New MR-based measures for the evaluation of age-related lumbar paraspinal muscle degeneration

Purpose Although signal intensity on T2W axial images is sensitive in detection of fatty infiltration to assess paraspinal muscle degeneration, it is affected by inhomogeneities of magnetic fields and individual variabilities. The purpose of this study was to propose reference adjusted signal measures on T2W axial images and determine their capacities in reflecting age-related lumbar paraspinal muscle degeneration. Methods Lumbar MR images of 421 population-based subjects (177 men and 244 women, mean age 53.1 years, range 19.8–87.9 years) were studied. A custom software Spine Explore (Tulong 2.0) was used to automatically obtain paraspinal measurements of multifidus, erector spinae and psoas major. FCSA/TCSA was defined as functional cross-sectional area relative to total cross-sectional area of paraspinal muscle. Two new signal measures were canal-adjusted and cerebrospinal fluid (CSF)-adjusted signal, defined as the ratio between mean signal measurements and the mean signal of the canal and CSF. Results The raw signal measurements of the paraspinal muscles were weakly correlated to age ( r = 0.28–0.39, P < 0.001). When the signal of canal ( r = 0.43–0.59, P < 0.001) or CSF ( r = 0.45–0.61, P < 0.001) was used as reference, the correlations substantially increased. Signal measurements of three paraspinal muscles, adjusted or not, were strongly associated with Goutallier score ( ρ = 0.60–0.65, P < 0.001) and FCSA/TCSA ( r = −0.64 to −0.82, P < 0.001). Greater Goutallier score was associated with greater age ( r = 0.38–0.60, P < 0.001), while Lumbar indentation value (LIV) not. Conclusion On routine T2W axial MR images the adjusted signal measurements using an internal reference of CSF or canal can better reflect age-related degenerative changes in the paraspinal muscles.