A Science Odyssey
People and Discoveries

CT scan and MRI introduced
1972 - 1985

The use of x-rays in medicine was a huge breakthrough at the turn of the century. The problem with x-rays, though, is that they're two-dimensional. Organs of the same density look the same. But British engineer Godfrey Hounsfield came up with an improvement on the 70-year-old technology. It combined x-ray images with a computer. If you took many x-rays of the same area, at slightly different angles, a computer could put the information from the x-rays together to create a cross-sectional image. He made a prototype in 1971 and the following year tried it out on a patient. Her physicians suspected she had a brain lesion, and with Hounsfield's equipment they were able to see clearly a dark, circular cyst in her brain.

Hounsfield called this technology a CT (computerized tomography) scan, also called a CAT scan (computerized axial tomography). It was especially useful for looking at head injuries and brain problems, because it showed about 100 times greater detail in soft tissues than traditional x-rays. Hounsfield was knighted and won the 1979 Nobel Prize.

In the 1980s another imaging technique was added to the tools of medicine. Nuclear magnetic resonance is a technology that, using a gigantic magnet, can line up the protons -- or nuclei of hydrogen atoms -- in an object (or organism) to align with the north-south polarity of the magnet. A computer "reads" this to create an image in a process known as MRI, magnetic resonance imaging. MRI is excellent for observing soft tissues because they have a higher water (and therefore hydrogen) content than bone. MRI can give an image of any plane through the body, while the patient's experience consists of lying still in a body-sized tube, and hearing the clicks of the machinery.

For many situations, MRI is the preferred diagnostic tool -- especially for brain imaging, although CT scan is still chosen for strokes because it is better at detecting hemorrhage. The drawback of MRI technology is that it is tremendously expensive, hard for smaller hospitals to afford.

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