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Published online before print April 15, 2008, 10.1148/radiol.2473070965
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(Radiology 2008;247:747-753.)
© RSNA, 2008

Genitourinary Imaging

Opacification of Urinary Bladder and Ureter at CT Urography: Effect of a Log-rolling Procedure and Postvoiding Residual Bladder Urine Volume1

Sooah Kim, MD 2, Lihuan L. Wang, MD, Jay P. Heiken, MD, Cary L. Siegel, MD, Charles F. Hildebolt, DDS, PhD, and Kyongtae T. Bae, MD, PhD

1 From Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo. From the 2006 RSNA Annual Meeting. Received June 8, 2007; revision requested August 13; revision received September 18; accepted October 16; final version accepted November 13. Address correspondence to K.T.B., Department of Radiology, University of Pittsburgh School of Medicine, 200 Lothrop St, Pittsburgh, PA 15213 (e-mail: baek{at}upmc.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Purpose: To retrospectively evaluate the effect of a log-rolling procedure and postvoiding residual (PVR) bladder urine volume on opacification of urinary bladder and ureters at multi–detector row computed tomographic (CT) urography.

Materials and Methods: Institutional review board approval was obtained, and informed consent was waived for this retrospective HIPAA-compliant study. Triple-phase 16– or 64–detector row CT urographic images in 166 patients (88 men, 78 women; mean age, 58.9 years; range, 22–89 years) were evaluated retrospectively. Immediately prior to excretory phase scanning, 67 patients did and 99 did not undergo a log-rolling procedure on the CT table. PVR bladder urine volume was quantified as the largest cross-sectional area of the bladder measured on unenhanced images (PVR values). The degree of bladder opacification was quantified as the percentage of the total cross-sectional area of the bladder that was opacified on excretory phase images. Ureteral opacification was quantified as the percentage of ureteral length that contained enhanced urine. On the basis of PVR values, patients were stratified into four subgroups (≤2000, >2000 to ≤3000, >3000 to ≤4000, and >4000 mm2). The Wilcoxon rank sum and Student t tests were used to evaluate differences.

Results: Median degree of bladder opacification of the log-rolling versus non–log-rolling group was 100% versus 78% for PVR values of 2000 mm2 or less (P < .01), 99% versus 79% for PVR values of more than 2000 to 3000 mm2 or less (P = .01), 89% versus 79% for PVR values of more than 3000 to 4000 mm2 or less (P < .05), and 64% versus 69% for PVR values of more than 4000 mm2 (P = .96). There was no significant difference between ureteral opacification and log rolling or between bladder and ureteral opacification (P > .05).

Conclusion: Use of a log-rolling procedure prior to excretory phase CT urography increases the percentage of bladder opacification in patients with PVR values of 4000 mm2 or less. No difference in ureteral opacification was observed between the log-rolling and non–log-rolling groups.

© RSNA, 2008


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Multi–detector row computed tomographic (CT) urography is increasingly being used for the evaluation of patients with hematuria, patients suspected of having urinary tract abnormalities, and patients with tumors. CT urographic techniques are, however, still evolving, and no clear consensus about the optimal CT urographic protocol has been reached (1–4).

Maximizing opacification and distention of the urinary tract during the excretory phase of enhancement is desirable because it is believed that doing so improves detection of urothelial neoplasms and other abnormalities in the pelvicaliceal systems, ureters, and bladder. Various protocol modifications have been applied to the standard CT urographic examination to improve the opacification and distention of the urinary tract (1–11). To our knowledge, however, the effect of rolling the patient on the CT table immediately prior to the excretory phase image acquisition has not been studied. To our knowledge, although patients usually are asked to empty their bladders prior to CT urography, findings from the evaluation of the effect of postvoiding residual (PVR) bladder urine volume on the opacification of the urinary tract have not been reported.

Thus, the purpose of our study was to retrospectively evaluate the effect of a log-rolling procedure and PVR bladder urine volume on opacification of the urinary bladder and ureters at multi–detector row CT urography.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Institutional review board approval was obtained, and informed consent was waived for this retrospective Health Insurance Portability and Accountability Act–compliant study.

Patients
On the basis of our consideration that opacification of the urinary bladder and ureters might be improved with a log-rolling procedure, our department-approved clinical CT urographic scanning protocol included a log-rolling procedure immediately prior to excretory phase scanning as of January 2005. Of 223 consecutive patients who underwent multi–detector row CT urography between April 2004 and July 2005, 57 patients who had undergone total or partial cystectomy at the time of the CT examination were excluded. Thus, a total of 166 patients were included in our study; the log-rolling group consisted of 67 patients, and the non–log-rolling group consisted of 99 patients. The entire study group consisted of 78 women and 88 men (mean age, 58.9 years; range, 22–89 years); the log-rolling group included 30 (45%) women and 37 (55%) men (mean age, 58.0 years; range, 23–89 years), and the non–log-rolling group included 48 (48%) women and 51 (52%) men (mean age, 59.5 years; range, 22–86 years). Patients were referred for multi–detector row CT urography as part of an evaluation for hematuria (n = 139), known or suspected urothelial neoplasm (n = 4), flank or back pain (n = 15), or urinary tract infection (n = 8).

CT Urographic Imaging Protocol
Multi–detector row CT urography had been performed by using either a 16–detector row (Somatom Sensation 16; Siemens Medical Solutions, Forchheim, Germany) or a 64–detector row (Somatom Sensation 64; Siemens Medical Solutions, Forchheim, Germany) CT scanner. All patients received 1000 mL of water orally 15–30 minutes before the examination and were instructed to void immediately before the examination. The protocol consisted of three phases of CT: unenhanced, nephrographic, and excretory. CT was performed with the patient in the supine position without abdominal compression or administration of a diuretic.

For the 16–detector row CT urographic protocol, an unenhanced CT scan from the kidneys to the urinary bladder was first obtained by using 16 x 1.5-mm collimation, 120 kVp, and 118–234 mAs. The kidneys were scanned again during the nephrographic phase at 100 seconds after the administration of 125 mL of 350 mg of iodine per milliliter intravenous contrast material (Optiray 350; Tyco Healthcare Mallinckrodt, St Louis, Mo) at a flow rate of 2 mL/sec with 16 x 1.5-mm collimation, 120 kVp, and 116–281 mAs. Then, patients received an intravenous drip infusion of 120 mL of normal (0.9%) saline. The abdomen and pelvis were rescanned during the excretory phase 10 minutes after the administration of contrast medium, with 16 x 1.5-mm collimation, 120 kVp, and 104–257 mAs. The 64–detector row CT urographic protocol was similar to the 16–detector row CT urographic protocol except for the use of 64 x 0.6-mm collimation and minor variations in the tube current–time product (104–247 mAs for unenhanced CT, 104–299 mAs for nephrographic phase CT, and 109–318 mAs for excretory phase CT).

For the log-rolling protocol, patients were asked to roll 360° on the CT table immediately prior to excretory phase scanning. A topogram was repeated to recenter the abdominopelvic scanning range. The excretory phase images were reconstructed transversely with a section thickness of 1 mm.

Image Analysis
CT images were retrieved from the institutional picture archiving and communication system and were sent to a clinical workstation (Leonardo; Siemens Medical Solutions, Iselin, NJ). The images were displayed with the standard soft-tissue window settings (window width, 400 HU; window level, 30 HU). The unenhanced images were reviewed to select the largest cross-sectional transverse area of the urinary bladder. The inner bladder boundary was manually delineated by one of the authors (S.K., who had 3 years of experience in interpretation of CT urographic images) to measure the area as an index to quantify PVR bladder urine volume.

The evaluation of bladder and ureteral opacification on the excretory phase CT images was performed separately 2 weeks after the measurement of PVR bladder urine volume on the unenhanced CT images to prevent any influence of one on the other. The excretory phase images were displayed with the standard soft-tissue window setting and were reviewed to select the image with the largest cross-sectional area. The inner boundary of the entire bladder was delineated manually by using a workstation computer mouse. The boundary points were added by clicking the mouse button; each new point was connected to the previous one, and the boundary was completed when the last point was connected to the initial one. The area within the boundary, which corresponded to the total cross-sectional area of the bladder, was computed with the workstation measurement tool. Similarly, the contrast material–filled portion of the bladder was delineated, and its area was measured (Fig 1). (Hereafter, the opacified area measurement for PVR bladder urine volume on CT images will be referred to as the PVR value.) For the purpose of this study, only the portion of the bladder that contained the highest-attenuation urine was considered to be opacified. The degree of bladder opacification was quantified in terms of a percentage by calculating the ratio of the contrast material–filled portion to the total cross-sectional area of the bladder. Bladder opacification was assessed by one reader (S.K.).


Figure 1A
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  		Figure 1a: Transverse CT urographic images obtained with non–log-rolling procedure in 41-year-old woman. (a) Unenhanced CT scan shows urinary bladder with a total PVR value of 3996 mm2. (b) Contrast material–enhanced CT scan obtained during excretory phase in same patient shows 71% opacification of urinary bladder by calculating ratio (percentage) of contrast material–filled portion (4411 mm2) to total cross-sectional area of bladder (6194 mm2).

 

Figure 1B
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  		Figure 1b: Transverse CT urographic images obtained with non–log-rolling procedure in 41-year-old woman. (a) Unenhanced CT scan shows urinary bladder with a total PVR value of 3996 mm2. (b) Contrast material–enhanced CT scan obtained during excretory phase in same patient shows 71% opacification of urinary bladder by calculating ratio (percentage) of contrast material–filled portion (4411 mm2) to total cross-sectional area of bladder (6194 mm2).

 
The excretory images were displayed and scrolled to assess the degree of ureteral opacification with the consensus of two readers (S.K. and L.L.W., each of whom had 3 years of experience in interpretation of CT urographic images). A ureteral segment was considered opacified if it contained enhanced urine (Fig 2). The percentage of ureteral opacification was quantified by calculating the ratio of the number of transverse images that depicted the enhanced ureter to the total number of transverse images in which the ureter was demonstrated. The entire length of the ureter from the ureteropelvic junction to the ureterovesical junction and the pelvic ureter (inferior margin of the sacroiliac joint to the ureterovesical junction) were assessed for the evaluation of the relationship between bladder and ureteral opacification.


Figure 2A
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  		Figure 2a: Transverse excretory phase CT urographic images of (a) proximal, (b) lower, and (c) pelvic ureter in 65-year-old man. Right pelvic ureter was not opacified.

 

Figure 2B
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  		Figure 2b: Transverse excretory phase CT urographic images of (a) proximal, (b) lower, and (c) pelvic ureter in 65-year-old man. Right pelvic ureter was not opacified.

 

Figure 2C
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  		Figure 2c: Transverse excretory phase CT urographic images of (a) proximal, (b) lower, and (c) pelvic ureter in 65-year-old man. Right pelvic ureter was not opacified.

 
Statistical Analysis
The patients were stratified according to PVR value subgroups (≤2000 mm2, >2000 to ≤3000 mm2, >3000 to ≤4000 mm2, and >4000 mm2), and statistical comparisons of the degree of bladder and ureteral opacification were made between the log-rolling and non–log-rolling patients for each of the stratified subgroups.

Statistical analysis was performed with software (JMP, release 5.0.1, SAS Institute, Cary, NC; MedCalc, version 9.2.1.0, MedCalc Software, Mariakerke, Belgium). Data distributions were tested for normality with Shapiro-Wilk W tests and were tested for equality of variances with O'Brien, Brown-Forsythe, Levene, and Bartlett tests. For nonpaired comparisons of data that had normal distributions and equal variances, the Student t test was used; otherwise, the Wilcoxon rank sum test was employed. For paired comparisons with normally distributed differences, the paired t test was used. For paired comparisons with nonnormally distributed differences, the Wilcoxon signed rank test was used. For normally distributed differences, 95% confidence intervals (CIs) for the mean differences were calculated, and for nonnormally distributed differences, 95% CIs for the median differences were calculated. The Fisher exact test was used to test for differences in sex between the log-rolling and non–log-rolling groups. A P value of less than .05 indicated a significant difference.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Patient Groups
Sex distribution between the log-rolling and non–log-rolling groups was not significant (P = .75, Fisher exact test). Ages for the two groups were normally distributed (P ≥ .10, Shapiro-Wilk W test), and the variances were equal (P > .05, O'Brien, Brown-Forsythe, Levene, or Bartlett test). The mean age for the 99 subjects in the non–log-rolling group was 59 years ± 14 (standard deviation), and the mean age for the 67 subjects in the log-rolling group was 58 years ± 16. The 1-year difference (95% CI: –3, 6) in age in years between groups was not significant (P = .55, Student t test).

PVR Bladder Urine Volume Measurements
PVR values ranged from 476 to 7606 mm2 for the log-rolling group and from 43 to 9097 mm2 for the non–log-rolling group. The numbers of patients in the PVR value subgroups of 2000 mm2 or less, more than 2000 to 3000 mm2 or less, more than 3000 to 4000 mm2 or less, and more than 4000 mm2 were 15, 12, 15, and 25, respectively, for the log-rolling group and were 25, 18, 14, and 42, respectively, for the non–log-rolling group. For most comparisons, Shapiro-Wilk W tests indicated that data for one or both of the groups were nonnormally distributed (P < .05) and/or that the variances for the two groups were not equal (P < .05, O'Brien, Brown-Forsythe, Levene, or Bartlett test). Summary statistics are presented as medians and ranges.

Ureter and Bladder Opacification
When PVR values were 2000 mm2 or less, a Wilcoxon rank sum test indicated that patients in the log-rolling group had higher percentages of bladder opacification (median, 100%; range, 67%–100%) than did patients in the non–log-rolling group (median, 78%; range, 11%–100%) (Fig 3); the median difference was 16% (95% CI: 0%, 39%), and P < .01. The Wilcoxon rank sum test indicated similar results for patients with PVR values from more than 2000 to 3000 mm2 or less; for the log-rolling group, the median was 99% and the range was 58%–100%, and for the non–log-rolling group, the median was 79% and the range was 11%–100%; the median difference was 16% (95% CI: 0%, 29%), and P = .01. For patients with PVR values from more than 3000 to 4000 mm2 or less, the median and range were 89% and 2%–100%, respectively, for the log-rolling group, and the median and range were 79% and 11%–100%, respectively, for the non–log-rolling group; the median difference was 9% (95% CI: 0%, 17%), and P < .05. However, for patients with PVR values of more than 4000 mm2, a Student t test indicated that there was no difference in percentage of opacification between log-rolling group patients (median, 64%; range, 12%–100%) and non–log-rolling group patients (median, 69%; range, 5%–100%); the median difference was –15% (95% CI: –27%, 9%), and P = .96. Thus, the log-rolling procedure produced significantly greater percentages of bladder opacification for the three subgroups with smaller PVR values (ie, ≤2000, >2000 to ≤3000, and >3000 to ≤4000 mm2) but not for the subgroup with the largest PVR value (ie, >4000 mm2).


Figure 3
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  		Figure 3: Comparison of bladder opacification in log-rolling and non–log-rolling groups according to subgroups of PVR opacified areas. Data points are spread horizontally to minimize overlapping. Ends of boxes are 25th and 75th quantiles (quartiles). Lines across middle of boxes are medians. Interquartile range is difference between quartiles. Lines (whiskers) extend from boxes to outermost points that are within distance computed as 1.5 (interquartile range).

 
Wilcoxon rank sum tests indicated no difference in opacification of the ureters between patients who did and did not undergo log rolling for any of the PVR value subgroups: (a) For PVR values of 2000 mm2 or less, the median and range for the log-rolling group and the non–log-rolling group were 99% and 0%–100%, respectively; the median difference was –1% (95% CI: –26%, 25%), and P = .78 (Fig 4). (b) For PVR values of more than 2000 to 3000 mm2 or less, the median and range for the log-rolling group and non–log-rolling group were 100% and 0%–100%, respectively; the median difference was 0% (95% CI: –20%, 1%), and P = .62. (c) For PVR values of more than 3000 to 4000 mm2 or less, the median and range for the log-rolling group and the non–log-rolling group were 100% and 0%–100%, respectively; the median difference was 0% (95% CI: –1%, 1%), and P = .86. (d) For PVR values of more than 4000 mm2, the median and range for the log-rolling group were 100% and 20%–98%, respectively, and the median and range were 100% and 22%–100%, respectively, for the non–log-rolling group; the median difference was 0% (95% CI: –15%, 0%), and P = .74.


Figure 4
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  		Figure 4: Comparison of ureteral opacification in log-rolling and non–log-rolling groups according to subgroups of PVR opacified areas. Data points are spread horizontally to minimize overlapping. Ends of boxes are 25th and 75th quantiles (quartiles). Lines across middle of boxes are medians. Interquartile range is difference between quartiles. Lines (whiskers) extend from boxes to outermost points that are within distance computed as 1.5 (interquartile range).

 
No significant difference was found between bladder opacification and opacification for the entire length of the ureter (mean difference, 7.3% [95% CI: –0.4%, 15.1%]; P = .06, paired t test) or for opacification of the pelvic ureter (median difference, –4.2%; range, –64% to 100% [95% CI: –16%, 0%]; P = .57, Wilcoxon signed rank test).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Although researchers in several studies (5,6,12) have reported improved opacification of the intrarenal collecting systems and ureters when abdominal compression is applied during CT urography, those in another study (8) found no improvement with the compression. Findings in other studies (7–9) have suggested that pelvicaliceal and ureteral opacification is improved with supplemental intravenous saline hydration during CT urography. More recently, improved ureteral opacification and distention have been demonstrated when furosemide is administered intravenously 2–3 minutes prior to contrast medium administration (11). Investigators in still another study (13) demonstrated reliable opacification of the upper urinary tract and ureters with intravenous furosemide administration combined with excretory phase scan timing that was based on single-section test images obtained through the distal ureters. Although researchers in one study (12) reported improved opacification of the middle and distal ureters when patients were scanned in the prone position, those in another study (7) failed to demonstrate such an improvement with prone patient positioning.

Our study results demonstrate that patient log rolling just prior to excretory phase image acquisition improves bladder opacification in most patients but does not improve opacification of the ureters. The improved bladder opacification can be attributed to improved upper urinary tract collecting system emptying when the patient passes through the prone position during the log-rolling maneuver combined with improved mixing of the contrast-enhanced and unenhanced urine within the bladder. The lack of improvement in bladder opacification after log rolling in patients with a large PVR value (ie, area measurement of >4000 mm2) may be related to elevated pressure within the bladder and associated decreased emptying into the bladder of opacified urine from the ureters. This lack of improvement in bladder opacification in patients with a large PVR value underscores the importance of minimizing bladder volume prior to CT urography. Minimal bladder volume can be achieved by having patients void immediately prior to the start of CT urography. Selected patients who cannot void completely may benefit from catheter drainage of the bladder immediately prior to the examination.

A log-rolling maneuver to improve the uniformity of bladder opacification has been reported in studies of virtual cystoscopy (14,15). For CT urography, an advantage of log rolling relative to prone positioning of the patient for the excretory phase image acquisition is that prone positioning is uncomfortable for some patients and may not be feasible for others (some postoperative patients). Almost all patients undergoing CT urography are capable of log rolling, even patients who have undergone cystectomy with ileal diversion. However, such patients may not be able to maintain prone positioning during the CT examination because of discomfort from lying on their ileostomy bags and, in some cases, external or internal catheters.

Lack of improvement in ureteral opacification after log rolling is more difficult to explain but may be related to ureteral peristaltic activity occurring between completion of the log rolling and commencement of the excretory phase image acquisition. In addition, the relatively high baseline percentage of 85% for ureteral opacification without log rolling makes it difficult to show a significant improvement with log rolling.

One disadvantage of the technique used in our study is that a second CT scout image (topogram) was obtained after the log-rolling maneuver to ensure proper positioning of the excretory phase scan volume. This additional image and its associated small increase in the overall radiation dose to the patient can be eliminated by marking the patient's position at the initial reference CT scanning table position, which is denoted by the projection of a built-in linear laser light beam in the CT scanner, with a piece of tape prior to log rolling.

Our study had limitations. Our log-rolling protocol consisted of a single 360° rotation of the patient on the CT table prior to the excretory phase acquisition. It is possible that more aggressive maneuvers for contrast material mixing, as suggested by other investigators (16), might have resulted in a greater difference between the log-rolling and non–log-rolling patient groups.

With regard to ureteral opacification, we evaluated only the percentage of ureteral length opacified and did not assess the degree of ureteral distention. In addition, we did not evaluate opacification of the intrarenal collecting systems.

Additional limitations of our study were that we used two-dimensional transverse images for the assessment of bladder opacification rather than three-dimensional volumetric measurements, and we did not assess the attenuation homogeneity of the urine within the bladder.

There could also be factors, such as time, that we did not include in our analysis but that could be responsible for at least some of the differences between the log-rolling and non–log-rolling groups.

Furthermore, in our CT urographic protocol, all our patients were asked to void immediately prior to CT, and we assessed the effectiveness of log rolling only in these patients. Although it would have been interesting to include and investigate patients who were not asked to void as a control group, doing so was not feasible in our retrospective study.

Finally, our study was designed to assess bladder and ureteral opacification, and we did not attempt to assess differences in the detection of urothelial abnormalities between the log-rolling and non–log-rolling patient groups, for which a much larger study would be needed.

In summary, our results indicate that use of a log-rolling procedure prior to excretory phase image acquisition at CT urography increases the percentage of the bladder lumen that is opacified when the PVR value at the start of the examination is 4000 mm2 or less. We found no difference in ureteral opacification between the log-rolling and non–log-rolling groups.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
References
 


   FOOTNOTES
 

Abbreviations: CI = confidence interval • PVR = postvoiding residual

2 Current address: Department of Radiology, New York University Medical Center, New York, NY. Back

Author contributions: Guarantors of integrity of entire study, S.K., L.L.W.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, S.K., L.L.W., J.P.H., K.T.B.; clinical studies, S.K., L.L.W.; statistical analysis, C.F.H.; and manuscript editing, all authors

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 

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