Acoustic-resolution photoacoustic microscopy based on an optically transparent focused transducer with a high numerical aperture
Cheng Fang, Jun Zou
Abstract
This Letter reports acoustic-resolution-photoacoustic microscopy (AR-PAM) based on a new optically transparent focused polyvinylidene fluoride (PVDF) transducer with a high acoustic numerical aperture (NA) of 0.64. Owing to the improved fabrication process, the new transducer has a much higher NA (0.64) than the previously reported low-NA transducer ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">N</mml:mi> <mml:mi mathvariant="normal">A</mml:mi> </mml:mrow> </mml:mrow> <mml:mo>=</mml:mo> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>0.23</mml:mn> </mml:mrow> </mml:math> ). The acoustic center frequency and (pulse-echo) bandwidth are also increased to 36 and 44 MHz, respectively, which provides a 38 µm acoustic focal spot size and 210 µm acoustic depth of focus. For demonstration, AR-PAM was conducted on a twisted wire target in water and chicken breast tissue, and in vivo on a mouse tail. The imaging results show that high acoustic resolution and sensitivity can be achieved with a simple and compact setup to resolve the target at different depths. Such capabilities can be useful for the development of new AR-PAM systems for handheld, wearable, and even endoscopic imaging applications.