CT Urography is a new technique used to evaluate patients presenting with obstructive uropathy and hematuria. Obstructive uropathy is described as structural impedance to the flow of urine anywhere in the urinary tract.
CT urography is a developing concept that combines portion of IVP and CT into one examination. Hence,requiring only a single dose of IV administrated iodinated contrast media. IVP and CT each have strengths and weaknesses in the evaluation of urinary tract. CT is superior for detection of urinary stones and for the evaluation of renal parenchyma and adjacent organs. IVP is better for evaluation of pylelocaliceal collecting system and ureters because of superior spatial resolution (˜4 lines per mm of screen film radiography) compared with that of CT( ˜0.7 lines per mm for abdominal CT).
IVP is considered superior for delineation of calyceal and
papillary anatomy, collecting ducts mucosal details and small filling defects. In our experience we have found that 10% of urinary tract abnormalities were depicted more clearly or appreciated only on screen film urographic images when compared with CT cross sectional images. Hence, by combining the strengths of each study into one i.e., CT Urography examination, the urinary tract can be evaluated more thoroughly in a single session.
The benefit of CT urography is its ability to depict the normal urinary tract anatomy including both the renal parenchyma, the collecting structures and ureters.
CT Urography is performed with 150 ml of non ionic contrast media @ 3 ml per second with pressure injector. High contrast volume is required because tissue density determined by iodine concentration, is important for mass and lymph node detection. Acquisition is taken with patient in supine position, un-enhanced images are obtained to evaluate the presence of calcification and to allow determination of unenhanced attenuation value of any focal lesion in the kidneys. Unenhanced scan of kidney area are taken at
low mAs (60 to 80 mAs) with 5 mm thickness and 1.5 mm tube colimation. Then abdomen from domes to pelvis is scanned in portal venous phase i.e., at 60 sec delay from the start of the injection with 1.5 mm tube collimation and 10 mm slice thickness. Thin reconstruction of 2 x 2 mm thickness is done. Third acquasition is taken at 300 sec i.e. in nephrographic phase and a topogram is taken after that which shows the excertory system.
To simplify the procedure and to reduce the number of phases necessary, a split bolus technique of contrast administration is used. In this technique 50 ml of contrast is injected with compression band inplace on the upper abdomen, after 90 sec. of the first injection 100 ml of contrast is given at the rate of 3ml/sec resulting in scanning during a simultaneous nephrographic and excretory phases. Nephrographic and excretory phase images have
been shown to be superior to corticomedullary phase images in the detection and characterization of renal masses.










With abdominal compression good contrast distension of the collecting systems can be achieved. That is comparable to or superior to that of onventional excretory urography. Axial reconstruction of 2X2 mm thickness of both the first and second set of data are sent to Wizard of 16 Slice Sensation, which we are using in our Institute, for further evaluation where coronal reformation, Maximum Intensity projection (MIP), curved reformated images or VRT images are also obtained. 3-D reformation of CT data in the coronal plane provides a more familier representation of the collecting systems showing the calices, fornices, infandibula, renal pelvis and ureter in continuity.
Conclusion : 3D reformatted images have been shown to be acceptable alternative to preferable conventional excretory urographic images because CT urography can image both the renal parenchyma and urothellium, a wide range of diseases can be identified. In our experience CT urography has been successful in clearly depicting anatomic variants, stone disease, inflammatory process, benign and malignant neoplasms.