Impact of Tin Spectral Filtration In Renal Stone Imaging In Photon-Counting CT
Abstract
Purpose
Tin filtration has shown improved dose efficiencies in conventional CT for renal stone imaging. Photon-counting CT (PCCT) enables virtual monoenergetic image (VMI) reconstructions that can enhance stone conspicuity. This study evaluates potential dose-efficiency benefits of tin filtration with PCCT when renal stone imaging is performed using monoenergetic reconstructions.
Methods
A Mercury phantom was scanned on a PCCT system (NAEOTOM Alpha, Siemens Healthineers) to evaluate calcium contrast-to-noise ratio (CNR) as a function of phantom size. Ultra-high resolution acquisitions were performed at 120 kV (non-tin) and 100 kV with tin filtration (100Sn) at a fixed CTDIvol. Images were reconstructed as 65 keV VMI and low-energy threshold images (T3D) using medium- and high-resolution kernels (Br44 and Br64). Renal stone detectability was performed using a QRM phantom containing 1-, 3-, and 5-mm calcium stones. For 120 kV and 100Sn acquisitions, images were reconstructed using identical reconstruction settings. Scan dose was systematically varied to identify the minimum dose at which each stone size was detectable.
Results
Calcium CNR decreased with increasing phantom size for all conditions. At a given size, 100Sn VMI reduced calcium CNR relative to T3D, while 120 kV VMI increased CRN relative to T3D. For T3D reconstructions, 100Sn and 120 kV VMI demonstrated higher CNR than 100Sn with 65 keV VMI for small to medium phantom sizes, with comparable trends at larger sizes. In the QRM phantom, when reconstructed with the higher-resolution Br64 kernel, 100Sn enabled visualization of 1-mm calcium stones, whereas corresponding non-tin reconstructions did not consistently demonstrate detectability at the same dose levels.
Conclusion
In PCCT, the dose-efficiency advantages of tin filtration in conventional renal stone imaging depend on reconstruction strategy. Tin filtration degrades calcium CNR for VMI imaging while improving or preserving performance in total-energy reconstructions, particularly for high-resolution tasks.