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

Figures

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  Fig. 1. Schematic procedure of study. First, non-enhanced spectral CT scan was performed on all animals, and fat concentration and baseline iodine concentration of BAT and WAT were measured. Rats were then randomly divided into NE group (n = 12) and saline group (n = 12) injected with NE and saline, respectively. NE infusion was performed, followed by contrast-enhanced spectral CT, which measured changes in iodine concentrations of BAT and WAT. BAT = brown adipose tissue, NE = norepinephrine, WAT = white adipose tissue

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  Fig. 2. Time-enhancement curve in BAT with injection of contrast medium. A. ROI (red circle) was placed on BAT of interscapular region. B. Zero point on x-axis is starting point of contrast medium injection. Vertical gray bar indicates time of contrast-enhanced spectral CT scan. ROI = region of interest

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  Fig. 3. Lipid-containing phantom imaging by spectral CT (lipid fraction ranging from 0% to 100%). A. Fat-base imaging of phantom. B. Graph showing strong correlation between known lipid content (%) and fat concentration measured by spectral CT (r2 = 0.996, p < 0.001).

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  Fig. 4. Examples of fat-based material decomposition image of BAT and WAT. A. Red circles indicate positions of ROIs used to calculate material concentrations. B. Fat concentrations of selected ROIs on BAT and WAT. Fat concentration was significantly lower in BAT than in WAT. ***p < 0.001.

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  Fig. 5. Histological characteristics of BAT and WAT. A. Histological analysis of BAT and WAT sections, including H&E staining and immunohistochemistry of UCP1 (× 400; scale bar, 50 µm). B. Adipocyte size of WAT was significantly larger than that of BAT. UCP1 content of BAT was significantly higher than that of WAT. ***p < 0.001. H&E = hematoxylin and eosin, HIS-S = histological semi-automatic vacuole segmentation procedure, UCP1 = uncoupling protein 1

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  Fig. 6. Quantification of iodine concentration in BAT and WAT after NE injection by contrast-enhanced spectral CT. A, B. Changes in iodine concentration in BAT (yellow circle) after saline or NE injection. B. Although iodine concentration was not different between two groups at baseline, it increased considerably greater in NE group than in saline group in contrast-enhanced spectral CT imaging. C, D. Changes in iodine concentration in WAT (yellow circle) after saline or NE. D. No significant changes in iodine concentration was observed in WAT in both groups. Limited increase in iodine concentration from baseline to contrast-enhanced spectral CT was observed. ***p < 0.001.

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  Fig. 7. Comparisons of vasculization of BAT and WAT. A. BAT/aorta ratio of iodine concentration in NE group (0.32 ± 0.07) was significantly higher compared to saline group (0.12 ± 0.07; p < 0.001). In contrast, there was no significant difference in WAT/aorta ratio between NE (−0.08 ± 0.03) and saline (−0.13 ± 0.07) groups (p > 0.05). B. Immunohistochemical analysis of BAT and WAT for α-SMA and CD31 (× 400; scale bar, 50 µm) demonstrated larger number of micro-vessels in BAT. ***p < 0.001. α-SMA = alpha-smooth muscle actin