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The birth of the first CT scanner

Guang-Zhong Yang, D.N. Firmin

Journal Article
IEEE Engineering in Medicine and Biology Magazine
Volume 19
Issue 1
April, 2000

From the day that Wilhelm Roentgen showed the world the the X-ray picture of his wife Bertha's left hand in 1895, the myth and power of X-rays startled a generation of scientists, engineers, and physicians. More than 70 years later, while medical imagers were still pursuing sharper and clearer X-ray pictures, an epoch-making new concept was brewing-computerized digital tomography. This is a concept that allows noninvasive imaging of the true three-dimensional morphology of the human organs, and it has since become the foundation of most computerized medical imaging techniques. The person who turned this concept into a reality was Sir Godfrey Hounsfield. In 1967, Hounsfield devised a computer program that performed image reconstruction. To prove that it would work, he simulated a scan of a synthetic object by the computer and then reconstructed it back to its original shape. The accuracy of the reconstruction was very impressive: greater than 1 in 10,000. Hounsfield found the maximum safe dose of radiation that could be given to a patient, and hence calculated the maximum number of photons that could be collected. From this, he calculated that the picture could be reconstructed to an accuracy of better than 0.5%. This was orders of magnitude more accurate than conventional X-rays. He saw that with this accuracy, there would be a chance of seeing differences between soft tissues within the body

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