title: Time-gated optical system for depth-resolved functional brain imaging.
abstract: We present a time-domain optical system for functional imaging of the adult head. We first describe the instrument, which is based on a Ti:Sapphire pulsed laser (wavelength 750-850 nm) and an intensified CCD camera enabling parallel detection of multiple fibers. We characterize the system in terms of sensitivity and signal-to-noise ratio, instrument response function, cross-talk, stability, and reproducibility. We then describe two applications of the instrument: the characterization of baseline optical properties of homogeneous scattering media, and functional brain imaging. For the second application, we developed a two-part probe consisting in two squares of 4 x 4 sources and 3 x 3 detectors. The laser source is time-multiplexed to define 4 states of 8 sources that can be turned on during the same camera frame while minimizing cross-talk. On the detection side, we use for each detector 7 fibers of different lengths creating an optical delay, and enabling simultaneous detection in 7 windows (by steps of 500 ps) for each detector. This multiple window detection allows depth sensitivity. The imaging probe was tested on dynamic phantoms and a preliminary result on an adult performing a motor task shows discrimination between superficial and cortical responses to the stimulus on both hemispheres.
authors.affiliation: Massachusetts General Hospital, Athinoula A. Martinos Center, Photon Migration Imaging Laboratory, Building 149, 13th Street, Charlestown, Massachusetts 02129, USA. juliette@nmr.mgh.harvard.edu
authors.forename: Juliette
authors.initials: J
authors.lastname: Selb
authors.forename: Danny K
authors.initials: DK
authors.lastname: Joseph
authors.forename: David A
authors.initials: DA
authors.lastname: Boas
mesh_terms: D000328:Adult; D001921:Brain / Q000166:cytology / Q000502:physiology*; D001931:Brain Mapping / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005071:Evoked Potentials / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D007834:Lasers; D008297:Male; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D041622:Tomography, Optical / Q000295:instrumentation* / Q000379:methods