FDG PET in traumatic brain injury

Objectives Mild traumatic brain injury (TBI) is the leading injury among recently deployed veterans. An imaging gold standard to objectively assess the functional brain changes in mild TBI is yet to be established. In this study, we evaluated the FDG-PET brain findings in veterans who had sustained neuropsychological symptoms after mild TBI.

Methods PET studies of 37 veterans (34 male, 3 female, 22-53 year old) with a history of mild TBI and persistent neuropsychological complaints were quantitatively evaluated. All patients had no abnormal findings on MRI or CT. By using the region of interests based PET analysis software (NeuroQ 3.0,Syntermed, Inc.), brain images were registered and transformed to standardized brain map, which is clustered into 47 standard regions. The metabolic activity in each region is analyzed by comparing patient group and control group derived from 50 asymptomatic normal subjects.

Results Statistical significances (one group t test, P<0.05) were found in 35 out of 47 regions between patient group and control group (17 regions with hypermetabolism, 18 with hypometabolism). Relative hypometabolism is noted in left Broca, left temporal lobe(multiple segments), thalami and left cingulate cortex. Relative hypermetabolism is identified in associative visual cortex and right Broca. The FDG metabolism from the left- and the right-sides of the same region are highly correlated, except for these regions: Broca (cor=0.35; P < 0.05), inferior parietal cortex (cor=0.45; P < .05), sensorimotor cortex (cor=0.41, P < 0.05), and parietotemporal cortex (cor=-.12, N.S.).

Conclusions Previous studies of mild TBI demonstrated abnormal brain metabolism with normal brain structure. Our study identified significant abnormalities in brain metabolism particularly in areas related to memory, language and vision. Although there is significant variability among different individuals, there is a pattern of abnormality which is better demonstrated in group analysis. Large scale studies are needed to establish the FDG metabolic pattern for clinical evaluation, and possibly prognosis of mild TBI