Table 1.

Major hardware configurations of PAI with representative performance metrics.

Technique	Full Name	Brief Description	Resolution	Imaging Depth
OR-PAM	Optical Resolution - Photoacoustic Microscopy 49, 50	A laser is focused to a diffraction-limited spot with a microscope objective and the generated acoustic signal is focused with a concave acoustic lens to be detected by a broadband ultrasound transducer.	~0.5 - 3.0 μm	~1.2 mm
AR-PAM	Acoustic Resolution - Photoacoustic Microscopy 3	A dark-field ring of light is focused onto tissue and a concave acoustic lens focuses the acoustic signal to a broadband ultrasound transducer.	~45 μm	~5 mm
PAT/PACT	Photoacoustic Tomography / Computed Tomography 5	A pulsed illumination beam excites a region of interest and a linear or circular transducer arrayreceives acoustic signal for image generationusing inverse/back-projection algorithms.	0.1 - 1.0 mm	Multiple centimeters possible
PAE	Photoacoustic Endoscopy 60	Optical excitation, acoustic transduction, and mechanical scanning components are confined to the distal tip of an endoscope.	31 - 170 μm	1 - 7 mm