Lumbar and paraspinal muscle degeneration is usually associated with increased fat in marrow and muscle. With fat tissue increases in bone marrow, bone mineral density and bone strength will be reduced. Raised intramuscular and intermuscular fat may reduce the myofibrillar force and affecting daily life activity which has become a serious social problem with the rapidly aging society . However, only a few studies attempted to measure fat content in lumbar vertebrae marrow and lumbar paraspinal muscle. The objective of this study was to evaluate the reliability of fat content measurement of lumbar vertebrae marrow and lumbar paraspinal muscle using an multi-echo 3D DIXON method called mDIXON-quant for fat fraction quantification.A total of 31 volunteers (15 males and 16 females, mean age, 30.74±8.46 years) were included in this study. All subjects underwent liver mDIXON-quant MR imaging on a 3.0T MR Scanner (Ingenia, Philips Healthcare, Best, Netherlands) by an radiologist and this examinations were repeated by another radiologist within 2 weeks. Scan parameters of the single breathhold mDIXON-quant were as follows: TR, 9.1 ms; TE1, 1.33ms; 6echos with delta TE 1.3ms; FOV 180 × 140 × 90 mm, FA=3°, resolution=2.5×2.5×3.0mm, SENSE=2, NSA=2, Scan time=12.5ms. After MR images acquisition, the radiologists measured fat content of L3, psoas (PS), erector spinae (ES), and multifidus (MF) muscles on the central L3 axial MR images on ISP V7 workstation (Philips Healthcare, Best, the Netherlands)(Figure1). Each radiologist independently measured fat content, and after 2 weeks they repeated the same measurements and were blinded to their previous results. Reliability was estimated by evaluating the repeatability of the intra-observer agreement for the two measurements by the same observer and the reproducibility of the inter-observer agreement for the measurements by the two observers for each subjects. Spearman’s correlation, intra-class correlation coefficients (ICC) with 95% confidence interval (CI) were applied to confirm the reliability of the mDIXON-quant method in measuring fat content of lumbar vertebrae marrow and lumbar paraspinal muscle using IBM SPSS Statistics 20.0 (Armonk, New York, USA).Table1 summerize subjects basic characteristics and corresponding multi-parametric results. Mean fat content of L3, PS, ES, and MF was 38.19%, 3.52%, 3.48%, 3.53% for males and 32.11%, 3.40%, 7.06%, 7.14% for females. The repeatability of measurement of fat content, T2* and R2* of L3, PS, ES, MF was high, the intra-observer ICC were 0.997, 0.984, 0.997, 0.995 for fat content, 0.963, 0.979, 0.984, 0.946 for T2*, 0.989, 0.946, 0.977, 0.938 for R2* from observer A and 0.948, 0.974, 0.963, 0.995 of fat content,0.976, 0.976, 0.913, 0.937 of T2*, 0.958, 0.928, 0.881, 0.936 of R2* for observer B. The reproducibility of measurement of fat content, T2* and R2* of L3, PS, ES, MF was high, the inter-observer ICC were respectively 0.984, 0.981, 0.977, 0.998 of fat content, 0.959, 0.918, 0.973, 0.960 of T2*, and 0.954, 0.929, 0.933, 0.939 of R2*.In previous studies, MRS is one of most commonly used methods in measuring fat content, the scan time and resolution limited its application . Compared with MRS, mDIXON could generate water, fat as well as in-phase and opposed-phase images. Few studies have assessed the reliability of fat content measurement of lumbar vertebrae marrow and lumbar paraspinal muscle using mDIXON-quant imaging. In this study, the repeatability and reproducibility of mDIXON-quant were high, it may provide a new approach for lumbar vertebrae marrow and lumbar paraspinal muscle fat content quantification.Fat content measurement of lumbar vertebrae marrow and lumbar paraspinal muscle using mDIXON-quant imaging has high reliability and be potentially applied in clinical practice.