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Multislice CT urography: state of the art

¹ Department of Radiology, University of Michigan, Ann Arbor, Michigan, USA and Department of Radiology, The Churchill Hospital, Oxford, UK

Correspondence: Richard H Cohan, MD, Department of Radiology, Room B1D502G, University of Michigan Hospital, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0030, USA

	Abstract

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Recent improvements in helical CT hardware and software have provided imagers with the tools to obtain an increasingly large number of very thin axial images. As a result, a number of new applications for multislice CT have recently been developed, one of which is CT urography. The motivation for performing CT urography is the desire to create a single imaging test that can completely assess the kidneys and urinary tract for urolithiasis, renal masses and mucosal abnormalities of the renal collecting system, ureters and bladder. Although the preferred technique for performing multislice CT urography has not yet been determined and results are preliminary, early indications suggest that this examination can detect even subtle benign and malignant urothelial abnormalities and that it has the potential to completely replace excretory urography within the next several years. An important limitation of multislice CT urography is increased patient radiation exposure encountered when some of the more thorough recommended techniques are utilized.

	Introduction

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Patients with suspected urinary tract disease are often referred for multiple studies such as excretory urography (EU), ultrasound (US), CT or MRI. Multi-examination work-ups require much patient effort and are expensive. A single imaging test that comprehensively evaluates the urinary tract has advantages both in terms of convenience and cost.

CT is already widely acknowledged to be superior to EU and US in its ability to detect and characterize renal masses [1, 2]. Recently, its superiority in detecting urolithiasis compared with EU, US and MRI (which cannot directly image calcification) has also been accepted [3, 4]. The last remaining potential limitation of CT for examination of the urinary tract is its perceived limited accuracy in assessment of the mucosal surfaces of the renal collecting systems and ureters.

With the recent development of multislice helical CT, it has become possible to obtain a large number of very thin-section axial CT images through the entire renal collecting systems, ureters and bladder in a very short period of time. This allows for more detailed evaluation of the urothelium. As a result, many institutions have started to evaluate the use of CT as a partial or complete replacement to EU.

This article reviews recent developments in the use of multislice CT for complete evaluation of the urinary tract. Several different techniques will be discussed. Preliminary results will be presented suggesting that renal collecting system and ureteral abnormalities can be detected with high sensitivity. Potential interpretive and technical problems will be addressed. Multislice CT urography (MSCTU) exposes patients to increased radiation: estimates for the radiation dose will be provided. Finally, preliminary reported data addressing the cost effectiveness of substituting MSCTU for EU will be presented.

	CT urographic techniques

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Any comprehensive radiographic evaluation of the urinary tract (whether using CT, EU or a combination of the two) requires preliminary pre-contrast images to visualize calculi, followed by post-contrast injection imaging in the nephrographic phase to evaluate the renal parenchyma. Subsequent assessment of the lumina of the urinary tract is then obtained after its opacification by excreted contrast-laden urine.

With these requirements in mind, recent approaches to the performance of CT urography (CTU) can be divided into two major groups: (1) hybrid CTU–EU in which CT images are combined with conventional radiographs obtained before and/or after axial image acquisition; and (2) pure CTU, in which imaging is performed entirely with CT scanning equipment.

Combination or hybrid CTU–EU
Several approaches have been considered for performing hybrid studies. In one early report [5], a CT scan was performed within 2 h of completion of an excretory urogram, utilizing only the intravenous contrast material that had been injected for the urogram. As an alternative method, CT can be performed prior to conventional radiography. Utilizing this technique, unenhanced CT is performed first for detection of renal and ureteral calculi. Subsequently, standard contrast-enhanced abdominal CT is performed to evaluate the kidneys and other abdominal organs for masses. The patient is then moved to a conventional radiography room for additional abdominal radiographs to assess the renal collecting systems, ureters and bladder, as would be obtained with conventional EU.

No matter which approach is utilized, timing of CT and conventional radiography for hybrid studies can be a problem. If CT is performed following a complete urogram, the nephrograms will have faded dramatically, potentially reducing the accuracy of CT in detecting and characterizing renal masses. Furthermore, use of plain radiography rather than unenhanced CT to assess patients for urolithiasis is problematic because CT is much more sensitive than conventional radiography for detecting calculi. Conversely, if the conventional films follow CT, the phase of optimal collecting system and ureteral opacification may have passed. Obviously, if good quality hybrid studies are to be performed, a radiography room must be readily and conveniently available near a CT scanner, and the patient must have one modality performed within a few minutes of the other.

As a response to this timing difficulty, one institution has installed X-ray equipment in a CT scanning room [6]. This solution will likely not be widely adopted because such CT room modification is expensive and use of the installed radiography equipment is restricted almost entirely to those patients who are referred for CTU. There is a significant cost of slowing down patient throughput in a modified CT room while plain abdominal radiographs are obtained, processed and assessed for adequacy. Also, since CTU represents only a fraction of CT examinations, the radiography equipment will likely be underutilized.

Performing CTU exclusively on a CT scanner: using the scan projection radiograph
Many investigators [7–13] have chosen to evaluate patients exclusively on the CT scanner by obtaining digital scout or scan projection radiographs in lieu of conventional radiographs. These can be obtained preliminarily to detect radiopaque calculi or, as an alternative, unenhanced axial CT images can be obtained. Intravenous contrast material is then injected. Axial image acquisition is then performed during the nephrographic phase of renal enhancement to assess any renal parenchymal masses. Following this, additional scan projection radiographs are obtained during the excretory phase so that the renal collecting systems and ureters can be evaluated.

This technique offers the advantage of requiring only CT scanning equipment rather than both standard X-ray machinery and a CT scanner. A significant limitation is the inferior resolution of scan projection radiographs compared with conventional radiographs. In response to this, software has been developed that reconstructs the scan projection radiographs so that they more closely resemble plain radiographs. Studies assessing whether unenhanced or enhanced scan projection radiographs can approach conventional film–screen radiographs in their accuracy for detecting renal collecting system and ureteral pathology are ongoing. In one recent report, the image quality of the enhanced scan projection radiographs was found to be superior to standard scan projection radiographs, although conventional radiography was still superior in detecting urolithiasis [14]. Another study found that even standard scan projection radiographs were as capable of detecting urothelial abnormalities (not limited to calculi) as conventional radiography [15]. However, it must be emphasized that the latter study [15] included only a small number (60) of patients, and only a few of these had any pathology.

Multislice CTU
Many investigators have decided to perform CTU in a manner that relies entirely on axial image acquisition. Although the specifics vary, all of these approaches rely on the same principle: their protocols include a large series of very thin-section (2.5 mm thickness or less) axial images obtained through the kidneys, ureters and bladder after renal excretion has begun. This thin-section excretory phase series is used to evaluate the urinary tract in detail and replaces conventional radiographic images or post-injection scan projection radiographs. At many institutions, the excretory phase images are reconstructed at overlapping intervals (usually 50% or 1.25 mm or less), with the reconstructed images serving as the source of coronal and/or sagittal reformatting or three-dimensional images (usually obtained in the coronal and/or oblique planes).

	Multislice CTU: variations in number of series and acquisition timing

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
At most institutions, CTU relying entirely on axial image acquisition (henceforth referred to as multislice CT urography (MSCTU)) utilizes several independent series of images. Most investigators begin with an initial "renal stone" CT, consisting of 3–5 mm thick images from the upper poles of the kidneys to the symphysis. These unenhanced scans are utilized to detect urinary tract calculi, as well as to assist in the characterization of any detected renal masses. Following contrast material administration (usually consisting of 100–150 ml of a 300 mg I ml^–1 concentration of non-ionic contrast material infused at a rate of 2–4 ml s^–1), enhanced images are then usually obtained through the kidneys (using 2.5–5 mm slice thickness) during the nephrographic phase of renal enhancement (beginning at least 100 s following the initiation of contrast material injection) to optimize sensitivity in detecting and accuracy in characterizing renal masses. Finally, after another delay of anywhere from 5 min to 15 min, at least one series of excretory phase images is obtained through the kidneys, ureters and bladder.

A number of variations on the sequences utilized for imaging have been assessed. Many investigators have obtained three sets of images: an unenhanced series, a nephrographic phase series, and one excretory phase series [10, 12, 13]. Nephrographic phase scans can be performed from the lung bases through the kidneys. This allows for all portions of the upper abdominal organs to be included on at least one series of images [9]. One group [9] has acquired two excretory phase series, one at 300 s and another at 450 s, for a total of four series of images. The rationale for using two excretory phase series is that all segments of both ureters are more likely opacified at least once if two excretory phase sets are obtained rather than one.

The group using this technique recently compared the quality of the renal collecting systems and ureters at each of the two time intervals to determine whether or not one of these two excretory phase acquisitions could be eliminated [16]. The authors found the number of opacified ureteral segments as well as renal collecting system and proximal ureteral distention to be greater at 450 s than 300 s [16]. The 300-s delay excretory phase series offered no advantages to the 450-s series. As a result of this study, the authors decided to eliminate the earlier excretory phase series from their MSCTU protocol. This group has recently modified its technique so that the excretory phase images are obtained at 720 s, rather than 450 s (Caoili et al, pers. comm.) based on their findings that distention and opacification improve with longer time delays. Nevertheless, elimination of one of the two excretory phases will likely result in more unopacified ureteral segments. Two series will always have a better chance of opacifying the entire ureter than one series.

Some researchers have been regularly performing MSCTU with only one contrast-enhanced series. Two groups obtain this single enhanced series during the late excretory phase, 15 min after injection of contrast material [17, 18]. In an interesting approach, Chow and Sommer [7] have been performing their CT urograms using a split bolus of contrast material. This allows the authors to obtain nephrographic and excretory phase images of the kidneys simultaneously. The authors first administer a bolus of 40 ml of contrast material at a rate of 2 ml s^–1. After 2 min, an additional 80 ml of contrast material is injected, also at a rate of 2 ml s^–1. After an additional 90 s, thin section images are acquired through the kidneys and proximal ureters, during which time the first bolus has already opacified the collecting systems and ureters while the second bolus is still providing nephrographic phase enhancement of the renal parenchyma. A second series of images through the mid to lower abdomen and pelvis is then obtained using a longer delay. The authors report good success with this technique, although there are a few theoretical drawbacks. This approach relies upon a small volume of contrast material to opacify and distend the renal collecting systems and proximal ureters. It also relies upon a relatively small volume of contrast material to enhance the remainder of the abdomen during the portal venous phase should, for example, assessment of the liver and pancreas also be desired. Finally, excreted contrast material in the renal collecting systems can create artefacts, which may interfere with assessment of the renal parenchyma [19], although others have indicated that this is not a common problem [20].

No matter how many phases are utilized and no matter what type of image timing is employed, frequent non-opacified segments of ureter remain a problem [8, 10, 16]. There is a concern that small urothelial lesions could be missed if they are located in these ureteral segments.

	Additional manoeuvres to optimize urinary tract distention and opacification

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Several additional manoeuvres can be employed when performing MSCTU in an attempt to improve renal collecting system and ureteral distention and opacification, and thereby possibly improving the sensitivity of this study in detecting urinary tract abnormalities.

Compression
Extrapolating from EU, a number of researchers have utilized abdominal compression [7, 9, 21–23]. Chow and Sommer [7] obtain initial excretory phase images of the kidneys with compression, then release the compression before obtaining excretory phase images of the lower abdomen and pelvis. In comparison, two groups [21, 23] release compression immediately prior to the only excretory phase image acquisition series (of the kidneys, ureters and bladder), whilst a third group [9] releases compression immediately before the second of two excretory phase series (each of which includes the kidneys, ureters and bladder).

Several studies have suggested that use of compression is beneficial. McNicholas et al [21] found that CT scanning performed after release of compression produced opacification of the distal ureters similar to EU and significantly better distal ureteral opacification than supine CTU performed without compression. Opacification of the mid ureters was also significantly better for compression CTU than for CTU obtained without compression. Heneghan et al [23] found renal collecting system and ureteral opacification using MSCTU with abdominal compression followed by compression release to be equal to or better than that of EU. Another group found that compression significantly improved distention of the renal calices, infundibula, pelves and proximal ureters compared with post-compression release scans through these structures [16]. However, there was no significant improvement in distention when compression images were compared with those obtained in a group of patients in whom no compression was applied [16]. Similarly, in this series, use of abdominal compression and compression release scanning did not result in improved distention of the lower ureters or in any improved urinary tract opacification compared with no compression. It remains to be seen whether the slight advantage offered by using abdominal compression found in some of these studies results in improved detection of urinary tract pathology.

Saline hydration
As an alternative to compression as a method to improve distention, a number of investigators have chosen to hydrate patients with a bolus of normal saline immediately prior to or following contrast material injection. McTavish et al [10] administered 250 ml of 0.9% saline immediately after intravenous injection of 100 ml of 300 mg I ml^–1 contrast material. Excretory phase imaging was only performed after the full bolus of saline had been infused. The authors reported that distal ureteral opacification was significantly improved in patients receiving saline hydration compared with a control group. They also noted that the degree of opacification that could be obtained when performing MSCTU with saline hydration was not significantly different from that obtained with EU. However, differences in opacification of the renal collecting system and other ureteral segments between the saline hydration and control groups were not significant. Still, the authors concluded that saline hydration allows for more reliable visualization of the urinary tract because it improves distal ureteral visualization.

A study by Maher et al [24] did not find saline hydration to be of any benefit. In this study patients received a split bolus of contrast material (similar to the technique employed by Chow and Sommer [7]). In addition, patients also received an intravenous infusion of 100 ml of 0.9% saline after the first bolus of contrast material. This dose of saline did not improve urinary tract opacification, although distention of some urinary tract segments (renal pelvis, upper ureter and mid ureter) increased slightly when the saline hydration patients were compared with a control group.

Inampudi et al [16] also assessed the effect of normal saline on urinary tract distention and opacification. These investigators chose to perform saline hydration MSCTU studies by administering a bolus of 250 ml of 0.9% saline immediately prior to contrast material injection. With this technique they found that patients who had saline hydration studies demonstrated only small improvements in urinary tract distention and opacification compared with patients who did not receive saline. Only opacification of the upper tracts (renal collecting systems and proximal ureters) was significantly better in the saline group.

Administration of frusemide
One group has elected to use a low dose of a diuretic to improve urinary tract visualization [8]. These investigators administered 10 mg of intravenous frusemide 3–5 min before contrast material administration for MSCTU in 16 patients. They found that frusemide-enhanced MSCTU allowed for near-complete or complete opacification of all 32 renal collecting systems and of 30 of 32 ureters. They also concluded that diuretic-enhanced MSCTU was more accurate in the depiction of pelvicalyceal details compared with MSCTU performed using saline hydration.

	Variations in the amount or rate of contrast material to be injected

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
To perform MSCTU, published studies have utilized intravenous injections of 100–150 ml of approximately 300 mg I ml^–1 of non-ionic contrast material at rates of 2–4 ml s^–1, as detailed above. However, no study has evaluated whether any particular method of administration within this range is superior to any other (in maximizing accuracy in detecting pathology) or whether yet another method of contrast material administration might be superior.

	Image review and post-processing

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Given the large number of axial CT images obtained through the urinary tract, image review is most efficiently performed on a workstation. Wide windowing during excretory phase image interpretation is essential. The high attenuation contrast material being excreted into the urinary tract can obscure renal collecting system and ureteral abnormalities such as tiny urothelial tumours, blood clots and renal tubular ectasia when standard soft tissue windowing is employed.

If a workstation is not available, it would be preferable to review the CT images on the CT scanner console, so that not every image need be filmed. At our institution, filmed images are only needed by the clinical services for demonstration purposes. To prevent excessive film expenses, only a fraction of the obtained images (usually no more than one of every four excretory phase images) is filmed. Given the large number of images and small lesions being sought, it is unrealistic to expect to interpret hard-copy images for primary diagnosis.

Most institutions performing MSCTU create reformatted images in one fashion or another. Multiplanar and three-dimensional (3D) reformatted images are aesthetically pleasing. Also, our clinical colleagues appreciate them because visualization of the data in the coronal plane more closely resembles visualization of EU films and because, if needed, these images can be more effectively used for pre-operative planning.

Multiplanar reformats (often in the coronal and/or sagittal plane) can be created by the radiologist at the time of image interpretation for dynamic interactive viewing. 3D reconstructions are also frequently created. With current CT scanners, three different 3D reconstruction algorithms have generally been utilized: volume rendering, maximum intensity projection and average intensity projection (the last two algorithms obtained from a designated thickness or "slab" that includes the kidneys, renal collecting systems, ureters and bladder but which excludes overlying bones, when possible) (Figure 1). While rarely used for other multislice CT examinations, average intensity projection images have gained some favour with those performing MSCTU because the images most closely resemble conventional radiographs obtained during EU.

View larger version (89K): [in this window] [in a new window]   Figure 1. Three-dimensional reconstructions for multislice CT urography. The three most commonly employed reconstruction algorithms, (a) average intensity projection, (b) maximum intensity projection and (c) volume rendering, are illustrated in a 59-year-old male in whom the CT urogram failed to demonstrate any abnormalities.

It is likely not necessary that each of these post-processing techniques be employed for each patient; however, it is not yet clear which techniques are superior. Only one presented study has attempted to compare post-processing techniques [17]. In this report, the authors concluded that none of the three 3D reconstruction algorithms evaluated (volume rendering, maximum intensity projections or shaded-surface display) offered distinct advantages in terms of calyceal visualization and urinary tract opacification over any of the other algorithms. The authors concluded, however, that volume rendering was the preferred technique because these images were quickly created (taking only 4 min, on average, to produce) and were least dependent on technical factors (such as image acquisition timing). We have also found that good quality volume rendered images can be more easily created by technologists than can good quality maximum or average intensity projection images, because decisions regarding which slab must be included in the reconstructed image need not be made. By simply cutting off bones anterior or posterior to the kidneys, excellent volume rendered images can be obtained, each of which images the urinary tract in its entirety.

Given the scarcity of data regarding which, if any, reconstruction techniques should be employed, at the present time each radiologist must make his or her decisions about which reconstructions to create and who will create them. Regardless, axial image review is essential. Using current techniques, urothelial neoplasms are detected with much greater sensitivity on axial images than on the 3D reconstructions. In one recent MSCTU review of 27 subsequently diagnosed upper tract transitional cell carcinomas, 24 could be visualized on axial images but only 6 (25%) could be detected on the 3D reconstructions [25].

	Currently recommended CTU technique

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
There is currently much variation in the technique used for performing MSCTU and no research has yet demonstrated a distinct advantage of any one approach over another. The reader is referred to previously cited articles for the technique (hybrid or pure CT) that he or she wishes to employ. Even more confounding is the recent emergence of 8-row and 16-row multislice scanners, with each of these machines requiring evaluation. At the present time the authors employ different techniques at their two institutions. Both techniques involve initial performance of non-contrast CT; however, one author (NCC) uses a split bolus technique followed by a single combined nephrographic and excretory phase acquisition, whilst the other employs a single injection of contrast material followed by two contrast-enhanced series, one during the nephrographic phase and the other during the excretory phase. The latter technique is summarized in Tables 1 and 2.

	Preliminary results using CTU

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

	MSCTU for detection of malignant upper tract uroepithelial abnormalities

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
MSCTU has demonstrated excellent sensitivity in detecting upper tract uroepithelial neoplasms (Figures 2 and 3). Caoili et al [25] have evaluated more than 370 high-risk patients with MSCTU. Of 27 patients ultimately diagnosed as having upper tract uroepithelial neoplasms, 24 could be identified on axial MSCTU images [25]. As previously stated, only a minority of these (six) could be detected on 3D reconstructed images. The misses on 3D imaging included several patients with non-obstructive circumferential ureteral wall thickening who did not have luminal irregularity or narrowing (Figure 4). The authors speculated that these neoplasms would also not have been identified had the patients been studied with EU instead of CT. This appearance was not completely specific for cancer, however, since benign ureteral oedema or inflammation also presented as circumferential urothelial thickening in a few patients, with this thickening having an appearance identical to that produced by malignancy.

View larger version (123K): [in this window] [in a new window]   Figure 2. Transitional cell carcinoma. (a) Coronal reformatted image demonstrates a large mass in the mid left ureter (arrows). (b) This mass is also well visualized on the subsequent retrograde pyelogram.

View larger version (88K): [in this window] [in a new window]   Figure 3. Transitional cell carcinoma. (a) Axial image demonstrates a circumferential mass surrounding the upper pole infundibulum of the left kidney. (b) This mass produces irregularity of the contour of the infundibulum, which is well seen on the coronal reformatted image (arrow). This was subsequently confirmed to represent a transitional cell carcinoma.

View larger version (156K): [in this window] [in a new window]   Figure 4. Transitional cell carcinoma. Circumferential ureteral wall thickening is present in the mid left ureter of this patient who presented with haematuria (arrow). Note that the ureteral lumen is not narrowed significantly. No abnormality was detected on the three-dimensional reconstructions. It is likely that an excretory urogram would have been normal as well. Subsequent ureteroscopy confirmed that the thickening was produced by an infiltrative transitional cell carcinoma.

In yet another multi-institutional study [11] of 350 consecutive patients with haematuria, MSCTU correctly diagnosed 158 of 171 subsequently proved lesions suspected to be the cause of the haematuria. However, this series only included one patient with an upper tract transitional cell carcinoma, which was correctly identified.

Mueller-Lisse et al [13] performed MSCTU on 26 patients with painless macroscopic haematuria and/or known recurrent urinary cancer and found MSCTU to be highly sensitive in identifying uroepithelial tumours, but only moderately specific in excluding this diagnosis.

Management of the very high-risk patient (for urothelial malignancy) who has negative or equivocal MSCTU remains uncertain but is not significantly different from the similar situation of a negative excretory urogram. It might be reasonable to perform either a follow-up CT urogram over a short interval of time or to perform ureteroscopy or retrograde pyelography for further evaluation in this situation.

	MSCTU for detection of benign upper tract uroepithelial abnormalities

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
For MSCTU to completely replace EU, MSCTU must be able to detect benign as well as malignant upper urinary tract abnormalities with at least comparable sensitivity to urography. The MSCTU appearance of a number of benign upper tract abnormalities has been described, including caliectasis, calyceal diverticula, papillary necrosis, renal tubular ectasia (Figure 5), parapelvic cysts, ureteritis cystica, benign ureteral strictures, blood clots, fibroepithelial polyps, mucus and ureteral endometrioma [9, 11, 12, 26]. All of these benign renal collecting system abnormalities are visualized on axial CT images; however, when there is adequate collecting system and ureteral opacification they are also easily recognized on 3D or coronal reformatted images [7, 9]. When excretion is delayed (usually owing to obstruction), renal collecting system and ureteral dilatation are best appreciated on axial images [9].

View larger version (87K): [in this window] [in a new window]   Figure 5. Renal tubular ectasia. (a) Wide windowing while viewing the kidneys is necessary to visualize the discrete linear collections of contrast material (arrow) in the renal pyramids in this patient with renal tubular ectasia. (b) The ectasia is also well demonstrated on maximum intensity projection reconstructions (arrows).

	Bladder abnormalities

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Because cystoscopic evaluation and surveillance is routinely employed as the standard of care for patients with haematuria and/or at high risk for urothelial abnormalities, accurate assessment of the bladder by MSCTU is less critical than is evaluation of the upper urinary tract. Nevertheless, initial studies have suggested that MSCTU can detect many bladder malignancies. MSCTU demonstrated 25 proven bladder abnormalities in 23 of the 65 patients studied by Caoili et al [9], 9 of which subsequently proved to be transitional cell carcinomas. One focal lesion at the bladder base was initially missed, but could be identified on retrospective review. In the study by McCarthy and Cowan [12], only one bladder cancer was not detected by MSCTU, whilst in the series by Lang et al [11] all four subsequently diagnosed bladder transitional cell carcinomas and one urachal adenocarcinoma were correctly identified.

Once a bladder abnormality is detected, in some instances MSCTU may suggest whether the abnormality is malignant or benign. Many urothelial neoplasms produce mural filling defects or focal bladder wall thickening, while diffuse uniform bladder wall thickening often represents benign disease such as cystitis or changes related to obstructive uropathy from prostatic enlargement [9]. Bladder haematomas can occasionally be correctly identified owing to their high attenuation on pre-contrast scans.

Unfortunately, there is overlap in the appearance of benign and malignant bladder abnormalities. In the study of Caoili et al [9], two patients had focal bladder wall thickening resulting from asymmetric radiation cystitis whilst one patient had diffuse bladder wall thickening due to infiltrative transitional cell carcinoma. In the series reported by Lang et al [11], three false positive diagnoses of bladder cancer were made owing to misinterpretation of two inflammatory lesions and one submucosal haematoma as malignancies. Also, some benign bladder pathology has been missed on MSCTU, particularly small bladder neoplasms and cystitis producing only minimal bladder wall thickening [9].

	Limitations in interpreting MSCTU

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
Limitations produced by normal physiology
The most common and perplexing problem that limits the diagnostic quality of MSCTU is lack of adequate contrast opacification and distention of the upper urinary tract. Delayed excretion and, therefore, absent or poor opacification are expected in patients with urinary tract obstruction or even non-obstructive dilatation if severe enough. In such cases, however, mural or intraluminal urinary tract abnormalities are usually well outlined by surrounding unopacified fluid-attenuation urine within distended collecting systems or ureters.

Ureteral non-opacification is a more significant problem when the unopacified segment is not dilated. This problem is not uncommon. It usually occurs as a result of peristalsis and is generally more common in the distal ureters. In one series [16], portions of the distal ureters were not opacified 33% of the time at 300 s and 24% of the time at 450 s. In such cases, subtle intrinsic lesions producing tiny intraluminal filling defects might be missed if they are located in the unopacified segments. Rarely, a contracted segment of ureter during peristalsis has even mimicked the concentric urothelial thickening of a pathological process, resulting in a false positive study. Of course, ureteral non-opacification is also a problem during EU. Our current practice follows EU in assuming that a non-dilated, non-thickened, non-opacified ureteral segment is normal. However, the option of ureteral fluoroscopy, which some employ in this situation during EU, is not available with MSCTU.

Another potential problem relates to the layering of contrast-enhanced urine dependent to unopacified urine in bladders and or full/dilated renal collecting systems. Urothelial abnormalities are more difficult to detect if they are not outlined by opacified urine. Although in our experience this is not a common problem, we have encountered one case in which a large transitional cell carcinoma in the anterior aspect of the bladder was not prospectively identified for this reason. This problem could be reduced or eliminated by having the patient roll over several times to facilitate mixing of enhanced and unenhanced urine.

Anatomic variants may also occasionally lead to confusion at the time of image interpretation. These include ureteral kinks, intraluminal mucus and prominent papillae. Ureteral kinks may produce focal areas of narrowing or apparent thickening, thereby mimicking focal ureteral strictures or even tiny neoplasms (Figure 6) [9]. In these instances the reformatted images may be helpful in demonstrating the presence of a kink. Rarely, intraluminal mucus may be extensive and viscous enough to mimic a focal intrinsic renal collecting system lesion [12]. Finally, prominent papillae may occasionally produce pronounced concave impressions on adjacent calyces that may be mistaken for filling defects. Careful scrutiny of the axial images usually facilitates differentiation of normal papillae from pathology. The papillary impressions are nearly always multiple, similar to one another, and bilaterally symmetric.

View larger version (98K): [in this window] [in a new window]   Figure 6. Ureteral kink mimicking a filling defect. (a) An axial image demonstrates an apparent tiny filling defect (arrow) in the proximal left ureter. This filling defect is caused by tortuosity of the ureter associated with a ureteral kink. (b) Although the presence of the kink can be suspected by reviewing the axial images sequentially, it is more easily identified on a coronal three-dimensionally reconstructed image.

Time limitations
As previously emphasized, review of the source axial images is required for accurate detection of renal collecting system and upper tract abnormalities. As there may be over 1000 transverse images to review per examination, interpretation is labour and time intensive. Furthermore, the radiologist must take the time to evaluate other imaged intra-abdominal organs for pathology on each imaging phase. Utilization of such a large number of images, with each demonstrating a great deal of information, contrasts markedly with EU, where the radiologist focuses on evaluation of the kidneys, ureters and bladder and only on a few images. Producing 3D reformatted images, which may help both the radiologist and our clinical colleagues, may also be time consuming, labour intensive and costly.

	Radiation dose

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
As with other multiphase abdominal CT protocols, MSCTU can expose the patient to substantial radiation, which must be considered when deciding upon an appropriate technique for performing MSCTU. Several authors have estimated patient radiation exposure, using a variety of approaches.

Herts [26] estimated that multislice CT exposes a patient to an estimated surface radiation dose of 2 rem for each series of acquired images. Thus, according to Herts, three- and four-phase MSCTU protocols would expose patients to doses of 6 rem and 8 rem, respectively. In comparison, the approximate patient radiation exposure resulting from an EU protocol consisting of 10–14 radiographs (which exceeds that utilized at many institutions) was estimated to be similar, ranging from 5 rem to 7 rem.

McTavish et al [10] estimated that skin and total effective radiation doses resulting from their three-phase MSCTU protocol were 74.1 mGy and 22.6 mGy, respectively, compared with calculated doses of 81.2 mGy and 11.4 mGy for EU. Whilst the skin doses for the two studies were comparable, the total effective dose resulting from MSCTU was nearly twice that for EU.

Caoili et al [9] derived their estimates of patient radiation by determining the effective absorbed radiation for MSCTU and EU (measured in sieverts (Sv) rather than gray (Gy)). By doing so, the authors found that their four-phase MSCTU protocol resulted in an effective radiation dose of 25–35 mSv for an average size male. This greatly exceeded the 5–10 mSv dose for the 10–12 film EUs performed at the same institution. However, if one assumes that most of the patients included in this study, all of whom were at high risk of having significant urinary tract disease, would have otherwise been studied with both EU and standard, single-phase enhanced CT, the radiation difference was not nearly as pronounced. MSCTU exposed patients to only approximately 1.5 times as much radiation as would a combination of EU and conventional single-phase CT.

Given the incremental radiation exposure from MSCTU, one institution has restricted its use generally to patients who are older (over the age of 40 years) and in whom there is a very high risk of malignant urinary tract disease, as determined by a urologist [9]. At this institution, clinicians other than urologists are not permitted to routinely order this study. In contrast, despite the increased radiation, other investigators [11] have suggested that MSCTU be performed for routine evaluation of haematuria.

Whilst the carcinogenic risks of increased radiation from multiphase CT should not be underestimated, they must be weighed against the not insignificant risks of missing malignant urinary tract pathology at an early stage when it can often be most effectively treated. Radiation risks are greatest in younger patients. They are much less likely to be significant in the generally older patient population referred for MSCTU.

There are several ways in which MSCTU radiation dose can be reduced. One of the three or four phases might be eliminated (although this might decrease study accuracy). Alternatively, mA can be reduced for one or more phases.

	Cost effectiveness

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
To date, only one study has assessed the cost effectiveness of MSCTU [28]. Gupta et al [28] found that when EU was performed as the first imaging examination, additional imaging was obtained in almost half of the patients. In comparison, when MSCTU was performed first, additional studies were obtained in only 10% of patients. In patients evaluated first with EU, follow-up studies doubled final mean per patient USA Medicare reimbursements from $93 (for EU alone) to $191. In comparison, in patients evaluated first with MSCTU, follow-up studies only added $18 to the reimbursement rate (which increased from $325 for CT alone to $343).

	Indications for MSCTU

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
At the present time there is no consensus of opinion as to which patients should undergo CTU. While some authors have advocated that this technique be performed as a screening test in any patient who develops haematuria [11], we have reserved this study for older patients at high risk of developing a urothelial malignancy. Some have allowed any physician to order a CT urogram [11], whilst we have restricted the ability to order this study to urologists. We believe that MSCTU could be performed to evaluate any urinary tract condition that can be imaged radiographically, but its actual use in practice requires careful consideration of patient history, level of risk of urinary tract pathology and the amount of radiation to which the patient is exposed for an individual CT urographic technique.

	Summary and need for ongoing investigations

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 
MSCTU is a promising technique; however, experience is preliminary and much additional investigation is needed. Direct comparison of EU and MSCTU findings in a prospective study has yet to be performed. However, MSCTU has been demonstrated to be more accurate than retrograde pyelography [12], an imaging test assumed to be superior to EU for evaluating the renal collecting systems and ureters. Already, when comparison is made with EU a number of distinct advantages and disadvantages can be identified (Table 3). As CT hardware and software continue to improve, these relative advantages and disadvantages will likely change (with the former increasing and the latter decreasing in number and significance). Even now, many investigators are pursuing refinements in CT technique in an attempt to maximize study accuracy whilst minimizing patient radiation exposure. Despite many uncertainties, there appears to be an emerging consensus of opinion that MSCTU has the potential to completely replace conventional EU over the next few years [29, 30].

Received for publication May 27, 2003. Revision received July 28, 2003. Accepted for publication August 7, 2003.

	References

Top Abstract Introduction CT urographic techniques Multislice CTU: variations in... Additional manoeuvres to... Variations in the amount... Image review and post-processing Currently recommended CTU... Preliminary results using CTU MSCTU for detection of... MSCTU for detection of... Bladder abnormalities Limitations in interpreting... Radiation dose Cost effectiveness Indications for MSCTU Summary and need for... References

 

1. Warshauer DM, McCarthy SM, Street L, Bookbinder MJ, Glickman MG, Richter J, et al. Detection of renal masses: sensitivities and specificities of excretory urography/linear tomography, US, and CT. Radiology 1988;169:363–5.[Abstract/Free Full Text]
2. Jamis-Dow CA, Choyke PL, Jennings SB, Linehan WM, Thakore KN, Walther MM. Small (<or=3-cm) renal masses: detection with CT versus US and pathologic correlation. Radiology 1996;198:785–8.[Abstract/Free Full Text]
3. Smith RC, Verga M, McCarthy S, Rosenfield AT. Diagnosis of acute flank pain: value of unenhanced CT. Am J Roentgenol 1996;166:97–101.[Abstract/Free Full Text]
4. Levine JA, Neitlich J, Verga M, Dalrymple N, Smith RC. Ureteral calculi in patients with flank pain: correlation of plain radiography with unenhanced CT. Radiology 1997;204:27–31.[Abstract/Free Full Text]
5. Perlman ES, Rosenfield AT, Wexler JS, Glickman MG. CT urography in the evaluation of urinary tract disease. J Comput Assist Tomogr 1996;20:620–6.[CrossRef][Medline]
6. McCollough CH, Bruesewitz MR, Vrtiska TJ, King BF, LeRoy AJ, Quam JP, et al. Image quality and dose comparison among screen–film, computed and CT scanned projection radiography: applications to CT urography. Radiology 2001;221:395–403.[Abstract/Free Full Text]
7. Chow LC, Sommer FG. Multidetector CT urography with abdominal compression and three-dimensional reconstruction. Am J Roentgenol 2001;177:849–55.[Free Full Text]
8. Nolte-Ernsting CC, Wildberger JE, Borchers H, Schmitz-Rode T, Gunther RW.; Multi-slice CT urography after diuretic injection: initial results. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 2001;173:176–80.[Medline]
9. Caoili EM, Cohan RH, Korobkin M, Platt JF, Francis IR, Faerber GJ, et al. Urinary tract abnormalities: initial experience with multi-detector row CT urography. Radiology 2002;222:353–60.[Abstract/Free Full Text]
10. McTavish JD, Jinzaki M, Zou KH, Nawfel RD, Silverman SG. Multi-detector row CT urography: comparison of strategies for depicting the normal urinary collecting system. Radiology 2002;225:783–90.[Abstract/Free Full Text]
11. Lang EK, Macchia RJ, Thomas R, Ruiz-Deya G, Watson RA, Richter F, et al. Computerized tomography tailored for the assessment of microscopic hematuria. J Urol 2002;167:547–54.[CrossRef][Medline]
12. McCarthy CL, Cowan NC. Multidetector CT urography (MD-CTU) for urothelial imaging. Radiology 2002;225(P):237.
13. Mueller-Lisse UG, Mueller-Lisse UL, Hinterberger J, Schneede P, Reiser MF. Tri-phasic MDCT in the diagnosis of urothelial cancer. Eur Radiol 2003;13(S1):146–7.[CrossRef]
14. Kawashima A, LeRoy AJ, King BF, Vrtiska TJ, Hsieh J, Hattery RR. Comparison of CT scanned projection radiographs (SPR) utilizing enhanced algorithms with original CT scan SPR and conventional screen–film radiographs (FSR) in detecting urolithiasis and with respect to image quality. Radiology 2002;225(P):236.
15. Coll DM, Sosa RE, Smith RC. CT urography for evaluation of the urothelial system: are plain films still necessary? Radiology 2002;225(P):237.
16. Inampudi P, Caoili EM, Cohan RH, Ellis JH, Korobkin M, Platt JF, et al. Effect of compression, saline administration, and prolonging acquisition delay on images obtained during multidetector CT urography (MDCTU). AJR 2003;180(S):71.
17. Frauenfelder T, Boehm T, Michael M, Marincek S, Wildermuth S. The urinary collecting system: different post-processing methods (MIP, SSD, VR) using multidetector-CT-datasets versus conventional intravenous urography. Eur Radiol 2003;13(S1):147.[CrossRef]
18. Girish G, Agarwal SK, Salim F, Brown PWG, Morcos SK. Single-phase multislice CT urography: initial experience. Eur Radiol 2003;13(S1):147.
19. Sussman SK, Illescas FF, Opalacz JP, Yirga P, Foley LC. Renal streak artifact during contrast enhanced CT: comparison of high versus low osmolality contrast media. Abdom Imaging 1993;18:180–5.[Medline]
20. Yuh BI, Cohan RH. Different phases of renal enhancement: role in detecting and characterizing renal masses during helical CT. Am J Roentgenol 1999;173:747–55.[Abstract/Free Full Text]
21. McNicholas MMJ, Raptopoulos VD, Schwartz RK, Sheiman RG, Zormpala A, Prassopoulos RK, et al. Excretory phase CT urography for opacification of the urinary collecting system. Am J Roentgenol 1998;170:1261–7.[Abstract/Free Full Text]
22. Caoili EM, Cohan RH, Korobkin M, Platt JF, Francis IR, Gebremariam A, et al. Effectiveness of abdominal compression during helical renal CT. Acad Radiol 2001;8:1100–6.[CrossRef][Medline]
23. Heneghan JP, Kim DH, Leder RA, DeLong D, Nelson RC. Compression CT urography: a comparison with IVU in the opacification of the collecting system and ureters. J Comput Assist Tomogr 2001;25:343–7.[CrossRef][Medline]
24. Maher MM, Jhaveri KS, Lucey BC, Sahani DV, Saini S, Mueller PR. Does the administration of saline flush during CT urography (CTU) improve ureteric distention and opacification? A prospective study. Radiology 2001;221(P):500.
25. Caoili EM, Inampudi P, Cohan RH, Ellis JH, Korobkin M, Platt JF, et al. MDCTU of upper tract uroepithelial malignancy. AJR 2003;180(S):71.
26. Herts BR. The current status of CT urography (2002). Crit Rev Comput Tomogr 2002;43:219–41.[CrossRef][Medline]
27. Caoili EM, Cohan RH, Inampudi P, Ellis JH, Korobkin M, Platt JF, et al. Experience with multidetector CT urography (MDCTU) in 370 patients. Am J Roentgenol 2003;180(S):71.
28. Gupta KB, Silverman SG, McTavish JD, O'Leary M, Bernazzani J. The impact on diagnostic yield, practice patterns, and cost of using CT urography rather than intravenous urography in the evaluation of hematuria. Radiology 2001;221(P):501.
29. Laissy JP, Abecidan E, Karila-Cohen E, Ravery V, Schouman-Claeys E. IVU: a test of the past without future? Prog Urol 2001;11:552–61. [In French.][Medline]
30. Thomsen HS, Lendequist S, Brems-Dalgaard E. Retirement plan for a 70-year-old. Intravenous urography disembarks from uroradiology. Ugeskr Laeger 2002;164:1484–8. [In Danish.][Medline]

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