n. imaging of a *fistula. X-rays can be used to visualize the fistula after injection of a radiopaque *contrast medium, usually through an opening in the skin after inserting a catheter, to see the extent of a fistula and the structures with which it communicates. In *haemodialysis patients, contrast is injected through a needle into the vessels around the surgical fistula to look for blockages or narrowings that are compromising flow. *Magnetic resonance imaging is the procedure of choice for examining fistulae around the rectum and anus.
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