MRI-based hippocampal volumetrics: data acquisition, normal ranges, and optimal protocol.

The process of producing magnetic resonance (MR) volume measurements can be divided into considerations of acquisition and postprocessing of the MR data. With careful attention to both of these, precise and reproducible measurements can be achieved. A statistical description of hippocampal measurements in normal volunteers must be available for comparison if volumetrics are employed either for clinical or research purposes. A wide range in "normal" hippocampal volume is present in the studies of normal young adults that have been reported to date. This variability is most probably due to interinstitutional differences in hippocampal boundary criteria, and in the software employed for counting pixels in a defined region of interest (ROI). Because the numeric output from the volume measurement procedure is highly technique-dependent, the statistical description of "normal" should be determined or calibrated at each institution wishing to use these techniques.