How many minutes after injection does the greatest concentration of contrast medium appear in the kidneys?

Answer is 15-20 minutes after injection.

Explanation:

Contrast medium can be explained as a medium that helps in making the internal structures more visible when introduced or injected into the body. This is done during radiography, X-ray. Examples are gadolinium and barium sulfate.

The contrast medium is useful in diagnosing medical conditions.

It should be noted that, this contrast medium has a negative effect on the kidney, by causing contrast -induced acute kidney injury, that is, acute renal failure, ARF. This effect usually occurs within 24-72 hrs after injection.  

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meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.