Muscle fat fraction in neuromuscular disorders: Dual-echo dual-flip-angle spoiled gradient-recalled mr imaging technique for quantifi cation - A feasibility study

Purpose: To prospectively evaluate the muscle fat fraction (MFF) measured with dual-echo dual-fl ip-angle spoiled gradientrecalled acquisition in the steady state (SPGR ) magnetic resonance (MR) imaging technique by using muscle biopsy as the reference standard. Materials and Methods: After ethics approval, written informed consent from all patients was obtained. Twenty-seven consecutive patients, evaluated at the Neuromuscular Disorders Center with a possible diagnosis of neuromuscular disorder, were prospectively studied with MR imaging of the lower extremities to quantify muscle fatty infi ltration by means of MFF calculation. Spin-density- and T1-weighted fast SPGR inphase and opposed-phase dual-echo sequences were performed, respectively, with 20° and 80° fl ip angles. Round regions of interest were drawn by consensus on selected MR sections corresponding to anticipated biopsy sites. These were marked on the patient's skin with a pen by using the infrared spider light of the system, and subsequent muscle biopsy was performed. MR images with regions of interest were stored on a secondary console where the MFF calculation was performed by another radiologist blinded to the biopsy results. MFFs calculated with dual-echo dual-fl ip-angle SPGR MR imaging and biopsy were compared by using a paired t test, Pearson correlation coeffi cient, and Bland-Altman plots. P value of <05 was considered to indicate a statistically signifi - cant difference. Results: The mean MFFs obtained with dual-echo dual-fl ip-angle SPGR MR imaging and biopsy were 20.3% (range, 1.7%- 45.1%) and 20.6% (range, 3%-46.1%), respectively. The mean difference, standard deviation of the difference, and value were 2 0.3, 1.3, and 2 1.3 ( P > 2), respectively. The Pearson correlation coeffi cient was 0.995; with the Bland-Altman method, all data points were within the ± 2 SDs limits of agreement. Conclusion: The results show that dual-echo dual-fl ip-angle SPGR MR imaging technique provides reliable calculation of MFF, consistent with biopsy measurements.