How Low Can We Go in Contrast-Enhanced CT Imaging of the Chest?: A Dose-Finding Cadaver Study Using the Model-based Iterative Image Reconstruction Approach

Abstract

Dose reduction may compromise patients because of a decrease of image quality. Therefore, the amount of dose savings in new dose-reduction techniques needs to be thoroughly assessed. To avoid repeated studies in one patient, chest computed tomography (CT) scans with different dose levels were performed in corpses comparing model-based iterative reconstruction (MBIR) as a tool to enhance image quality with current standard full-dose imaging. Twenty-five human cadavers were scanned (CT HD750) after contrast medium injection at different, decreasing dose levels D0-D5 and respectively reconstructed with MBIR. The data at full-dose level, D0, have been additionally reconstructed with standard adaptive statistical iterative reconstruction (ASIR), which represented the full-dose baseline reference (FDBR). Two radiologists independently compared image quality (IQ) in 3-mm multiplanar reformations for soft-tissue evaluation of D0-D5 to FDBR (-2, diagnostically inferior; -1, inferior; 0, equal; +1, superior; and +2, diagnostically superior). For statistical analysis, the intraclass correlation coefficient (ICC) and the Wilcoxon test were used. Mean CT dose index values (mGy) were as follows: D0/FDBR=10.1±1.7, D1=6.2±2.8, D2=5.7±2.7, D3=3.5±1.9, D4=1.8±1.0, and D5=0.9±0.5. Mean IQ ratings were as follows: D0=+1.8±0.2, D1=+1.5±0.3, D2=+1.1±0.3, D3=+0.7±0.5, D4=+0.1±0.5, and D5=-1.2±0.5. All values demonstrated a significant difference to baseline (P<.05), except mean IQ for D4 (P=.61). ICC was 0.91. Compared to ASIR, MBIR allowed for a significant dose reduction of 82% without impairment of IQ. This resulted in a calculated mean effective dose below 1mSv.