Estimating whole body intermuscular adipose tissue from single cross-sectional magnetic resonance images

Adipose tissue and its distribution are risk factors for metabolic abnormalities (4, 13, 15, 19, 24, 29). There is a need to quantify the size of specific adipose tissue compartments in vivo and to relate this information to metabolic risk factors and function. Invasive measures have been replaced by noninvasive imaging techniques that are safe and do not disturb the internal medium. Recent advances in MRI have allowed investigators to quantify, at the whole body level, total adipose tissue (TAT) and its subcompartments, subcutaneous (SAT), visceral (VAT), and intermuscular adipose tissue (IMAT). Although whole body measures are desirable when investigating systemic conditions or diseases, it is not always practical or feasible for investigators to acquire a whole body MRI scan. A shorter protocol involving fewer slices is often desirable. Our laboratory recently described an IMAT depot located between muscle bundles, as measured on whole body MRI (7, 31). IMAT is defined as the adipose tissue visible on MRI images between muscle groups and beneath the muscle fascia. Subsequently, Albu et al. (1) found, in premenopausal African-American women who had significantly higher insulin resistance and acute insulin response to glucose than did their white counterparts, that whole body IMAT, but not VAT or SAT, was an important independent correlate of insulin resistance. Previously, IMAT in a single midthigh slice measured by computed tomography (CT) showed that insulin resistance was associated with increased subfascial adipose tissue in obese adults (10) and thinner older persons (11). Goodpaster and colleagues (10) also found that adipose tissue located beneath the fascia lata and, therefore, adjacent to skeletal muscle (SM), was significantly negatively correlated with insulin resistance, whereas adipose tissue located above the fascia (i.e., SAT) and removed from SM was not (10). Therefore, this depot is potentially important in understanding metabolic disease. A comprehensive evaluation of whole body IMAT requires a whole body MRI or CT scan. Since acquiring a whole body scan demands considerable resources, including time required of subject in the scanner, costs of acquisition and image analyses, and for CT the issue of large radiation dose, a question arises as to whether it might be preferable or more cost effective to use one or more cross-sectional slices or combination of slices to estimate whole body IMAT in lieu of a whole body IMAT scan. Such a decision requires information on the predictive value of a subset of slices. The primary aim of this study was to determine which slice location, or combination of slice locations, provides the best estimates of whole body IMAT and to quantify the predictive value of these slice locations.