IMAGING

Split-bolus MDCT urography with synchronous nephrographic and excretory phase enhancement
Chow LC, Kwan SW, Olcott EW, Sommer G
Department of Radiology, Stanford University School of Medicine, Stanford, CA, USA
AJR Am J Roentgenol. 2007; 189: 314-22

• Objective: Our purpose was to evaluate the utility of CT urography performed using a split contrast bolus that yields synchronous nephrographic and excretory phase enhancement.
• Materials and Methods: Five hundred consecutive patients referred for evaluation of possible urinary tract abnormalities (327 for painless hematuria) underwent CT urography with unenhanced scanning of the abdomen and pelvis and scanning during concurrent nephrographic and excretory phase enhancement produced by administration of a split contrast bolus. The enhanced abdomen scan was obtained with abdominal compression; the enhanced pelvis scan was obtained after release of compression. Findings from axial sections and coronal maximum intensity projections were correlated with clinical follow-up and, as available, with laboratory and other imaging studies including cystoscopy, ureteroscopy, urine cytology, surgery, and pathology. Follow-up management for each patient was determined by the clinical judgment of the referring physician.
• Results: CT urography identified 100% of pathologically confirmed renal cell carcinomas (n = 10) and uroepithelial malignancies involving the renal collecting system or ureter (n = 8). An additional nine renal masses were identified for which no pathologic proof has yet been obtained, including eight subcentimeter solid renal masses and one multiloculated lesion. Fourteen of 19 confirmed cases of uroepithelial neoplasm involving the bladder were identified. CT urography yielded one false-positive for bladder tumor, two false-positives for ureteral tumor, and one patient with a bladder mass who refused further evaluation. CT urography yielded sensitivity and specificity of 100% and 99% and 74% and 99% and positive predictive value and negative predictive value of 80% and 100% and 93% and 99% for the renal collecting system and ureter and bladder, respectively. CT urography was ineffective in identifying 11 cases of noninfectious cystitis. CT urography also depicted numerous other congenital and acquired abnormalities of the urinary tract.
• Conclusion: Split-bolus MDCT urography detected all proven cases of tumors of the upper urinary tract, yielding high sensitivity and specificity. The split-bolus technique has the potential to reduce both radiation dose and the number of images generated by MDCT urography.
  
  
• Editorial Comment
  Multidetector CT-urography (MDCT-urography) has been shown to be an effective single comprehensive examination in the evaluation of patients with hematuria or with risk for the development of urothelial malignancies. Since protocols for MDCT urography varies from each institution, most MDCT urography images are obtained in the unenhanced phase (detection of calculi), nephrographic-phase (detection of renal masses) and excretory-phase (detection of urothelial lesions). The authors present their results with a new protocol called split-bolus MDCT urography where the unenhanced phase is followed only by a combined nephrographic and excretory phase. During split-bolus, CT-urography the intravenous injection of contrast material is performed in two steps. First, 40 ml is injected at 2 ml/s and after 120 second from the beginning of the first injection, the remaining 80 ml is injected. This technique showed high sensitivity and specificity, for the detection of all proven cases of tumors of the upper urinary tract. The main objective with MDCT-urography is to detect all possible causes of hematuria while using the lowest possible radiation dose to the patient. As shown by the authors the split-bolus technique has the potential to reduce both radiation dose and the number of images generated by MDCT urography. In our opinion this protocol is ideal for patients submitted to previous cystoscopy since we might miss some small tumors within a fully distended and opacified bladder .As we have discussed previously in this journal (volume 33, number 3, pages 435-436), we consider “the bladder-wall phase” (scans at 60 or 70 seconds after intravenous injection of the total amount of contrast), essential for the detection of small bladder tumors. However, this “bladder phase wall” has the drawback of significant increase in the effective radiation dose to the patient (18 to 25 mGy).

Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging
Vera Cruz Hospital
Campinas, São Paulo, Brazil