MR urography

Riccabona M (2002a) Potential of modern techniques in paediatric uroradiology. Eur J Radiol 43 110-121 Riccabona M, Simbrunner J, Ring E et al (2002b) Feasibility of MR-urography in neonates and infants with anomalies of the upper urinary tract. Eur J Radiol 12 1442-1450 Riebel TW, Nasir R, Weber K (1993) US-guided hydrostatic reduction of intussusception in children. Radiology 188 513-516... 

In patients with locally advanced or recurrent cervical cancer, it is often necessary to exclude ureteral obstruction, which can be done on transverse T2-weighted images that also serve to assess the paraaortic lymph nodes. In addition, coronal T2-weighted turbo-spin echo (TSE) sequences enable excellent evaluation for possible urinary retention and require little extra time to acquire. In addition, contrast-enhanced MR urography can be performed to exclude tumor-induced hydronephrosis. 

In recent years, concepts and techniques pertaining to CT urography (CTU) and MR urography (MRU) have been evolving. As the technology continues to improve, CTU and MRU will combine CT and MRI with the ultimate diagnostic capabilities of intravenous urography. 

In conclusion, CT and MR urography post-processing techniques are able to offer a precise, noninvasive anatomical definition of the entire urinary tract with both external and endoluminal points of view, and also help to extract the most relevant and useful diagnostic information, particularly in surgical planning. 

Kawashima A, Glockner JF, King BF Jr (2003) CT urography and MR urography. Radiol Clin North Am 41 945-961 Kawashima K, Vrtiska TJ, LeRoy AJ et al (2004) CT urography. RadioGraphics 24 535-58 Kenney PJ (2003) CT evaluation of urinary lithiasis. Radiol Clin North Am 41 979-999... 

Nolte-Ernsting CC, Adam GB, Gunther RW (2001) MR urography examination techniques and clinical applications. Eur Radiol 11 355-372... 

Roy C, Saussine C, Jahn C et al (1994) Evaluation of RARE-MR urography in the assessment of ureterohydronephro-sis. J Comput Assist Tomogr 18 601-608 Rubin GD (2003) 3-D imaging with MDCT. Eur J Radiol 45[Suppl 1] S37-S41... 

The improved anatomic and functional information obtained with MR urogaphy will provide new insights into the underlying pathophysiology of urinary tract disorders. As a result, it is likely that MR urography will replace renal scintigraphy in the evaluation of renal tract disorders in children in the near future. 

For each patient the key features derived from MR urography include calculation of differential renal function (both volume and Patlak) (vDRF and pDRF), signal versus time curves for each kidney and the aorta, individual kidney GFR index of each kidney, concentration and excretion from each compartment, renal and calyceal transit times and overall anatomic diagnosis. It is important to understand that we have two methods to determine the differential renal function one based on volume and one based on the individual kidney GFR as determined by the Patlak plot. In most cases these are symmetric however, when there is a difference in these two measures of DRF it implies a change in renal hemodynamics that may ultimately provide information about which kidneys will benefit from surgery. 

The parameters routinely assessed by MR urography include the overall anatomic diagnosis, vDRF and pDRF, renal and calyceal transit times, signal intensity versus time curves and individual GFR index for each kidney. 

The distal ureteric anatomy is also well demonstrated with MR urography (Avni et al. 2001). Ectopic ureteric insertion either in single systems or in combination with duplex systems can usually be obtained on the delayed post-contrast images or on theT2-weightedimagesinmarkedlydilatedorpoorly functioning system (Fig. 1.2.11). The diagnosis of... 

Another advantage of MR urography over other modalities is the ability to characterize the anatomy and morphology of the renal parenchyma itself. 

Hydronephrotic kidneys that cannot accommodate a fluid challenge develop signs of decompensation on MR urography. These include a delayed, dense nephrogram, delayed calyceal and renal transit times and a difference between the pDRF and vDRF >4. 

Anomalies of renal position and rotation are well demonstrated by the high resolution anatomic images. Horseshoe and ectopic kidneys can be easily separated from the background and overlying tissues. Pelvic kidneys in particular, which often are significantly smaller than the normally positioned kidney, are well demonstrated with MR urography (Fig. 1.2.13). Hypoplastic kidneys associated with ureteric ectopia and supernumerary kidneys, which have been difficult to demonstrate with other imaging modalities, can usually be demonstrated even if there is minimal renal function. 

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