In the current form of multi-parametric photoacoustic microscopy (PAM), imaging hemoglobin concentration and blood flow speed requires dense sampling. Moreover, large-scale recording beyond the focal zone of ultrasonic transducer requires time-consuming mechanical scan of the optical-acoustic dual foci. Thus, the image acquisition time of multi-parametric PAM has been severely limited by the laser repetition rate and the focal diameter of the transducer.
Here, we report an ultrahigh-speed multi-parametric PAM with 1.2-MHz A-line rate for simultaneous real-time imaging of hemoglobin concentration, blood oxygenation, and blood flow in the mouse brain. Capitalizing on the pronounced stimulated Raman scattering in pure silica-core polarization-maintaining single-mode optical fibers, a dual-wavelength (532 and 558 nm) nanosecond laser with 1.2-MHz pulse repetition rate has been developed. Using a weakly focused ultrasonic transducer, we have achieved real-time acquisition of multi-parametric PAM images at a frame rate of 2.2 Hz over the 250-μm-diameter acoustic focal zone. By employing optical-mechanical hybrid scan, 25 dual-wavelength B-scans can be acquired simultaneously within one mechanical-scan trip, leading to a 25-fold improvement of imaging
speed. As a result, the imaging frame rate is improved from 0.08 Hz in the conventional multi-parametric PAM to 2.2 Hz.
The utility of this new PAM technology has been demonstrated in a mouse model of epilepsy by studying the dynamic neurovascular uncoupling during status epilepticus.