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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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