title: Forty-five degree backscattering-mode nonlinear absorption imaging in turbid media.
abstract: Two-color nonlinear absorption imaging has been previously demonstrated with endogenous contrast of hemoglobin and melanin in turbid media using transmission-mode detection and a dual-laser technology approach. For clinical applications, it would be generally preferable to use backscattering mode detection and a simpler single-laser technology. We demonstrate that imaging in backscattering mode in turbid media using nonlinear absorption can be obtained with as little as 1-mW average power per beam with a single laser source. Images have been achieved with a detector receiving backscattered light at a 45-deg angle relative to the incoming beams' direction. We obtain images of capillary tube phantoms with resolution as high as 20 microm and penetration depth up to 0.9 mm for a 300-microm tube at SNR approximately 1 in calibrated scattering solutions. Simulation results of the backscattering and detection process using nonimaging optics are demonstrated. A Monte Carlo-based method shows that the nonlinear signal drops exponentially as the depth increases, which agrees well with our experimental results. Simulation also shows that with our current detection method, only 2% of the signal is typically collected with a 5-mm-radius detector.
authors.affiliation: University of Rochester, The Institute of Optics, 275 Hutchinson Road, Rochester, New York 14627, USA. cui@optics.rochester.edu
authors.forename: Liping
authors.initials: L
authors.lastname: Cui
authors.forename: Wayne H
authors.initials: WH
authors.lastname: Knox
mesh_terms: D000042:Absorption; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008027:Light; D036641:Microscopy, Fluorescence, Multiphoton / Q000295:instrumentation*; D009391:Nephelometry and Turbidimetry / Q000295:instrumentation*; D017711:Nonlinear Dynamics; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity