Medical imaging refers to any technology that makes the invisible inner workings of the body visible, without the need for a scalpel. Doctors use it for measuring, screening, diagnosing a condition and following treatments. Imaging has come a long way since German physicist Wilhelm Roentgen took the first X-ray more than 100 years ago, showing the bones of his wife’s hand – and her wedding ring. Many advances have occurred in the last 50 years.
X-ray (also called radiography). Uses electromagnetic radiation that various tissues absorb at different rates depending on their density and composition, so bones appear white, organs gray, air-filled lungs black. Used for fractures, obstructions, lung ailments, dental cavities, mammograms, angiograms, bone density tests and, in the form of radiotherapy, to attack cancers.
Ultrasound (sonography). Bounces high-frequency sound waves off tissue to create real-time video of organs, blood vessels, joints and a growing fetus. Uses no radiation.
CT scan or CAT scan (Computer Axial Tomography). Processes X-rays taken from various angles in a computer to create cross-sectional “slices” in 2-D or 3-D. Used for internal injuries, blood clots, tumours and in the brain.
PET scan (Positron Emission Tomography). A nuclear medicine technique that involves injecting patients with a radiotracer. Detectors then capture the radioactive gamma rays emitted. Depicts metabolic irregularities to diagnose heart disease and cancers. SPECT (Single Photon Emission Computed Tomography) is a less expensive alternative.
MRI (magnetic resonance imaging). Uses a large magnetic tube to temporarily “line up” water particles in the body, then reads signals produced by radio waves against those particles to create 2-D or 3-D images. Uses no radiation. Can show structure and function of many areas, including the spinal cord and brain.
Medical imaging, which now uses digital technology instead of film, is becoming increasingly high-resolution, precise and fast. Clinicians may use two or more techniques for diagnosing or treating a condition. “Now there are almost no major diseases where you don’t do imaging first,” says Mark Henkelman, a professor of medical biophysics, and one of the world’s top imaging experts.
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