Evaluating CMR

Measuring Intra-abdominal Fat

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Figure 3: Greyscale non-segmented and segmented magnetic resonance imaging (MRI) abdominal image at L4-L5 in an obese woman

Figure 3: Greyscale non-segmented and segmented magnetic resonance imaging (MRI) abdominal image at L4-L5 in an obese woman

MRI and CT are the only in vivo methods available to directly and accurately quantify intra-abdominal fat. Intra-abdominal fat is the fat that is located within the abdominal muscle wall and that surrounds the organs (or viscera). On average, it accounts for only 12% and 5% of total body fat content in men and women respectively (See Figure 3 in Computed Tomography). As with skeletal muscle, it is costly and labour intensive to take measures of intra-abdominal fat using multiple images. Consequently, intra-abdominal fat is normally assessed using a single MRI or CT image at L4-L5 (Figure 3). However, due to differences between the methods, intra-abdominal fat values as determined by CT are not necessarily comparable to those determined by MRI (17, 18).

As discussed in the Computed Tomography section, there is a growing literature demonstrating the importance of intra-abdominal fat as a strong predictor of numerous metabolic abnormalities (19-30). Prospective studies have shown that intra-abdominal fat predicts future hypertension (28) and type 2 diabetes (30) independent of factors such as age, BMI, weekly energy expenditure, and metabolic risk factors. Intra-abdominal fat has also recently been reported to increase risk for all-cause mortality (31). Given the harmful effects of intra-abdominal fat, individuals should take steps to reduce their intra-abdominal fat and ensure it does not increase. However, as it is not possible to routinely measure intra-abdominal fat using MRI and CT, emphasis should be placed on routine measurement of waist circumference, which is the best surrogate measure currently available.

Reference

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