Split-Bolus MDCT Urography with Synchronous Nephrographic and Excretory Phase Enhancement

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1 Split-olus MDCT Urography Genitourinary Imaging Original Research Lawrence C. Chow 1,2 Sharon W. Kwan 1 Eric W. Olcott 1,3 Graham Sommer 1 Chow LC, Kwan SW, Olcott EW, Sommer G Keywords: bladder, CT, kidney, ureter, urography DOI: /JR Received June 3, 2005; accepted after revision March 22, Department of Radiology, Stanford University School of Medicine, Stanford, C. 2 Present address: Department of Radiology, Oregon Health and Science University, MC L340, 3181 SW Sam Jackson Park Rd., Portland, OR ddress correspondence to L. C. Chow (chowl@ohsu.edu). 3 Department of Radiology, V Palo lto Health Care System, Palo lto, C. JR 2007; 189: X/07/ merican Roentgen Ray Society Split-olus MDCT Urography with Synchronous Nephrographic and Excretory Phase Enhancement OJECTIVE. Our purpose was to evaluate the utility of CT urography performed using a split contrast bolus that yields synchronous nephrographic and excretory phase enhancement. MTERILS ND 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). n 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. onventional excretory urography C (EU) has for many decades been the standard for the imaging evaluation of the upper urinary tract. In recent years, however, cross-sectional imaging techniques have rapidly supplanted EU for many indications. Currently, the only remaining major application for the venerable EU is in the evaluation of patients with painless hematuria, primarily for the detection of upper urinary tract malignancy. lthough EU remains a good method for imaging the urothelium, it is clearly inferior to cross-sectional imaging techniques such as CT for evaluating the renal parenchyma. The application of CT, however, in the evaluation of the urothelium has been hampered by poor depiction of the renal collecting system and ureters by various factors, including limited longitudinal resolution, poor urinary tract distention, and obscuration of the urothelium by dense excreted contrast material. With current advances in MDCT and careful attention to the specifics of CT protocol design, each of these obstacles is surmountable. Early work in this area has shown that it is possible to combine the benefits of EU with those of cross-sectional imaging into a single CT study termed CT urography, which depicts both the renal parenchyma and the collecting system and ureters [1 5]. Published work in this area has used the capabilities of MDCT scanners to image the 314 JR:189, ugust 2007

2 Split-olus MDCT Urography TLE 1: MDCT Urography Technique Phase Compression Coverage LightSpeed QX/i LightSpeed Ultra Unenhanced abdomen and pelvis None Diaphragm to symphysis pubis 4 x 3.75 mm; 5-mm contiguous recon; pitch, 1.5 (HiSpeed mode) Contrast-enhanced abdomen Inflated Diaphragm to iliac crests 4 x 2.5 mm; 2.5-mm recon; 1.25-mm interval; pitch, 1.5 (HiSpeed) Contrast-enhanced pelvis fter release Iliac crests to symphysis pubis 4 x 2.5 mm; 2.5-mm recon; 1.25-mm interval; pitch, 1.5 (HiSpeed) Note LightSpeed QX/i and LightSpeed Ultra are manufactured by GE Healthcare. recon = reconstruction. abdomen with thin sections before and after contrast administration during corticomedullary, nephrographic, and excretory phases, often resulting in three or four imaging passes during the course of a single examination [2, 3, 5]. Clearly, such methods raise concern for the total radiation dose being imparted to patients and also result in large numbers of axial source images that must be interpreted. The purpose of this study was to evaluate the utility of a split-bolus CT urography technique that depicts the kidneys during synchronous nephrographic and excretory phases, reducing the number of imaging passes required per examination, for the detection of urinary tract malignancy and other potential causes of hematuria. Materials and Methods Study Population The study population consisted of 500 consecutive patients (189 women, 311 men; mean age, 55 years) undergoing MDCT urography during a 36-month period from pril 2000 through March Twenty patients underwent two examinations each, resulting in a total of 520 examinations performed during this period. Three hundred twenty-seven patients were referred for painless hematuria, 33 for known or suspected urinary tract calculi, 32 for hematuria with flank or back pain, 15 for hematuria with dysuria, 22 for evaluation of known renal lesions, 14 for possible urinary tract obstruction, five with pelvic pain, 14 with chronic or recurrent urinary tract infection, 14 with history of prior urinary tract malignancy, and 24 with other miscellaneous indications. lthough referring physicians are urged to use CT urography primarily as a tool for evaluation of painless hematuria, it is not unexpected that requests for the study are made in other clinical settings. This research was performed under an institutional review board approved protocol. 8 x 2.5 mm; 5-mm contiguous recon; pitch, x 1.25 mm; 1.25 mm recon; 0.6-mm interval; pitch, x 1.25 mm; 2.5 mm recon; 1.25-mm interval; pitch, 1.35 Fig. 1 CT urogram in 41-year-old man with microhematuria. No cause for hematuria was identified in this patient. and, Maximum-intensity-projection (MIP) images from normal CT urogram show areas of peristalsis within ureters (arrows, ) resulting in undulating appearance of ureteral contours. bdominal data set () was acquired with abdominal compression in place; pelvic data set () was acquired after release of compression. Small amount of overlap between two acquisitions ensures that there are no gaps in coverage resulting from slight differences in breath-hold. MDCT Urography cquisition Technique ll CT urography was performed on LightSpeed MDCT scanners (4-MDCT LightSpeed QX/i or 8- MDCT LightSpeed Ultra, GE Healthcare) using similar techniques (Table 1). ll patients were asked to drink 900 ml of water while in the waiting area approximately 20 minutes before scanning. IV contrast material (Omnipaque 300 [iohexol], GE Healthcare) was administered with a split-bolus technique as follows: 40 ml was administered at a rate of 2 ml/s after the unenhanced phase. fter a 4-minute delay, an additional 80 ml was administered at 2 ml/s and the abdominal compression device was inflated. The contrast-enhanced, breath-hold abdominal phase images were acquired 120 seconds after the second contrast bolus, yielding images in synchronous nephrographic and excretory phases of enhancement. Subsequently, the compression device was removed, and contrast-enhanced pelvic images were obtained to show the pelvic ureters. small overlap in coverage of the abdominal and pelvic phase images was prescribed to ensure that there were no gaps in coverage resulting from slight changes in the degree of inspiration between the two breath-holds. Digital scout images were obtained before the unenhanced phase and immediately after the contrastenhanced abdomen and pelvis phases. Image Reconstruction In addition to axial images, coronally reformatted maximum-intensity-projection (MIP) and average-intensity-projection images were generated in all cases as follows. Individual thick-slab MIP and average-intensity-projection images of the enhanced right and left kidneys and proximal ureters in a double-oblique plane truly coronal to the kidneys were generated. Enhanced thick-slab MIP and average-intensity-projection images including both kidneys and ureters were generated (Fig. 1). Stacks of sliding thin-slab MIP images (5-mm thick, 2-mm overlap) in a double-oblique plane truly coronal to the kidneys were generated JR:189, ugust

3 from both unenhanced and contrast-enhanced data sets (Fig. 2). Thick slab coronal and sagittal MIP and average-intensity-projection images of the pelvic ureters were generated. dditional reformatting with volume rendering and curved planar reformation was performed on occasion on an as-needed basis but was not performed routinely. ll image reconstructions were generated on an dvantage Workstation (GE Healthcare). C Fig year-old man with new onset of painless hematuria and infundibular transitional cell carcinoma. and, xial () and sagittal () images of right kidney from CT urography show method of prescribing double-oblique plane, coronal to kidney, from which sliding thin-slab maximum-intensity-projection (MIP) images are generated. C and D, Coronal thin-slab MIP images show circumferential mass encasing upper pole infundibulum (arrows). Image Interpretation and Clinical Follow-Up ll images, including axial source images and all reconstructions, were primarily interpreted in soft-copy format on a PCS workstation (Centricity, GE Healthcare) by one of six attending radiologists in the abdominal imaging section with a minimum of 6 years of experience in interpreting abdominal CT. Images were viewed with different window and level settings appropriate for evaluation of the renal parenchyma or for the collecting structures and ureters. The results of MDCT urography were retrospectively compared with the results of other imaging examinations such as cystoscopy; retrograde studies and ureteroscopy; laboratory studies including urine cytology; and, when available, surgery and pathology. In patients who had a negative workup, clinical follow-up was obtained through review of patient medical records to determine whether urinary tract abnormalities D were ultimately diagnosed after the initial workup. The retrospective review of the medical chart was performed in part by all four authors. Mean followup duration was 468 days with a median follow-up duration of 433 days. Sensitivity, specificity, and positive and negative predictive values of MDCT urography were calculated for the detection of pathologically proven urothelial malignancies. Results Urothelial Tumors Nineteen of 27 pathologically proven urothelial tumors of the urinary tract were detected with MDCT urography. Sensitivity and specificity for detection of upper tract urothelial tumors were 100% and 99%, respectively, including the pelvicaliceal system (n = 5) (Figs. 2 and 3) and ureters (n = 3) (Fig. 4). Positive and negative predictive values for upper tract urothelial tumors were 80% and 100%, respectively. Upper tract tumors ranged in size from 3 mm to 2.7 cm, with a mean diameter of 1.7 cm. In no cases were tumors of the pelvicaliceal system or ureters discovered with other studies or during the course of clinical follow-up in the setting of a negative MDCT urogram. Two ureteral tumors were identified on MDCT for which no pathologic confirmation has been obtained: one patient was a poor surgical candidate (a complex aortic dissection was found incidentally during the same study) and the other had a retrograde pyelogram and ureteroscopy that showed a frondlike lesion consistent with hypertrophic inflammatory changes, and thus no biopsy was performed. These lesions were not included in the final calculation of sensitivity and specificity because no pathologic proof was available. MDCT urography resulted in two falsepositive findings for a ureteral tumor. In one case, circumferential wall thickening of the distal left ureter yielded only inflammatory changes on repeated ureteroscopic biopsy (Fig. 5). In the second case, a ureteral filling defect was thought to be a papillary tumor on ureteroscopy, but on biopsy, the tissue was consistent with a scar. The majority of the urothelial tumors were located within the urinary bladder (Fig. 6), and all five false-negative findings were for bladder tumors. In all, there were 19 tumors of the bladder, of which 14 were detected on MDCT urography, with a mean diameter of 2.9 cm and a range of cm. Missed tumors were all less than 5 mm. Of these, 14 were pathologically confirmed transitional cell carcinoma, two were papillomas, and three had unproven pathology but were confirmed on cystoscopy. 316 JR:189, ugust 2007

4 Split-olus MDCT Urography Fig year-old woman with intermittent gross painless hematuria. and, Coronal maximum-intensity-projection (MIP) images of right kidney show soft-tissue mass (open arrows) filling lower pole calyx and infundibulum with extension into renal pelvis (black arrow, ). Patient underwent right nephroureterectomy, which revealed invasive transitional cell carcinoma. Fig. 4 Ureteral transitional cell carcinoma., xial image from CT urography shows irregular lobulated filling defect (arrows) within distal right ureter in 85- year-old man with painless hematuria. Ureteroscopy confirmed finding and patient underwent ureterectomy with reimplantation. Pathology revealed high-grade transitional cell carcinoma with invasion into muscularis propria., Oblique maximum-intensity-projection (MIP) image from CT urography in 72-year-old man with ureteral transitional cell carcinoma shows soft-tissue filling defect within distal left ureter (solid arrows). Contracted segment of ureter from peristalsis (open arrow) is also seen. There was one false-positive for a bladder tumor in which the mass turned out to be an enlarged prostate on cystoscopy. For the urinary bladder, MDCT urography yielded 74% sensitivity, 99.8% specificity, positive predictive value of 93%, and negative predictive value of 99%. Renal Cell Carcinoma Ten of 10 pathologically confirmed renal cell carcinomas (Fig. 7) were identified by MDCT urography, yielding a sensitivity of 100%. The mean size of the neoplasms was 4.6 cm with a range of cm. Seven of these patients Fig year-old man with history of bladder transitional cell carcinoma. Patient had undergone resection and bacille Calmette Guérin (CG) treatment with negative cystoscopy. xial image from CT urography shows circumferential thickening of distal left ureter (open arrows) with periureteric stranding, thought to represent recurrent tumor, and normal right ureter (arrow). Ureteroscopy revealed stricture in this region with no visible tumor. Ureteroscopic biopsy of this region, performed on two separate occasions 2 years apart, revealed only inflammatory changes with no carcinoma. Follow-up imaging over past 4 years has shown no significant change in appearance of this stricture. Fig year-old man with painless hematuria. xial image from CT urography shows pedunculated mass (white arrow) with narrow, stalklike attachment (open arrow) arising from bladder trigone near left ureteral orifice. Transurethral resection revealed high-grade papillary transitional cell carcinoma. Small filling defect (black arrow) medial to right ureteral orifice represents normal interureteric ridge and should not be mistaken for tumor. lthough bladder tumors can be seen with CT urography, its sensitivity remains low and it should not be substituted for cystoscopy. were ultimately staged at T1 N0 M0, two at T2 N0 M0, and one at T3a N0 M0. One of these patients had undergone sonography only 16 days earlier, which showed normal kidneys. Two patients underwent intraoperative laparoscopic sonography that confirmed the presence of a re- JR:189, ugust

5 Fig year-old man with one episode of gross, painless hematuria and right renal cell carcinoma., Coronal thick-slab maximum-intensity-projection (MIP) image from CT urography performed on 4-MDCT scanner, which simulates conventional excretory urography, shows no abnormality because of small size of mass, which does not deform lateral renal contour or renal collecting system., Sagittal image from CT urography clearly shows mass (arrows) involving anterior upper pole. nal tumor. In one patient, pathologically confirmed synchronous renal cell and transitional cell carcinomas were identified. Eight additional small solid renal masses (all < 1 cm) with radiologic appearances consistent with renal cell carcinoma were identified on MDCT urography in six patients (two had bilateral lesions). No pathologic proof has been obtained for these cases because the patients were either poor surgical candidates or opted for conservative management. The presence of one small renal lesion worrisome for malignancy on MDCT urography could not be confirmed with additional imaging workup. In this patient with underlying polycystic kidney disease, a 12-mm exophytic renal lesion appeared to enhance by 25 H. Neither transabdominal nor intraoperative sonography showed a solid renal mass. Urolithiasis Renal calculi were identified in a total of 95 patients on MDCT urography. lthough the majority of stones were small, measuring less than a centimeter in maximal diameter, three patients had a staghorn calculus. In 33 patients, stones were identified within the ureters or renal pelves. Four stones were in the renal pelvis, two in the proximal ureter, eight in the mid ureter, and 19 in the distal ureter or at the ureterovesical junction. In two patients, stones were present within partially duplicated ureters. Interestingly, both were seen at the junction of the duplicated proximal ureters where they coalesced into a single distal ureter. Four stones were found in the bladder. Five patients had medullary nephrocalcinosis (Fig. 8). ll of these stones were identified on the unenhanced CT images. No false-negative CT urograms were identified in which a stone was detected either clinically or by other imaging techniques after a negative CT urogram was obtained. Congenital nomalies MDCT urography showed congenital anomalies in 15 patients. Duplication of the right collecting system was seen in five patients (Fig. 9), the left collecting system in seven patients, and bilateral duplication in two patients. Two patients had a horseshoe kidney, one of which was associated with bilateral hydronephrosis. Fig year-old man with flank pain. Curved planar reformation image through left kidney and ureter from unenhanced scan shows medullary nephrocalcinosis, multiple calculi, within distal left ureter (solid arrow); ureteral thickening; and extensive periureteric stranding (open arrows). Hydronephrosis and Hydroureter Thirty patients were identified with hydronephrosis; 23 were unilateral and seven were bilateral. Fourteen of these 30 patients had concomitant ureterectasis. Seven cases of ureterectasis without hydronephrosis were found; five were unilateral and two were bilateral. Causes for hydronephrosis or hydroureter included stones (n = 18), transitional cell carcinoma (n = 3), horseshoe kidney (n = 1), postsurgical (n = 5), postinflammatory (n = 1), prostatic hypertrophy (n = 1), and idiopathic (n =8). Miscellaneous One patient was found to have papillary necrosis resulting from sickle cell disease (Fig. 10). Renal tubular ectasia (Fig. 11) was identified in four patients. Pathologic Findings in Other Systems Other clinically significant findings outside of the urinary tract included a complex aortic dissection, extensive deep vein thromboses, a porcelain gallbladder, Crohn s 318 JR:189, ugust 2007

6 Split-olus MDCT Urography Fig year-old woman with microscopic hematuria. and, Coronal maximum-intensity-projection (MIP) image of abdomen () and coronal oblique MIP image of pelvis () from CT urography show complete duplication of right renal collecting system with completely separate upper pole (black arrows) and lower pole (white arrows) ureters all way to level of bladder, both with orthotopic bladder insertion. Urologic workup, including cystoscopy, was otherwise completely normal, and cause for hematuria was not identified. Fig year-old woman with intermittent gross hematuria for 5 days. and, Maximum-intensity-projection (MIP) images from CT urography show pooling of contrast material within multiple papillae bilaterally (open arrows) consistent with papillary necrosis. Filling defect within left renal pelvis (solid arrow, ) was shown to represent blood clot at ureteroscopy. Patient was later found to have sickle cell trait. disease with fistula formation, and intraductal papillary mucinous tumor of the pancreas (found in two patients). Two patients were identified as having severe degenerative disk disease, which was ultimately determined to be responsible for their symptoms of lower back pain and pelvic pain, respectively. Other important findings included cholelithiasis (n = 21), diverticulosis (n = 18), appendicolith (n = 3), ovarian mucinous cystadenoma (n = 1), and ruptured breast implant (n =1). Discussion It has been previously shown that CT urography allows detection of urinary tract calculi and renal parenchyma and urothelial lesions in a single, noninvasive examination [1, 3, 5]. Typical protocols require multiple image acquisitions to obtain the unenhanced, contrast-enhanced nephrographic, and contrast-enhanced excretory phase images. The unenhanced images show urinary tract calculi with very high sensitivity and specificity [6 9]. Contrast-enhanced images acquired in the nephrographic phase are useful for identification of lesions within the renal parenchyma. Used in conjunction with unenhanced images, the presence or absence of enhancement is also useful in distinguishing neoplasms from other processes. Finally, contrast-enhanced images in the excretory phase are used to evaluate for urothelial lesions. This portion of the examination requires high spatial resolution to detect small urothelial tumors with high sensitivity. In the past, the limited longitudinal spatial resolution of CT compared with excretory urography precluded some centers from completely replacing excretory urography with CT urography [10]. This problem has been overcome with the advent of MDCT, which makes possible rapid acquisition of isotropic data sets and production of multiplanar reconstructions with excellent spatial resolution in the nontransverse plane. The proliferation of MDCT examinations has raised concern about radiation exposure. This is of particular relevance with CT urography in which repeated acquisitions may be performed. The average effective radiation dose from CT urography has been estimated to be in the range of msv, with actual values depending on the specific protocol used [11, 12]. Other previously reported CT urography techniques require multiple contrast-enhanced acquisitions, resulting in a minimum of three imaging passes through the abdomen [2 5, 12, 13]. Our technique reduces the total radiation dose by eliminating one or more imaging passes. y administering IV contrast material in two boluses separated by a suitable time delay, nephrographic and excretory phases are acquired in a single imaging pass. With all other scanning parameters held constant, this technique clearly reduces the effective radiation dose when compared with MDCT urography protocols using a single contrast bolus. The majority of our patients underwent CT urography as part of the workup for hema- JR:189, ugust

7 Fig. 11 Coronal maximum-intensity-projection (MIP) image from CT urography of 51-year-old woman with microscopic hematuria and interstitial cystitis. Medullary pyramids show striated, paint-brush appearance of renal tubular ectasia. turia. In many medical centers, a combination of EU and unenhanced and contrast-enhanced abdominopelvic CT is used in the assessment of such patients. The split-bolus protocol requires only two full imaging passes through the abdomen and pelvis and thus exposes patients to a similar amount of radiation as a standard unenhanced and contrast-enhanced abdominopelvic CT. y eliminating the additional radiation exposure from EU, the split-bolus CT urography protocol could theoretically result in a radiation dose reduction compared with a workup performed with a combination of EU and CT. nother often-cited issue with MDCT is the large number of images produced. n added advantage of the split-bolus protocol is that fewer images for interpretation are generated because one acquisition sequence is eliminated. On the other hand, reducing redundancy in the contrast-enhanced nephrographic and excretory phases may reduce the likelihood of visualization of the entire collecting system. Segments of the ureter that may be unopacified or in peristalsis during the contrast-enhanced acquisition will not have another chance to be captured during a second imaging pass. Our CT urography protocol incorporates the use of digital scout images obtained immediately after the contrast-enhanced abdomen and pelvis phases, to augment the likelihood of visualizing the entirety of the ureters [14], with only a minimal incremental increase in radiation dose, which is far less than an additional CT pass would incur. One of the greatest challenges of MDCT urography remains obtaining images with good distention and opacification of the renal collecting systems and ureters. Proposed techniques for optimizing urinary tract distention include the use of prone imaging, abdominal compression, and either IV or oral hydration [1 5, 13, 15]. Prone imaging has shown little or no advantage over the other techniques [2 4]. We have opted to use abdominal compression in all patients for whom compression is not contraindicated because of its acknowledged benefits when used in conjunction with conventional EU. Some controversy has arisen as to the necessity for abdominal compression with CT urography, with a recent study suggesting that compression does not improve urinary tract visualization [13]. In addition to compression, all patients in this study were hydrated with oral water before scanning to aid urinary tract distention and lower the density of intraluminal contrast material. prospective comparison of IV versus oral hydration techniques in 40 patients undergoing compression MDCT urography revealed no statistically significant difference in intraluminal density, streak artifact from luminal contrast material, or urinary tract distention or opacification [15]. Finally, the scanning delay time for excretory phase imaging must be considered for optimal urinary tract visualization. Caoili et al. [13] showed an advantage to excretory phase imaging at 450 seconds versus 300 seconds. This would support excretory phase imaging performed with an effective delay time of 420 seconds for the kidneys and upper ureters and 450 seconds for the pelvic ureters with the split-bolus protocol used in this study. Since this study was conducted, we have adjusted our technique to 80 ml for the first bolus and 60 ml for the second bolus, with an interbolus delay of 6 minutes, with the objective of improving opacification, but further investigation is required to determine the optimal allocation of contrast dose between the first and second boluses and the optimal delay between boluses. Limited data exist on the sensitivity of MDCT urography for detecting urothelial lesions. In a retrospective review of patients with surgically proven transitional cell carcinoma of the upper urinary tract, preoperative MDCT detected 88% (15/17) of renal collecting system tumors and 94% (14/15) of ureteral tumors [16]. In a series of 106 patients with hematuria, unexplained hydronephrosis, or both, Cowan and McCarthy [17] showed MDCT urography to be superior to retrograde ureteropyelography, conventional EU, and sonography in the detection of urothelial abnormality. In a retrospective study of 65 patients by Caoili et al. [5], MDCT urography found 15 of 16 foci of transitional cell carcinoma, with the one missed lesion occurring at the base of the bladder. much lower incidence of urothelial carcinoma was found in our patient population, with 24 pathologically proven cases in a series of 500 patients. In the detection of upper urinary tract urothelial neoplasms, our study showed 100% sensitivity, confirming the value of this technique for the detection of upper urinary tract neoplasms. The marked difference in incidence of urothelial neoplasms between these two studies most likely results from the difference in patient populations. Whereas the study by Caoili et al. included only patients at high risk for urinary tract disease (42 of 65 patients [65%] with a prior history of urothelial neoplasm), our study evaluated a screening population, with only 2.8% (14/500) with a prior history of urothelial neoplasm. There were two false-positive studies in this series for upper urinary tract urothelial tumors. In one case, repeated ureteroscopic biopsy of circumferential urothelial thickening revealed only inflammatory changes. Interestingly, in the other case, direct visualization with ureteroscopy also yielded a false-positive result with visualization of a papillary ureteral filling defect that was initially detected by MDCT urography and thought to be neoplastic by both studies. lthough these two cases were considered examples of falsepositive findings for tumor, true morphologic abnormalities did exist in both. Our CT urography protocol was 74% sensitive in the detection of bladder tumors. lthough CT has been shown to detect bladder lesions with sensitivities up to 90 95% using specialized virtual cystography and reconstruction techniques [18, 19], our protocol was not similarly optimized for visualizing the bladder because cystoscopy is routinely performed on patients with hematuria at our institution. Small tumors at the ureteral orifices were missed, possibly due to the normal protrusion that is often seen in that region. Mixing artifacts within the bladder can also result in false-positive and false-negative interpreta- 320 JR:189, ugust 2007

8 Split-olus MDCT Urography tions. Despite the improvements in CT spatial resolution, the use of an anatomic imaging approach will not provide the ability to identify the presence of flat bladder tumors such as carcinoma in situ. Conventional cystoscopy still remains the gold standard for evaluation of the bladder urothelium, and patients with hematuria should ideally undergo both CT urography and conventional cystoscopy. The split-bolus protocol also accurately detected all instances of renal cell carcinoma, suggesting that synchronous acquisition of nephrographic and excretory phases does not compromise the ability to visualize the renal parenchyma. One caution regarding this imaging protocol is that early phase contrast-enhanced images, such as during the arterial or corticomedullary phase, are not obtained. Thus, this protocol may be suboptimal for the accurate staging of tumors once they are detected, and such patients may require an additional study for staging. Given the low incidence of malignancy in our series, however, we believe that the benefit of reduced radiation dose to most patients who had no malignancy outweighs the inconvenience of possible reimaging to the few patients with malignancy. We have found that it remains imperative that the axial source images are viewed and interpreted and that appropriate tailored window and level settings be used when evaluating the collecting system and ureters so that dense intraluminal contrast material does not obscure fine urothelial detail and, potentially, small urothelial lesions. In addition to axial images, certain simple reconstructions can be of great benefit. In particular, simple sliding thin-slab (3 mm) and thick-slab (35 50 mm) MIP or average-projection images of each kidney in a doubleoblique plane to the patient but truly coronal to the kidney in question provide the most intuitive display of the data. lthough the MIP algorithm emphasizes the densely enhanced collecting system, the nature of the MIP algorithm may result in obscuration of lesions lower in attenuation than surrounding high-attenuation structures. This is particularly true for small lesions such as small urothelial tumors and is exacerbated by the increasing thickness of the MIP slab. Thus, one must be cautioned to not interpret the MIP images, particularly the thick-slab MIPs, in isolation. Despite this limitation, the utility of these images lies in the ability to quickly convey overall anatomic features in an intuitive fashion. Thus, the images are useful for communicating information to busy clinicians who may not be inclined to scroll through all of the axial source images. Our referring clinicians and urologists have found these images to be most helpful in clarifying anatomic relationships in the setting of renal masses and visualizing the extent of diffuse renal processes such as medullary nephrocalcinosis, acute or chronic pyelonephritis, papillary necrosis, or renal tubular ectasia. Such images may be particularly helpful to the urologist who is planning nephron-sparing surgery. These images can also be helpful in the detection of small or subtle lesions. In our series, one tiny (3 mm) renal pelvic transitional cell carcinoma was initially missed on the axial images but detected on the coronal oblique reconstructed thin-section images. lthough this study includes the largest patient series for CT urography reported in the literature at the time of writing, the low incidence of urothelial tumors limits our ability to assess the effectiveness of this technique in detecting urothelial neoplasms. larger multicenter study will likely be necessary to fully evaluate CT urography for this capacity. Furthermore, this study did not directly compare the split-bolus protocol with other CT urography protocols or with EU. nother weakness of this study was that primary interpretations of the CT urography studies were reviewed and a blinded reinterpretation of the studies was not performed. Finally, not all patients received confirmatory studies and, indeed, often the CT urography results were used to guide subsequent evaluation. The relatively long average clinical follow-up duration (468 days) for patients with negative CT urography results should help to mitigate the lack of a pathologic gold standard in many cases; however, sensitivity and specificity calculations should be used with caution in light of this bias. In summary, we have shown that a split-bolus protocol for CT urography can be used successfully to evaluate for urinary tract calculi, renal abnormalities, and urothelial lesions in one simple, noninvasive examination. lthough this study did not include a direct comparison between this technique and other MCDT urography protocols, our data suggest that the sensitivities and specificities in detecting a variety of abnormalities are comparable to other protocols. Perhaps more important, the strong negative predictive values provided by this CT urography protocol suggest that a urinary tract malignancy is highly unlikely in the setting of a negative CT urogram. The split-bolus protocol reduces radiation dose to patients and results in a smaller number of images for interpretation compared with other MDCT urography protocols. When compared with hybrid CT and EU strategies for the evaluation of hematuria, split-bolus CT urography provides equivalent if not superior visualization of the upper urinary tracts, reduced radiation exposure, and added logistic convenience. Given the significant advantages of this protocol, we believe that it has potential as an alternative to existing MDCT urography protocols and EU for the evaluation of the urinary tract. References 1. Chow LC, Sommer FG. Multidetector CT urography with abdominal compression and three-dimensional reconstruction. JR 2001; 177: Heneghan JP, Kim DH, Leder R, DeLong D, Nelson RC. Compression CT urography: a comparison with IVU in the opacification of the collecting system and ureters. J Comput ssist Tomogr 2001; 25: McTavish JD, Jinzaki M, Zou KH, Nawfel RD, Silverman SC. 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9 FOR YOUR INFORMTION tidetector computed tomography urography. Semin Urol Oncol 2002; 20: Nawfel RD, Judy PF, Schleipman R, Silverman SG. Patient radiation dose at CT urography and conventional urography. Radiology 2004; 232: Caoili EM, Inampudi P, Cohan RH, Ellis JH. Optimization of multi-detector row CT urography: effect of compression, saline administration, and prolongation of acquisition delay. Radiology 2005; 235: Chow LC, Sommer FG. Multidetector CT urography with abdominal compression and reconstruction by sliding thin-slab maximum intensity projection. (abstr) Radiology 2001; 221(P): Saket R, Chow LC, Schraedley-Desmond P, Sommer FG. Optimizing split-bolus CT urography: a comparison of protocols employing pharmacologic diuresis vs. abdominal compression. (abstr) Proceedings of the Society of Uroradiology. Scottsdale, Z: Society of Uroradiology, 2004: Casalino, D, William LW, Williams DH, Lang C, Vi H, Miller FH. MDCT detection of upper urinary tract transitional cell carcinoma. (abstr) Proceedings of the Soceity of Uroradiology, Scottsdale, Z: Society of Uroradiology, 2004: Cowan N, McCarthy C. Multidetector CT urography for urothelial imaging. (abstr) Proceedings of the Society of Uroradiology. Cancun, Mexico: Society of Uroradiology, 2003: Yazgan C, Fitoz S, tasoy C, Turkolmez K, Yagci C, kyar S. Virtual cystoscopy in the evaluation of bladder tumors. Clin Imaging 2004; 28: Song JH, Francis IR, Platt JF, et al. ladder tumor detection at virtual cystoscopy. Radiology 2001; 218: Unique new customized medical search engine service from RRS! RRS GoldMiner is a new keyword- and concept-driven search engine that provides instant access to radiologic images published in peer-reviewed journals. For more information, visit JR:189, ugust 2007