RESUMO
PURPOSE: To investigate reduction of radiation exposure in unenhanced CT in suspicion of renal calculi using a tin-filtered high tube voltage protocol compared to a standard low-dose protocol without spectral shaping. MATERIALS AND METHODS: A phantom study using 7 human renal calculi was performed to test both protocols. 120 consecutive unenhanced CT examinations performed due to suspicion of renal calculi were included in this retrospective, monocentric study. 60 examinations were included with the standard-dose protocol (SP) (100âkV/130âmAs), whereas another 60 studies were included using a low-dose protocol (LD) applying spectral shaping with tin filtration of high tube voltages (Sn150âkV/80âmAs). Image quality was assessed by two radiologists in consensus blinded to technical parameters using an equidistant Likert scale ranging from 1-5 with 5 being the highest score. Quantitative image quality was assessed using regions of interest in abdominal organs, muscles, and adipose tissue to analyze image noise and signal-to-noise ratios (SNR). Commercially available dosimetry software was used to determine and compare effective dose (ED) and size-specific dose estimates (SSDEmean). RESULTS: All seven renal calculi of the phantom could be detected with both protocols. There was no difference regarding calcluli size between the two protocols except for the smallest one. The smallest concretion measured 1.5âmm in LD and 1.0âmm in SP (ground truth 1.5âmm). CTDIvol was 3.36âmGy in LD (DLP: 119.3 mGycm) and 8.27âmGy in SP (DLP: 293.6 mGycm). The mean patient age in SP was 47â±â17 years and in LD 49â±â13 years. Ureterolithiasis was found in 33 cases in SP and 32 cases in LD. The median concretion size was 3âmm in SP and 4âmm in LD. The median ED in LD was 1.3âmSv (interquartile range (IQR) 0.3âmSv) compared to 2.3âmSv (IQR 0.9âmSv) in SP (pâ<â0.001). The SSDEmean of LD was also significantly lower compared to SP with 2.4âmGy (IQR 0.4âmGy) vs. 4.8âmGy (IQR 2.3âmGy) (pâ<â0.001). The SNR was significantly lower in LD compared to SP (pâ<â0.001). However, there was no significant difference between SP and LD regarding the qualitative assessment of image quality with a median of 4 (IQR 1) for both groups (pâ=â0.648). CONCLUSION: Tin-filtered unenhanced abdominal CT for the detection of renal calculi using high tube voltages leads to a significant reduction of radiation exposure and yields high diagnostic image quality without a significant difference compared to the institution's standard of care low-dose protocol without tin filtration. KEY POINTS: · Tin-filtered CT for the detection of renal calculi significantly reduces radiation dose.. · The application of tin filtration provides comparable diagnostic image quality to that of SP protocols.. · An increase in image noise does not hamper diagnostic image quality.. CITATION FORMAT: · Gassenmaier S, Winkelmann MT, Magnus J etâal. Low-Dose CT for Renal Calculi Detection Using Spectral Shaping of High Tube Voltage. Fortschr Röntgenstr 2022; 194: 1012â-â1019.