Table 1.

Summary of the major advances, trends, and challenges of PAI systems for clinical translation

PA imaging system	Features	Technique advances and trends	Disease models	Translational challenges	References
PAM	Laser focusing, high ultrasound frequency, raster scanning	High frame rate, wavefront engineering, microelectromechanical systems	Melanoma imaging, port-wine stains, ophthalmology diagnosis	Shallow penetration depth, limited FOV	[59, 90–92]
PAFC	Single cell detection, high resolution	Specific disease targets, ultrasensitive abnormal cells detection	Circulating tumor cells, hematologic diseases	Shallow detection depth, low sensitivity	[24, 93]
PAE	Circumferential sector scan, interior imaging	Miniaturized probe, coregistered PAE/EUS system	Gastrointestinal tract imaging, atherosclerosis detection, lymph node imaging	Probe size, motion artifacts, robustness	[35, 36, 94]
PACT	Circular scanning, inverse reconstruction algorithm, large FOV	Detection geometries, parallel data-acquisition, sophisticated reconstruction	Human breast cancer, primate brain imaging through skull, hypoxic-ischemic encephalopathy	Strong artifacts, suboptimal spatial resolution and imaging speed	[10, 50, 95]
PA mammoscope	Flat ultrasonic transducer array, fast DAQ, large field-of-view (FOV).	NIR laser or microwave excitation, real-time imaging	Human breast cancer diagnosis	Patient-instrument interface, and relatively low spatial resolution	[84]
Ultrasound array based PAT	Dual-modality, adaptable from clinical ultrasound system	Handheld probe, portable	SLN mapping, human ovarian tissue, rat bone and joint imaging	Low SNR, Imaging accuracy	[64, 96, 97]