| Objective:To discuss the feasibility of a reduction of tube voltage and lowconcentration contrast medium,in decreasing radiation dose and iodine-load of contrast medium and maintaining the image quality for renal CT enhanced scanning.Methods:Our study was approved by the hospital ethics committee.Written informed consent was obtained from all subjects.The subjects included in the conditions as follows: adults in 18.5kg/m2≤BMI < 28kg/m2,and the waist circumference(male/female)<100cm/95 cm,patients with contrast agent allergy,renal insufficiency,and other contrast agents were excluded.40 subjects were randomly assigned to the control group and the experimental group,with 20 patients in each group.All men underwent three phases enhanced CT scan.The scanning protocol is as follows: the control group used a tube voltage of 120 k Vp,using the contrast agent Omnipaque 300(300mg I/ml in concentration)100ml;the experimental group used a tube voltage of 100 k Vp,using the contrast medium iodixanol 270(270mg I/ml in concentration)80ml;the other scan parameters are exactly the same for the two groups.The noise value of the image,the CT value of the cortex,medulla, lesion and abdominal aorta in both cortical and parenchymal phases,and the CT value of the inferior vena cava during the parenchymal phase were measured at the workstation.The contrast to noise ratio(CNR)and signal to noise ratio(SNR)were calculated and compared for both cortical and parenchymal phases.Independent blinded reading by two radiologists with more than 5 years of experience.According to the diagnostic effect of renal lesions,image noise,soft tissue contrast,renal parenchyma anatomy and texture sharpness,subjective scoring was evaluated with a 4-point system: 4-satisfied,3-acceptable,2-diagnositic,1-unacceptable.The average score of two doctors was used as the image quality score of the patient.Independent sample t test was performed on objective data and rank sum test was conducted on subjective score by using SPSS 16.0 software.The effective dose(ED)and the iodine-load in each group were calculated and compared.Results:There was no significant difference in subjective scores between the control group and the experimental group(p>0.05).In the cortical phase,the CT values of renal cortex,medulla and abdominal aorta in the experimental group were(170±21)HU,(77±9)HU,(328±44)HU,significantly higher than those in the control group(p=0.001,p=0.005,p=0.008).In the parenchymal phase,the CT value of the renal medulla in the experimental group was(242± 61)HU,which was significantly higher than that of the control group(p=0.026).There were no significant differences between the two groups in the CT value of the lesion in both cortical and parenchymal phases,and the CT value of the cortex,abdominal aortathe and inferior vena cava during the parenchymal phase(p>0.05).The noise in two groups were 6±0.8 and 7.6±1.5 respectively.The noise of the experimental group was significantly higher than that of the control group(p=0.001).No statistically significant difference was found between the two groups in SNR and CNR(p>0.05).Conclusion:In the adults of 18.5kg/m2≤BMI<28kg/m2 and the waist circumference(male/female)< 100cm/95 cm,renal CT enhanced scan with a tube voltage of100 k Vp and 270 mg I/ml contrast medium 80 ml,can maintain a good image quality and reduce the radiation dose by 42% and iodine-load by 28%. |
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