Imaging of spontaneous canine mammary tumors using fluorescent contrast agents

We present near-infrared frequency-domain photon migration imaging for the lifetime sensitive detection and localization of exogenous fluorescent cont rast agents within tissue-simulating phantoms and actual tissues. We employ intensity-modulated excitation light that is expanded and delivered to the surface of a tissue or tissue-simulating phantom, The intensity-modulated fluorescence generated from within the volume propagates to the surface and is collected using a gain-modulated image-intensified charge-coupled devic e camera. From the spatial values of modulation amplitude and phase of the detected fluorescent light, micromolar volumes of diethylthiatricarbocyanin e iodide (tau = 1.17 ns) and indocyanine green (ICG) (tau = 0.58 ns) embedd ed 1.0 cm deep in a tissue phantom are localized and discriminated on the b asis of their lifetime differences. To demonstrate the utility of frequency -domain fluorescent measurements for imaging disease, we image the fluoresc ence emitted from the surface of in vivo and ex vivo canine mammary gland t issues containing lesions with preferential uptake of ICG. Pathology confir ms the ability to detect spontaneous mammary tumors and regional lymph node s amidst normal mammary tissue and fat as deep as 1.5 cm from the tissue su rface.