What is a magnetic resonance urogram?

An alternative to conventional IVP or CT IVP. Magnetic resonance urography employs one or both of the following techniques: (1) heavily T2-weighted images, which show fluid-containing structures as high signal, or (2) Gd-enhanced T1 weighted, excretory magnetic resonance urography, in which excreted Gd opacifies the collecting systems.
It has limited spatial resolution, so magnetic resonance urography is best reserved for patients who cannot undergo IVP or CT IVP.
Coronal thick slabs (4 cm) in multiple obliq-uities provide a global overview of the collecting systems.
If calyectasis or ureterectasis is identified, the level of obstruction and the cause are sought. Obstruction from stricture, extrinsic compression, or filling defects can be assessed without IV contrast administration. Filling defects in the fluid may be stones, tumor, blood clot, sloughed papilla, or fungus balls. Periureteral edema suggests an acutely obstructing stone.
Gd-enhanced excretory magnetic resonance urography is performed using T1-weighted imaging with fat saturation obtained as a volume acquisition (3D) in the coronal plane.
Normal findings include uptake and excre-tion of the high signal contrast into undilated collecting systems. With IV Gd, kidney function can be assessed in addition to morphology of the collecting systems. Limitations of this technique include poor excretion of contrast due to renal obstruction or renal insufficiency.
For both techniques, adequate hydration is essential and IV furosemide administration may be required to achieve adequate urinary distension.