Evaluation of a new magnetic resonance imaging method for quantitating adipose tissue areas.

We have developed a new magnetic resonance imaging (MRI) protocol to quantitate intraabdominal and subcutaneous fat and have validated it by comparing measurements of fat areas by MRI with those obtained by computed tomography (CT) in 11 asymptomatic volunteers who all had a single CT and MRI image taken at the level of the umbilicus. The new MRI protocol was based on a water-fat separation method by which the slice selection routines excite water and fat protons in different positions along the slice select direction. This method performed more reliably than earlier methods based on phase differences between water and fat signals. Fat areas measured by MRI exceeded those measured by CT by 8-22 percent, and fat areas and ratios obtained by MRI correlated well with CT (r = 0.98 for areas and, for ratios, r = 0.81). The ratio of intraabdominal/subcutaneous fat measured by MRI in seven males was significantly greater than that in four females. We also compared the new method with a previously published inversion recovery (IR) method in seven additional volunteers. Agreement between the two methods was excellent, and the major differences were technical: the IR protocol produced images that may require custom image processing programs when obtained on some scanners. Comparability of the two methods provides further reassurance of the validity of both. MRI presents an attractive opportunity for directly measuring intraabdominal fat in order to correlate this with metabolic parameters and to visualize changes during weight loss.

Adipose tissue determinations in cadavers--a comparison between cross-sectional planimetry and computed tomography.

The adipose tissue surfaces in 11 slices (+/- 5 cm from the umbilicus) were compared in two cadavers using computed tomography (CT) versus planimetry of band-sawed slices of the corresponding sections. A very close correlation was found with partial correlations of around 0.90. Retroperitoneal fat formed a considerable proportion of the total adipose tissue surface in the slices. The results were similar whether fat was defined as -250 to -50, -190 to -30, or -140 to -40 Hounsfield units. These data indicate that CT measurements agree closely with a direct morphometric method and thus can be used as a 'gold standard' for future development. The fact that fat which is located extraperitoneally, but still intraabdominally, constitutes a significant proportion of the slice surface in the umbilical region indicates that data relating intraabdominal fat measurements to metabolic functions must be interpreted with caution.