Normal MR Spectroscopic Findings of the Cerebellum and Pons: Comparison of the Results between Intra-Unit and Inter-Unit Studies

Choi, Joon ll; Chang, Kee Hyun; Song, In Chan; Do, Kyung Hyun; Lee, Joon Woo; Lee, Sang Hyun; Yoo, Tn Kyu; Han, Moon Hee

Abstract

PURPOSE: The purposes of this study are to evaluate normal MR spectroscopy (MRS) data of the cerebellum and pons, and to evaluate intra-unit and inter-unit differences of the results.
MATERIALS AND METHODS
Nine normal volunteers (mean age 23 years) were studied with two 1.5 Tesla MR units (A and B units). A total of four sessions of MRS study were performed with two sessions in each MR unit in each volunteer. In each session, MRS data were obtained from bilateral cerebellar hemisphere and pons. MRS was performed using spin-echo single voxel technique with repetition time of 2000 ms, echo time of 288ms and 128 averagings. Voxel size was 2x2x1.5 cm in the cerebellum and 1.5x1.5x1.5 cm in the pons. Metabolite ratios of NAA/Cho, NAA/Cr, NAA/(Cho+Cr) and Cr/Cho (both peak heights and the peak areas) were compared among the results of four sessions of MRS for evaluation of intra-unit and inter-unit differences.
RESULTS
In the cerebellum, mean ISD values of peak height NAA/Cho, NAA/Cr, NAA/(Cho+Crl) and Cr/Cho ratios obtained in the first session of A unit were 1.08+/-0.16, 1.44+/-.286, 0.61+/-.09 and 0.76+/-,13, respectively. Comparing with the results of the second session, intra-unit differences were 3-7%. In B unit intra-unit differences were 1-9% , except for 22% of Cr/Cho ratio. Inter-unit differences between A and B units were 1-26%. In the pons, mean (SD values of peak height NAA/Cho, NAA/Cr, NAA/(Cho+Crl and Cr/Cho ratios obtained in the first session of A unit were 1.51+/-.35, 3.35+/-.78, 1.02+/-.16 and 0.47+/-,14, respectively. Mean NAA/Cho, NAA/Cr and NAA/(Cho+Cr) ratios of the pons were significantly higher than those of the cerebellum. Intra-unit differences were 2-21% in A unit and 4-l8% in B unit. Inter-unit differences between A and B units were 1-l8%. The mean values obtained by using peak area were generally higher and wider in range than those of peak height in both units.
CONCLUSION
Mean NAA/Cho, NAA/Cr and NAA/(Cho+Cr) ratios of the cerebellum were significantly lower than those of the pons. Intra-unit differences of most metabolites ratios were generally not significant, whereas inter-unit differences were greater than intra-unit differences in more metabolite ratios. Therefore, normal MRS data of the cerebellum and the pons should be obtained in every MR unit, before MRS applications in the diseases of the cerebellum and the pons.