Multiparametric MRI characterization of level dependent differences in lumbar muscle size, quality, and microstructure

Abstract

Magnetic resonance imaging (MRI) is a diagnostic tool that can be used to noninvasively assess lumbar muscle size and fatty infiltration, important biomarkers of muscle health. Diffusion tensor imaging (DTI) is an MRI technique that is sensitive to muscle microstructural features such as fiber size (an important biomarker of muscle health), which is typically only assessed using invasive biopsy techniques. The goal of this study was to establish normative values of level‐dependent lumbar muscle size, fat signal fraction, and restricted diffusion assessed by MRI in a highly active population. Forty‐two active‐duty Marines were imaged using a (a) high‐resolution anatomical, (b) fat‐water separation, and (c) DT‐MRI scan. The multifidus and erector spinae muscles were compared at each level using two‐way repeated measures ANOVA. Secondary analysis included Three dimensional (3D) reconstructions to qualitatively assess lumbar muscle size, fatty infiltration, and fiber orientation via tractography. The erector spinae was found to be larger than the multifidus above L5, with lower fat signal fraction above L3, and a less restricted diffusion profile than the multifidus above L4, with this pattern reversed in the lower lumbar spine. 3D reconstructions demonstrated accumulations of epimuscular fat in the anterior and posterior regions of the lumbar musculature, with minimal intramuscular fatty infiltration. Tractography images demonstrated different orientations of adjacent lumbar musculature, which cannot be visualized with standard MRI pulse sequences. The level dependent differences found in this study provide a normative baseline, for which to better understand whole muscle and microstructural changes associated with aging, low back pain, and pathology.

Assessment of fitting methods and variability of IVIM parameters in muscles of the lumbar spine at rest

“…Our results here and in a previous, independent study (41) suggest that diffusion characteristics differ in the paraspinal muscles as a function of spinal segment. The observation of changing mean diffusivity over the span of the lumbar spine may draw into question the assumption of spatial uniformity, however we note that spatial consistency was assumed within one spinal segment, not across the entire spine.…”

“…The observation of changing mean diffusivity over the span of the lumbar spine may draw into question the assumption of spatial uniformity, however we note that spatial consistency was assumed within one spinal segment, not across the entire spine. Indeed, differences in IVIM parameters across the spinal segments are likely to reflect differences in structure and physiology of the paraspinal muscles from cranial to caudal, including differences in size (including the relative contribution of erector spinae vs. multifidus), tissue composition, and metabolic capacity (41)(42)(43). We also note that the IVIM parameters were generally more variable at L1 and L5, potentially due to respiratory motion at the superior extent and coil sensitivity at the inferior extent.…”

Fatty infiltration of the erector spinae at the upper lumbar spine could be a landmark for low back pain

“…It has been suggested that multifidus was the primary stabilizer of the lumbar spine whereas the erector spinae helped to stabilize the lumbar spine and conveyed motion of the trunk. 57 A recent study also showed that obese patients had fatty paraspinal muscles at the upper lumbar levels and IVDD/Modic changes at the lower lumbar levels. 58 In this study, we observed that patients with LBP had more fatty infiltration in their erector spinae at L2-L3 and L3-L4 levels concomitant with milder fatty infiltration in the multifidus at the corresponding levels and spinal degeneration (severe IVDD and Modic changes) at the lower lumbar levels.…”

“…It has been suggested that multifidus was the primary stabilizer of the lumbar spine whereas the erector spinae helped to stabilize the lumbar spine and conveyed motion of the trunk 57 . A recent study also showed that obese patients had fatty paraspinal muscles at the upper lumbar levels and IVDD/Modic changes at the lower lumbar levels 58 .…”