Current Clinical Concerns in CT: Results : Protocols
CT Urogram
1. With respect to Siemens Sensation 4: What slice thickness, collimation, contrast amount and dilution and time delay should we use for CT urogram. Is the saline mixed with the contrast or injected after? The referring MD wants IVP like pictures. Sometimes we are able to get the entire ureters and other times not. How small should the recon slices be for MPR and MIP?
| Answer: For the 3D, we use InSpace and use volume rendering. On a 4 slice, I would get a 4 minute delay after contrast injection (120 ml) and use 1.25 mm thick sections reconstructed at 1 mm intervals. The key is good 3D volume rendering. My new talk on the kidneys in the lecture section of www.ctisus.com addresses these issues. |
2. With respect to 4 slice MDCT: protocol suggestions? We perform noncontrast, kidneys followed by CT abd/pelvis at 1 mm with IV contrast following a delay, and then reconstruct MIPS for IVP CT equivalent. Any additions or subtractions from this proposal?
| Answer: We do a set of images in addition, at 40 seconds, and then get delayed scan at around 4 minutes post injection, and do the CT urograms off of that. A helpful tip is to give 1000 cc of water 15-20 minutes pre-study to allow for better distension of the ureters and renal pelvis. |
3. When using 1 mm slices and volume rendered 3D to produce the urogram, do you also review the axial images or are the 3D reconstructions sufficient for diagnosis?
| Answer: I do both interactively, including the coronal display. I do have many cases where only the CT urogram shows the findings, and the axial CT's prospectively do not. |
4. What technique are you using for Siemens Sensation 16 CT urography?
| Answer: Please see our protocols on the website. If you have any other questions, please let me know. |
5. When do you label an exam a "urogram"? When you inject contrast or when just visualizing kidney stones?
| Answer: I label it a CT urogram when I get delayed images (4-5 minutes post injection) and create 3D maps of the renal pelvis and collecting system. See our newest renal teaching files for nice examples. |
6. We have a new quad Toshiba with vitrea workstation. I am trying to get the GU docs to stop ordering IVPs but they need diagnosis specific protocols and some references. Also, do you have any info of CT-IVP, and I would like to know more about the renal protocols, when you inject contrast beforehand. How to and for which diagnosis?
| Answer: We do CT urograms routinely as a replacement for IVPs. We inject 120 ml of Omnipaque 350 and scan at 4 minutes post injection. We also give the patients 1000 cc of water to drink prior to the study. We then do volume rendering using .75 mm thick sections reconstructed at .5 mm intervals, to get the best CT urograms. Check the new kidney teaching files (11,12) for some case studies. |
7. What is the timing for injections and compression, applied and released for CT urography?
| Answer: We give the patients 1000 ml of water to drink 10-15 minutes pre-study to provide a fluid load. We inject 120 cc of Omnipaque-350 and get scans for the CT urogram at 4 minutes post injection. This is studied in a 3D volume with volume rendering. See case examples in our latest kidney teaching file module. We do not use compression. We opacify the ureters in nearly all cases. |
8. How can I get a better ureter contrast with our 4 slice GE Lightspeed Plus CT?
| Answer: I have found that 1000cc of cold water 15 minutes prestudy, followed by 120 cc of Omnipaque and a 4 minute delay post injection work great. I will be posting some images with 3D MDCT and this technique in the kidney teaching file. |
9. I have a Phillips 4 slice scanner. Will be doing my first CT urography. The scanner did not come with VRT, planning to use MPRs for excretory phase images. Do you use water, and if so, how much, and do you mix with methylcellulose?
| Answer: We give 1000 cc of water over a 15-20 minute period. This also helps with opacification at 4 minute urograms, by giving a water load. The 3D VRT images are becoming awesome, and will post in the teaching file. |
10. I am trying to make a CT urography protocol for our Picker/Marconi single detector. When there is no stone visible on unenhanced scans, and the patient has hematuria, what series will be sensible to follow up with? What will be the delay? Is it sensible to do one cortical phase and one excretory phase, which will increase the radiation?
| Answer: We will do 30 second and 4 minute acquisitions. The 4 minute views create awesome CT urograms. |
11. With respect to "routine CT urogram" for hematuria as a first study: Do you always do 3D? How much additional radiologist time does the 3D portion take, and does this have to be done at the main console as opposed to on PACs? Assuming 1-2 mm sections for non-contrast, nephrogram and delayed images, does the radiologist view all original axial sections for all phases as well as 3D reconstructions?
| Answer: Our hematuria protocol combines the use of axial, multiplanar and 3D imaging. All of the post processing is done by the radiologist on a workstation, including generation of 3D vascular maps, as well as CT urography. The average time for doing these studies after one has sufficient experience is in the 5 minute range. |
ReferencesMac Tavish JD, Jinzaki M, Zou KH, Nawfel RD and Silverman SG. MDCT Urography: Comparison of strategies for depicting the normal urinary collecting system. Radiology 2002; 225: 783-790.
- Summary: Underscoring the challenge of reliably depicting the normal urinary collecting system, this study compared several MDCT urogram protocols in 51 patients with hematuria or suspicious renal mass. (These were compared to 17 patients with hematuria and normal urinary collecting system and ureters on conventional IVU.) Using 4 slice MDCT, the CT urogram included 3 acquisitions. Unenhanced datasets were acquired with 4 x 2.5 mm collimation. One-hundred mL of IV contrast with 300 mgI/ml was infused at 3 mL/second. The nephrographic phase was initiated 100 seconds following the onset of contrast infusion, using 4 x 2.5 mm collimation, and pyelographic phase after 8-10 minutes, with 4 x 1 mm collimation. The 51 patients were divided into 3 groups: (1) 17 positioned prone, (2) 17 positioned prone and administered a supplement of 250 mL of normal saline and (3) 17 were positioned supine and administered supplemental saline. The saline was administered by gravity infusion from a hanging 250 mL bag, initiated immediately following contrast infusion. Reconstruction techniques included 1.25 mm thick transverse sections with 1 mm increment, 3 x 3 mm coronal sections and MIP reconstructions. The distal ureter was the most difficult region to opacify, and mean distal ureter opacification was significantly improved by the saline supplement. Prone positioning did not result in a significant increase in mean opacification compared to supine positioning.
Kawashima , MD, PhD, Terri J. Vrtiska, MD, Andrew J. LeRoy, MD, Robert P. Hartman, MD, Cynthia H. McCollough, PhD and Bernard F. King, Jr, MD Current practice issues: CT Urography RadioGraphics 2004;24:S35-S54
- Summary: Included in this review article are descriptions of CT technique for CT urography commonly encountered pathologic conditions. The two techniques (CT alone vs. CT combined with radiographic images) are discussed in detail. This article provides CME credit.