The role of the radiologist
Ultrasound results are not final until a doctor has reviewed the images and written a report. In most cases, this doctor is a radiologist, which is a doctor who specialized in medical imaging. It is the radiologist's role to look at all of the pictures, as well as lab results and notes about symptoms, and then describe what is seen. Ultrasound is just one type of imaging these doctors review! Others are x rays, CT (or "CAT scans"), MRI, and more.
In some cases a different type of doctor will look at the images. In Obstetrics and Gynecology it is often the Ob Gyn doctor in the office who reviews the ultrasound. For echocardiograms it is a cardiologist. But in these cases as well, the ultrasound is not final until the doctor has made a report.