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 tomography (PET), reproducible positioning of the head can facilitate spatial alignment of images and quantitative analysis. To achieve this aim, we constructed a plastic head frame and tested the positioning reproducibility on a high-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 sequential 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 less than the spatial resolution of modern animal PET scanners. Brain regions of interest defined on one scan and copied across subsequent scans of a frame-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 assessment for serial PET studies.

Anatomical localization schemes for use in positron computed tomography using a specially designed headholder.

A headholder system is described for use in the correlation of images obtained with positron computed tomography (PCT) and other neuroradiological imaging modalities. Methods are described for defining brain anatomy from PCT images by the use of projection schemes from tomographic data. Cross-correlation of images between positron CT and standard lateral skull films, X-ray computed tomography (XCT), and two-dimensional rectilinear positron images are discussed. Such methods allow for improved reproducibility of head positioning and more precise cortical localization necessary in studies of normal brain function as well as in neuropathological conditions.