VISUAL AND SEMIQUANTITATIVE ANALYSIS OF CORTICAL FDG-PET SCANS IN CHILDHOOD EPILEPTIC ENCEPHALOPATHIES

The optimal method for analyzing PET scans in children being considere d for epilepsy surgery is unresolved: Fully quantified methods are inv asive, and the required controls are generally unavailable. We sought to compare visual inspection with semiquantitative analysis for the de tection of cortical metabolic defects. Methods: Thirty-two children wi th cryptogenic epileptic encephalopathies were studied prospectively w ith F-18-fluorodeoxyglucose (FDG) PET. Visual inspection was performed on separate occasions by independent observers, Four-millimeter circu lar regions of interest were used to sample radiotracer uptake in sele cted cortical regions. Asymmetry between homologous regions were calcu lated to detect focal abnormalities. Bilateral and diffuse abnormaliti es were assessed by comparing the ratio of cortical-to-cerebellar upta ke in patients with historical age-matched controls. The sensitivity a nd specificity of visual inspection was compared with that of semiquan titative analysis for the detection of focal, bilateral and diffuse co rtical metabolic abnormalities. Results: Visual inspection revealed fu ll inter-rater agreement for the presence of major focal abnormalities . The sensitivity and specificity for visual inspection compared to se miquantitative analysis were 77% and 92%, respectively, with semiquant itative analysis often revealing abnormalities to be more extensive th an had been suspected visually. Compared with semiquantitative analysi s, visual inspection had a low sensitivity but high specificity for th e detection of bilateral and diffuse hypometabolism. Conclusion: Semiq uantitative analysis gives clinically useful information additional to that obtained from visual inspection.