The Dangers of CT Scanning

Introduction

The discovery of x-rays in 1895 was an important landmark in the development of medicine. However, a major limitation of conventional x-rays was that it lacks depth; therefore many internal structures were superimposed on each other. With the help of computers, scientists developed methods to solve this problem. One such method was computed tomography (CT), which was developed in the early 1970's by Godfrey Hounsfield and Allen Cormack.

The first clinical CT scanners were installed between 1974 and 1976. The original systems were dedicated to head imaging only, but “whole body” systems with larger patient openings became available in 1976. CT became widely available by about 1980. In the early 1980's a couple of hospitals in Lebanon (including AUBMC) acquired this technology. There are now more than 6,000 CT scanners installed in the U.S. and more than 30,000 installed worldwide.

How does it work?

Like all other x-ray machines, CT scanners, employ x-rays to produce images of internal body structures. X rays are a type of radiation that is capable of penetrating solid materials to differing degrees, depending on their density and thickness. In conventional radiology, an image is produced by placing a detector, such as a photographic film, behind the patient and then directing a beam of x rays toward it. The radiation passes through the patient's body and interacts with the film. X rays that strike the film produce dark areas after processing, body structures that are easily penetrated by x rays, such as skin, show up as dark regions. Other structures such as muscle, soft tissue, and organs allow different amounts of x rays through them and show up as gray areas. Bones, which do not allow x rays to pass through them, show up as bright white areas.

In the single slice CT, a fine pencil like x-ray beam passes through the body and is detected by a line of detectors. Both the x-ray tube and the detectors rotate fully around the patient, then x-ray is stopped and the patient table is slightly moved inward or outward and the process is repeated until all the needed area of interest is scanned. So scanning the head (or any other organ) is somehow similar to the way slices of cheese are cut at a certain sizes when we buy it in the supermarket. In the multi slice CT, the x-ray beam is wider and is detected by an array i.e. many lines of detectors placed next to each other, thereby allowing the generation of more slices during one rotation. We talk now about multslice scanners that can generate at the same time 16 or 32 or 40 or 64 slices (Diederich & Wormanns, 13-19). Newer ones that can generate 256 slices are also coming soon. Another major difference from single slice CT scanners is that the x-ray can be kept on while the patient table is moved. This also increases the speed of scanning the patient.

Overuse of CT scans

Doctors are ordering too many unnecessary diagnostic CT scans, exposing their ...