An investigation into the effect of body mass index on the agreement between whole-body fat mass determined by MRI and air-displacement plethysmography

Objective: To validate MRI fat measurement protocols using purpose built test objects and by comparison with air-displacement plethysmography (ADP) whole-body fat measurements in non-obese subjects. Methods: Test objects of known fat concentration were used to quantify the accuracy of the MRI measurements. 10 participants with a body mass index in the range 18-30 underwent whole-body MRI using two different Dixon-based sequences (LAVA Flex and IDEAL IQ) to obtain an estimate of their whole-body fat mass. The MRI determined fat mass was compared to the fat mass determined by ADP. Results: MRI test object measurements showed a high correlation to expected fat percentage (r > 098). The participant MRI and ADP results were highly correlated (r = 0.99) but on average (mean +/- standard deviation) MRI determined a higher fat mass than ADP (3.8 +/- 3.1kg for LAVA Flex and 1.9 +/- 3.2kg for IDEAL IQ). There was no trend in the difference between MRI and ADP with total fat mass. Conclusion: The good agreement between MRI and ADP shows that Dixon-based MRI can be used effectively as a tool in physiological research for non-obese adults. Advances In knowledge: This work found that for ten non-obese subjects body mass index had no effect on the MRI determination of whole-body fat mass.