Image quality evaluation of dual-layer spectral CT in comparison to single-layer CT in a reduced-dose setting.

Objectives: To quantitatively and qualitatively evaluate image quality in dual-layer CT (DLCT) compared to single-layer CT (SLCT) in the thorax, abdomen, and pelvis in a reduced-dose setting.
Methods: Intraindividual, retrospective comparisons were performed in 25 patients who received at least one acquisition of all three acquisition protocols SLCT _low (100 kVp), DLCT _high (120 kVp), and DLCT _low (120 kVp), all covering the venous-phase thorax, abdomen, and pelvis with matched CTDI _vol between SLCT _low and DLCT _low . Reconstruction parameters were identical between all scans. Image quality was assessed quantitatively at 10 measurement locations in the thorax, abdomen, and pelvis by two independent observers, and subjectively with an intraindividual forced choice test between the three acquisitions. Dose-length product (DLP) and CTDI _vol were extracted for dose comparison.
Results: Despite matched CTDI _vol in acquisition protocols, CTDI _vol and DLP were lower for SLCT _low compared to DLCT _low and DLCT _high (DLP 408.58, 444.68, 647.08 mGy·cm, respectively; p < 0.0004), as automated tube current modulation for DLCT _low reached the lower limit in the thorax (mean 66.1 mAs vs limit 65 mAs). Noise and CNR were comparable between SLCT _low and DLCT _low (p values, 0.29-0.51 and 0.05-0.20), but CT numbers were significantly higher for organs and vessels in the upper abdomen for SLCT _low compared to DLCT _low . DLCT _high had significantly better image quality (Noise and CNR). Subjective image quality was superior for DLCT _high , but no difference was found between SLCT _low and DLCT _low .
Conclusions: DLCT _low showed comparable image quality to SLCT _low , with the additional possibility of spectral post-processing. Further dose reduction seems possible by decreasing the lower limit of the tube current for the thorax.
Key Points: • Clinical use of reduced-dose DLCT is feasible despite the required higher tube potential. • DLCT with reduced dose shows comparable objective and subjective image quality to reduced-dose SLCT. • Further dose reduction in the thorax might be possible by adjusting mAs thresholds.