Evaluation of virtual unenhanced CT obtained from dual-energy CT urography for detecting urinary stones

Abstract

Objective: The aim of our study was to determine if virtual unenhanced CT (VUCT) is equivalent to unenhanced CT (UCT) for detecting urinary stones. Methods: Our institutional review board approved this retrospective study, which was compliant with the Health Insurance Portability and Accountability Act. A total of 80 stones were detected in 32 patients among 146 consecutive patients undergoing dualenergy CT urography. The number and size of stones were recorded on nephrographic VUCT (NVUCT) and excretory VUCT (EVUCT) images, respectively. UCT was a reference of standard for the number and size of stones. Image quality of VUCT was qualitatively assessed using a five-point scale. Repeated-measures analysis of variance with post-test was used for statistical analysis. Results: 62 stones in 29 patients were detected on NVUCT and 59 stones in 27 patients were detected on EVUCT. The size of stones detected on NVUCT or EVUCT was significantly smaller compared with stones on UCT (p,0.05). The size of stones detected on UCT, NVUCT and EVUCT ranged from 1.4 to 19.2 mm (mean, 4.6 mm), 0 to 19.2 mm (mean, 3.6 mm) and 0 to 18.7 mm (mean, 3.6 mm), respectively. 18 stones were missed on NVUCT and 21 were missed on EVUCT. The sizes ranged from 1.4 to 3.2 mm (mean, 2.1 mm) and 1.4 to 3.2 mm (mean, 2.2 mm) on UCT, respectively. VUCT was inferior to UCT regarding image quality (p,0.05). Conclusion: VUCT missed a significant number of small stones probably owing to poor image quality compared with UCT. Subsequently, VUCT cannot replace UCT for detecting urinary stones. Urolithiasis is a common cause of haematuria. Unenhanced CT (UCT) is considered a gold standard for diagnosing this disease entity because it is more sensitive to detecting urinary stones than simple radiography and ultrasound [1][2][3]. Therefore, UCT is an essential CT protocol that should be included for CT urography. Dual-energy CT (DECT) imaging can reconstruct virtual unenhanced CT (VUCT) images from contrastenhanced CT images. As VUCT is equivalent to UCT in characterising renal masses, radiation dose to patients can be reduced during CT scans using dual-energy sources [4,5]. DECT is also useful in evaluating composition of urinary stones, uric acid stones can be differentiated from calcified stones [6][7][8][9][10]. However, there are few in vitro or in vivo reports about the validity of VUCT in detecting urinary stones [11][12][13]. Still, it is unclear whether or not VUCT can be an alternative imaging to UCT for diagnosing urolithiasis.The purpose of our study was to determine whether or not VUCT is equivalent to UCT in detecting urinary stones. Methods and materialsThis retrospective study was approved by our institutional review board and informed consent was waived. PatientsBetween September 2009 and March 2010, a total of 146 patients (male-to-female ratio, 73:73; age range, 23-87 years; mean age 56 years) underwent CT urography due to one of the following chief complaints: microscopic haematuria (n560), gross haematuria (n525), flank discomfort (n546) ...

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