The CT protocol included the heart and abdomen using a non-contrast CT scan performed using GE (GE 750HD 64 and GE LightSpeed VCT 64 Birmingham and Oakland Centers, respectively; GE Healthcare, Waukesha, Wisconsin) or Siemens (Sensation 64, Chicago and Minneapolis Centers; Siemens Medical Solutions, Erlangen, Germany) multidetector CT scanners and has been described previously(7 (link)). Quality control and image analysis was performed at a core reading center (Wake Forest University Health Sciences, Winston-Salem, North Carolina).
NAFLD was defined as liver attenuation (LA) < 51 Hounsfield Units (HU, equivalent to a liver/spleen ratio < 1.0) after exclusion of other causes of liver fat (Figure 2)(7 (link), 8 (link)). Measurement of LA was performed in the right lobe of the liver using CT slices through the upper abdomen and was reported as the average of nine measurements on three slices using circular regions of interest of 2.6 cm2. The interclass correlation coefficient between different readers on a random selected sample of 156 participants was 0.975 for LA, indicating high reproducibility of CT measured LA in this study. The methods for assessment of adiposity within the CARDIA study have also been described previously(7 (link)).