Revisiting Radiographic L5-S1 Parallelism Using MRI T1 Mapping

Abstract

Purpose:Thirty years ago, we reported that parallel aspect of the L5-S1 disc on a lateral view of the spine might be considered to be an initial stage of disk degeneration. The current study represents an attempt to increase the validity of parallel sign on conventional radiograph using MR real T1 mapping.Methods:Forty-four young asymptomatic volunteers (mean age 21.6 ± 2.3) underwent lumbar spine MRI, twice the same day, morning and afternoon. Dedicated sequences using the inversion-recovery technique were used to calculate the T1 relaxation time. A region of interest (ROI) representing the nucleus pulposus was defined in each disk. The volunteers were stratified according to the presence or absence of a parallel morphology of L5-S1. Correlation between endplates angles, sacral slopes and T1 values were then evaluated.Results:L5-S1 space looks parallel for angles <10° (mean value 6.9° ± 1.4°). Sacral slope was lower in parallel disks (31.7 ± 4.9° vs. 40.1 ± 5.6°), showing a significant difference of 8.4° (p < 0.05). The T1 relaxation values show a significant difference between the two groups (p < 0.05) with a difference of 96 ms for the morning (1090.9 ± 33.3 ms for the parallel group and 1186.9 ± 41.2 ms for the non-parallel) and 121.9 ms for the afternoon (respectively 1004.7 ± 22.2 ms and 1126.6 ± 12.9 ms).Conclusion:The difference between the two groups suggests that parallel morphology of the L5-S1 disk is associated with lower water content.

DI-5-Cuffs: Lumbar Intervertebral Disc Proteoglycan and Water Content Changes in Humans after Five Days of Dry Immersion to Simulate Microgravity

“…The protein (glycosaminoglycan) content was measured on MRI T1 mapping sequences. The protein IVD content has been previously calculated by MRI [54][55][56], but to our knowledge, it has never been measured in a microgravity simulation study. A relaxometry analysis was performed with a T1 vibe sagittal multi echo (flips angles 2-7-10-15 degrees) with FoV 260 mm, TR 5.07 ms, TE 1.69 ms, and slice 5.0 mm.…”