2 & 3D Imaging of Contrast Agents in Animal Models

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Near Infrared (NIR) optical imaging technologies provide sensitive localization of small heterogeneities deep within the human breast using intrinsic absorption (mua) and scattering (mus'). In order to achieve a further enhancement of the sensitivity and specificity (S/S) of cancer detection by the optical method, we propose to refocus our activity in this competitive renewal application towards extrinsic contrast in cancers in animal models. The proposed work will first determine the Figure of Merit, M, of the extrinsic agents and to quantify the increase in M with NIR contrast agents using both fluorescence and absorbance detection of the very small (20 pmole) amounts of extrinsic probes in animal tumors. Several instrumentation schemes are required for these studies and include: 1) An improved phased array system with localization of indocyanine green (ICG) demonstrated in model systems to 0.2 mm and 9L glioma 20 p moles of ICG is proposed for animal tumors including prostate cancer and human breast cancer detection where S/S can be evaluated in early, small tumors. Two other instruments appropriate to the animal models will be employed. 2) A flying spot scanner of 1 mm resolution for superficial tumors (mouse only) and adapted to imaging the NIR fluorescence signals. 3) a three-dimensional imager with less than 50 micron resolution requiring snap freezing of the tumor will be used to localize contrast agents in all non-human tumors. The latter system is essential to a critical evaluation of the phased array system. Seven NIR contrast agents based upon ICG and including molecular beacons will be compared in animal models using the above mentioned detection methods. Quantitative comparison will be afforded using the Figure of Merit(M) based upon tumor/tissue contrast agent (C), retention time (R)(min), and fluorescence quantum yield ratio (Q). M is calculated on the basis of a linear model (i.e., the product of these three quantities). Thus, an intensive, ambitious quantitative evaluation of currently available contrast agents will afford an animal model data base transfer to human breast tumors using FDA approved ICG (and others later) and phased array localization co-registered with gadolinium chelate tumor MRI images in "bench to bedside" studies (NIH Workshop, September 14-17, 2000).