Korean J Radiol.  2020 Feb;21(2):248-256. 10.3348/kjr.2019.0111.

Quantification of Fat Concentration and Vascular Response in Brown and White Adipose Tissue of Rats by Spectral CT Imaging

Affiliations
  • 1Department of Radiology, Zhongda Hospital, Jiangsu Key Laboratory of Molecular and Functional Imaging, Medical School of Southeast University, Nanjing, China. jsh0836@hotmail.com

Abstract


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.

Keyword

Spectral CT imaging; Histology; Brown adipose tissue; White adipose tissue; Fat concentration; Vascular

MeSH Terms

Adipose Tissue
Adipose Tissue, Brown
Adipose Tissue, White*
Animals
Iodine
Norepinephrine
Rats*
Tomography, X-Ray Computed
Iodine
Norepinephrine
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