a doctor who has completed training in a general medical specialty and then takes even more training in a more specific sub-area of that specialty

a doctor who is trained or certified as a specialist and then receives additional training in a specific area called a subspecialty

a physician who has completed training in a general medical specialty and then takes additional training in a more specific area of that specialty called a subspecialty

an imaging physician who has specialized in a particular imaging technology (such as a CAT scan or an ultrasound) or on a particular part of the body (such as cardiac or brain scans)