1971

CT Scan

Godfrey Hounsfield (1919–2004)

The modern CT (Computed Tomography) scan machine is an impressive piece of equipment. These machines combine the skills of several engineering disciplines to form rich, complex medical images depicting the inside of the human body, paving the way for more complex system such as the MRI.

Imagine the typical X-ray machine, which sits on one side of a body part—for instance, a hand. A piece of photographic film (or a digital sensor) sits on the other side. X-rays are so energetic that they can travel through the body part and hit the film. Varying tissues inside the body obstruct the X-rays to different degrees, so bones largely block X-rays while soft tissue is much less opaque. An X-ray machine can form an image of bones and some softer structures, but the image is two-dimensional and can be difficult to interpret.

Now imagine an X-ray source producing a pencil-like beam of X-rays, with a sensor six feet away that can detect the strength of the ray after passing through the body. Mount these two parts on a ring. Lay a person down with the ring around her. And spin the ring. The X-rays shoot through the body at hundreds of different angles. Now slide the ring down the body, forming slices of data as it goes.

A computer can look at the data coming off the sensor. Imagine that it receives 180 readings for all 180 degrees of the half circle. By applying complex algorithms to the readings, a computer can use the data from the sensor to reconstruct a slice of the patient’s body, showing different tissues and their positions inside the body. By stacking the slices, the computer can build a detailed 3D model of the interior of the patient’s body. This is a CT scan, which first became available to doctors in 1971. Invented by British electrical engineer Godfrey Hounsfield in 1967, it ultimately earned him the 1979 Nobel Prize for Physiology and Medicine.

SEE ALSO MRI (1977), Surgical Robot (1984).

Pictured: A high-definition CT scanner.