Cross Calibration of Two Dual Energy Densitometers and Comparison of Regional Adipose Tissue Measurements by iDXA and MRI

Our Research unit (NIDDK) recently acquired a new x-ray unit (the General Electric (GE) Lunar iDXA) for measurement of body composition (how much fat someone has as a percent of their weight). This machine provides clearer and crisper images. The unit also has a larger table to allow patients up to 450 lbs (204 kg) to be scanned. The larger table allows for easier positioning of tall and heavy patients. We would like to use this new machine in the future but want to see whether our current DXA unit (the Lunar Prodigy Densitometer by GE) and the Lunar iDXA Densitometer (GE) measure the same percentage of a person s body fat. If there are measurement differences between the two machines, we will develop a way to convert the new results to more closely match the results from the current DXA unit. Thus, in this study, we will be asking volunteers to undergo scanning for measurement of body fat on both machines on the same day. Fat within the belly which is around organs (called visceral fat or VAT) is linked to more bad health outcomes than fat which is just underneath the skin (called subcutanoues fat or SAT). Along with standardizing the DXA - body composition measurement results we would like to compare VAT and SAT estimates from iDXA with values obtained by MRI. The precise MRI measurements completely avoid radiation exposure for the volunteers but are far more time consuming. Knowing that the results of iDXA match up with or correlate with the MRI results would allow us to use iDXA measurements to estimate visceral and subcutaneous adipose tissue depots in ongoing and the future studies.