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Technical Innovation |
1 All authors: The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 601 N. Caroline St./3235A, Baltimore, MD 21287.
Received September 14, 2004;
accepted after revision February 16, 2005.
Address correspondence to S. Kawamoto
(skawamo1{at}jhmi.edu).
Keywords: excretory phase • MDCT • opacification • water ingestion
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For evaluation of the renal collecting system and ureters, optimal opacification and distention is essential. Various techniques to optimize opacification and distention of the renal collecting system and ureters have been reported in the literature. To optimize opacification, abdominal compression [1-5], saline infusion [6, 7], multiple acquisitions [2], prone positioning [1, 6, 7], and furosemide administration [7] have been successfully used. Abdominal compression has also been used to improve distention of the renal collecting system [4].
As a part of a routine 3-phase CT examination in patients with suspected urinary tract abnormalities, we evaluated the degree of opacification of the renal collecting system and ureters on excretory-phase images obtained without abdominal compression, prone positioning, or IV administration of saline or furosemide. Instead, 750-1,000 mL of water was ingested as oral contrast and for diuresis. The purpose of this study is to evaluate the degree of opacification of the renal collecting system and ureters on excretory-phase contrast-enhanced CT using only oral ingestion of water without abdominal compression, saline infusion, or prone positioning.
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CT Technique
All examinations were performed on a Sensation 16 scanner (Siemens Medical
Solutions). After being kept on NPO (nothing by mouth) status for at least 2-3
hr, each patient ingested 750-1,000 mL of water over a 15-20 min period before
scanning began. Nearly all patients were able to drink the entire 750-1,000 mL
of water without difficulty.
For administration of IV contrast material, a 20-gauge peripheral line was inserted into an antecubital fossa vein and 120 mL of iohexol (Omnipaque 350, Amersham Health) was injected at an injection rate of 3 mL/sec. The protocol for evaluation of the patients included the following 3-phase scanning procedure: unenhanced scan through the kidneys to just below the symphysis pubis, arterial phase scan of the kidneys at 25 sec after IV contrast injection, and excretory-phase scan from the kidneys to just below the symphysis pubis at 240 sec after IV contrast injection.
For unenhanced scans, parameters were 3-mm slice thickness and 3-mm increments. For arterial and excretory phases, parameters were 0.75-mm slice thickness and 0.5-mm reconstruction increments. Parameters for contrast-enhanced scans were 16 x 0.75 mm detector collimation, 12 mm per rotation table speed, 0.5-sec gantry rotation speed, 120 kVp, and 120-150 mAs.
All image data were reconstructed with the body soft-tissue algorithm and sent to a freestanding commercially available workstation (Leonardo, Siemens Medical Solutions) using InSpace software (Siemens) in the original resolution of 512 x 512. Excretory-phase data were used to evaluate the degree of opacification of the collecting system and ureters. InSpace software is the volume imaging application for interactive viewing of volume data available on the Leonardo workstation. It provides reviewers real-time axial scrolling, interactive multiplaner reformatting, and 3D rendering for review of images.
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Each urinary tract was divided into four segments: renal calices and
infundibula, renal pelvis, upper ureter above the iliac crest, and lower
ureter below the iliac crest. The degree of opacification for each segment was
evaluated using a scale from 1 to 3. Scores were 3 = complete opacification of
the entire renal collecting system or ureter, 2 = near complete (80-99%)
opacification of the renal collecting system or ureter, and 1 = no or poor
(
79%) opacification of the renal collecting system or ureter.
Interobserver agreement was assessed using kappa statistics. Values of kappa
greater than 0.75 indicate strong agreement beyond chance, values between 0.40
and 0.79 indicate fair to good, and values below 0.40 indicate poor agreement.
Abnormal findings were also recorded if present.
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values for the degree of
opacification of the calyx and infundibulum of 0.46, renal pelvis 0.72, upper
ureter 0.86, and lower ureter 0.61. Four patients had mild dilatation of the renal collecting system and ureter on one side. The affected side of the renal collecting system and ureter was completely or nearly completely opacified in these four patients. One patient had a transitional cell carcinoma of the renal pelvis and had a ureteral stent (Figs. 3A, 3B, and 3C), one patient had a benign ureteral stricture, and the other two patients had an external compression on the ureter—one patient from the iliac artery and the other from a large bladder diverticulum.
Other abnormal findings included bilateral calyceal blunting with cortical scarring because of recurrent reflux nephropathy in one patient (Figs. 4A and 4B), bilateral duplicated renal collecting system in one patient, and stretching of the renal collecting system because of parapelvic cysts in three patients. A solid renal mass was found in six patients.
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However, abdominal compression may be contraindicated and thus may not be applied in some patients, such as those with abdominal aortic aneurysm [8]. With prone positioning, McNicholas et al. [1] reported that there was a significantly higher opacification score of the mid ureter compared with supine positioning. McTavish et al. [6] reported that with supplemental 250 mL of IV saline solution administration, there were significantly improved mean opacification scores in the distal ureters in procedures performed with prone or supine positioning.
When supplemental saline was administered, 94% of all segments achieved greater than 50% opacification. However, there was no statistically significant difference between supine and prone positioning with this technique [6]. Nolte-Ernsting et al. [7] reported that with a 250-mL saline infusion, there was complete or near-complete opacification of the ureters in 60% and pelvicaliceal system in 90% in 10 ureters and 10 pelvicaliceal systems in five patients, which further improved to 94% and 100% with IV administration of 10 mg of furosemide in 32 ureters and 32 pelvicaliceal systems in 16 patients.
In our series, oral hydration was devised as a simple substitution for the previously reported techniques of abdominal compression, saline infusion, and furosemide administration and allowed for a minimal amount of wait time for the patient and reduced the effect on workflow and room utilization. With the average CT acquisition with 16-MDCT scanners in the range of 10-30 sec, a short delay that does not compromise study quality is a welcome benefit to a smooth and efficient clinical operation in 32 ureters and 32 pelvicaliceal sytems in 16 patients.
There were several limitations of our study. First, in this study we were unable to compare the results with those of patients who did not ingest water. We used oral hydration not only to increase opacification of the renal collecting system and ureter but also to reduce the possibility of renal toxicity and to improve evaluation of stomach and bowel as negative oral contrast. Because of the advantages of oral hydration, we thought it would be unethical in clinical practice to use a control group that did not have oral hydration. Second, four patients had mild unilateral hydronephrosis and hydroureter, which may account for better opacification scores. Third, we used relatively short delay time of 4 min to obtain excretory-phase images and were unable to make a comparison with a longer delay.
In conclusion, excretory-phase CT with oral hydration opacified the calyx/infundibulum completely in 57% and nearly completely in 38%, opacified the renal pelvis completely in 94.5% and nearly completely in 3.5%, and opacified the upper ureter completely in 78% and nearly completely in 6.5% by the average of two reviewers. The distal ureter was the most difficult segment to opacify, but it was opacified completely in 58.5% and nearly completely in 13% of the cases.
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