The overall goal of our animal studies is to evaluate how various in vitro functional and morphological parameters compare with MRI/31p-MMR and PET data of brain tumor growth and response to steroid therapy. PET data will include blood flow, oxygen consumptionand 18F-2-Fluoro-2-deoxyglucose uptake. The studies are designed to quantitate data using in vivo MRI/MRS and PET techniques as well as established in vitro assay procedures. In the canine work, MRI and PET studies will be performed on the same animals using localization techniques that will provide examination of the same tissue sample volume. The results of both non invasive in vivo procedures will be correlated to in vitro detailed morphometric-histological analysis of the tumors as well as brain/ tumor tissue specific gravity measurements and blood flow determinations using microsphere techniques. High resolution (microscopy) imaging procedures will be employed to study rabbit brain tumors as a function of their growth and response to therapy aimed at reducing tumor induced edema. The MRI high resolution images will be compared to detailed histological evaluation of the sample volume area. Tumor associated edema will be quantitated using measurements of Tl and T2 relaxation times and compared to direct in vitro measurements of tumor and edematous brain tissue water content extravasation of plasma proteins and vascular - extravascular space compartment determinations. The proposed studies address timely and important issues relating to the information provided and the potential clinical applications of MRI/MRS and PET.