Differential computed tomographic attenuation of metabolically active and inactive adipose tissues: preliminary findings

Abstract

This study investigates differences in computed tomography Hounsfield units between metabolically active (brown fat) and inactive adipose tissues (white fat) due to variations in their densities. Positron emission and computed tomographic data from 101 pediatric and adolescent patients were analyzed. Regions of metabolically active and inactive adipose tissues were identified, and standard uptake values and Hounsfield units were measured. Hounsfield units of active brown fat were more positive (P < 0.001) than inactive fat (-62.4 ± 5.3 vs -86.7 ± 7.0) and the difference was observed in both males and females.

Figures

Figure 1

Flowchart of image analysis process. All cases were first reviewed by radiologists to determine the presence or absence of visually evident metabolically active adipose tissue (MAAT). From the BAT-visualized cases, HUs and SUVs of metabolically active bilateral regions at the interscapular, neck, and supraclavicular levels are computed first. Corresponding regions in the BAT-non-visualized cases were then computed next. Finally, distributions in metabolically inactive adipose tissue (MIAT), selected to be subcutaneous fat, were computed from all cases.

Figure 2

Histogram of the distribution of cases analyzed across the months during which PET/CT examination was performed. Black portions denote the BAT-visualized cases and gray portions represent the BAT-non-visualized cases.

Figure 3

Bar plot illustrating the differences in PET SUVs between MAAT and MIAT.

Figure 4

Bar plot illustrating the differences in CT HUs between MAAT and MIAT.

Figure 5

Scatter plot of HUs and SUVs for MAAT (solid circles) and MIAT (open circles). The gray region denotes a range of SUVs (0.8 to 1.2) where no data points reside.

Figure 6

Co-registered (a) CT and (b) PET images from two subjects. Arrows point to symmetrical uptake of radiotracers by BAT in foci with high SUVs, which correspond to negative HU voxels in the associated CT images. The third row illustrates segmented MIAT (mostly subcutaneous WAT) and interscapular BAT, with a difference of more than 20 HUs in both subjects. Note that the BAT foci are located bilaterally and ventrally.