These are the medical specialists, doctors who have initially trained for 13 years to become experts in the diagnosis of illness and injury using modern imaging technology, and then further honed their skills through experience and continuing professional development.
Radiodiagnosis can be as straightforward as recognising pneumonia on a chest x-ray but...
every human body is unique and how it manifests disease can vary greatly. The first task of the radiologist is to determine whether the appearance on the image is a variation of the normal picture, or falls outside of the normal spectrum and indicates a problem. Then follows analysis to decide if the finding represents an active problem vs a mishap from the past, if the abnormality is related to current symptoms and test results vs a coincidental finding, and then to assess the severity of the pathology which has been demonstrated. Are further tests needed to confirm the diagnosis or narrow down the list of possibilities? Or to assess how extensive the real problem is, to guide surgery or other treatment for the best achievable outcome.
Often a diagnosis can only be made by comparing the results of different examinations. This integration of information across a spectrum of symptoms, clinical findings reported by your doctor, laboratory test results, and previous/current imaging findings, is the art of medicine and is where the radiologist really earns his or her keep. The aim is always to make the correct diagnosis, as early as possible, and using the least number of tests (thereby limiting your exposure to the risks of further tests, saving you time, money and the anxiety of not knowing, and ensuring the best achievable outcome for your particular health condition and stage of diagnosis).