Quantitative analysis of emphysema in 3D using MDCT: Influence of different reconstruction algorithms

PurposeThe aim of the study was to compare the influence of different reconstruction algorithms on quantitative emphysema analysis in patients with severe emphysema.Material and methodsTwenty-five patients suffering from severe emphysema were included in the study. All patients underwent inspiratory MDCT (Aquilion-16, slice thickness 1/0.8 mm). The raw data were reconstructed using six different algorithms: bone kernel with beam hardening correction (BHC), soft tissue kernel with BHC; standard soft tissue kernel, smooth soft tissue kernel (internal reference standard), standard lung kernel, and high-convolution kernel. The only difference between image data sets was the algorithm employed to reconstruct the raw data, no additional radiation was required. CT data were analysed using self-written emphysema detection and quantification software providing lung volume, emphysema volume (EV), emphysema index (EI) and mean lung density (MLD).ResultsThe use of kernels with BHC led to a significant decrease in MLD (5%) and EI (61–79%) in comparison with kernels without BHC. The absolute difference (from smooth soft tissue kernel) in MLD ranged from −0.6 to −6.1 HU and were significant different for all kernels. The EV showed absolute differences between −0.05 and −0.4 L and was significantly different for all kernels. The EI showed absolute differences between −0.8 and −5.1 and was significantly different for all kernels.ConclusionThe use of kernels with BHC led to a significant decrease in MLD and EI. The absolute differences between different kernels without BHC were small but they were larger than the known interscan variation in patients. Thus, for follow-up examinations the same reconstruction algorithm has to be used and use of BHC has to be avoided.