Ok. A radioloGIST is someone who has already achieve a degree in medicine. Being a radiologist is their specialised field, they analyse images and so forth (like how a nueroloGIST is a specialised field after a medicine degree)
A radioGRAPHER is the person who takes the picture. I think the course for this in university is called Bachelor of Radiation Physics I think? Somewhere along the lines of that anyway.
OR simpler. PhotoGRAPHER=radioGRAPHER