Abstract
In this paper a multi-wavelength optical-resolution photoacoustic microscopy (OR-PAM) system using stimulated Raman scattering is demonstrated for both phantom and in vivo imaging. A 1-ns pulse width ytterbium-doped fiber laser is coupled into a single-mode polarization maintaining fiber. Discrete Raman-shifted wavelength peaks extending to nearly 800 nm are generated with pulse energies sufficient for OR-PAM imaging. Bandpass filters are used to select imaging wavelengths. A dual-mirror galvanometer system was used to scan the focused outputs across samples of carbon fiber networks, 200μm dye-filled tubes, and Swiss Webster mouse ears. Photoacoustic signals were collected in transmission mode and used to create maximum amplitude projection C-scan images. Double dye experiments and in vivo oxygen saturation estimation confirmed functional imaging potential.
Highlights
Photoacoustic microscopy (PAM) provides high contrast imaging based on physiological differences in the optical absorption of tissues [1,2,3,4,5]
The output of a 1-ns pulse width, ytterbium-doped fiber laser (IPG Photonics) capable of pulse repetition rates (PRR) from 20 to 600 kHz was coupled into a 6-m polarization-maintaining single-mode fiber (PMSMF) (HB-450, Fibercore Inc., UK) to generate stimulated Raman scattering (SRS) peaks using a fiber launch system (MBT621D/M, Thorlabs Inc.)
The results show that the C-scan opticalresolution photoacoustic microscopy (OR-PAM) images are in good agreement with the spectrometer results
Summary
Photoacoustic microscopy (PAM) provides high contrast imaging based on physiological differences in the optical absorption of tissues [1,2,3,4,5]. As the predominant endogenous optically absorbing molecule in tissues, hemoglobin has been imaged using PAM to provide functional imaging of blood oxygen saturation and consumption in vivo. Acousticresolution PAM derives its lateral spatial resolution from acoustic focusing, while opticalresolution photoacoustic microscopy (OR-PAM) can achieve micron-scale resolution by using optical focusing to determine lateral resolution. By taking advantage of the high optical absorption of hemoglobin and micron-scale optical spot sizes, OR-PAM has proven invaluable for visualizing superficial capillary networks non-invasively and label-free, in vivo [6,7]. OR-PAM has proven useful for quantifying functional parameters down to capillary sizes [8]. Fiber and microchip lasers have recently been introduced as high-repetition-rate sources for realtime OR-PAM [9, 18]; the wavelength tunability was limited
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