The invention: A technique that collects X-ray data from solid, opaque masses such as human bodies and uses a computer to construct a three-dimensional image.
The people behind the invention:
Godfrey Newbold Hounsfield (1919- ), an English
electronics engineer who shared the 1979 Nobel Prize in
Physiology or Medicine Allan M. Cormack (1924-1998), a South African-born American
physicist who shared the 1979 Nobel Prize in Physiology or
Medicine
James Ambrose, an English radiologist
A Significant Merger
Computerized axial tomography (CAT) is a technique that collects X-ray data from an opaque, solid mass such as a human body and uses a sophisticated computer to assemble those data into a three-dimensional image. This sophisticated merger of separate technologies led to another name for CAT, computer-assisted tomography (it came to be called computed tomography, or CT). CAT is a technique of medical radiology, an area of medicine that began after the German physicist Wilhelm Conrad Rontgen’s 1895 discovery of the high-energy electromagnetic radiations he named “X rays.” Rontgen and others soon produced X-ray images of parts of the human body, and physicians were quick to learn that these images were valuable diagnostic aids.
In the late 1950′s and early 1960′s, Allan M. Cormack, a physicist at Tufts University in Massachusetts, pioneered a mathematical method for obtaining detailed X-ray absorption patterns in opaque samples meant to model biological samples. His studies used narrow X-ray beams that were passed through samples at many different angles. Because the technique probed test samples from many different points of reference, it became possible—by using the proper mathematics—to reconstruct the interior structure of a thin slice of the object being studied.
Cormack published his data but received almost no recognition because computers that could analyze the data in an effective fashion had not yet been developed. Nevertheless, X-ray tomography— the process of using X-rays to produce detailed images of thin sections of solid objects—had been born. It remained for Godfrey Newbold Hounsfield of England’s Electrical and Musical Instruments (EMI) Limited (independently, and reportedly with no knowledge of Cormack’s work) to design the first practical CAT scanner.
A Series of Thin Slices
Hounsfield, like Cormack, realized that X-ray tomography was the most practical approach to developing a medical body imager. It could be used to divide any three-dimensional object into a series of thin slices that could be reconstructed into images by using appropriate computers. Hounsfield developed another mathematical approach to the method. He estimated that the technique would make possible the very accurate reconstruction of images of thin body sections with a sensitivity well above that of the X-ray methodology then in use. Moreover, he proposed that his method would enable
Godfrey Newbold Hounsfield
On his family farm outside Newark, Nottinghamshire, England, Godfrey Newbold Hounsfield (born 1919), the youngest of five children, was usually left to his own devices. The farm, he later wrote, offered an infinite variety of diversions, and his favorites were the many mechanical and electrical gadgets. By his teen years, he was making his own gadgets, such as an electrical recording machine, and experimenting with homemade gliders and water-propelled rockets. All these childhood projects taught him the fundamentals of practical reasoning.
During World War II he joined the Royal Air Force, where his talent with gadgets got him a position as an instructor at the school for radio mechanics. There, on his own, he built his an oscilloscope and demonstration equipment. This initiative caught the eye of a high-ranking officer, who after the war arranged a scholarship so that Hounsfield could attend the Faraday Electrical Engineering College in London. Upon graduating in 1951, he took a research position with Electrical and Musical Instruments, Limited (EMI). His first assignments involved radar and guided weapons, but he also developed an interest in computers and in 1958 led the design team that put together England’s first all-transistor computer, the EMIDEC1100. This experience, in turn, prepared him to follow through on his idea for computed tomography, which came to him in 1967.
EMI released its first CT scanner in 1971, and it so impressed the medical world that in 1979 Hounsfield and Allan M. Cormack shared the Nobel Prize in Physiology or Medicine for the invention. Hounsfield, who continued to work on improved computed tomography and other diagnostic imagining techniques, was knighted in 1981.
researchers and physicians to distinguish between normal and diseased tissue. Hounsfield was correct about that.
The prototype instrument that Hounsfield developed was quite slow, requiring nine days to scan an object. Soon, he modified the scanner so that its use took only nine hours, and he obtained successful tomograms of preserved human brains and the fresh brains of cattle. The further development of the CAT scanner then proceeded quickly, yielding an instrument that required four and one-half minutes to gather tomographic data and twenty minutes to produce the tomographic image.
In late 1971, the first clinical CAT scanner was installed at Atkinson Morley’s Hospital in Wimbledon, England. By early 1972, the first patient, a woman with a suspected brain tumor, had been examined, and the resultant tomogram identified a dark, circular cyst in her brain. Additional data collection from other patients soon validated the technique. Hounsfield and EMI patented the CAT scanner in 1972, and the findings were reported at that year’s annual meeting of the British Institute of Radiology.
Hounsfield published a detailed description of the instrument in 1973. Hounsfield’s clinical collaborator, James Ambrose, published on the clinical aspects of the technique. Neurologists all around the world were ecstatic about the new tool that allowed them to locate tissue abnormalities with great precision.
The CAT scanner consisted of an X-ray generator, a scanner unit composed of an X-ray tube and a detector in a circular chamber about which they could be rotated, a computer that could process all the data obtained, and a cathode-ray tube on which tomograms were viewed. To produce tomograms, the patient was placed on a couch, head inside the scanner chamber, and the emitter-detector was rotated 1 degree at a time. At each position, 160 readings were taken, converted to electrical signals, and fed into the computer. In the 180 degrees traversed, 28,800 readings were taken and processed. The computer then converted the data into a tomogram (a cross-sectional representation of the brain that shows the differences in tissue density). A Polaroid picture of the tomogram was then taken and interpreted by the physician in charge.
Consequences
Many neurologists agree that CAT is the most important method developed in the twentieth century to facilitate diagnosis of disorders of the brain. Even the first scanners could distinguish between brain tumors and blood clots and help physicians to diagnose a variety of brain-related birth defects. In addition, the scanners are believed to have saved many lives by allowing physicians to avoid
the dangerous exploratory brain surgery once required in many cases and by replacing more dangerous techniques, such as pneumoencephalography, which required a physician to puncture the head for diagnostic purposes.
By 1975, improvements, including quicker reaction time and more complex emitter-detector systems, made it possible for EMI to introduce full-body CAT scanners to the world market. Then it became possible to examine other parts of the body—including the lungs, the heart, and the abdominal organs—for cardiovascular problems, tumors, and other structural health disorders. The technique became so ubiquitous that many departments of radiology changed their names to departments of medical imaging.
The use of CAT scanners has not been problem-free. Part of the reason for this is the high cost of the devices—ranging from about $300,000 for early models to $1 million for modern instru-ments—and resultant claims by consumer advocacy groups that the scanners are unnecessarily expensive toys for physicians. Still, CAT scanners have become important everyday diagnostic tools in many areas of medicine. Furthermore, continuation of the efforts of Hounsfield and others has led to more improvements of CAT scanners and to the use of nonradiologic nuclear magnetic resonance imaging in such diagnoses.
See also Amniocentesis; Electrocardiogram; Electroencephalogram; Mammography; Nuclear magnetic resonance; Pap test; Ultrasound; X-ray image intensifier.
