Dose Exposure and Diagnostic Capability of Split Bolus Computed Tomography Urography (CTU): Comparison with Single Bolus Technique

Objectives: To compare CT urography (CTU) split bolus with standard protocol in terms of urinary tract opacification, parenchymal and vascular enhancement, and radiation dose exposure. To assess split bolus CTU diagnostic capability. Methods: Forty-eight patients (18-83 years) were retrospectively analysed: 24 (study group) performed a split-bolus CTU (combined nephrographic-excretory phase), 24 (control group) a single bolus protocol. On combined and portal venous phases, quantitative analysis of intraluminal opacification and parenchymal-vascular enhancement (HU) was achieved by placing regions of interest (ROI) in urinary tract, liver, spleen, kidneys, abdominal aorta and inferior vena cava. The corresponding mean HU values were compared between 2 groups. Qualitative analysis of urinary intraluminal opacification was performed by two radiologists using a four-point scale; inter-observer agreement was calculated. Radiation dose was calculated as Dose Length Product (DLP) and Computed Tomography Dose Index Volume (CTDIvol). The diagnostic capability was evaluated using a 2-point scale, using histology, imaging follow-up and endoscopy as reference standard. Results: The split-bolus protocol demonstrated lower mean urinary attenuation compared to the control group but no differences in quality of urinary tract opacification or in parenchymal-vascular enhancement. Mean DLP was lower (p = 0.045) in the study group (reduction of 37%). Split-bolus protocol answered the clinical question in 22/24 cases. Conclusions: With a comparable urinary tract opacification, parenchymal organs and vessels enhancement, split-bolus CTU results in a proper accuracy with a dose reduction of 37%, as compared to single-bolus protocols.