| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Original Research |
1 Department of Radiology, Medical College of Wisconsin, Milwaukee, WI.
2 Department of Radiology, Froedtert Memorial Lutheran Hospital, 9200 W
Wisconsin Ave., Milwaukee, WI 53226.
3 Medical College of Wisconsin, Milwaukee, WI.
4 Department of Biostatistics, Medical College of Wisconsin, Milwaukee,
WI.
Received November 30, 2004;
accepted after revision January 17, 2005.
Address correspondence to G. S. Sudakoff
(gsudakof{at}mcw.edu).
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
MATERIALS AND METHODS. One hundred eight CT urography and enhanced CTDR examinations were reviewed. Fifty-four patients were given a saline bolus during CT urography, and 54 patients underwent CT urography without a saline bolus. Urinary collecting system opacification was evaluated by group (saline vs nonsaline), imaging technique (CT urography alone vs CT urography plus enhanced CTDR), number of enhanced CTDR images, and site of nonopacified urinary segments. Using a multivariate logistic regression model, we determined significance of variables and odds of complete opacification.
RESULTS. In the saline group, 248 nonopacified sites were identified on CT urography alone and 95 sites with CT urography plus enhanced CTDR. In the nonsaline group, 185 nonopacified sites were identified on CT urography alone and 59 sites with CT urography plus enhanced CTDR. Combining both groups, 433 nonopacified sites were identified with CT urography alone and 154 sites with CT urography plus enhanced CTDR. Multivariate logistic regression showed significance for group (p = 0.010), imaging method (p < 0.0001), number of enhanced CTDR images (p = 0.048), and site of segment opacification (p < 0.0001). The renal pelvis shows the greatest odds and the distal ureter the lowest odds for complete opacification by group or imaging method.
CONCLUSION. The addition of a saline bolus offers no improvement, whereas the addition of enhanced CTDR offers significant improvement in collecting system opacification during CT urography.
Keywords: contrast media • CT technique • digital radiography • MDCT • urinary tract
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Evaluation of uroepithelial abnormalities requires that the intrarenal collecting system (IRCS), ureters, and bladder be adequately opacified and distended. The sensitivity and accuracy of detecting uroepithelial abnormalities by excretory urography or CT urography are affected by ureteral peristalsis, which often causes inadequate ureteral opacification. Techniques that improve ureteral opacification would be extremely useful for improving the diagnostic capabilities of CT urography. In a study by McTavish et al. [6], supplemental saline infusion during CT urography was evaluated and found to improve opacification of the distal ureters. In addition, a recent study by Sudakoff et al. [5] showed that opacification of the entire urinary collecting system is improved with the addition of enhanced CT digital radiography (CTDR) immediately after CT urography in patients with urinary diversions. The purpose of this study was twofold: to determine whether supplemental saline infusion improves opacification of the urinary collecting system during CT urography and to determine whether the addition of enhanced CTDR during CT urography improves visualization of the urinary collecting system with or without supplemental saline infusion.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
Fifty-four consecutive patients (17 women, 37 men) who received supplemental saline infusion and 54 consecutive patients (26 women, 28 men) who did not receive supplemental saline infusion during their CT urography and enhanced CTDR examinations were evaluated to determine which technique was superior in rendering opacification of the urinary collecting system. The 108 patients had an age range of 20-88 years (mean age, 56.4 years). All patients who underwent CT urography and enhanced CTDR had a recent (< 30 days) serum creatinine level of 1.6 mg/dL or less.
All patients undergoing CT urography were instructed to receive a cleansing bowel preparation (identical to what we use for excretory urography) and take nothing by mouth 4 hr before the examination. This preparation includes ingestion of 10 oz (294 mL) of magnesium citrate 14-16 hr before the examination, four bisacodyl tablets 10 hr before the examination, a clear liquid diet the evening before the examination, and one bisacodyl suppository 2 hr before the examination. The number of patients who followed the bowel preparation for the CT urography examination is not known and was not recorded in our database.
All CT urography examinations were performed on an 8- or 16-MDCT scanner (LightSpeed Ultra and LightSpeed Pro 16, GE Healthcare). Scanning was performed with the patient in the supine position and with no external compression. Before scanning, a 20-gauge IV catheter was inserted into an appropriate vein of the wrist or antecubital fossa with a dual connector port. The examination was performed in three phases. The first phase consisted of a noninfused scan from the lung bases through the pelvic floor with 5-mm collimation and a pitch of 1.35:1 or 1.375:1 (8- or 16-MDCT scanners, respectively).
The second phase began after the injection of 40 mL of IV contrast material (iohexol [Omnipaque 300, Amersham Health, Inc.]) via a power injector at a rate of 1.5 mL/sec. After a delay of 10 min, an additional 110 mL of contrast material was injected via power injector at a rate of 3.0 mL/sec. Scanning commenced 100 sec after the start of the second contrast injection and was performed from the dome of the diaphragm through the floor of the pelvis. Scans in this combined second stage (nephropyelographic stage) were obtained during a single breath-hold with 1.25-mm detector collimation, 1.35:1 or 1.375:1 pitch, and a 50% reconstruction overlap.
The third phase consisted of performing enhanced CTDR of the abdomen and pelvis 1 min after the completion of axial imaging (300 mAs, 80 kVp) (Rad View Scout, GE Healthcare). The enhanced CTDR examination was monitored by an attending radiologist to determine whether the urinary collecting system was adequately opacified. If the collecting system was judged to be incompletely opacified, the enhanced CTDR scanning was repeated. No more than three enhanced CTDR images were routinely obtained per CT urography examination (obtained 1, 3, and 5 min after the completion of axial imaging). In two patients, a fourth enhanced CTDR image was obtained within 60 sec of the third enhanced CTDR image. The data obtained from the combined CT urography and enhanced CTDR examination were transferred to a workstation (Advantage 4.2, GE Healthcare) for 3D rendering.
Patients who received supplemental saline infusion were scanned using an identical protocol except for the administration of 250 mL of saline immediately after the first injection of IV contrast material (40 mL). A 250-mL bag of 0.9% sodium chloride was hung on an IV pole approximately 3-4 ft (0.9-1.2 m) above the level of the patient's chest and connected via a Silastic IV connector tubing to the dual connector port of the patient's IV. The supplemental saline was infused at the fastest rate possible (i.e., wide open) to ensure that saline infusion was complete before scanning.
Data obtained during the second phase of the CT urography examination (nephropyelographic) were transferred to independent workstations for 3D rendering of the kidneys, ureters, and bladder using maximum-intensity-projection (MIP) and average-intensity-projection (AIP) techniques. Reformatted coronal images of the kidneys, oblique coronal images of the kidneys and ureters individually, and coronal and oblique images of bladder were obtained.
Image review was conducted by three reviewers, in which no more than two reviewers were present for a review session. A single reviewer was present for all sessions. All images were evaluated by consensus. All reviewers were blinded to supplemental saline infusion, specific clinical indication for examination, clinical history, and date of the examination. The axial images from the nephropyelographic phase (phase 2) were first reviewed to identify the presence of urinary or extraurinary abnormalities. The 3D rendered MIP and AIP images were evaluated for urinary collecting system opacification (Figs. 1A and 1B). The reviewers were asked to grade opacification of the urinary collecting system during CT urography alone and combined CT urography plus enhanced CTDR. The urinary collecting system was divided into six separate segments: IRCS, upper pole; IRCS, lower pole; IRCS, renal pelvis; proximal ureter (the ureteropelvic junction to the iliac crest); mid ureter (iliac crest to the inferior margin of the sacroiliac joint); and distal ureter (inferior margin of the sacroiliac joint to the ureterovesicular junction) (Fig. 2). Bladder opacification was not evaluated in this study. Opacification of a collecting system segment was considered present (opacified) or absent (nonopacified) only. A segment was considered nonopacified if it was judged to be nonvisualized, to be incompletely or poorly visualized, or to show a focal or linear site of nonopacification. Sites of nonopacification with and without supplemental saline, occurring with CT urography alone and combined CT urography and enhanced CTDR, were recorded.
|
Using these binary data, we created a multivariate logistic regression model using generalized estimating equations. Variables for patient group (saline vs nonsaline), imaging method (CT urography vs CT urography plus enhanced CTDR), collecting system site, number of enhanced CTDR images, patient age, and patient sex were entered into the model one at a time in stepwise model building. Two-way interactions between variables were considered. The statistical analysis was performed using SAS statistical software (SAS Institute).
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In the group of 54 patients who did not receive supplemental saline infusion, a total of 185 nonopacified sites were identified (89 sites, right; 96 sites, left) on CT urography alone and 59 sites with the combined techniques of CT urography plus enhanced CTDR (23 sites, right; 36 sites, left) (Table 1). In the group of 54 patients who received supplemental saline bolus, a total of 248 sites of nonopacification were identified on CT urography alone (126, right; 122, left) and 95 sites with the combined technique of CT urography and enhanced CTDR (53, right; 42, left) (Table 2). Evaluating total sites of nonopacification in both nonsaline and saline groups showed 433 sites on CT urography alone (215, right; 218, left) and 154 sites with the combined technique of CT urography plus enhanced CTDR (76, right; 78, left) (Table 3).
|
|
|
The results of the multivariate logistic regression showed the following variables to be significant: patient group (nonsaline vs saline), imaging method (CT urography plus enhanced CTDR vs CT urography), number of enhanced CTDR images, and collecting segment site (Table 4). Neither patient sex nor patient age was significant after controlling for other variables in the model (p = 0.97 and 0.74, respectively). The nonsaline group showed 1.85 times greater odds of complete opacification when compared with the saline group (Table 4). The combined imaging method of CT urography plus enhanced CTDR showed 4.45 greater odds of complete opacification compared with CT urography alone. Patients who had three or more enhanced CTDR images showed 1.60 times greater odds of complete opacification as compared with patients who only had two enhanced CTDR images (Table 4). This result suggests a tendency toward greater odds of complete opacification in patients when a larger number of enhanced CTDR images are obtained sequentially. Including this variable in the statistical model adjusts for unequal numbers of enhanced CTDR images among patients and groups.
|
|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CT urography performed on single-detector helical CT scanners using thin collimation to achieve high spatial resolution of the entire urinary collecting system is not possible during a single breath-hold. The recent development of MDCT scanners, which acquire near isotropic data sets, allows rapidly acquired multiphase scans to be obtained during a single breath-hold. Once these data are transferred to an independent workstation, multiplanar 3D rendering of the entire genitourinary system can be performed [1-8]. Axial and 3D reformatted images of the genitourinary system obtained with MDCT urography offer greater spatial resolution than single-detector helical CT and closely approximate that obtained with excretory urography [7].
Complete visualization of the opacified urinary collecting system continues to be a significant imaging challenge regardless of which technique is used (excretory urography or CT urography). Attempts to maximize opacification during excretory urography have met with limited success and include multiple image acquisitions, inflatable ureteral compression devices, and prone and supine patient positioning [9-11]. Incomplete opacification of the ureters, particularly the distal ureter, secondary to peristalsis is a well-documented limitation during CT urography [2-6, 8]. The use of additional axial acquisitions to attempt visualization of ureteral segments that were initially nonopacified is not practical due to high patient radiation dose. In our experience and that of others [6], ureteral compression devices offer little if any benefit during CT urography. These devices are generally ineffective in large or obese patients, produce artifacts on 3D reformatted images, and require more than one acquisition to scan the entire collecting system. Prone positioning during excretory CT has been reported to improve opacification of the distal ureters [12]. However, McTavish et al. [6] found no improvement in distal ureteral opacification with patients in the prone position during CT urography. In addition, many patients who undergo CT urography often cannot tolerate prone positioning because of degenerative changes of the spine, kyphosis, chronic obstructive lung disease, ostomies, or obesity.
Few techniques have been reported to improve opacification of the urinary collecting system during CT urography. McTavish et al. [6] reported improved opacification in the distal left ureter during CT urography with the use of a supplemental saline bolus. In their study, 17 patients underwent CT urography (prone position) and were compared with 34 patients who underwent CT urography (17 supine, 17 prone) with supplemental saline. Maher et al. [13], using the nephropyelographic technique during CT urography, showed no improvement in collecting system opacification in 20 patients who received a 100-mL saline bolus compared with 20 patients who did not receive a supplemental saline bolus. We have previously reported that the combined technique of CT urography plus enhanced CTDR significantly improved opacification of the entire urinary collecting system in 30 patients with urinary diversions compared with CT urography alone [5]. We decided to evaluate whether supplemental saline bolus improves opacification of the urinary collecting system during CT urography and whether the addition of enhanced CTDR during CT urography improves opacification with or without saline bolus.
Enhanced CTDR is a modification of conventional CTDR not commercially available. Four modifications to enhanced CTDR are essential when compared with conventional CTDR: adaptive enhancement, overlapped data sampling, use of an optimized filter, and use of a deconvolution filter [8, 14, 15]. Adaptive enhancement uses an algorithm to calculate multiple directional gradients that ultimately minimizes undershoot-overshoot enhancement (alternating bright and dark bands) at high contrast-low contrast interfaces [8, 14, 15]. Overlapping data sampling ensures a more precise and accurate design of the filter that significantly improves filter flexibility and subsequently produces an image that appears nearly identical to that of a conventional radiograph [8, 14, 15]. The addition of a deconvolution filter improves the z-axis high contrast spatial resolution approximately 20-30% when compared with conventional CTDR (1.2-1.3 lp/mm for enhanced CTDR compared with < 1.0 lp/mm for conventional CTDR) [8, 14]. The resolution of enhanced CTDR is less than film-screen radiography, computerized radiography, or digital radiography (4.0, 3.0, 2.5 lp/mm, respectively) [14]. The radiation exposure associated with a single enhanced CTDR image is essentially identical to that of a conventional abdominal radiograph using a stationary grid that delivers a skin exposure of 330 mR (0.85 x 10-4 C/kg) and effective dose of 0.54 mSv (412 mR [1.06 x 10-4 C/kg] effective skin exposure and 0.52 mSv for an abdominal radiograph with a standard grid) [8, 14]. The radiation exposure to a patient by a routine abdominal-pelvic CT scan delivers an effective skin exposure of approximately 2,500 mR (6.54 x 10-4 C/kg) and an effective dose of 11 mSv [8, 14]. The effective dose of an excretory urography examination consisting of four 14 x 17 inch (36 x 43 cm) anteroposterior radiographs, three 10 x 12 inch (25 x 30 cm) anteroposterior radiographs, and four to six tomograms (70 kVp and 67 mAs) for a 70-kg man is 5-10 mSv [2]. Obtaining up to three enhanced CTDR images during a routine CT urography examination delivers approximately 1.62 mSv in additional radiation exposure to the patient; this is just slightly greater than one tenth the dose of a routine abdominal-pelvic CT scan.
On the basis of the number of nonopacified sites, our data indicate that no improvement of urinary collecting system opacification occurs with the addition of a supplemental saline bolus during CT urography [6] (Tables 1, 2, and 4). Contrary to the results of McTavish et al. [6], our findings indicate no improvement in distal ureteral segment opacification with the addition of a saline bolus during CT urography (Tables 1 and 2). Our data show that urinary collecting system opacification is significantly improved with the addition of enhanced CTDR during CT urography with or without the use of a saline bolus (Tables 1, 2, and 4). If both patient groups are considered together, the use of the combined technique of CT urography plus enhanced CTDR significantly improved opacification, as shown by comparing the number of nonopacified sites for the combined technique with that of CT urography alone (Table 3).
The reason for the discrepancy between our results and those previously reported concerning supplemental saline bolus during CT urography is unclear. Possible factors may include variability in the patient population and their hydration status. In our patient population, all patients had a serum creatinine of 1.6 mg/dL or less and were restricted from drinking fluids 4 hr before their examination. Another consideration is that a saline bolus may induce an increase in frequency or magnitude of renal pelvic and ureteral peristalsis, resulting in fewer opacified sites during CT urography. In the prior study by McTavish et al. [6], the age range of their population, criteria level of serum creatinine to perform CT urography, and hydration restriction were not mentioned. In our study, a split IV contrast dose (nephropyelographic technique) of 150 mL of 300 mg I/mL was used, whereas a single injection of 100 mL of 300 mg I/mL was used in the study by McTavish and colleagues. The scan delay times and administration time of the saline bolus were identical in the two studies. The differences in the volume of contrast material might account for the differences in opacification between the two studies, but we think this is unlikely. In our study, using the nephropyelographic technique (split contrast dose), no more than 40 mL of contrast material is excreted by the kidneys before imaging compared with 100 mL of contrast material used in the excretory phase of CT urography by McTavish and colleagues. The use of the nephropyelographic technique has the added benefit of less radiation dose to the patient, using only two image acquisitions compared with three or more used by others in performing CT urography [1-4, 6-8, 16].
In our study, grading of urinary collecting system segments was binary—that is, judged either completely opacified or nonopacified. In the study by McTavish et al. [6], urinary collecting system segments were graded by percentage: for example, 0%, < 50%, 50-99%, 100% opacification. We believe the binary method used in our study reflects a more accurate approach in evaluating urinary collecting system opacification during CT urography. We recognize that partial or incomplete opacification of the urinary collecting system may offer useful information in diagnosing uroepithelial abnormalities. However, segments that are partially or incompletely opacified cannot confidently be considered either normal or free of disease.
In a recent study, we reported on improved opacification of the urinary collecting system using the combined technique of CT urography with enhanced CTDR in evaluating patients with urinary diversions (compared with CT urography alone) [5]. Patients were evaluated in the prone position using CT urography in an attempt to improve opacification of urinary collecting systems often markedly dilated because of a diseased bladder or complication of urinary diversion. We did not evaluate whether improved opacification occurs in the prone versus the supine position when performing CT urography. Since its inception at our institution, CT urography has been routinely performed in patients with intact bladders in the supine position mainly because of patient comfort and ease of performing the examination. Furthermore, McTavish and colleagues compared opacification of both prone and supine positions during CT urography and found no significant difference.
The addition of enhanced CTDR while performing CT urography significantly improved urinary collecting system opacification compared with CT urography alone in our study. This effect was seen with or without the use of supplemental saline bolus. There are several possible reasons for improved opacification seen using this combined technique. Enhanced CTDR was performed at 1, 3, and 5 min after completion of axial scanning. This additional time delay may allow opacification of segments not previously opacified on axial scanning. Enhanced CTDR images are analogous to delayed excretory urography images that attempt to improve opacification and distention of nonopacified urinary collecting system segments not visualized on routine images. An additional benefit of enhanced CTDR images is the relative ease and speed by which they are obtained. The convenience of not having to move the patient from the CT scanner to obtain conventional abdominal radiographs avoids significant time delays and additional costs. The spatial resolution of enhanced CTDR is less than that of conventional radiography but is greater than that of conventional CTDR. In this study, all intraluminal abnormalities of the urinary collecting system were identified with both 3D rendered CT urography and enhanced CTDR images (Figs. 3A and 3B). In numerous instances, depiction of uroepithelial lesions was best on enhanced CTDR images compared with 3D rendered images (Figs. 4A and 4B). Although papillary abnormalities were best identified with 3D rendered MIP images, enhanced CTDR was able to identify nearly all papillary abnormalities, except one in a patient with focal papillary necrosis and another in a patient with mild medullary sponge disease (Figs. 4A and 4B). Enhanced CTDR alone could theoretically be used to evaluate the urinary collecting system. However, this technique suffers from the same limitations that influence excretory urography, which include large body habitus; abundant stool and bowel gas; overhydration; and limited ability to detect and discriminate small renal masses, urinary calculi, or extraurinary abnormalities.
|
|
|
|
Our study has several limitations. This was not an age-matched prospective study but rather a retrospective review of two groups of patients (saline vs nonsaline) evaluating urinary collecting system opacification during CT urography. Second, patients did not undergo two separate CT urography examinations with and without supplemental saline to compare urinary opacification. This protocol was not part of our institutional review board approval and would not have been acceptable due to high patient radiation dose. Finally, this study was not designed to compare the accuracy of enhanced CTDR to detect urinary abnormalities with 3D rendered CT urography. Further studies will be necessary to evaluate the ability of enhanced CTDR in depicting urinary abnormalities when compared with CT urography.
CT urography with 3D rendering is a relatively new technique that shows great potential in evaluating the genitourinary system, particularly as a screening procedure for patients with hematuria. CT urography has shown its ability to detect small urinary calculi, renal masses, and uroepithelial abnormalities. Despite technical advances, limitations in evaluating the entire urinary collecting system still exist. Opacification of the ureters remains the most elusive aspect in allowing CT urography to be used as an imaging technique for screening or detection of urinary abnormalities. The results of this study show that enhanced CTDR when combined with CT urography significantly improves opacification of the urinary collecting system, making this combined technique a more effective technique to evaluate the urinary system for abnormality. The use of a supplemental saline bolus offered no improvement in urinary collecting system opacification.
Acknowledgments
We thank Dr. Guillermo F. Carrera for his editorial assistance; Mary
Thielke, Maureen Levenhagen, and Jamie Meyer for assistance in 3D rendering
and data retrieval; and Jan Staedler for manuscript preparation.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  S. Kim, L. L. Wang, J. P. Heiken, C. L. Siegel, C. F. Hildebolt, and K. T. Bae Opacification of Urinary Bladder and Ureter at CT Urography: Effect of a Log-rolling Procedure and Postvoiding Residual Bladder Urine Volume Radiology, June 1, 2008; 247(3): 747 - 753. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J Richenberg Haematuria Imaging, March 1, 2008; 20(1): 57 - 72. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
