Visual and semiquantitative analysis of cortical FDG-PET scans in childhood epileptic encephalopathies

The optimal method for analyzing PET scans in children being considered for epilepsy surgery is unresolved: Fully quantified methods are invasive, and the required controls are generally unavailable. We sought to compare visual inspection with semiquantitative analysis for the detection of cortical metabolic defects.

Thirty-two children with cryptogenic epileptic encephalopathies were studied prospectively with 18F-fluorodeoxyglucose (FDG) PET. Visual inspection was performed on separate occasions by independent observers. Four-millimeter circular regions of interest were used to sample radiotracer uptake in selected cortical regions. Asymmetry between homologous regions were calculated to detect focal abnormalities. Bilateral and diffuse abnormalities were assessed by comparing the ratio of cortical-to-cerebellar uptake in patients with historical age-matched controls. The sensitivity and specificity of visual inspection was compared with that of semiquantitative analysis for the detection of focal, bilateral and diffuse cortical metabolic abnormalities.

Visual inspection revealed full inter-rater agreement for the presence of major focal abnormalities. The sensitivity and specificity for visual inspection compared to semiquantitative analysis were 77% and 92%, respectively, with semiquantitative analysis often revealing abnormalities to be more extensive than had been suspected visually. Compared with semiquantitative analysis, visual inspection had a low sensitivity but high specificity for the detection of bilateral and diffuse hypometabolism.

Semiquantitative analysis gives clinically useful information additional to that obtained from visual inspection.