A diagnostic test is a medical procedure used to identify the cause of a patient's symptoms. Common diagnostic tests include ultrasound, SCAN, and xray. Ultrasound is a non-invasive imaging technique that uses sound waves to create images of the inside of the body. A SCAN is an imaging technique that uses a computer to create detailed images of the inside of the body. Xray is an imaging technique that uses radiation to create images of the inside of the body.