Author: Xinhui Duan, Vivek Nair, Liqiang Ren, KyuHo Song, Kuan Zhang, Yue Zhang 👨🔬
Affiliation: Department of Radiology, UT Southwestern Medical Center 🌍
Purpose: To evaluate how tin-filtered spectral shaping in clinical photon-counting computed tomography (PCCT) affects noise magnitude across varying object sizes, radiation doses, and spectral reconstruction types.
Methods: An ACR CT phantom and two body rings were used to simulate three patient sizes (small: 20cm×20cm; medium: 33cm×26 cm; large: 40cm×30cm). Scans were performed on a clinical PCCT (NAEOTOM Alpha, Siemens) in QuantumPlus mode at 120 and 140kV, and in QuantumSn mode at Sn100 and Sn140kV (Sn: tin filter, 0.4mm). CTDIvol levels were set at 3, 8, and 12mGy for three phantoms with additional scans conducted at 50%, 25%, and 10% of these doses, matched across all tube voltages. Reconstructions included low-energy threshold images (T3D) and virtual monoenergetic images (VMIs) at 60 and 70keV, processed using quantum iterative reconstruction (QIR-3) with a body kernel (Br44). Noise magnitudes were measured by placing multiple regions of interest (ROIs) over the uniformity module. Noise levels were compared across all imaging conditions.
Results: Compared to 120kV, 140kV images consistently exhibited higher noise (up to 28%). Noise trends for tin-filtered images (Sn100kV and Sn140kV) varied with size, dose, and reconstruction type. Small phantom: Sn100kV showed up to 26% lower noise at 10% dose and comparable/lower noise (-7% to 9%) at doses ≥25%. Sn140kV had 27% lower noise at 10% dose but higher noise (4% to 25%) at higher doses. Medium phantom: Sn100kV noise was consistently comparable/lower across all doses, particularly at low dose levels. Sn140kV noise varied with reconstruction type, being lower for T3D but higher for VMIs. Large phantom: Trends matched medium-sized results, except Sn100kV at low doses (e.g., 60 keV VMI), where artifacts elevated noise.
Conclusion: Noise reduction with tin-filtered techniques on PCCT depends on size, dose, and reconstruction type. Sn100kV offers the most efficient noise reduction, particularly at low dose levels (<25%).