HIPPOCAMPAL VOLUMETRY WITH MAGNETIC-RESONANCE-IMAGING - A COST-EFFECTIVE VALIDATED SOLUTION

Purpose: The clinical utility of hippocampal volumetry is well documen ted, but the materials and techniques required to perform the procedur e are not widely available outside major research centers. We describe a personal computer-based method of volumetric data analysis. Methods : Using a 1.0-T scanner, we obtained 2-mm-thick tilted coronal MPRAGE magnetic resonance imaging (MRI) scans of 20 healthy volunteers aged 2 0-38 years. We used an inexpensive utility program to extract image in formation and an NIH Image for image analysis. The hippocampal formati ons were traced with a graphics tablet and landmarks described by Wats on et al. (Neurology 1992;42:1743-50). Overlays of individual observer s' tracings were used to fine tune the selection of landmarks and boun daries. Filled-in silhouette pairs generated from these ''training tra cings'' were compared to determine how well observers could visually q uantify area differences. Results: Visual detection of asymmetry of si lhouette pairs was sensitive, but the magnitude of asymmetry was under estimated. We achieved intraobserver coefficients of variation of righ t/left volume ratios between 0.82 and 3.16 and an interobserver range of volume ratios of 6%. In 20 healthy controls aged 20-38 years, the m ean right and left hippocampal volumes were 2,911 mm(3) and 2,836 mm(3 ), respectively. The lower limits of normal were 2,217 mm(3) for the r ight and 2,178 mm(3) for the left. The mean right/ left hippocampal ra tio was 1.03, and the limits of normal (3 SD) for this were 0.95 to 1. 10. Conclusions: Hippocampal volumetry can be performed reliably and e conomically. Our methodology makes it possible for different observers to generate consistent and comparable measurements.