Reducing Effective Radiation Dose In CT Urography For Urolithiasis: The Research Of Dual Energy CT

Objective：With the increasing availability of multi-detector computedtomography (MDCT), CT urography (CTU) has established one-stopexamination for the assessment of patients with hematuria. Typical CTUprotocols require more image acquisitions to obtain the unenhanced andmultiple post-contrast phases, which raises the effective radiation doseremarkably. How to decrease the dose without sacrifying image quality hasbeen a big challenge to radiologist. The aim of the present study is to evaluatethe value of dual energy CT in CTU for urolithiasis patients, by usingsplit-bolus single-phase scan to obtain virtual unenhanced images, with theimage quality and radiation dose compared.Methods: Forty-eight patients referred for abdominal pain and hematuriawere divided into experimental group and control group randomly. Patients inexperimental group underwent split-bolus iodine injection CTU usingdual-energy scan mode to obtain synchronous nephrographic-pyelographicphase. Patients in control group accepted single-bolus CTU using regular scanmode to acquire multiple phases (unenhanced, nephrographic phase, andpyelographic phase). Drinking500-1000mL water and intravenous injection20mg/2mL furosemide were performed to each patient before CTU. The totaldose of iodine contrast was90mL for each group. Images of optimal keV fordual energy protocol were generated. The CT values and CNRs in urinary tractwere measured segmentally and compared between the two groups. The sizeof the calculi and efficient radiation dose (ERD) of the scan were measured aswell. The CT value and CNR for each segment, and ERD for CT scan werecompared between the groups with Mann-Whitney U test.Results：The measurements for165segments in experimental group and164segments in control group were obtained. The optimal keV in dual energy protocol was52.1±2.21keV (48~58keV).35calculi were detected by virtualunenhanced images with minimal size of1.7mm. There were no significantdifference between two groups both in CT value measurements (Z＝-1.009~-0.113, P=0.307~0.910) and in CNR (Z＝-0.999~-0.309, P＝0.318~0.757). The mean ERD for the experimental group was13.01±1.02mSv, and was lowered for40%compared with control group (Z＝-2.145，P=0.032).Conclusions：The split-bolus sigle-phase dual energy CTU protocol withsynchronous nephrographic-pyelographic phase enhancement may providemore information for diagnosis to those patients with suspect urinary calculi,with the ERD decreasing significantly by omission of the unenhanced scanwithout any influence on image quality.