Comparison of spectral imaging and conventional CT in CT angiography of the kidney: image quality and radiation dose

Objective To compare the image quality and radiation dose of CTA of the kidney in patients using routine CT and the spectral imaging combination of different scanning protocols with the adaptive statistical iterative reconstruction 2.0 algorithm (ASIR 2.0). Methods A total of 90 patients who had undergone a CTA of the kidney were divided into three groups (A, B and C), with 30 patients in each group. Group A underwent a routine CT examination, and the scan parameters are:120 kVp, 30 to 650 mA, rotation time 0.5 s/r, scan FOV 50 cm×50 cm; while groups B and C underwent spectral imaging protocol 1 and 2, the scan parameters of spectral imaging protocol 1 and 2 are: rapid dual kVp (80-140 kVp) switching in 0.25 ms, 375 mA and 360 mA, rotation time 0.7 s/r and 0.6 s/r, scan FOV 36 cm×36 cm and 32 cm×32 cm, respectively. All images were reconstructured using ASIR 2.0. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of all images were calculated when the kidney CTA was completed. Each subjective image evaluation used a 5-point scoring method and was conducted by two independent radiologists. The CT dose index (CTDIvol) and dose-length product (DLP) were recorded, and the mean value was calculated. The DLP was converted to the effective dose (ED). All data were compared with Kruskal-Wallis test and one-way ANOVA. Results The energy level of 49 to 56 keV was found to provide the best CNR for displaying CTA of the kidney. There were significant differences in CT values, noise, SNR, CNR and subjective score between groups B, C and A (P 0.05). There were significant differences in ED among groups A, B and C (P<0.05), and the ED of groups A, B and C were (8.2±1.2), (5.2±0.9) and (4.4±0.7) mSv, respectively. Conclusion Spectral imaging with different scanning protocols can more effectively reduce the radiation dose than the routine CT scan mode for a kidney CTA while still maintaining diagnostic image quality, and protocol 2 of spectral imaging in our study is recommended. Key words: Renal Artery; Angiography; Tomography, X-ray computed; Radiation dosage