Photoacoustic remote sensing (PARS) microscopy is a novel photoacoustic modality which provides non-contact reflection-mode operation within optical penetration regimes. It has thus far demonstrated exceptional in vivo imaging capabilities with high signal-to-noise (greater than 70dB) and sub-cellular lateral resolution (on the order of 600 nm). Moreover, being non-contact opens a wide range of previously inaccessible imaging targets where acoustic coupling to the sample is impractical. One disadvantage of the technique however is the lack of time-gated depth discrimination which has long been a staple of more conventional photoacoustic methods. Rather, depth-resolving ability has been solely defined by the optical section provided by the primary objective lens. Here a pulsed short-wave infrared low-coherence detection beam in a spectral-domain OCT system is used to probe depth-resolved reflectivity before and immediately after visible pulsed excitation. A difference image between these A-scans reveals signals with optical absorption contrast. Simulations based on recently-developed time-domain modeling of low-coherence PARS reflectivity changes is used to generate software-phantom images. We used a 1310-nm ns-pulsed interrogation source with 45nm linewidth, along with a 532-nm ns-pulsed excitation beam. The effects of various material and apparatus parameters are discussed along with extensive analytical and simulation results. These showcase the potential capabilities of the approach, such as depth resolved spectral unmixing (with oxygen saturation) and discrimination of blood vessels in highly scattering media, along with foreseeable limitations and potential implementation issues.
Kevan L. Bell, Parsin Hajireza, and Roger Zemp, "Coherence-gated photoacoustic remote sensing microscopy (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 1049422 (Presented at SPIE BiOS: January 30, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2288574.5752219167001.
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