ABSTRACT
Objective:To carry out preliminarily study on the combination of high iodine flow rate (IDR) and high noise index (NI) in reducing radiation dose of CT angiography (CTA) for head and neck.Methods:A total of 120patients with lesions on head and neck who underwent head and neck CTA in the hospital were divided into high IDR combined with high NI group (high IDR+NI group, 50 cases) , middle IDR combined with middle NI group (middle IDR+NI group, 40 cases) and low IDR combined with low NI group (low IDR+NI group, 30 cases) according to the random number table method.The scanned images were reconstructed by the iterative reorganization algorithm (ASiR) 2.0.The CT values of head and neck, signal to noise ratio (SNR) , contrast noise ratio (CNR) of all images in three groups were analyzed objectively and scored subjectively.And the CT dose index (CTDI) , dose length product (DLP) , effective radiation dose (ED) of the iodine intake and radiation dose were recorded.Results:The differences of CT value of ascending aorta, upper common carotid artery or lower internal carotid artery among the three groups were no significant, respectively.The SNR and CNR in high IDR+NI group were significantly higher than those in middle IDR+NI group and low IDR+NI group (F=47.908, F=52.525, P<0.05) , respectively.And there was no significant difference in subjective scores among the three groups.The differences of CTDI, DLP and ED in high IDR+NI group were significantly lower than those in middle IDR+NI group and low IDR+NI group (F=224.861, F=199.610, F=412.443, P<0.05) , respectively.Conclusion:The combination of high IDR and high NI for patients who undergoes head and neck CT can reduce the radiation dose when ensure the image quality, and it is worthy in clinical application.
ABSTRACT
OBJECTIVE: To assess the effect of varying iodine flow rate (IFR) and iodine concentration on the quality of virtual unenhanced (VUE) images of the abdomen obtained with dual-energy CT. METHODS: 94 subjects underwent unenhanced and triphasic contrast-enhanced CT scan of the abdomen, including arterial phase, portal venous phase, and delayed phase using dual-energy CT. Patients were randomized into 4 groups with different IFRs or iodine concentrations. VUE images were generated at 70 keV. The CT values, image noise, SNR and CNR of aorta, portal vein, liver, liver lesion, pancreatic parenchyma, spleen, erector spinae, and retroperitoneal fat were recorded. Dose-length product and effective dose for an examination with and without plain phase scan were calculated to assess the potential dose savings. Two radiologists independently assessed subjective image quality using a five-point scale. The Kolmogorov-Smirnov test was used first to test for normal distribution. Where data conformed to a normal distribution, analysis of variance was used to compare mean HU values, image noise, SNRs and CNRs for the 4 image sets. Where data distribution was not normal, a nonparametric test (Kruskal-Wallis test followed by stepwise step-down comparisons) was used. The significance level for all tests was 0.01 (two-sided) to allow for type 2 errors due to multiple testing. RESULTS: The CT numbers (HU) of VUE images showed no significant differences between the 4 groups (p > 0.05) or between different phases within the same group (p > 0.05). VUE images had equal or higher SNR and CNR than true unenhanced images. VUE images received equal or lower subjective image quality scores than unenhanced images but were of acceptable quality for diagnostic use. Calculated dose-length product and estimated dose showed that the use of VUE images in place of unenhanced images would be associated with a dose saving of 25%. CONCLUSIONS: VUE images can replace conventional unenhanced images. VUE images are not affected by varying iodine flow rates and iodine concentrations, and diagnostic examinations could be acquired with a potential dose saving of 25%.
