Abstract
PurposeStudies using magnetic resonance imaging to assess lumbar multifidus cross-sectional area frequently utilize T1 or T2-weighted sequences, but seldom provide the rationale for their sequence choice. However, technical considerations between their acquisition protocols could impact on the ability to assess lumbar multifidus anatomy or its fat/muscle distinction. Our objectives were to examine the concurrent validity of lumbar multifidus morphology measures of T2 compared to T1-weighted sequences, and to assess the reliability of repeated lumbar multifidus measures.MethodsThe lumbar multifidus total cross-sectional area of 45 patients was measured bilaterally at L4 and L5, with histogram analysis determining the muscle/fat threshold values per muscle. Images were later re-randomized and re-assessed for intra-rater reliability. Matched images were visually rated for consistency of outlining between both image sequences. Bland-Altman bias, limits of agreement, and plots were calculated for differences in total cross-sectional area and percentage fat between and within sequences, and intra-rater reliability analysed.ResultsT1-weighted total cross-sectional area measures were systematically larger than T2 (0.2 cm2), with limits of agreement <±10% at both spinal levels. For percentage fat, no systematic bias occurred, but limits of agreement approached ±15%. Visually, muscle outlining was consistent between sequences, with substantial mismatches occurring in <5% of cases. Intra-rater reliability was excellent (ICC: 0.981–0.998); with bias and limits of agreement less than 1% and ±5%, respectively.ConclusionTotal cross-sectional area measures and outlining of muscle boundaries were consistent between sequences, and intra-rater reliability for total cross-sectional area and percentage fat was high indicating that either MRI sequence could be used interchangeably for this purpose. However, further studies comparing the accuracy of various methods for distinguishing fat from muscle are recommended.
Highlights
Over the last three decades, there has been a rapid increase in research interest regarding the role paraspinal muscles, and in particular the lumbopelvic stabilizing lumbar multifidi (LM), may play in relation to low back and leg pain
Bland-Altman bias, limits of agreement, and plots were calculated for differences in total cross-sectional area and percentage fat between and within sequences, and intra-rater reliability analysed
T1-weighted total cross-sectional area measures were systematically larger than T2 (0.2 cm2), with limits of agreement
Summary
Over the last three decades, there has been a rapid increase in research interest regarding the role paraspinal muscles, and in particular the lumbopelvic stabilizing lumbar multifidi (LM), may play in relation to low back and leg pain. Most of this research has utilized diagnostic and functional imaging methods, including diagnostic ultrasound [1,2,3,4], computed tomography (CT) [5,6,7], and magnetic resonance imaging (MRI) [8,9,10]. Various MRI methods have been employed to assess the LM, ranging from the standard T1-weighted and T2-weighted spin-echo (spin echo) imaging sequences, to more sophisticated approaches such as functional [12, 13], opposed-phase [14], or chemical-shift MR [15], and MR spectroscopy [16]. Spin echo (including fast/turbo spin echo) sequences are the most common methods used for MR imaging of the spine [17]. There are, important technical considerations between T1 and T2-weighted sequences that could affect their ability to assess the anatomy or fat/muscle distinction within the LM
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