Selective Metabolic Reduction in Gray Matter Acutely following Human Traumatic Brain Injury

Abstract

The aim of this study was to determine whether the apparent loss of overall gray-white matter contrast (GM/WM) seen on FDG-PET imaging reflects the differential changes of glucose metabolic rate (CMR_glc) in cortical gray mater (GM) and subcortical white mater (WM) following TBI. The clinical significance of the CMR_glc GM-to-WM ratio was also evaluated. Nineteen normal volunteers and 14 TBI patients were studied. Each subject had a quantitative FDG-PET, a quantitative H₂¹⁵O-PET and a MR scan acutely following TBI. Stabilities of the global and regional FDG lumped constants (LC) were studied. Parametric images (pixel unit: mg/min/100g) of FDG uptake rate (CUR_FDG) and CMR_glc were generated. The changes of CMR_glc in whole brain, GM and WM were studied separately by using a MRI-segmentation-based technique. The GM-to-WM ratios of both CUR_FDG and CMR_glc images were significantly (p < 0.001) decreased (>31%) in TBI patients. The global LC value reduced significantly (p < 0.01) in TBI patients. The CMR_glc decreased significantly (p < 0.001) in GM but not in WM (p > 0.1). Kinetic analysis revealed significant (p < 0.001) decrease of GM hexokinase activity in TBI patients. The GM-to-WM ratios of CMR_glc correlated (r = 0.64) with the initial Glasgow Coma Score (GCS) of TBI patients. The patients with higher CMR_glc GM-to-WM ratios (>1.54) showed good recovery 12 months after TBI. There was a selective CMR_glc reduction in cortical GM following TBI. The pathophysiological basis for the reduction in GM-to-WM CMR_glc ratio seen on FDG-PET imaging following TBI remains to be determined.