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Computed tomography History

The CT system was invented in 1972 by Godfrey Newbold Hounsfield of EMI Central Research Laboratories (now Sensaura owned by Creative Technology Ltd.) using X-rays. Allan McLeod Cormack of Tufts University independently invented the same process and they shared a Nobel Prize in medicine in 1979. The first scanner, known as the EMI Scanner, took several hours to acquire the raw data and several days to produce the images. The first EMI scanner was limited to making tomographic sections of the brain. It required the use of a water-containing device that enclosed the patient's head. The first CT system that could make images of any part of the body, and did not require the "water bottle" was the ACTA scanner designed by Robert S. Ledley, DDS at Georgetown University.

The first generation CT scanners used a pencil-thin beam of radiation directed at one or two detectors. The images were acquired by a "translate-rotate" method in which the x-ray source and the detector in a fixed relative position move across the patient followed by a rotation of the x-ray source/detector combination by one degree. Pairs of images were acquired in about 5 minutes. The first generation EMI scanner was limited to examining the brain.

The second generation of CT scanners increased the number of detectors and changed the shape of the radiation beam. The x-ray source changed from the pencil-thin beam to a fan shaped beam. The "translate-rotate" method was still used but there was a significant decrease in scanning time. Rotation was increased from one degree to thirty degrees.

The third generation of CT scanners made a dramatic change in the speed at which images could be obtained. In the third generation a fan shaped beam of x-rays was directed to an array of detectors that was fixed in position relative to the x-ray source. The slow "translate" portion of the scan was eliminated. Scan time per slice was reduced to 10 seconds initially.

The fourth generation of CT scanners achieved scan time similar to the third generation by employing a 360 degree ring of detctors that encircled the patient. The fan shaped x-ray beam rotated around the patient directed at detectors in a non-fixed relationship.

Improvements in CT scanner technology have developed with improvements in computer capabilities and detector technology and other improvements of movement of patients through the scanner.

Modern multi-detector, multi-row CT systems can complete a scan of the chest, for example, in less time than it takes for a single breath hold and display the computed images in near real time. Images that used to take hours to acquire and days to process are now accomplished in seconds. The number of cross sectional images that can be produced has increased from about a dozen to many hundreds.

In recent years, tomography has also been introduced on the micrometer level and is named Microtomography. But these machines are currently only fit for smaller objects or animals, and cannot yet be used on humans.

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