Key result
Cold stimulation in rats resulted in significantly lower interscapular BAT relative fat content (P=0.0064) and larger interscapular and perirenal BAT volumes (P=0.0017) as measured by MRI.
p-value: p=0.0064
Calibrated Dixon MRI with relative fat content scaling can accurately depict brown adipose tissue and measure differences in volume and fat concentration induced by cold stimulation in a rat model.
MRI quantifies cold-induced BAT changes in rats; extends preclinical validation but leaves open human translation.
BACKGROUND: To evaluate the possibility of quantifying brown adipose tissue (BAT) volume and fat concentration with a high resolution, long echo time, dual-echo Dixon imaging protocol. METHODS: A 0.42 mm isotropic resolution water-fat separated MRI protocol was implemented by using the second opposite-phase echo and third in-phase echo. Fat images were calibrated with regard to the intensity of nearby white adipose tissue (WAT) to form relative fat content (RFC) images. To evaluate the ability to measure BAT volume and RFC contrast dynamics, rats were divided into two groups that were kept at 4° or 22°C for 5 days. The rats were then scanned in a 70 cm bore 3.0 Tesla MRI scanner and a human dual energy CT. Interscapular, paraaortal, and perirenal BAT (i/pa/pr-BAT) depots as well as WAT and muscle were segmented in the MRI and CT images. Biopsies were collected from the identified BAT depots. RESULTS: The biopsies confirmed that the three depots identified with the RFC images consisted of BAT. There was a significant linear correlation (P < 0.001) between the measured RFC and the Hounsfield units from DECT. Significantly lower iBAT RFC (P = 0.0064) and significantly larger iBAT and prBAT volumes (P = 0.0017) were observed in the cold stimulated rats. CONCLUSION: The calibrated Dixon images with RFC scaling can depict BAT and be used to measure differences in volume, and fat concentration, induced by cold stimulation. The high correlation between RFC and HU suggests that the fat concentration is the main RFC image contrast mechanism.
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Romu et al. (2015) studied Brown adipose tissue characterization. Cold stimulation (4°C) vs. 22°C was evaluated on Relative fat content (RFC) and volume of brown adipose tissue depots (p=0.0064). Cold stimulation in rats resulted in significantly lower interscapular BAT relative fat content (P=0.0064) and larger interscapular and perirenal BAT volumes (P=0.0017) as measured by MRI.
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