Comparison of T1 relaxation times in adipose tissue of severely obese patients and healthy lean subjects measured by 1.5 T MRI.

Subcutaneous (SAT) and visceral adipose tissue (VAT) differ in composition, endocrine function and localization in the body. VAT is considered to play a role in the pathogenesis of insulin resistance, type 2 diabetes, fatty liver disease, and other obesity-related disorders. It has been shown that the amount, distribution, and (cellular) composition of adipose tissue (AT) correlate well with metabolic conditions. In this study, T1 relaxation times of AT were measured in severely obese subjects and compared with those of healthy lean controls. Here, we tested the hypothesis that T1 relaxation times of AT differ between lean and obese individuals, but also between VAT and SAT as well as superficial (sSAT) and deep SAT (dSAT) in the same individual. Twenty severely obese subjects (BMI 41.4 ± 4.8 kg/m(2) ) and ten healthy lean controls matched for age (BMI 21.5 ± 1.9 kg/m(2) ) underwent MRI at 1.5 T using a single-shot fast spin-echo sequence (short-tau inversion recovery) at six different inversion times (TI range 100-1000 ms). T1 relaxation times were computed for all subjects by fitting the TI -dependent MR signal intensities of user-defined regions of interest in both SAT and VAT to a model function. T1 times in sSAT and dSAT were only measured in obese patients. For both obese patients and controls, the T1 times of SAT (275 ± 14 and 301 ± 12 ms) were significantly (p < 0.01) shorter than the respective values in VAT (294 ± 20 and 360 ± 35 ms). Obese subjects also showed significant (p < 0.01) T1 differences between sSAT (268 ± 11 ms) and dSAT (281 ± 19 ms). More important, T1 differences in both SAT and VAT were highly significant (p < 0.001) between obese patients and healthy subjects. The results of our pilot study suggest that T1 relaxation times differ between severely obese patients and lean controls, and may potentially provide an additional means for the non-invasive assessment of AT conditions and dysfunction.

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