title: Muscle fat fraction in neuromuscular disorders: dual-echo dual-flip-angle spoiled gradient-recalled MR imaging technique for quantification--a feasibility study.
abstract: OBJECTIVE
  To prospectively evaluate the muscle fat fraction (MFF) measured with dual-echo dual-flip-angle spoiled gradient-recalled acquisition in the steady state (SPGR) magnetic resonance (MR) imaging technique by using muscle biopsy as the reference standard.
  
  
  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 infiltration by means of MFF calculation. Spin-density- and T1-weighted fast SPGR in-phase and opposed-phase dual-echo sequences were performed, respectively, with 20° and 80° flip 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-flip-angle SPGR MR imaging and biopsy were compared by using a paired t test, Pearson correlation coefficient, and Bland-Altman plots. P value of < .05 was considered to indicate a statistically significant difference.
  
  
  RESULTS
  The mean MFFs obtained with dual-echo dual-flip-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 t value were -0.3, 1.3, and -1.3 (P > .2), respectively. The Pearson correlation coefficient was 0.995; with the Bland-Altman method, all data points were within the ± 2 SDs limits of agreement.
  
  
  CONCLUSIONS
  The results show that dual-echo dual-flip-angle SPGR MR imaging technique provides reliable calculation of MFF, consistent with biopsy measurements.
authors.affiliation: Department of Radiological Sciences, Policlinico G. Martino, Via Consolare Valeria 1, 98125 Messina, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Gaeta
authors.forename: Emanuele
authors.initials: E
authors.lastname: Scribano
authors.forename: Achille
authors.initials: A
authors.lastname: Mileto
authors.forename: Silvio
authors.initials: S
authors.lastname: Mazziotti
authors.forename: Carmelo
authors.initials: C
authors.lastname: Rodolico
authors.forename: Antonio
authors.initials: A
authors.lastname: Toscano
authors.forename: Nicola
authors.initials: N
authors.lastname: Settineri
authors.forename: Giorgio
authors.initials: G
authors.lastname: Ascenti
authors.forename: Alfredo
authors.initials: A
authors.lastname: Blandino
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001706:Biopsy; D002648:Child; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology*; D009133:Muscular Atrophy / Q000473:pathology; D009468:Neuromuscular Diseases / Q000175:diagnosis*; D011446:Prospective Studies