Gem Spectrum Feasibility Study Renal Artery CT Angiography Using Low Doses Of Contrast Agents

[Objective] In order to reduce the potential risk of contrast-induced nephropathy, this study investigated the feasibility of low dose contrast medium in renal artery CT angiography using spectral CT.[Methods]30volunteers were randomly divided into2groups(A and B), and there were15volunteers in each group. There were6males and9females in group A, the mean age was43.9±9.7years, the mean weigh was63.0±9.0Kg and the mean BMI was22.3±3.0Kg/m2. There were7males and8females in group B, the mean age was44.8±10.3years, the mean weigh was65.1±6.5Kg and the mean BMI was22.6±2.1Kg/m2. All volunteers underwent arterial phase spectral CT imaging scans with a single tube, rapid dual kVp (80kVp and140kVp) switching technique. The GSI scan parameters included:helical,0.8s tube rotation time,40mm detector coverage, pitch factor:0.985:1,35cm DFOV. The non-ionic contrast media Iohexol (320mgl/ml) was injected with power injector at a rate of4.0ml per second through median cubital vein in the two groups. The dose of1.5ml/kg was used in group A, and the dose of0.8m l/kg was used in group B. Volunteers in the two groups were treated with30ml saline flush. The arterial phase were triggered5s after the density of descending aorta reached100HU on the monitoring scan.①An optimal monochromatic image set was selected for obtaining the best CNR for descending aorta in group B.②CT attenuation values, Image noise, signal-to-noise ratio(SNR) and contrast-to-noise ratio (CNR) of bilateral renal arteries were measured for each group and the image quality was recorded as excellent, good, and poor.③All dates were analyzed by SPSS16.0statistical software package. Between B and the optimal monochromatic image, the optimal monochromatic image and A, CT attenuation values, Image noise, signal-to-noise ratio(SNR) and contrast-to-noise ratio (CNR) of bilateral renal arteries was analyzed using t test. Image quality score was analyzed using X2test. Difference with P<0.05was considered as significa.[Results]①The age, weight, BMI were no significant difference between the two groups and the dose of contrast medium was significant difference between the two groups.②The monochromatic images at51keV were found to provide the best CNR for renal arteries. The monochromatic images had about80.1%,79.7%higher CT attenuation values and74.4%,83.4%higher image noise of the bilateral renal artery than the polychromatic images, and there was significant difference. SNR and CNR were no difference significant difference. Image quality was rated as excellent, good, poor for3,10and2volunteers in polychromatic images,10,5and0volunteers in the monochromatic images. There were significant differences between2groups.③The optimal monochromatic image had about13.0%,12.1%higher CT attenuation values;38.9%,42.3%higher image noise;22.7%,23.2%lower SNR and24.3%,26.4%lower CNR of the bilateral renal artery than group A. Image quality was rated as excellent, good, poor for12,3and0volunteers in group A and there was no significant difference.[Conclusion]①Monochromatic images at51keV for renal artery CT angiography could improve CNR for displaying renal arteries and improve the overall image quality.②It is feasible to use low dose contrast medium(0.8ml/kg) in spectral CT for the renal arteries. It may reduce the patients’ expenses and the potential risk of CIN.