3. Computed Tomography (CT Scan) A radiographic examination that produces a 3-d cross sectional view of an area of the body, displayed in slices.(8) Can demonstrate bone, organs, soft tissues and blood vessels. (1) May be performed with or without contrast medium
4. History On November 8, 1985, German physicist Wilhelm Conrad Roentgen discovered x-ray radiation (6) In 1956 South African Physicist Allan M. Cormack of Tufts University, Massachusetts, became interested in CT imaging in his spare time. In 1963-1964 published two articles on his theory of CT in the Journal of Applied Physics. Cormack came up with the idea that x-rays of the brain or body can be taken at different angles and wanted to program a computer to represent these 3-d images. (9) There was little medical interest in his idea at that time In 1972, British engineer Godfrey N Hounsfield of EMI Laboratories, constructed the first functional CAT scanner independently. (7)
7. Hounsfield While working at EMI Ltd in England, electrical engineer Godfrey Hounsfield began working on a computer that can take x-rays at different angles to create and image of an object in slices. In 1967 he built a prototype head CT scanner and tested it on a preserved human brain. He then tested it on a fresh cow’s brain from a butcher shop In 1971 EMI began manufacturing CT scanners and introduced the machine into the medical field. In 1972, the first human head was scanned at a small hospital; Atkinson Morley Hospital in London. In 1975 Hounsfield built a whole body CT scanner (5) Within 5 years more than 1000 CT scanners were being used all over the world
9. Nobel Prize In 1979 Hounsfield and Cormack were both awarded the Nobel Prize in Physiology and Medicine In 1981 Hounsfield was admitted in to the Royal Society and Knighthood.
10. Terminology Hounsfield Unit (HU)- mean attenuation of x-rays by different tissues.(3) Data Acquisition- method by which the patient is scanned to obtain enough data for image reconstruction. Beam Geometry- the size, shape, and motion of the x-ray beam and its path. Ray- part of the beam that falls on the detector. Scan plane- region where the x-ray tube and detectors rotate. (11)
11. Types of CT First Generation - a parallel beam is used, and the CT scanner operates on a translate-rotate principle. A single x-ray beam and 1-2 detectors translate across a patient to collect information, then the tube and detector rotate 1 o, and repeat for 180 oaround the patient. Second Generation - a fan beam is used, and also operates on the translate-rotate principle but with linear detector array (30 detectors), and multiple pencil beams. The x-ray beams translate across the patient again and collects information, then the tube and detectors rotate by larger increments and translate again for 180o(11)
15. Impact on Radiology Throughout the years, CT has become a very important tool in medical imaging It is now used not only to detect various diseases but for preventative medicine and screening as well. Because of CT, we can now visualize structures that would be seen superimposed in conventional x-ray. (10)
