Pharmacokinetics of ICG and HPPH-car for the detection of normal and tumortissue using fluorescence, near-infrared reflectance imaging: A case study

We present in vivo fluorescent, near-infrared (NIR), reflectance images of indocyanine green (ICG) and carotene-conjugated 2-devinyl-2-(1-hexyloxyethy l) pyropheophorbide (HPPH-car) to discriminate spontaneous canine adenocarc inoma from normal mammary tissue. Following intravenous administration of 1 .0 mg kg(-1) ICG or 0.3 mg kg(-1) HPPH-car into the canine, a 25 mW, 778 nm or 70 mW, 660 nm laser diode beam, expanded by a diverging lens to approxi mately 4 cm in diameter, illuminated the surface of the mammary tissue. Suc cessfully propagating to the tissue surface, ICG or HPPH-car fluorescence g enerated from within the tissue was collected by an image-intensified, char ge-coupled device camera fitted with an 830 or 710 nm bandpass interference filter. Upon collecting time-dependent fluorescence images at the tissue s urface overlying both normal and diseased tissue volumes, and fitting these images to a pharmacokinetic model describing the uptake (wash-in) and rele ase (wash-out) of fluorescent dye, the pharmacokinetics of fluorescent dye was spatially determined. Mapping the fluorescence intensity owing to ICG i ndicates that the dye acts as a blood pool or blood persistent agent, for t he model parameters show no difference in the ICC uptake rates between norm al and diseased tissue regions. The wash-out of ICG was delayed for up to 7 2 h after intravenous injection in tissue volumes associated with disease, because ICG fluorescence was still detected in the diseased tissue 72 h aft er injection. In contrast, HPPH-car pharmacokinetics illustrated active upt ake into diseased tissues, perhaps owing to the overexpression of LDL recep tors associated with the malignant cells. HPPH-car fluorescence was not dis cernable after 24 h, This work illustrates the ability to monitor the pharm acokinetic delivery of NIR fluorescent dyes within tissue volumes as great as 0.5-1 cm from the tissue surface in order to differentiate normal from d iseased tissue volumes on the basis of parameters obtained from the pharmac okinetic models.