Computerized Tomography or CT (also known as Computed Axial Tomography, or a “CAT Scan”) is a diagnostic imaging method that uses X-rays and computer software to form comprehensive 3D images of the inside of a patient’s body.  These images are then used to diagnose many different medical conditions, or can be used in cases of severe accidents to rapidly examine victims for internal injuries.  It is a fast and accurate tool with a wide variety of medical diagnostic uses.

How CT Imaging Works

A standard X-ray image is essentially a shadow; you shine a “light” on one side of an object, and a piece of film on the other side registers the silhouette of what’s inside the object.  This is the traditional X-ray picture seen so often on TV and in film.  Unfortunately, a 2D image such as this is only useful in some scenarios; often, a more comprehensive 3-dimensional image is required to fully see what’s inside a patient.  The ability to quickly see bones and multiple tissue types from all angles is one of the true strengths of CT imaging.

The CT scanner looks like a giant thick ring standing upright, something like a donut.  The patient lies down on a table, which slowly moves through the hole in the machine. The X-ray tube is mounted on a spinning, movable ring within the larger ring.  The movable ring also contains an array of X-ray detectors directly opposite the X-ray tube.  A computer-controlled motor turns the ring so that the X-ray tube and detectors revolve around the patient. Each full revolution scans a narrow, horizontal “slice” of the body. The computer moves the table farther into the hole in precise steps so the system can scan the next slice.

What CT Imaging Does

This process records X-ray slices across the body in a spiral motion. As the patient moves in precise steps through the scanner, the computer varies the strength of the X-rays in order to scan each type of tissue with the exact power needed for optimal imaging of that particular slice without exposing the patient to any unnecessary levels of radiation.  After the patient passes through the machine, all information from the scan is combined to form a detailed, 3-dimensional image of the body. It’s not usually necessary to scan the entire body, of course.  More often, only certain sections will be scanned, depending on the individual case.

Depending on the specific case, a contrast agent may be used to improve the visibility of certain internal structures.  These are typically iodine or barium based and are administered when particular tissue types or bodily functions are the focus of the CT scan.

Since they examine the body slice by slice from all angles, CT scans produce far more comprehensive pictures than conventional X-ray machines.  Doctors use CT scans to diagnose a wide variety of ailments, including multiple types of tumors, bowel pathology, bone and soft tissue injuries, lung infections, and pulmonary embolism, as well as to quickly identify injuries to internal organs in cases of trauma.  They are a powerful and essential tool of modern medicine.