Date Published: April 6, 2017
Publisher: Public Library of Science
Author(s): Hiroshi Juri, Takahiro Tsuboyama, Mitsuhiro Koyama, Kiyohito Yamamoto, Go Nakai, Atsushi Nakamoto, Kazuhiro Yamamoto, Haruhito Azuma, Yoshifumi Narumi, Gayle E. Woloschak.
To prospectively evaluate the ability of CT urography with a low-dose multi-phasic excretory phase for opacification of the urinary system.
Thirty-two patients underwent CT urography with low-dose multi-phasic s using adaptive iterative dose reduction 3D acquired at 5-, 10-, and 15-minute delays. Opacification scores of the upper urinary tracts and the urinary bladder were assigned for each excretory phase by two radiologists, who recorded whether adequate (>75%) or complete (100%) opacification of the upper urinary tract and urinary bladder was achieved in each patient. Adequate and complete opacification rates of the upper urinary tracts and the urinary bladder were compared among three excretory phases and among combined multi-phasic excretory phases using Cochran’s Q test.
There was no significant difference among three excretory phases with 5-, 10-, and 15-minute delays in adequate (56.3, 43.8, and 63.5%, respectively; P = 0.174) and complete opacification rates (9.3, 15.6, and 18.7%, respectively; P = 0.417) of the upper urinary tracts. Combined tri-phasic excretory phases significantly improved adequate and complete opacification rates to 84.4% and 43.8%, respectively (P = 0.002). In contrast, there were significant differences among three excretory phases for the rate of adequate (31.3, 84.4, and 93.8%, respectively; P<0.001) and complete opacification (21.9, 53.1, and 81.3%, respectively; P<0.001) of the urinary bladder. Multi-phasic excretory phases did not improve these rates because opacification was always better with a longer delay. Although multi-phasic acquisition of excretory phases is effective at improving opacification of the upper urinary tracts, complete opacification is difficult even with tri-phasic acquisition.
CT urography (CTU) is an excellent technique for the evaluation of calculi and masses in the urinary system [1–4]. Moreover, according to the guideline of European Society of Urogenital Radiology (ESUR), CTU is recommended as the first-line test for patients at high risk of urothelial carcinoma , and for these patients, a three-phase CTU protocol with single-bolus contrast material injection consisting of unenhanced, urothelial, and excretory phases is commonly used . The primary goal of the excretory phase (EP) in CTU is complete opacification of the entire urinary system, but incomplete opacification of the urinary system on the EP has been a problem with CTU due to the characteristic points of narrowing and peristalsis. Researchers have suggested several techniques to improve opacification of the upper urinary tracts [6–11], including longer delay for the EP, acquisition of bi-phasic EPs, oral hydration, intravenous diuretic, and abdominal compression. A log-rolling procedure prior to the EP scans was suggested to increase the percentage of bladder opacification . These previous studies assessed the opacification of each segment of the urinary systems separately. Therefore, the ability of CTU to achieve complete opacification of the entire urinary system of patients has not been clearly described, and optimal delay for opacification of the urinary system has not yet been standardized.
Our institutional review board (Full name: Ethnics Committee of Osaka Medical College) approved this prospective study. The individual in this manuscript has given written informed consent to publish these case details.
Our results demonstrated that longer delay time for EP showed a trend for a higher rate of complete opacification of the upper urinary tracts, and tri-phasic EPs significantly increased the rate of complete opacification. However, complete opacification of the upper urinary tracts was achieved in less than half of the patients even with tri-phasic EPs. Although previous studies have reported complete opacification rates of 37 to 95% for each segment of the upper urinary tract [8, 16], the numbers of patients with entirely opacified upper urinary tracts on CTU have not been reported. Moreover, complete opacification has been defined differently among the prior reports, with Meindle et al.  considering more than 75% opacification to be complete, whereas Hack et al.  defined complete opacification as 100% opacification. Therefore, we defined complete and adequate opacification as 100% and more than 75% opacification, respectively. To the best of our knowledge, this is the first report to precisely identify the complete opacification rate of the upper urinary tract by CTU.