Computed Tomography Scanning

X-rays are a form of electromagnetic radiation. During a Computed Tomography scan, several X-ray beams pass through the body at different angles.

As the X-ray beams pass through the body different tissues absorb different amounts of radiation from the X-rays. Special sensors mounted inside the Computed Tomography scanner measure the amount of radiation absorbed by different tissues: so that an anatomical picture can be built up of the area under investigation.

During a Computed Tomography scan, the patient lies very still on a table that is then moved into the scanner, with the patient on it.

The actual Computed Tomography scan is conducted inside a Computed Tomography scanner. This scanner is a large, square machine with a hole in the center.

A typical Computed Tomography scanner contains a variety of medical and technical instruments inside its housing including an x-ray tube, collimators and detectors.

During the Computed Tomography scan, the framework housing all the instruments rotates, and the x-ray tube moves around the patient's body to produce the required 3-D images.

One rotation takes about one second during which the x-ray tube emits a fan-like beam of x-rays onto the patient. These beams can be anywhere from 1 millimeter to 10 millimeters thick.

Detectors on the one side of the patient record the x-rays from the section of the patient's body being examined. Each x-ray leaves the patients body as an x-ray "snapshot", showing one position (angle). Many different "snapshots" (angles) are collected during one complete rotation.

The data from all of the X-rays is sent to a special computer, which uses the “snapshots” to form three-dimensional cross-sectional images of the scanned areas, called tomograms.

An X-ray technologist monitor every part of the Computed Tomography scan, though he or she will not actually be in the room with the patient. An intercom within the scanner allows the patient and technologist to communicate throughout the procedure.

Patients should expect to hear whirring sounds throughout the Computed Tomography scan; this is the sound of the gantry and x-ray tube rotating.

At times, the technologist may ask the patient to hold his or her breath to prevent the CT images from blurring.