Evaluation of a stereotactic frame for repositioning of the rat brain in serial positron emission tomography imaging studies

For serial imaging studies of the rat brain with positron emission tomograp hy (PET), reproducible positioning of the head can facilitate spatial align ment of images and quantitative analysis. To achieve this aim, we construct ed a plastic head frame and tested the positioning reproducibility on a hig h-resolution small-animal PET scanner, microPET. Two sets of ear bars, with tapers of either 18 degrees (sharp) or 45 degrees (blunt), were evaluated for their relative precision in securing the animal to the frame. For seque ntial positioning of an animal, average distances from the mean position of 0.51 mm (SD 0.41 mm) and 0.91 mm (SD 0.48 mm) were measured with the sharp and blunt ear bars, respectively. These results show that a rat brain can be reproducibly positioned using the frame, with a variation of position le ss than the spatial resolution of modern animal PET scanners. Brain regions of interest defined on one scan and copied across subsequent scans of a fr ame-repositioned animal resulted in an average coefficient of variation of 5.4% (SD 2.7%) using the sharp ear bars and 6.8% (SD 2.5%) using the blunt ear bars. This methodology has the potential to improve quantitative assess ment for serial PET studies. (C) 2001 Elsevier Science B.V. All rights rese rved.