Due to their high resolution, small animal MRI and PET scanners are invaluable tools in preclinical oncology. Histology provides an important complement to MRI and PET. Herein we propose a landmark system for highly accurate alignment of histology and autoradiography (AR) with MRI and PET on a rat tumor, using catheters punctured through the tumor and flushed with contrast agent. An FSA rat fibrosarcoma was grown on a Fischer 344 rat to 1.8 cm. The rat was anesthetized and placed into a cradle fitted to both a small animal 2 Tesla MRI (Oxford magnet) scanner and a MicroPET R4 (Concorde Microsystems). Three 18G catheters were punctured through the tumor parallel to the body axis in a triangular configuration. A fourth catheter was introduced diagonally to complete the information needed to establish the alignment uniquely. Catheters were interconnected with polyethylene tubing, flushed with magnevist solution for MRI contrast, and imaged by T2- and contrast-enhanced T1-weighted MRI. After transfer to the MicroPET, the tubes were flushed with 1.5 mCi of (18)F-deoxyglucose (FDG) and scanned by PET. FDG was then rinsed out of the tubing. After that, 1.5 mCi of FDG was injected i. v. into the animal and scanned by PET. The tumor was then dissected and snap frozen over liquid nitrogen together with the tubing, to preserve relative positions of the catheters. Cryoslicing of the tumor occurred perpendicular to the longitudinal axis, and sections underwent AR and staining for hematoxylin and eosin (H&E). The catheter hole locations can be clearly retrieved in MRI, PET, AR, and histology images. The arrangement of holes enables precise alignment among all modalities, providing the necessary input for computerized alignment. Unlike external markers, which may move, e.g. with the skin, these markers are locked into position relative to the internal structure of the tumor. Also unlike most external markers, these markers pass through every slice of the tumor and thus tie together 3D whole-tumor imaging modalities (MRI, PET) with histology and AR. This multi-modality strategy may provide new levels of accuracy in analytical experimental tumor biology. Funded by: NCI (CA40355, R24 CA92656), DOD (DAMD17-03-01-0367)

[Proc Amer Assoc Cancer Res, Volume 46, 2005]