Purpose: CT imaging of obese patients is limited by tradeoffs between image quality and radiation output (dose). For demanding clinical situations like abdominal imaging, sacrificing image quality may be required due to scanner output limits. In this study, we compared acquisition parameters and global noise (GN) between a standard, single-source (SS) CT protocol and a new dual-source (DS) protocol with enhanced radiation output capacity.
Methods: A total of 97 matched SS and DS scans from 49 patients were compared. Matched pairs were included if the tube voltage, reconstruction kernel, and scanner platform were consistent between scans from each protocol, and changes in patient weight and water equivalent diameter were <5%. GN was determined with a previously reported algorithm and its uncertainty within each protocol was established at the 95% prediction interval (PI, ±1.96σ). Prediction models were developed to estimate GN based on protocol type, CTDIvol, reconstruction kernel, and patient size parameters.
Results: The median±1σ increase in CTDIvol for DS scans from the matched pairs was 52±32% (21±11 mGy). The 95% PI for the uncertainty in GN was ±1.1 HU. GN in DS scans was reduced by more than 1.1 HU in 87% of matched pairs (ΔGN median±1σ: -2.5±1.7 HU). The prediction models could estimate GN with RMS error of 0.9 and 0.6 HU, respectively, for SS and DS scans. Model predictions for three example patient sizes showed that DS scans provide the same GN at a lower dose under nearly all achievable scanning conditions when compared to SS scans.
Conclusion: A DS protocol for obese patient CT imaging provides enhanced dose capabilities and reduces noise relative to our standard SS protocol which is limited in radiation output. The noise reduction benefits of the DS protocol improve with increasing patient size.