Multiple direction synthetic aperture focusing technique for acoustic-resolution photoacoustic microscopy

Abstract

Acoustic-resolution photoacoustic microscopy (AR-PAM) has great advantage over deep imaging depth when compared to optical-resolution PAM (OR-PAM). This is because that the point spread function (PSF) of AR-PAM is determined by the acoustic focus, which is relatively less scattered in biological tissues. In general, to maintain a high signal-to-noise ratio (SNR) and lateral resolution at a deep depth, AR-PAM uses an acoustic lens with a high numerical aperture (NA). The high NA lens provides high resolution and SNR in focal region, but significantly degrades the SNR and resolution in out-of-focus region. To overcome this problem, many researchers have introduced the synthetic aperture focusing technique (SAFT), which sums up the corresponding signals in the solid angle of the acoustic NA. However, the image enhancement of the conventional SAFTs has been limited because those techniques accumulate the signals without considering the actual photoacoustic (PA) wavefronts. In this study, we propose a novel SAFT that can overcome the existing limitation by exploiting each enhanced frequency components of the 1D SAFT images performed in multiple directions. As a result, we confirmed that the output AR-PAM image of our novel SAFT is superior to the existing SAFT image quality.