You have a pain in your side and your physician wants to investigate further with a CT scan.\nYour son injures his knee during a basketball game and the trainer says he\u2019ll most likely need an MRI.\nWhen it comes to medical imaging services, most people don\u2019t know one test from the next. Patients often wonder why their physician referred them to one test instead of another. Understanding what your physician ordered and why can help you feel more confident and be better prepared for your test.\nWith that in mind, here are the diagnostic technologies available at UPMC and the most common reasons why they are used:\nX-ray\nThe grandfather of all imaging technology, X-ray remains useful in detecting many health concerns, with limitations. A chest X-ray, for example, limited by two dimensional pictures, cannot detect subtle changes in growths over short periods of time. It is most beneficial to check for bone fractures and for viewing organs.\nCT (or CAT) Scan\nUses combined X-ray and computer technology to image bones, lungs, and other organs in three dimensions. The camera of the CT spirals around the patient\u2019s body and can provide multiple super-thin images.\nCT uses radiation to generate images with faster scanning (in most cases) than MRI. Some CT scans require an injection of a special iodine contrast before the scan. This contrast is absorbed by abnormal tissues and is detected by the CT scanner, giving physicians a clear view of the problem area.\nMRI\nPulses of radio waves and a powerful magnet work together to create clear images without radiation. For some MRI exams, contrast is used, much like a CT scan. However, MRI contrast is not iodine based (gadolinium), so people who are allergic to iodine can tolerate it. MRI is often used to diagnose cancers because it detects small tissue abnormalities.\nNuclear Medicine (including PET-CT)\nThis imaging technique visualizes the molecular structure of the body through radioactive agents. These agents attach to abnormal tissues and are highlighted in the image. Nuclear medicine visualizes body parts ranging from bones to heart to lungs, and shows the function of various body parts, which other imaging technologies cannot.\nUltrasound\nBy moving a specialized scanner over an area of the body, sound waves bounce off of internal organs, creating an instant image. Ultrasound is useful for visualizing the gallbladder, kidney stones, intestinal obstructions, and babies in utero. It uses no radiation and requires no contrast.\nDigital mammography \u2014 Uses compression and X-rays to create images of the inside of the breast. The images are viewed electronically using special high-resolution monitors. Screening mammograms are used to check for breast cancer in women who have no signs or symptoms of the disease. Diagnostic mammograms are used to check for breast cancer after a lump or other signor symptom of the disease has been found.\nEvery Study Examined\nRadiologists examine every imaging study and determine whether an additional test should be ordered. In the event an abnormality arises and a different look at the area could be beneficial, a second or third test may be ordered. It\u2019s the best way to investigate a potential problem without surgical intervention.