Quantitative magnetic resonance fat measurements in humans correlate with established methods but are biased

Abstract

Precision and accuracy of the quantitative magnetic resonance (QMR) system for measuring fat in phantoms and total body fat (TBF) in humans were investigated. Measurements were made using phantoms: oil, beef with water, beef with oil, and humans with oil and water. TBF(QMR) in humans was compared with TBF by a four-compartment model (TBF(4C)). The coefficient of variation (CV) for replicate TBF(QMR) was 0.437%. QMR fat was lower at 23 °C vs. 37 °C. The fat increase in QMR phantom studies was consistent with the oil increase. When oil was added with humans, the increase in TBF(QMR) was >250 g for the initial 250 g of oil. With additional oil increments, the increase in TBF(QMR) was consistent with the amount of oil added. When water was added with humans, the TBF(QMR) increased independent of the amount of water added. TBF(QMR) was significantly less (mean ± s.e.) than TBF(4C) (females: -0.68 ± 0.27 kg, males: -4.66 ± 0.62 kg; P = 0.0001), TBF(BV) (females: -1.90 ± 0.40 kg; males: -5.68 ± 0.75 kg; P = 0.0001), and TBF(D2O) for males, but greater for females (1.19 ± 0.43 kg vs. -3.69 ± 0.81 kg for males; P = 0.0003). TBF(QMR) was lower than TBF(iDXA) with the difference greater in males (P = 0.001) and decreased with age (P = 0.011). The strong linear relationships between TBF(QMR) and TBF(4C), TBF(BV), and TBF(D2O) with slopes consistent with unity suggest that modifications are required to improve the accuracy. Should the latter be accomplished, QMR holds promise as a highly precise, rapid, and safe, noninvasive method for estimating the amount of and changes in TBF in overweight and severely obese persons.

Conflict of interest statement

DISCLOSURE

Authors D.G., J.C.T., Q.H., J.W., and W.Y. declare no conflict of interest.

Figures

Figure 1

Quantitative magnetic resonance (QMR) system echo amplitude vs. sequential echo number (a) for a representative human subject and (b) corresponding representation for canola oil, lean pork, and water (normalized to mass) phantoms. Echo amplitude is in arbitrary (relative) units and not comparable between a and b. Courtesy of Echo Medical Systems, Houston, TX.

Figure 2

The effect of adding increments of oil with human subject to the Echo QMR measurement of fat (kg). The standard error of the difference between two means is 0.024 kg. There were 12 subjects with 12 measurements for each subject. QMR, quantitative magnetic resonance.

Figure 3

Comparisons of relationships between fat measured by different methods by gender. In each graph, the solid line is regression line and the broken line is line of identity. (a) Four-compartment model (4C) vs. Echo QMR fat (r = 0.956; P < 0.0001). (b) Dual-energy X-ray absorptiometry (iDXA) vs. Echo QMR fat (r = 0.937; P < 0.0001). (c) BodPod vs. Echo QMR fat (r = 0.945; P = 0.0001). (d) Deuterium oxide dilution (D2O) vs. Echo QMR fat (r = 0.927; P = 0.0001). QMR, quantitative magnetic resonance.