In vivo MR spectroscopy provides sensitive imaging biomarkers for radiation-induced brain injury

Jian-Ming Zhu*, Todd Atwood, J. Daniel Bourland, and Mike Robbins

Wake Forest University School of Medicine, Winston-Salem, NC, USA

Radiation-induced normal brain injury is a major limiting factor in the radiotherapy of brain tumor patients. There is growing concern over the risk of radiation-induced late effects in long-term cancer survivors, which may lead to chronic and progressive cognitive impairment. Noninvasive imaging techniques are required to study this significant side effect of brain tumor radiotherapy. Magnetic resonance spectroscopy (MRS) offers the promise for non-invasive determination of putative neuro-metabolic changes at the molecular levels that might help identify biomarkers responsible for this side effect of radiotherapy.

In this study, 20 rats were exposed to a clinically relevant dose of cranial irradiation, while 10 rats served as normal controls. Approximately one year after the irradiation, all animals were scanned with a 7T MRI scanner using high resolution MRI and MRS to determine the morphological and metabolic changes related to radiation induced injury. Neurochemical metabolites were measured by using in vivo localized single-voxel proton spectroscopy. Quantitative determination of metabolites was performed by using the LC Model. Significant metabolic differences were detected in the irradiated groups as compared to normal controls, indicating that in vivo MRS may serve as a sensitive imaging tool to diagnose radiological changes related to radiation-induced brain injury. This could also provide us a novel tool for in vivo investigation of the mechanisms related to radiation-induced brain injury.