It would be good when trying to determine if there's a build-up of plaque anywhere in a person's arteries and thus at risk of many different cardio-vascular diseases.

They use special dyes injected into arteries to facilitate seeing them. Similar things are done for examining the gastrointestinal tract of those who might have cancers somewhere in it.

You might also want to see if cancers have metastasized to other parts of the body to determine the extent of the disease.