METHODS FOR NORMALIZATION OF HIPPOCAMPAL VOLUMES MEASURED WITH MR

PURPOSE: To investigate the use of six cerebral measures as correlates for hippocampal volumes and, therefore, to enable normalized absolute hippocampal volumes to be calculated via two correction processes. ME THODS: Hippocampal volumes and six cerebral measures were estimated fr om MR data in 20 control subjects. Three of these measures (the crania l volume, the cerebral volume, and the midsagittal cranial area) were then applied to a group of 32 control subjects, and regression analysi s was performed to investigate the linear relationship between hippoca mpal volume and each measure. Division of hippocampal volume by cerebr al measure and correction via a covariance calculation enabled correct ed absolute hippocampal volumes to be determined for 32 control subjec ts and 23 patients with temporal lobe epilepsy, RESULTS: Correction pr ocesses reduced the variance in absolute hippocampal volumes in contro l subjects and enabled abnormally small absolute volumes to be defined . Of 11 patients with unilateral volume ratio abnormalities, 8 had uni lateral abnormally small absolute hippocampal volumes. Of 12 patients with normal volume ratios, 4 had bilateral abnormally small absolute h ippocampal volumes. CONCLUSION: Correction processes can define absolu te hippocampal volumes for correlation studies and may enable identifi cation of unsuspected bilateral hippocampal volume loss.