Contrast media are used during x-rays, CTs or MRIs, in order to enhance such imaging studies.
And it is generally believed, also by doctors, that contrast media could damage the kidneys. Especially patients with pre-existing kidney damage could have further kidney damage through contrast media. Doctors should use contrast media very sparingly, it is said, in order not to damage the health of the patients.
However, all important clinical studies about this question, one from 2014, and two from 2017, and a meta-analysis (that is a higher level of evidence) from 2018 cannot find a generally increased risk of kidney damage after contrast-enhanced CT.