CONCLUSIONES Y RECOMENDACIONES - FACULTAD DE INGENIERÍA TERMINACIÓN DE POZOS INTELIGENTES TESIS

CAT scanner

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 col-lects 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 to-mography (it came to be called computed toto-mography, or CT). CAT is a technique of medical radiology, an area of medicine that began after the German physicist Wilhelm Conrad Röntgen’s 1895 discov-ery of the high-energy electromagnetic radiations he named “X rays.” Röntgen and others soon produced X-ray images of parts of the human body, and physicians were quick to learn that these im-ages were valuable diagnostic aids.

In the late 1950’s and early 1960’s, Allan M. Cormack, a physi-cist 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 an-gles. Because the technique probed test samples from many different points of reference, it became possible—by using the proper mathe-matics—to reconstruct the interior structure of a thin slice of the ob-ject being studied.

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Cormack published his data but received almost no recognition because computers that could analyze the data in an effective fash-ion 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 God-frey Newbold Hounsfield of England’s Electrical and Musical In-struments (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 appro-priate computers. Hounsfield developed another mathematical ap-proach to the method. He estimated that the technique would make possible the very accurate reconstruction of images of thin body sec-tions with a sensitivity well above that of the X-ray methodology then in use. Moreover, he proposed that his method would enable 168 / CAT scanner

Medical technicians studying CAT scan results. (PhotoDisc)

researchers and physicians to distinguish between normal and dis-eased 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 suc-cessful tomograms of preserved human brains and the fresh brains of cattle. The further development of the CAT scanner then pro-CAT scanner / 169

Godfrey Newbold Hounsfield

On his family farm outside Newark, Nottinghamshire, En-gland, 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 elec-trical recording machine, and experimenting with homemade gliders and water-propelled rockets. All these childhood pro-jects 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 os-cilloscope 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 Elec-trical Engineering College in London. Upon graduating in 1951, he took a research position with Electrical and Musical Instru-ments, Limited (EMI). His first assignments involved radar and guided weapons, but he also developed an interest in comput-ers and in 1958 led the design team that put together England’s first all-transistor computer, the EMIDEC 1100. This experience, in turn, prepared him to follow through on his idea for com-puted 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. Cor-mack shared the Nobel Prize in Physiology or Medicine for the invention. Hounsfield, who continued to work on improved computed tomography and other diagnostic imagining tech-niques, was knighted in 1981.

ceeded 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 At-kinson 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 pro-cessed. The computer then converted the data into a tomogram (a cross-sectional representation of the brain that shows the differ-ences 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 disor-ders of the brain. Even the first scanners could distinguish between brain tumors and blood clots and help physicians to diagnose a va-riety of brain-related birth defects. In addition, the scanners are be-lieved to have saved many lives by allowing physicians to avoid 170 / CAT scanner

the dangerous exploratory brain surgery once required in many cases and by replacing more dangerous techniques, such as pneu-moencephalography, 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 be-came 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 tech-nique 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 res-onance imaging in such diagnoses.

See also Amniocentesis; Electrocardiogram; Electroencephalo-gram; Mammography; Nuclear magnetic resonance; Pap test; Ultra-sound; X-ray image intensifier.