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Background
MR urography is helpful to evaluate pathologies of the urinary tract for the following reasons. - Better contrast resolution. - No ionizing radiation, especially patients requiring frequent follow-up imaging. – Resolves pseudo-enhancement seen on CT. – Compared to nuclear scan, view anatomical and pathological conditions along with assessing function with near similar accuracy. - Help evaluate for other abnormalities in the abdomen and pelvis.

Educational Goals / Teaching Points
- Comprehensive technique for evaluation of the entire urinary tract, its vasculature and surrounding soft tissues. - Understand the principles underlying the imaging protocol for proper utilization and interpretation. - Static urography: based on T2-weighted sequences, for dilated or obstructed collecting systems. - Excretory urography: based on T1 and T1c (postcontrast) sequences, for visualization of nonobstructed systems. - Be aware of the pitfalls and how to avoid/troubleshoot them.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
A complete study includes (A) Conventional sequences: T1 and T2 fat saturated (FS), in and out of phase gradient-echo imaging. (B) Static fluid-based sequences: based on prolonged T2 relaxation time of urine; heavily T2-weighted thick (single-shot fast spin-echo) or thin section (half-Fourier rapid acquisition with relaxation enhancement); closely resembles an MRCP; may be performed as the only sequence in pregnancy or renal insufficiency. (C) Nephrographic and excretory urography: primarily a postcontrast, fat-suppressed T1-weighted 3D gradient-echo sequence; contrast optimization and distention of the ureters is important, achieved by varying combinations of IV hydration, diuretics (0.1 mg/kg furosemide), and oral restriction.

Conclusion
MR urography is a comprehensive technique for evaluation of the urinary tract; however, one must be aware of its limitations and pitfalls to use it to the best advantage.