title: Optimizing electrical impedance myography measurements by using a multifrequency ratio: a study in Duchenne muscular dystrophy.
abstract: OBJECTIVE
  Electrical impedance myography (EIM) is an electrophysiological technique for neuromuscular evaluation that is impacted by subcutaneous fat (SF). Exploiting the differing frequency dependences of muscle and fat, we assessed a 2-frequency EIM phase ratio in Duchenne muscular dystrophy (DMD) boys.
  
  
  METHODS
  Twenty-eight DMD boys aged 2-13years underwent EIM and the 6-minute walk test (6MWT). For each subject, 50kHz phase data was input into the numerator while 20-500kHz phase values were input into the denominator. We then performed correlation analyses seeking to identify the denominator frequency that simultaneously optimized SF and 6MWT correlations. This optimized ratio was then tested in 24 healthy boys.
  
  
  RESULTS
  50kHz phase correlated to 6MWT in DMD boys with R=0.52, p=0.0066, and to SF thickness with R=-0.67, p<0.001. An optimized ratio of 50/200kHz phase reduced the correlation of SF thickness to R=-0.075, p=0.45 while improving the relationship to the 6MWT (R=0.60, p=0.001). In normal subjects, the optimization decreased SF correlation from R=0.61 from R=0.16 with 6MWT correlation remaining unchanged.
  
  
  CONCLUSIONS
  The 50/200kHz EIM phase ratio removes the impact of SF while maintaining EIM's association with function.
  
  
  CONCLUSIONS
  The use of a phase ratio may enhance EIM's application for evaluation of neuromuscular disease.
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwartz
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Geisbush
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Mijailovic
authors.affiliation: Boston Children's Hospital, Harvard Medical School, Boston, MA, United States.
authors.forename: Amy
authors.initials: A
authors.lastname: Pasternak
authors.affiliation: Boston Children's Hospital, Harvard Medical School, Boston, MA, United States.
authors.forename: Basil T
authors.initials: BT
authors.lastname: Darras
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States. Electronic address: srutkove@bidmc.harvard.edu.
authors.forename: Seward B
authors.initials: SB
authors.lastname: Rutkove
mesh_terms: D000293:Adolescent; D000818:Animals; D002648:Child; D002675:Child, Preschool; D017097:Electric Impedance; D005080:Exercise Test / Q000379:methods / Q000592:standards*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020388:Muscular Dystrophy, Duchenne / Q000175:diagnosis* / Q000503:physiopathology*; D009213:Myography / Q000379:methods / Q000592:standards; D009924:Organ Culture Techniques; D051381:Rats; D050151:Subcutaneous Fat / Q000503:physiopathology*; D013552:Swine
keywords: Duchenne muscular dystrophy; Electrical impedance myography; Functional measures; Optimization; Subcutaneous fat