Determination of lower radiation dose limit for automatic measurement of adipose tissue.

The purpose of this study was to determine the lower limit of radiation dose required to measure visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) volumes when a fat quantification and noise reduction techniques (NRTs) are combined. For this purpose, we utilized CT colonography (CTC) images taken at low doses and manually segmented VAT and SAT fat volumes as ground truth. In order to derive the acceptable precision of the measurements needed to estimate the lower limit of radiation dose, we estimated the effect of different positioning during CT scanning on fat measurements using manually segmented VAT and SAT against normal dose. As a result, the acceptable accuracy of SAT and VAT was found to be 94.5% and 85.2%, respectively. Using these thresholds, the lower radiation dose limit required to accurately measure SAT using 5.25-mm slice-thick images was 1.5 mGy of size-specific dose estimates (SSDE), while the lower radiation dose limit required to accurately measure VAT was 0.4 mGy of SSDE. The lower dose limit for SAT and VAT combined was 1.5 mGy, which was equivalent to an estimated effective dose of 0.38 mSv. Alternatively, without noise reduction, SAT could not achieve acceptable accuracy even for images with a slice thickness of 5.25 mm, while VAT required noise reduction for images with a slice thickness of 1.25 mm, but could achieve acceptable accuracy without noise reduction for images with a slice thickness of 5.25 mm.