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CT urography and virtual endoscopy: promising imaging modalities for urinary tract evaluation

Department of Radiology, Asan Medical Center, University of Ulsan, 388-1 Poongnap-dong, Songpa-gu, Seoul 138-736, Korea

View larger version (70K): [in a new window]   Figure 1. Maximum intensity projection. (a) This technique selects and displays the maximum voxel value along a line of viewer's projection through a given volume. (b) An example of normal CT urography using maximum intensity projection.

View larger version (75K): [in a new window]   Figure 2. Volume rendering. (a) This technique takes the entire volume of data and displays each pixel according to the equation in the lower portion of the diagram. (b) An example of normal CT urography using volume rendering.

View larger version (86K): [in a new window]   Figure 3. Curved multiplanar reformation. (a) This technique displays all voxel values on the curve randomly drawn by the operator. (b) CT urography using this technique can show the entire urinary tract regardless of opacification.

View larger version (53K): [in a new window]   Figure 4. Virtual endoscopy. (a) This technique polarizes all the voxel value into air and solid. Voxel values under the given threshold are merged into air and those above the threshold into solid. Thereafter, the surface between the air and solid is displayed. (b) An example of virtual endoscopy for normal collecting system.

View larger version (152K): [in a new window]   Figure 5. Lateral view of CT urography using maximum intensity projection shows a stone (arrow) in the calyceal diverticulum (arrowheads) and a stone (arrow) in the proximal ureter.

View larger version (146K): [in a new window]   Figure 6. CT angiography using maximum intensity projection shows the dilated pelvicalyceal system (asterisk) of the right kidney and a branch of the renal artery (arrow) crossing the ureteropelvic junction.

View larger version (130K): [in a new window]   Figure 7. CT urographic images using (a) maximum intensity projection and (b) volume rendering shows complete duplication of the left urinary tract. The dilated upper moiety ureter (arrows) inserts into the vagina (arrowhead).

View larger version (109K): [in a new window]   Figure 8. Multiple urothelial carcinomas involving the collecting system and proximal ureter. (a) Intravenous urography shows a filling defect (arrow) in the proximal ureter. Although abrupt cut-offs of the collecting systems (arrowheads) are noted, the presence or absence of a mass is unclear. (b) CT urography using maximum intensity projection directly visualizes masses (arrowheads) in the collecting systems as well as in the proximal ureter (arrow). (c) Virtual endoscopy at the level of the proximal ureter shows an intraluminal mass (arrows). (d) Virtual endoscopy at the level of the renal pelvis shows a mass (arrows) filling the infundibulum and protruding into the pelvis. Note a normal infundibular lumen (asterisk).

View larger version (123K): [in a new window]   Figure 9. Recurrent cervical cancer invading the right distal ureter. (a) CT urography using curved multiplanar reformation shows a dilated right urinary tract (asterisk) due to a mass in the pelvic cavity (arrows). (b) Conventional axial CT image at the level of the right ureterovesical junction demonstrates the recurrent cervical mass (arrows) invading the right distal ureter (arrowhead).

View larger version (89K): [in a new window]   Figure 10. Ureteral metastasis from gastric cancer. (a) CT urography using maximum intensity projection shows irregular wall thickening (arrows) of the right proximal ureter. (b) Virtual endoscopy shows irregular lumen with multiple nodules (arrows) and ulcers (arrowheads).

View larger version (124K): [in a new window]   Figure 11. CT urography using maximum intensity projection shows a renal mass (arrowheads) invading the collecting system (arrow).

View larger version (107K): [in a new window]   Figure 12. Renal cell carcinoma which can be removed by partial nephrectomy. (a) CT urography using maximum intensity projection shows a renal mass (M) that is separated from the collecting system and therefore can be removed as sparing the adjacent collecting system. (b) Conventional axial CT image also demonstrates that the mass can be separated from the renal sinus fat (arrows).

View larger version (70K): [in a new window]   Figure 13. Bladder carcinoma. (a) Virtual cystoscopy looking at the left wall of the bladder shows a 4 mm sized polyp (arrow) near the left ureteral orifice (white arrowhead), confirmed as transitional cell carcinoma. Black arrowhead=urethral orifice. (b) Conventional cystoscopic image depicts a polyp protruding into the bladder lumen.

View larger version (97K): [in a new window]   Figure 14. Motion artefact distorts CT urography image (a) and causes false luminal irregularity on virtual endoscopy image (b).

View larger version (106K): [in a new window]   Figure 15. Importance of adjusting threshold in case of inadequate mixing of the contrast and urine. (a) Source CT image shows a fluid–fluid level (arrows) due to adequate mixing of the contrast and urine. (b) Virtual cystoscopy image with threshold of 190 HU shows artefact in the anterior wall of the bladder. (c) On virtual cystoscopy image with threshold of 100 HU, the artefact disappears and a small nodule (arrow), confirmed as transitional cell carcinoma, is noted.