title: Reflection-mode submicron-resolution in vivo photoacoustic microscopy.
abstract: 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 μm 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 ≈ 0.5 μm with an optical wavelength of 532 nm, an optical NA of 0.63. The axial resolution was measured at 15 μm. 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 ≈ 0.42 mm in optical-scattering soft tissue. As a comparison, both the submicron-resolution PAM and a 2.4 μm-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.
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Konstantin
authors.initials: K
authors.lastname: Maslov
authors.forename: Song
authors.initials: S
authors.lastname: Hu
authors.forename: Ruimin
authors.initials: R
authors.lastname: Chen
authors.forename: Qifa
authors.initials: Q
authors.lastname: Zhou
authors.forename: K Kirk
authors.initials: KK
authors.lastname: Shung
authors.forename: Lihong V
authors.initials: LV
authors.lastname: Wang
mesh_terms: D000818:Animals; D004423:Ear / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation*; D007909:Lenses; D051379:Mice; D033401:Microscopy, Acoustic / Q000295:instrumentation*; D008904:Miniaturization; D061088:Photoacoustic Techniques / Q000295:instrumentation*