Author: Xinhui Duan, Vivek Nair, Liqiang Ren, KyuHo Song, Vasantha Vasan, Kuan Zhang, Yue Zhang 👨🔬
Affiliation: Department of Radiology, UT Southwestern Medical Center 🌍
Purpose: Minimizing radiation dose is crucial in CT colonography (CTC) screening and diagnosis. Tin (Sn) prefiltration is readily incorporated into clinical photon-counting CT (PCCT) scanners, yet its impact on noise and dose efficiency remains unclear. This study evaluates the effects of Sn prefiltration on noise and dose efficiency in PCCT-based CTC imaging.
Methods: Phantom samples were prepared to simulate clinically relevant contrast enhancements: iodine (8.5–21.5 mg/mL), barium (5.9–11.8 mg/mL), and iodine–barium mixtures. These were placed within a multi-energy CT phantom of two sizes and scanned on a PCCT system (NAEOTOM Alpha, Siemens) at 120 kV, Sn100 kV, and Sn140 kV (tin filter thickness: 0.4 mm). Dose levels (small phantom: 0.8 and 1.4 mGy; large phantom: 2.9 and 5.5 mGy) were selected for CTC tasks and matched across all tube voltages. Images were reconstructed as threshold-low (T3D) and virtual monoenergetic images (VMIs) at 60 and 70 keV. Noise was quantified as the standard deviation within circular regions of interest placed over the iodine, barium, and mixture regions.
Results: Compared with 120 kV, Sn100 kV scans reduced noise by up to 11% across phantom sizes, dose levels, and reconstruction types. Sn140 kV provided noise levels similar to 120 kV in T3D reconstructions but showed increased noise (up to 23%) in VMIs.
Conclusion: Employing Sn100 kV on clinical PCCT scanners consistently reduces noise under a variety of imaging conditions. This improvement may translate to either lower effective doses or the potential for further radiation dose reductions in CTC. Conversely, Sn140 kV is dose-inefficient. For higher-dose scans, Sn100 kV (if tube current permits) or 120 kV may be preferable.