Opacification of the Upper Urinary Tract With MR Urography Compared to CT Urography

Images from a MDCT scan are reconstructed into thin slices which can be viewed in any orientation with similar image quality compared to the original axial images. Completely isotropic resolution in 16- to 64-slice CT can be achieved using 0.5- to 0.625-mm slice thickness. Resulting images have high noise levels unless the tube load is increased considerably. In most clinical situations a near-isotropic resolution with 1.0- to 1.5-mm effective slice thickness suffices for high-quality images created in any plane using MPR.

‬Research into the accuracy of CTU in the evaluation of possible UUT malignancy soon proved CTU to be a very sensitive and specific method with pooled sensitivity of 96% (range 88-100%), and pooled specificity of 99% (range 93-100%). Furthermore direct comparison confirmed the superiority of CTU over IVU in terms of sensitivity and specificity.

In order to reduce confusion in terminology, the European Society of Urogenital Radiology's (ESUR) CTU Working Group proposes to define CTU as "a diagnostic examination optimized for imaging the kidneys, ureters and bladder. The examination involves the use of MDCT with thin-slice imaging, intravenous administration of a contrast medium, and imaging in the excretory phase." ESUR guideline comprehensively addresses all aspects of CTU based on extensive literature review and on the opinion of leading researchers in this field.‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬ To begin with, hydrating the patient is beneficial to reduce possible contrast induced nephropathy especially in otherwise dehydrated or not well hydrated patient, and at the same time provides negative bowel contrast medium. Usually 1 liter of water is slowly ingested during a period of 20-60 minutes before the CTU examination or alternatively a maximum of 500 ml slow intravenous drip-infusion of 0.9% saline may be used in patients who cannot tolerate per oral hydration. Nevertheless the ESUR guideline also concludes that the net benefit of intravenous saline bolus hydration is probably minimal and its routine use is thus not advocated. Bowel preparation with positive contrast will inevitably interfere with the interpretation especially in the demonstrative quality of reformatted images and is not recommended. In diuretic-enhanced CT urography, the patients are asked to empty their bladder before starting the CTU examination, nevertheless the ESUR guidelines have no stand on this issue. The use of compression pads is a routine practice in IVU and consequently it was thought that this maneuver can be transferred to the CTU protocol. However after evaluating of the available evidence ESUR guideline do not advocate the use of compression.

Patients are scanned in supine position. Prone position is not advocated to be used routinely but can be used in special cases e.g. to reduce layering effects of the contrast medium, especially when the renal collecting system is dilated.

After the introduction of the rapid MDCT technology it became clear that this new imaging modality is more accurate than IVU in the initial workout of a wide range of UUT pathology. Images from a MDCT scan are reconstructed into thin slices which can be viewed in any orientation with similar image quality compared to the original axial images. Completely isotropic resolution in 16- to 64-slice CT can be achieved using 0.5- to 0.625-mm slice thickness. Resulting images have high noise levels unless the tube load is increased considerably. In most clinical situations a near-isotropic resolution with 1.0- to 1.5-mm effective slice thickness suffices for high-quality images created in any plane using MPR.