Reflection-mode submicron-resolution in vivo photoacoustic microscopy

Submicron-resolution photoacoustic microscopy (PAM) currently exists only in transmission mode, due to the technical difficulties of combining high numerical-aperture (NA) optical illumination with high NA acoustic detection. The lateral resolution of reflection-mode PAM has not reached <2 mu m in the visible light range. Here we develop the first reflection-mode submicron-resolution PAM system with a new compact design. By using a parabolic mirror to focus and reflect the photoacoustic waves, sufficient signals were collected for good sensitivity without distorting the optical focusing. By imaging nanospheres and a resolution test chart, the lateral resolution was measured to be similar to 0.5 mu m with an optical wavelength of 532 nm, an optical NA of 0.63. The axial resolution was measured at 15 mu m. Here the axial resolution was measured by a different experiment with the lateral resolution measurement. But we didn't describe the details of axial resolution measurement due to space limit. The maximum penetration was measured at similar to 0.42 mm in optical-scattering soft tissue. As a comparison, both the submicron-resolution PAM and a 2.4 mu m-resolution PAM were used to image a mouse ear in vivo with the same optical wavelength and similar pulse energy. Capillaries were resolved better by the submicron-resolution PAM. Therefore, the submicron-resolution PAM is suitable for in vivo high-resolution imaging, or even subcellular imaging, of optical absorption. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JBO.17.2.020501]