MRI Based Validation of Abdominal Adipose Tissue Measurements From DXA in Postmenopausal Women

Abstract

Introduction: Visceral adipose tissue (VAT) is a hypothesized driver of chronic disease. Dual-energy X-ray absorptiometry (DXA) potentially offers a lower cost and more available alternative compared to gold-standard magnetic resonance imaging (MRI) for quantification of abdominal fat sub-compartments, VAT and subcutaneous adipose tissue (SAT). We sought to validate VAT and SAT area (cm²) from historical DXA scans against MRI.

Methodology: Participants (n = 69) from the Women's Health Initiative (WHI) completed a 3 T MRI scan and a whole body DXA scan (Hologic QDR2000 or QDR4500; 2004-2005). A subset of 43 participants were scanned on both DXA devices. DXA-derived VAT and SAT at the 4th lumbar vertebrae (5 cm wide) were analyzed using APEX software (v4.0, Hologic, Inc., Marlborough, MA). MRI VAT and SAT areas for the corresponding DXA region of interest were quantified using sliceOmatic software (v5.0, Tomovision, Magog, Canada). Pearson correlations between MRI and DXA-derived VAT and SAT were computed, and a Bland-Altman analysis was performed.

Results: Participants were primarily non-Hispanic white (86%) with a mean age of 70.51 ± 5.79 years and a mean BMI of 27.33 ± 5.40 kg/m². Correlations between MRI and DXA measured VAT and SAT were 0.90 and 0.92, respectively (p ≤ 0.001). Bland-Altman plots showed that DXA-VAT slightly overestimated VAT on the QDR4500 (-3.31 cm²); this bias was greater in the smaller subset measured on the older DXA model (QDR2000; -30.71 cm²). The overestimation of DXA-SAT was large (-85.16 to -118.66 cm²), but differences were relatively uniform for the QDR4500.

Conclusions: New software applied to historic Hologic DXA scans provide estimates of VAT and SAT that are well-correlated with criterion MRI among postmenopausal women.

Keywords: Dual-energy X-ray absorptiometry; body composition; magnetic resonance imaging; subcutaneous fat; visceral fat.

Figure 1.

Representative example of abdominal visceral and subcutaneous fat quantification by MRI and DXA techniques. The MRI image (left) represents an axial slice at the L3-L4 intervertebral space; slice thickness is 10mm. The visceral adipose tissue (VAT) is colored in yellow and subcutaneous adipose tissue is colored in teal blue. The two-dimensional DXA (right) region of interest is demarcated by the red lines drawn at L4. The APEX software measures the visible lateral subcutaneous adipose tissue (LSAT) on the right and left sides from the medial edge of the LSAT to the lateral edge of LSAT (boxed in red). The measured LSAT is used to model the anterior-posterior (AP) subcutaneous adipose over the visceral cavity based on a proprietary formula. The software then adds the estimate of the SAT overlying the visceral cavity to the measured LSAT for a total abdominal SAT value for the ROI. This total abdominal SAT is subtracted, by the software, from the total abdominal fat measured by DXA to estimate DXA-visceral adipose tissue. A, android subregion

Figure 2.

Bland-Altman plot of MRI-DXA visceral (VAT, panel A) and subcutaneous (SAT, panel B) adipose tissue difference versus average of MRI and DXA for a single abdominal slice (QDR2000: n=43 and QDR4500: n=69)