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Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging
Published on: July 1, 2021
Quantification of Fat Concentration and Vascular Response in Brown and White Adipose Tissue of Rats by Spectral CT
Xin Gui Peng1, Zhen Zhao1, Di Chang1
1Department of Radiology, Zhongda Hospital, Jiangsu Key Laboratory of Molecular and Functional Imaging, Medical School of Southeast University, Nanjing, China.
Objective:
The purpose of the study was to non-invasively characterize and discriminate brown adipose tissue (BAT) from white adipose tissue (WAT) in rats using spectral computed tomography (CT) with histological validation.
Materials And Methods:
A lipid-containing phantom (lipid fractions from 0% to 100%) was imaged with spectral CT. An in vivo, non-enhanced spectral CT scan was performed on 24 rats, and fat concentrations of BAT and WAT were measured. The rats were randomized to receive intraperitoneal treatment with norepinephrine (NE) (n = 12) or saline (n = 12). Non-enhanced and enhanced spectral CT scans were performed after treatment to measure the elevation of iodine in BAT and WAT. The BAT/aorta and WAT/aorta ratios were calculated and compared, after which isolated BAT and WAT samples were subjected to histological and uncoupling protein 1 (UCP1) analyses.
Results:
The ex-vivo phantom study showed excellent linear fit between measured fat concentration and the known gravimetric reference standard (r² = 0.996). In vivo, BAT had significantly lower fat concentration than WAT (p < 0.001). Compared to the saline group, the iodine concentration of BAT increased significantly (p < 0.001) after injection of NE, while the iodine concentration of WAT only changed slightly. The BAT/aorta ratio also increased significantly after exposure to NE compared to the saline group (p < 0.001). Histological and UCP1 expression analyses supported the spectral CT imaging results.
Conclusion:
The study consolidates spectral CT as a new approach for non-invasive imaging of BAT and WAT. Quantitative analyses of BAT and WAT by spectral CT revealed different characteristics and pharmacologic activations in the two types of adipose tissue.
