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Genitourinary Imaging |
1 From the Division of Abdominal Imaging and Intervention, Department of Radiology (S.G.S., S.A.A., K.J.M., K.T., J.G.B.) and Renal Division, Department of Medicine (J.L.S.), Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115. Received February 14, 2005; revision requested April 13; revision received August 4; accepted September 1; final version accepted December 21. Address correspondence to S.G.S. (e-mail: sgsilverman{at}partners.org).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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Materials and Methods: Institutional review board approval for review of patient images and medical records was obtained; informed consent was not required for this HIPAA-compliant study. Excretory phase images from multi–detector row CT urography in 87 patients (44 women, 43 men; age range, 21–83 years; mean, 53 years) were reviewed. Examinations were performed with, in addition to intravenous contrast medium, 250 mL of intravenous normal saline alone (n = 35), both 250 mL of normal saline and 10 mg of intravenous furosemide (n = 26), or 10 mg of furosemide alone (n = 26). Three readers, blinded to the imaging technique used, individually assigned opacification scores to each of six urinary collecting system segments. Urinary distention was assessed by one reader by measuring transverse widths of the proximal, middle, and distal ureteral segments. Mean opacification scores for each segment and mean ureteral width measurements for each technique were compared by using the Student t test.
Results: Mean opacification scores achieved with furosemide were significantly higher than those achieved with saline for the middle (P 
.008) and distal (P < .001) ureteral segments. Similarly, mean ureteral widths were significantly higher with furosemide than with saline for the middle (P .04) and distal segments (P = .01). There was no overall benefit of administering both saline and furosemide.
Conclusion: To optimize opacification and distention of the normal urinary collecting system, contrast material–enhanced multi–detector row CT urography may be supplemented with intravenous furosemide alone.
© RSNA, 2006
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INTRODUCTION |
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With the introduction of multi–detector row CT, the entire abdomen and pelvis can be imaged in a single breath hold with thinly collimated images (11). As a result, the urinary tract can be imaged with spatial resolution (in both transverse and nontransverse planes) that is sufficient to image the urothelium. Multi–detector row CT has been used to perform urography in an examination that includes unenhanced and enhanced images of the urinary tract and provides intravenous urography–like coronal images during the excretory phase (11,12). Multi–detector row CT urography has been shown to depict normal ureters (11) and reveal urothelial disease (12).
As at conventional intravenous urography, visualization of the intrarenal collecting system and ureter at multi–detector row CT urography depends on opacification and distention. A fundamental problem with multi–detector row CT urography (and with any imaging technique for attempting to image the entire urinary collecting system) is that, because of peristalsis, it is difficult to obtain a single image in which all urinary tract segments are opacified and distended. It has been shown that supplementing the contrast material used at multi–detector row CT urography with intravenous saline improves opacification of the collecting system and ureters (11). However, despite these findings, some patients' ureters may still not be fully opacified or distended (11). Therefore, the purpose of our study was to retrospectively evaluate whether administration of intravenous furosemide, either alone or in addition to intravenous saline, improved the depiction of the normal urinary collecting system at multi–detector row CT urography.
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MATERIALS AND METHODS |
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Institutional review board approval for viewing images and medical records of patients undergoing multi–detector row CT urography was obtained before the initiation of this study, which was compliant with the Health Insurance Portability and Accountability Act. Written informed consent was not required.
Because the pathologic causes of hydronephrosis and hydroureter would affect our ability to compare the techniques without bias, two patients with ureteropelvic obstruction (one from the group that had received both saline and furosemide, and one from the group that had received furosemide alone) were excluded. Similarly, three patients with obstructing urinary calculi (two of whom had received both saline and furosemide and one of whom had received furosemide) were excluded. One patient examined during the period in which the multi–detector row CT urography protocol included furosemide alone was excluded because of unclear documentation of the protocol in the medical record.
The study population therefore consisted of 87 patients, of whom 43 were men. The patients ranged in age from 21 to 83 years (mean, 53 years). After some patients were excluded as described above, there were 35 patients in the group that received saline alone, 26 in the group that received intravenous saline and furosemide, and 26 in the group that received intravenous furosemide alone. Using a one-way analysis of variance and Fisher exact tests, we found that there was no statistically significant difference among the three groups with respect to age and sex.
Multi–Detector Row CT Urography Technique
Multi–detector row CT urography was performed by using either a four–detector row (SOMATOM Volume Zoom; Siemens Medical Solutions, Forchheim, Germany) or a 16–detector row (SOMATOM Sensation 16; Siemens Medical Solutions) CT scanner. All patients were asked to void immediately before the examination and were given 900 mL of water orally. A three-scan CT protocol was used. The four–detector row CT urography protocol was as follows: For the unenhanced scan, the abdomen and pelvis were imaged by using 2.5-mm collimation with a pitch of 1.00–1.25, 120 kVp, and 155–200 mA. The kidneys were imaged during the nephrographic phase, 100 sec after intravenous administration of 100 mL of iopromide (Ultravist 300; Berlex Laboratories, Madison, NJ) at a rate of 3 mL/sec by using 2.5-mm collimation, a pitch of 1.00–1.25, 120 kVp, and 155–200 mA. The abdomen and pelvis were scanned during the excretory phase, 15 minutes after the contrast medium was injected, by using 1.0-mm collimation, a pitch of 0.65–1.00, 120 kVp, and 165–185 mA.
The 16–detector row CT urography protocol was as follows: For the unenhanced scan, the abdomen and pelvis were imaged by using 1.5-mm collimation with a pitch of 0.875, 120 kVp, and 160–280 mA. The kidneys were scanned during the nephrographic phase, 100 sec after intravenous administration of 100 mL of iopromide at a rate of 3 mL/sec by using 1.5-mm collimation, a pitch of 0.875, 120 kVp, and 160–280 mA. The abdomen and pelvis were scanned during the excretory phase, 15 minutes after the contrast medium was injected, by using 0.75-mm collimation, a pitch of 0.82–1.00, 120 kVp, and 160–280 mA. The mean effective dose for patients examined with the four–detector row CT scanner has been reported to be 14.8 mSv ± 3.1 (16).
Excretory phase images were analyzed for this investigation and were reconstructed transversely with 5-mm-thick sections at 5-mm increments and coronally with 3-mm-thick sections at 3-mm increments. Maximum intensity projection images and curved planar reformatted images were also reconstructed from 1.25-mm-thick images obtained at 1.0-mm increments with the four–detector row CT scanner and from 0.75-mm-thick images obtained at 0.5-mm increments with the 16–detector row CT scanner.
Furosemide (Lasix; Abbott Laboratories, North Chicago, Ill) at a dose of 10 mg was administered intravenously over 1 minute by a nurse or a physician 2–3 minutes before the contrast medium was injected. Furosemide was not administered if the patient reported a history of allergy to furosemide or other sulfa drugs or if the patient's systolic blood pressure was less than 90 mm Hg. Two hundred and fifty milliliters of saline was infused intravenously by using gravity immediately after administration of the contrast medium.
Image Analysis
Each collecting system was divided into the following six anatomic segments: the upper intrarenal collecting system (the calices and infundibula in the upper half of the kidney), the lower intrarenal collecting system (the calices and infundibula in the lower half of the kidney), the renal pelvis, the proximal portion of the ureter (above the iliac crest), the middle portion of the ureter (to the level of the sciatic notch), and the distal portion of the ureter (below the sciatic notch). This resulted in 12 anatomic segments per patient, or 1044 segments in the study. Three readers (S.G.S., K.J.M., and K.T., with 15, 7, and 6 years, respectively, of experience in reading CT scans of the genitourinary system), who were blinded to the technique used to acquire a given image, individually reviewed the transverse, coronal, maximum intensity projection, and curved planar reformatted images obtained from the excretory phase scans and assigned an opacification score for each segment.
The scoring system for opacification was as follows: A score of 0 indicated that the segment was unopacified; a score of 1, that less than 50% of the segment was opacified; a score of 2, that 50%–99% of the segment was opacified; and a score of 3, that the entire segment was opacified. The maximum ureteral width was determined for each proximal, middle, and distal ureteral segment by a single reader (S.A.A., a fellow in abdominal imaging) using the transverse images and at portions of the ureter that were not adjacent to iliac or other vessels that might have compressed the ureters and at portions of the ureter that were not coursing obliquely through the imaging plane. All images were reviewed by using a picture archiving and communication system (IMPAX 4.1; Agfa Medical Imaging, Greenville, SC).
Statistical Methods
Readers' scores for each segment for each technique were analyzed for interobserver variability by using a two-way analysis of variance, and P values were compared. These values were computed separately for the right and the left sides. Because the interobserver variability was significantly high in some of the segments (P < .008), and because our main objective was to evaluate techniques, the readers' scores for each patient were averaged to yield a mean opacification score for each segment for each technique. For each anatomic segment, the mean opacification scores and mean maximum ureteral widths (in millimeters) were compared across techniques by using a one-tailed two-sample Student t test. We applied the Bonferroni correction to adjust for multiple testing of hypotheses and thus tested for significance against an 
level of .017. These comparisons were performed separately for the right and left sides. With these statistical tests, P values were considered approximate and anticonservative because we approximated ordinal scores with the assumption of continuous distributions of the opacification scores.
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RESULTS |
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Comparison of Mean Maximum Ureteral Width between Techniques
Overall, mean maximum ureteral widths were higher when multi–detector row CT urography was performed with furosemide than when it was performed with saline (Figs 4, 5). The mean maximum widths of the middle ureteral segments when multi–detector row CT urography was performed with furosemide (6.08 mm for the right side, 5.96 mm for the left) were significantly higher than the widths for the same segments when the examination was performed with saline (5.30 mm for the right side [P = .04], 4.87 mm for the left [P = .01]). The mean maximum widths of the distal ureteral segments when multi–detector row CT urography was performed with furosemide (4.53 mm for the right side, 4.61 mm for the left) were also significantly higher than the widths for the same segments when the examination was performed with saline (3.84 mm for the right side, 3.93 mm for the left; P = .01 for both) (Figs 4, 5).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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To explain our findings, it is important to consider the physiologic effects of the fluids and substances administered to the patients. First, water, which was administered orally to all patients, induces mild diuresis. A water load decreases systemic osmolality by a small percentage that is large enough to inhibit release of antidiuretic hormone (17). Once antidiuretic hormone is inhibited, hypotonic diuresis without a change in glomerular filtration rate ensues within approximately 20 minutes in a person with normal renal function. Second, saline-induced diuresis occurs predominantly through an increase in glomerular filtration rate, as well as through a volume expansion–induced increase in atrial natriuretic peptide and inhibition of aldosterone (18,19). The mechanism of action of furosemide involves inhibition of sodium chloride reabsorption in the renal thick ascending limb of Henle, with a subsequent decrease in fluid reabsorption in the renal medulla (18,19). Two features that distinguish saline-induced diuresis from furosemide-induced diuresis are (a) saline increases glomerular filtration rate, while furosemide does not increase and may even decrease glomerular filtration rate to a small extent and (b) furosemide increases urine flow rate more promptly and to a greater extent than does saline, particularly in a "water-loaded" subject. Therefore, because contrast medium is mostly filtered, saline increases opacification of the collecting system by increasing contrast medium excretion (18,20). Third, furosemide, by promptly increasing urinary flow rate, decreases urinary transit time in any one segment (19). Finally, urinary transit time varies among urinary segments; transit time is prolonged in the renal pelves (where there is a greater capacity or reservoir effect) relative to the ureters (21–23).
Therefore, as regards our study findings, we believe that, by increasing urine flow rate, furosemide increased opacification and distention by presenting more contrast medium to all segments of the urinary tract. The effects of furosemide were greater than those of saline in the middle and distal ureteral segments because the diuretic effects of furosemide were more rapid and of greater magnitude. In addition, by decreasing transit time, furosemide made more contrast medium available to the middle and distal ureteral segments. Because the ureters are smaller in caliber than the renal pelves, to maintain a constant flow through the urinary tract, velocity must increase within the narrower conduit, thereby delivering more contrast medium to the ureters. Our data suggest that the predominant factor in ureteral opacification was decreased transit time rather than differences in the amount of contrast medium filtered among the different protocols. The effect of saline was greater than that of furosemide in the renal pelves because the capacity of the renal pelves is greater than that of the ureters; therefore, the predominant factor in renal pelvis opacification was not transit time but rather the amount of filtered contrast medium, which was increased in only the patients who received saline.
Furosemide was found to be helpful in opacifying 94% of ureters in 16 patients in a relatively recent study (15). However, that study included a small number of patients, and, although saline was used in five patients, the two techniques were not compared. Others have described techniques for achieving a fully opacified and distended collecting system. A single–detector row CT urographic technique has been described (24) in which the excretory phase of contrast medium excretion was imaged with two scans—one scan of the intrarenal collecting system with application of an abdominal compression device, and one scan of the ureters after the device was removed. An abdominal compression device, which has been used for many years during intravenous urography, is purported to distend the intrarenal collecting system. When the device is removed, the ureters distend as a result of a "bolus" effect.
Indeed, studies (24,25) have revealed improved distention of the upper tracts when a compression device is used. However, results of a recent study (26) showed that abdominal compression during multi–detector row CT urography did not significantly improve distention or opacification of any portion of the urinary tract. Also, compression devices are often ineffective in obese patients and are relatively contraindicated in patients with abdominal aortic aneurysms, acute obstruction, or abdominal stomas and in patients who have recently undergone abdominal surgery (27). Finally, these devices require imaging of the urinary tract to be divided into two components—imaging of the intrarenal collecting system and imaging of the ureters— therefore, a single image of the entire urinary tract is not possible.
A four-scan multi–detector row CT urography protocol has been reported (12). In addition to the unenhanced and nephrographic phase scans, two excretory phase scans were included, one each at 300 and 450 sec. Two scans during the excretory phase were used to increase the chance that a given ureteral segment was opacified. However, in general, patient radiation dose is higher if two scans are performed instead of one. Radiation exposure is an important issue in the choice of CT urographic technique. Skin doses for a similar three-scan CT urography protocol (without current modulation software) were comparable to those at intravenous urography, but the total effective dose was approximately 50% higher (16). Use of tube current modulation software can help reduce radiation dose substantially (28). As the CT table and the patient move through the CT gantry during a continuous x-ray exposure, tube current is adjusted to account for different body part thicknesses. Quantum noise in the projections is adjusted to maintain a desired noise level in the image and to improve dose efficiency (28). Dose estimates at multi–detector row CT urography performed with tube current modulation software deserve further study.
Multi–detector row CT with a split dose of contrast medium has been described (29). Relative to the protocol we used, this technique is advantageous in that it reduces the number of scans from three to two: An unenhanced scan and an enhanced scan that yields both a nephrogram resulting from an injected contrast medium dose of 80 mL (300 mg/mL) and a pyelogram from a dose of 40 mL injected 2 minutes earlier (29). The disadvantages of this technique are largely theoretical. When the contrast medium dose is divided into two, less contrast material is available to create a nephrogram and less is available to opacify the collecting system. However, the former issue could be overcome by using a higher dose of contrast medium, and the latter issue could be overcome by adding furosemide to the regimen.
In our study, opacification scores were assigned by three independent readers who were blinded to the technique used to acquire the image. Because measurement of width is more objective, only one reader measured the maximum ureteral widths. However, the benefit of furosemide was confirmed in both of these situations. A limitation of our study was its retrospective nature and small sample size. In the future, a prospective randomized study would be helpful to corroborate our findings. Also, our opacification scoring system was limited in that, for example, a ureteral segment that was 50% opacified received the same score as one that was 99% opacified. However, we intended to use a simple reproducible scoring system that was comparable with our existing scoring system (11).
We intended to test statistically the equivalence of the mean opacification scores and ureteral widths among the three techniques. Hence, we used a two-sample t test with unequal variances for our analysis. A nonparametric Wilcoxon test would have been appropriate if we had compared median values. Our study examined how well anatomic structures were depicted. Additional studies are needed to determine if furosemide provides any benefit in the detection and characterization of urothelial abnormalities.
Finally, as with the administration of any drug, the benefits of administration of furosemide need to be weighed against the risks. We found the use of furosemide during multi–detector row CT urography to be safe. Although one episode of mild urticaria could have been attributed to furosemide rather than to the contrast medium, it was the radiologists' impression at time of the incident that the reaction was likely related to the contrast medium. The safety of furosemide is further supported by our department's experience; we have had no reports of adverse reactions related to furosemide administered during nuclear medicine or MR imaging examinations.
At multi–detector row CT urography, administration of intravenous furosemide helped opacify and distend the urinary collecting system and ureters better than did the administration of intravenous saline; administration of both agents did not achieve better overall results than administration of furosemide alone. The use of saline, with or without furosemide, resulted in significantly higher opacification scores in only the renal pelves. However, the mean opacification scores for the right (2.72) and left (2.69) renal pelves when multi–detector row CT urography was performed with furosemide alone were still excellent. Furthermore, there was less distention of the middle and distal ureteral segments when both furosemide and saline were used than when furosemide alone was used. Therefore, our routine protocol now employs intravenous furosemide, with intravenous saline reserved for patients with an allergy to furosemide or other sulfa drugs and for patients with a systolic blood pressure of less than 90 mm Hg.
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ADVANCES IN KNOWLEDGE |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, S.G.S., S.A.A.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, S.G.S., S.A.A., K.J.M., J.L.S.; clinical studies, S.G.S., S.A.A., K.J.M., K.T.; statistical analysis, S.A.A., J.G.B.; and manuscript editing, all authors
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References |
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