Near-Infrared Fluorescence Contrast-Enhanced Imaging with Area Illumination and Area Detection: The Forward Imaging Problem

Fluorescence frequency-domain photon migration measurements were acquired from tissue phantoms, each containing a fluorescent target, by means of area illumination and area detection on the same surface and for the first time, to our knowledge, compared with predictions computed with a numerical solution to the coupled photon diffusion equations. We accomplished area illumination and area detection using a planar, intensitymodulated excitation light source and a gain-modulated intensified charge-coupled device camera, respectively. A 1-ml vessel containing 1- (mu)m solution of Indocyanine Green in 1% Liposyn was immersed 1 cm deep in each 512-ml tissue phantom. For most tissue phantoms, the background surrounding the 1-ml target was composed of Liposyn solution containing Indocyanine Green or 3,3 ʹ-Diethylthiatricarbocyanine Iodide such that the targetto-background ratio of fluorescence yield was =>10:1. Measurements of fluorescence modulation amplitude and phase were predicted with a mean error ranging from 10.1% to 13.6% and 0.56 (degree) to 1.72 (degree), respectively. These numbers are similar to those obtained by use of single-pixel frequency-domain photon migration techniques and validate the potential use of area illumination and area detection for biomedical imaging of tissues. Results also demonstrate that target-to-background ratios of fluorescence yield and fluorescence lifetime significantly affect target detectability.