{Reference Type}: Journal Article
{Title}: Achieving depth-independent lateral resolution in AR-PAM using the synthetic-aperture focusing technique.
{Author}: Gao R;Xue Q;Ren Y;Zhang H;Song L;Liu C;Gao R;Xue Q;Ren Y;Zhang H;Song L;Liu C;
{Journal}: Photoacoustics
{Volume}: 26
{Issue}: 0
{Year}: Jun 2022
{Factor}: 9.656
{DOI}: 10.1016/j.pacs.2021.100328
{Abstract}: Acoustic-resolution photoacoustic microscopy (AR-PAM) is a promising imaging modality that renders images with ultrasound resolution and extends the imaging depth beyond the optical ballistic regime. To achieve a high lateral resolution, a large numerical aperture (NA) of a focused transducer is usually applied for AR-PAM. However, AR-PAM fails to hold its performance in the out-of-focus region. The lateral resolution and signal-to-noise ratio (SNR) degrade substantially, thereby leading to a significantly deteriorated image quality outside the focal area. Based on the concept of the synthetic-aperture focusing technique (SAFT), various strategies have been developed to address this challenge. These include 1D-SAFT, 2D-SAFT, adaptive-SAFT, spatial impulse response (SIR)-based schemes, and delay-multiply-and-sum (DMAS) strategies. These techniques have shown progress in achieving depth-independent lateral resolution, while several challenges remain. This review aims to introduce these developments in SAFT-based approaches, highlight their fundamental mechanisms, underline the advantages and limitations of each approach, and discuss the outlook of the remaining challenges for future advances.