MR Spectroscopic Changes in the Rat Hippocampus following Proton Radiosurgery

Abstract

Purpose: To identify MR spectroscopic changes in the rat hippocampus following proton radiosurgery. Methods and Materials: A group of 12 rats were treated with Bragg peak proton beam irradiation involving the right hippocampus. Single doses of 30 CGE, 50 CGE, 70 CGE, 90 CGE were delivered to groups of 3 animals using single fraction technique. Animals were imaged using a standard 3 T GE Signa MRI at 4 months following treatment. An untreated animal was also studied. A 3″ surface coil was employed to obtain T1 weighted coronal pre- and post-gadolinium images (TR 600 and TE 30) and dual echo T2 weighted coronal images (TR 3000, TE 30/90). Volumetric analysis with custom software was done to evaluate areas of increased signal on T2 weighted images and the development of hydrocephalus was examined. Animals were sacrificed and specimens of the treated hippocampus were harvested for High Resolution Magic Angle Spinning MR Spectroscopy (HRMAS) followed by histopathology of the tissue samples. Peak values of choline, creatine, N-acetyl aspartate and lipids were evaluated and compared. Results: Peak tissue injury occurred in the surviving 90 CGE animal by both T2 weighted and post-gadolinium imaging. Gadolinium enhancement was seen in decreasing volumes of tissue at dosage levels from 90 to 50 CGE. Hydrocephalus was seen on the untreated side in the 90 CGE animal likely because of mass effect, while it was seen in small degrees in the side of treatment in the 70 and 50 CGE animals. Histopathology showed changes at 90 and 70 CGE, but not at 50 or 30 CGE at this time point using H and E stains. HRMAS showed spectroscopic changes in the surviving 90 and 70 CGE animals but not in the 50 and 30 CGE animals. Statistical significance was not reached because of the small sample size. Conclusions: Following single dose proton radiosurgery of rat hippocampus, HRMAS is able to identify metabolic changes induced by radiation. Studies built on these principles may help develop non-invasive MR spectroscopic methods to distinguish radiation changes from tumor recurrence.

Radiation Injury to the Normal Brain Measured by 3D‐Echo‐Planar Spectroscopic Imaging and Diffusion Tensor Imaging: Initial Experience

“…While the deleterious effects of radiation in the human hippocampus have not been reported, a previous study has reported abnormal metabolite levels in the rat hippocampus after proton therapy. 41 The complex pathological events after radiation have been confirmed by histopathological studies in animal models [42][43][44] and postmortem human brain specimens. 45 Previous 1 H MRS studies [7][8][9][10][11][12] used single voxel or single slice multi-voxel methods and thus were limited to a small region of the brain.…”

Dynamic contrast-enhanced susceptibility-weighted perfusion MRI (DSC-MRI) in a glioma model of the rat brain using a conventional receive-only surface coil with a inner diameter of 47mm at a clinical 1.5T scanner

“…With this setup, clinical designs can be simulated and therapies can be monitored in animal models beyond morphometric studies (Brockmann et al, 2006;Beuf et al, 2006;Deutscher et al, 2006;Johnson et al, 2006;Li et al, 2006;Rabinov et al, 2006) as well as before or beside clinical application in humans.…”

Gamma Knife for Functional Diseases

“…These experimental studies tended to support the dose effect found in humans [59]. Several magnetic resonance spectroscopy studies show, at around 12 months (the usual delay for major clinical and radiological changes), a strong reduction in choline, creatine, and N-acetylaspartate, with an elevation in lactate, pointing out the lack of normal oxidative metabolism (ischemia) [60][61][62][63][64][65].…”