Skeletal muscle attenuation determined by computed tomography is associated with skeletal muscle lipid content

The purpose of this investigation was to validate that in vivo measurement of skeletal muscle attenuation (MA) with computed tomography (CT) is associ ated with muscle Lipid content. Single-slice CT scans performed on phantoms of varying lipid concentrations revealed good concordance between attenuat ion and lipid concentration (r(2) = 0.995); increasing the phantom's Lipid concentration by 1 g/100 ml decreased its attenuation by similar to 1 Houns field unit (HU). The test-retest coefficient of variation for two CT scans performed in six volunteers was 0.51% for the midthigh and 0.85% for the mi dcalf, indicating that the methodological variability is low. Lean subjects had significantly higher (P < 0.01) MA values (49.2 +/- 2.8 HU) than did o bese nondiabetic (39.3 +/- 7.5 HU) and obese Type 2 diabetic (33.9 +/- 4.1 HU) subjects, whereas obese Type 2 diabetic subjects had lower MA values th at were not different from obese nondiabetic subjects. There was also good concordance between MA in midthigh and midcalf (r = 0.60, P < 0.01), psoas (r = 0.65, P < 0.01), and erector spinae (r = 0.17, P < 0.01) in subsets of volunteers. In 45 men and women who ranged from lean to obese (body mass i ndex = 18.5 to 35.9 kg/m(2)), including 10 patients with Type 2 diabetes me llitus, reduced MA was associated with increased muscle fiber lipid content determined with histological oil red O staining (P = -0.43, P < 0.01). In a subset of these volunteers (Pt = 19), triglyceride content in percutaneou s biopsy specimens from vastus lateralis was also associated with MA (r = - 0.58, P = 0.019). We conclude that the attenuation of skeletal muscle in vi vo determined by CT is related to its lipid content and that this noninvasi ve method may provide additional information regarding the association betw een muscle composition and muscle function.