DMD-based random-access optical-resolution photoacoustic microscopy

The scanning mechanism is a major technical focus in optical-resolution photoacoustic microscopy. Flexible scanning access with fast scanning speed is desired to monitor biological and physiological dynamics with high temporal resolution. We developed random-access optical-resolution photoacoustic microscopy (RA-OR-PAM) using a digital micromirror device (DMD). Each micromirror on the DMD can be independently controlled, allowing imaging of regions of interest with arbitrary user-selected shapes without extraneous information. A global structural image is first acquired, and the regions of interest are selected. The laser beam then scans these regions exclusively, resulting in a faster frame rate than in a conventional raster scan. This system can rapidly scan arbitrarily shaped regions of interest with a lateral resolution of 3.6 μm within a 40×40 μm2 imaging area, a size comparable to the focal spot size of a 50 MHz ultrasound transducer. We demonstrated the random-access ability of RA-OR-PAM by imaging a monolayer of red blood cells. This system was then used to monitor blood flow in vivo within user-selected capillaries in a mouse ear. By imaging only the capillary of interest, the frame rate was increased by up to 13.3 times.