Virtual endoscopy of the upper urinary tract based on contrast material-enhanced MR urography data sets.

Purpose: To investigate the feasibility of reconstructing a virtual endosco py from MR imaging data sets of the upper urinary tract. Method:The data ob tained from 28 contrast-enhanced MR urographic examinations (5 normal; 23 p athologic) were postprocessed to reconstruct a virtual ureterorenoscopy (VU RS) using a threshold image segmentation. The visualization of the upper ur inary tract was based on the acquisition of T-1-weighted 3D gradient-echo s equences after intravenous administration of gadolinium-DTPA and a prior in jection of low-dose furosemide. Results: The employed MR urography techniqu e created in all 28 cases a complete and strong contrast enhancement of the urinary tract. These 3D sequence data allowed the reconstruction of a VURS , even when the collecting system was not dilated. The best accuracy was pr ovided by the MR urography sequences with the smallest voxel size. Moreover , the data; acquisition based on a breath-hold technique has proved superio r to that using a respiratory gating. Inside the renal pelvis, all calices could be assessed by turning the virtual endoscope in the appropriate direc tion. The visualization of the ureteral orifices in the bladder was also po ssible. All filling defects that were diagnosed by MR urography could be ev aluated from the endoluminal view using the VURS. The exact characterizatio n of the lesions based only on the assessment of the surface structure was difficult. Conclusion: A virtual endoscopy of the upper urinary tract can b e successfully reconstructed using the data sets of high-resolution 3D MR u rography sequences.