses

A large surface area transducer is preferable to be used to detect extremely weak photoacoustic signals in mammography due to its high sensitivity. The lateral resolution is limited by the small acceptance angle of such a transducer. We introduce an excellent material for an acoustic lens used to enlarge the transducer's acceptance angle. Our acoustic characterizations showed that this material has tissue-like acoustic impedance, large speed of sound and low acoustic attenuation. These acoustic properties ensures an excellent acoustic lens material. We further investigated the acoustic irradiation pattern of a 1 MHz, 5 mm x 5 mm single element transducer. Transducer irradiation pattern with and without acoustic lens made from our proposed material and common used lens material are simulated using the Field II program and also the k-wave package. Good agreement has been achieved comparing the simulation results from two different methods. Both simulations show that the proposed material not only enlarged the acceptance angle of the transducer but also minimized the signal loss compared to the common used lens material. We conclude that the proposed material can be used as an excellent acoustic lens for photoacoustic tomography.