INTRA-OBSERVER AND INTEROBSERVER VARIABILITY OF MRI-BASED VOLUME MEASUREMENTS OF THE HIPPOCAMPUS AND AMYGDALA USING THE MANUAL RAY-TRACING METHOD

We studied the intra- and interobserver variability of volume measurme nts of the hippocampus (HC) and the amygdala as applied to the detecti on of HC atrophy in patients with complex partial seizures (CPE), meas uring the volumes of the HC and amygdala of 11 normal volunteers and 1 2 patients with presumed CPE, using the manual ray-tracing method. Two independent observers performed these measurements twice each using h ome-made software. The in intra- and interobserver variability of the absolute volumes and of the normalised left-to-right volume difference s (delta V) between the HC (delta V-HC), the amygdala (delta V-A) and the sum of both (delta V-HCA) were assessed. In our mainly right-hande d normals, the right HC and amygdala were on average 0.05 and 0.03 mi larger respectively than on the left. The interobserver variability fo r volume measurements in normal subjects was 1.80 mi for the HC and 0. 82 mi for the amygdala, the intraobserver variability roughly one thir d of these values. The interobserver variability coefficient in normal s was 3.6% for delta V-HCA, 4.7% for delta V-HC and 7.3 % for delta V- A. The intraobserver variability coefficient was 3.4% for delta V-HCA, 4.2 % for delta V-HC amd 5.6 % for delta V-A. The variability in pati ents was the same for volume differences less than 5% either side of t he interval for normality, but was higher when large volume difference s were encountered, is probably due to the lack of thresholding and/or normalisation. Cutoff values for lateralisation with the delta V were defined. No intra- or interobserver lateralisation differences were e ncountered with delta V-HCA and delta V-HC. From these observations we conclude that the manual ray-tracing method is a robust method for la teralisation in patients with TLE. Due to its higher variability, this method is less suited to measure absolute volumes.