Interobserver and within-subject variances of T 2-relaxation time and 1H-metabolite ratios in the normal hippocampus

Abstract

Purpose To investigate the magnetic resonance (MR) reproducibility of normal hippocampal volume (HV), temporal lobe volume (TLV), transversal relaxation time (T 2) and 1H-MR spectroscopy ( 1H-MRS) metabolite ratios. Materials and methods Two sets of HV, TLV, T 2 and MR spectroscopic metabolite signal ratios were determined in 27 healthy volunteers. HV and TLV were measured with a T 1-weighted MR sequence; whereas T 2 measurements were performed with conventional spin-echo (CSE) and fast spin-echo (FSE) MR imaging sequences. The interobserver and within-subject variances of T 2 measurements were estimated. Results Estimated right and left HV coefficients of variation (CV) = 0.13. FSE T 2 measurements showed no significant differences in the interobserver (CV = 0.02) and within-subject variances (CV = 0.02). Measurements showed no differences in the interobserver (CV = 0.02) and within-subject (CV = 0.04) variances for the CSE T 2 of the right and left hippocampi. Metabolite ratios between N-acetyl aspartate (NAA) and creatine (Cr), choline (Cho) and creatine, and NAA and choline plus creatine (Cho + Cr) for the right hippocampus were 2.29 ± 0.19, 1.52 ± 0.14 and 0.91 ± 0.05, respectively. Metabolite ratios for the left hippocampus were 2.18 ± 0.10, 1.48 ± 0.10 and 0.88 ± 0.06, respectively. Conclusions HV, TLV, T 2 and 1H MRS metabolite ratio measurements showed fair reproducibility with small CVs, and no differences in the interobserver and within-subject variances, including no differences between right and left TLV, and in the right and left T 2.