Optical imaging in the frequency domain

摘要

Abstract: oratory has developed a modular laser tomography system, with pulsed or amplitude modulated (MHz to GHz), near infrared lasers that deliver a probing beam to the tissue of interest through a fiber optic. After the incoming light is scattered and attenuated by the tissue, a detector or imaging fiber optic bundle delivers it to a point detector (photomultiplier tube) which is heterodyned with the modulation frequency to yield the phase delay and demodulation resulting from the light-tissue interaction. The CCD electronics are phase-locked with those of the digitizer to minimize pixel jitter and, in addition, an external clock synchronizes the detector units with the modulated laser source. The digitized time slices are integrated into four bins corresponding to four quadrants of the cross correlation period. The final processing step, a fast Fourier transform, generates the phase shift, demodulation, and average intensity data suitable for image reconstruction. !11