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Intra- and interobserver variability of MRI-based volume measurements of the hippocampus and amygdala using the
E Achten1, K Deblaere, C De Wagter
1MR Department 1K12, University Hospital Gent, Belgium. rik.achten@rug.ac.be
Insights
The manual ray-tracing method reliably detects hippocampus and amygdala lateralization in temporal lobe epilepsy (TLE) patients. However, it is less suitable for measuring absolute volumes due to variability.
Area of Science:
- Neuroimaging
- Epilepsy Research
- Quantitative Anatomy
Background:
- Hippocampal atrophy is a key indicator in temporal lobe epilepsy (TLE).
- Accurate volume measurement of the hippocampus (HC) and amygdala is crucial for diagnosing HC atrophy and lateralizing seizures.
- Variability in measurement techniques can impact diagnostic accuracy.
Purpose of the Study:
- To assess the intra- and interobserver variability of manual ray-tracing for HC and amygdala volume measurements.
- To evaluate the robustness of this method for detecting HC atrophy and lateralization in complex partial seizures (CPE).
Main Methods:
- Manual ray-tracing was used to measure HC and amygdala volumes in 11 healthy volunteers and 12 CPE patients.
- Two independent observers performed measurements twice using custom software.
- Variability was assessed for absolute volumes and normalized volume differences (deltaV) of HC, amygdala, and their sum.
Main Results:
- Interobserver variability for absolute HC and amygdala volumes was 1.80 ml and 0.82 ml, respectively.
- Intraobserver variability was approximately one-third of interobserver variability.
- Variability coefficients for normalized volume differences (deltaV) in healthy subjects were low (e.g., 3.6% for deltaV(HCA)).
- No significant intra- or interobserver differences were found for deltaV(HCA) and deltaV(HC), indicating robust lateralization.
Conclusions:
- The manual ray-tracing method is a reliable technique for lateralizing temporal lobe epilepsy (TLE) using normalized volume differences.
- The method demonstrates higher variability for absolute volume measurements, making it less suitable for this purpose.
Abstract:
We studied the intra- and interobserver variability of volume measurments of the hippocampus (HC) and the amygdala as applied to the detection of HC atrophy in patients with complex partial seizures (CPE), measuring the volumes of the HC and amygdala of 11 normal volunteers and 12 patients with presumed CPE, using the manual ray-tracing method. Two independent observers performed these measurements twice each using home-made software. The intra- and interobserver variability of the absolute volumes and of the normalised left-to-right volume differences (deltaV) between the HC (deltaV(HC)), the amygdala (deltaV(A)) and the sum of both (deltaV(HCA)) were assessed. In our mainly right-handed normals, the right HC and amygdala were on average 0.05 and 0.03 ml larger respectively than on the left. The interobserver variability for volume measurements in normal subjects was 1.80 ml for the HC and 0.82 ml for the amygdala, the intraobserver variability roughly one third of these values. The interobserver variability coefficient in normals was 3.6% for deltaV(HCA), 4.7% for deltaV(HC) and 7.3% for deltaV(A). The intraobserver variability coefficient was 3.4% for deltaV(HCA), 4.2% for deltaV(HC) amd 5.6% for deltaV(A). The variability in patients was the same for volume differences less than 5% either side of the interval for normality, but was higher when large volume differences were encountered, is probably due to the lack of thresholding and/or normalisation. Cutoff values for lateralisation with the deltaV were defined. No intra- or interobserver lateralisation differences were encountered with deltaV(HCA) and deltaV(HC). From these observations we conclude that the manual ray-tracing method is a robust method for lateralisation in patients with TLE. Due to its higher variability, this method is less suited to measure absolute volumes.