Approaches to Normalization of Spinal Cord Volume: Application to Multiple Sclerosis

BACKGROUND AND PURPOSE To determine the proper method for the normalization of spinal cord volume. MATERIALS AND METHODS A group of 34 multiple sclerosis (MS) patients (28 relapsing and 6 progressive) and 15 healthy controls had whole spinal cord 3-mm thick T2-weighted axial fast spin-echo magnetic resonance imaging (MRI) images obtained at 3T. For each participant, four volumes were measured (C2-3 volume, cervical cord volume, thoracic cord volume, and whole cord volume). The volumes were normalized by the number of slices and three potential measures of body size (intracranial volume [ICV], body mass index, and body surface area) using the proportional method. RESULTS All raw volumes and volumes normalized by number of slices or ICV were significantly lower in progressive MS patients compared to relapsing MS patients/healthy controls (P < .05). In addition, C2-3 volume and cervical cord volume were significantly correlated with Expanded Disability Status Scale score (P < .05). All regional volumes showed high intercorrelation, and normalization by the number of slices significantly increased some correlations. Regarding reliability, whole cord volume regardless of normalization technique had lower coefficient of variation than C2-3 volume. CONCLUSIONS Since normalization factor had limited impact on reliability and the ability to detect differences, normalization by the number of slices is recommended.