title: Modulation of an optical needle's reflectivity alters the average photon path through scattering media.
abstract: We introduce the concept of deliberate placement of absorbers to alter the average path of photons through tissue for a biomedical optical device. By changing the reflectivity of a needle that separates a source and detector, the average photon path through a turbid medium can be changed. Totally reflective needles have photon scattering density functions similar to a point source and detector in an infinite medium. An absorbing needle moves the average photon path of photons that reach the detector away from the needle. Thus, by modulating the reflectivity of the needle, it is possible to modify the sensitive volume, and simple tomography data should be possible. These results are confirmed by Monte Carlo simulations and experiment. Experiments include moving a black target relative to an optical "needle" and measuring the resulting intensity and phase lag of light reaching a detector at the distal end of the needle.
authors.affiliation: University of Illinois at Urbana-Champaign, Department of Physics, Laboratory for Fluorescence Dynamics, MC-704, 1110 West Green Street, Urbana, Illinois 61801-3080, USA. psimonso@uiuc.edu
authors.forename: Paul
authors.initials: P
authors.lastname: Simonson
authors.forename: Enrico
authors.initials: E
authors.lastname: D'Amico
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
mesh_terms: D001706:Biopsy / Q000295:instrumentation*; D003198:Computer Simulation; D017076:Computer-Aided Design; D003952:Diagnostic Imaging / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008027:Light; D015233:Models, Statistical; D009339:Needles; D055096:Optical Devices; D017785:Photons; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity