Purpose: To explore the acquisition parameter space in dual source DECT by analyzing the impact of kVp, Quality Reference mAs ratio (QRMr=QRM(A):QRM(B)), and pitch on image quality.
Methods: A custom anthropomorphic phantom (25Hx32Wx25Lcm) was constructed with soft tissue-mimicking material and organ-mimicking inserts simulating liver, pancreas, kidney, aorta, bone, and water, with realistic organ-specific HU values, size and relative positions. Each organ contained a cylindrical insert that simulates iodinated organ tissue. The phantom was scanned on a Siemens dual-source scanner with single-energy (SE) and DECT. A standard DECT protocol (90/Sn150kVp, QRMr=1.6, pitch=0.6) was considered as baseline and subsequent DECT scans were performed by individually varying pitch (0.9,1.2), QRMr (1.2,2,4), and kVp (70/Sn150, 80/Sn150 and 100/Sn150). QRM(A) and QRM(B) were adjusted to maintain CTDIvol of 7.5mGy. CNR,SNR, and noise were calculated and compared using ANOVA for all organs on SECT and mixture DECT images.
Results: Pitch of 0.6 on average improved the CNR by 11±4.2% (p<0.05) compared to other investigated pitch values while changing pitch from 0.6 to 1.2 had no significant impact on the noise or organ HU (p>0.7). Among the four tested kVp pairs, although 70/Sn150kVp resulted in the highest average noise level (p<0.05), it improved the CNR by an average of 14.1±8.2% (p<0.05) in iodinated tissues with no significant impact on CNR of non-iodinated organs. The changes in QRMr from 1.2 to 4 did not introduce any visible artifacts or changes in noise performance (p>0.5).
Conclusion: Increasing pitch from the vendor-recommended value (0.6) to higher ones did not significantly impact CT number accuracy and noise performance in mixture images, implying the possibility of using faster scans to mitigate motion artifacts. With similar CTDIv, CNR was higher in all DECT contrast-enhanced images compared to SECT, indicating the feasibility of reducing patient exposure with an optimized DECT protocol while maintaining/improving CNR.