CHEMICAL-SHIFT IMAGING AT 4.7 TESLA OF BROWN ADIPOSE-TISSUE

In vivo distinction between small deposits of brown adipose tissue (BA T) and surrounding tissues may be difficult. In this article, we propo se an experimental paradigm, based on techniques of chemical shift mag netic resonance imaging (CSI), which can improve the methods presently available for the study of BAT. Male rats were examined in an imager- spectrometer equipped with a 4.7 T magnet. Proton spectra of isolated BAT deposits showed that both fat and water protons contributed signif icantly to the genesis of the magnetic resonance signal. An unequivoca l definition of BAT deposits was obtained by three (respectively, spin -echo, water-selective, and fat-selective) images. The spin-echo (SE), T1-weighted image provided the best anatomical description of the str uctures. The images selective for fat-protons displayed the degree of lipid accumulation in each area. The images selective for water-proton s provided an internal control of adipose tissue localization. The pro posed paradigm allows an unequivocal definition of BAT deposits and ap pears particularly useful in studies where experimental manipulation ( i.e., cold acclimation or drug treatment) produces changes in this tis sue.