Measurement of magnetization transfer ratio (MTR) from cervical spinal cord: Multicenter reproducibility and variability

Abstract

Background: Assessing the multicenter variability of magnetization transfer ratio (MTR) measurements in the spinal cord of healthy controls is the first step toward investigating its clinical use as a biomarker.

Purpose: To analyze the between-session, between-participant, and between-scanner variability of MTR measurements in automatically extracted regions of interest in the cervical cord of healthy controls.

Study type: Control study.

Population: Forty-four participants, distributed across five MRI scanners (all from the same manufacturer). Ten participants were scanned twice in the same scanner, and 10 others were scanned twice in two different scanners.

Field strength/sequence: 3D-gradient echo images, centered on C5, without and with magnetization transfer prepulse at 3T.

Assessment: We calculated the mean MTR for different vertebral levels in the whole cord (WC), as well as in the white matter and gray matter, and determined the between-session, between-participant, and between-scanner variabilities.

Statistical tests: Coefficients of variation and intraclass correlations (ICCs) for the different variabilities and their associated confidence intervals.

Results: The MTR measurements for Levels C4-C6 (near the slab center) exhibited a mean value in WC of 34.6 pu and a pooled standard deviation of 0.9 pu. The between-session coefficient of variation was estimated as 2.3% (ICC = 0.63), the between-participant coefficient as 1.6% (ICC = 0.32), and the between-scanner coefficient as 0.7% (ICC = 0.05). The resulting aggregate coefficient of variation was 2.9%, which was sufficiently low to detect an MTR reduction of 1 pu between groups of about 45 participants (Type-I error rate: 0.05; Type-II error rate: 0.10).

Data conclusion: The good between-scanner reproducibility and low overall variability in cervical spinal cord MTR measurements in a control population might pave the way for multicenter analyses in various neurological diseases with moderate cohort sizes.

Level of evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1777-1785.

Keywords: MTR; multicenter; quantitative MRI; reproducibility; spinal cord.