Imaging

Belgians had decided to bring x-rays into practical use in hospitals throughout the country! Nevertheless, it was soon clear that a major new diagnostic tool had been presented to the medical world, and there was little surprise when Roentgen received a Nobel Prize in Physics in 1901.

Meanwhile, in March 1896, Henri Becquerel, professor of physics at the Muséum National d'Histoire Naturelle in Paris, while investigating Roentgen's work, wrapped a fluorescent mineral, potassium uranyl sulfate, in photographic plates and black material in preparation for an experiment requiring bright sunlight. However, a period of dull weather intervened, and prior to actually performing the experiment, Becquerel found that the photographic plates were fully exposed. This led him to write: "One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver salts." Becquerel received a Nobel prize, which he shared with Marie and Pierre Curie, in 1903, but it was to be many years before the use of spontaneous radioactivity reached maturity in medical investigation in such applications as isotope scanning and radioimmunoassay.

The use of a fluoroscopic screen on which to view x-ray pictures was implicit in Roentgen's original discovery and soon became part of the routine equipment not only of hospitals but even of shoe shops, where large numbers of children's shoe fittings were carried out in the days before the true dangers of radiation were appreciated. However, the greatest value of the real-time viewing approach only emerged following the introduction of electronic image intensifiers by the Philips company in 1955.

Within months of the introduction of planar x-rays, physicians were asking for a technique that would demonstrate the body in three dimensions. This challenge was taken up by a number of scientists in different countries, but because of the deeply ingrained habit of reviewing only the national, not the international, literature, these workers remained ignorant of each other's progress for many years.

Carl Mayer, a Polish physician, first suggested the idea of tomography in 1914. André-Edmund-Marie Bocage in France, Gustav Grossmann in Germany, and Allesandro Vallebona in Italy all developed the idea further and built their own equipment. George Ziedses des Plantes in the Netherlands pulled all these strands together in the 1930s and is generally considered the founder of conventional tomography.

Further progress had to wait for the development of powerful computers, and it was not until 1972 that Godfrey Hounsfield, an engineer at EMI, designed the first computer- assisted tomographic device, the EMI scanner, installed at Atkinson Morley Hospital, London, an achievement for which he received both a Nobel prize and a knighthood.

Parallel with these advances in x- ray imaging were ongoing attempts to make similar use of the spontaneous radioactivity discovered by Becquerel. In 1925, Herrman Blumgart and Otto Yens made the first use of radioactivity as a biomarker when they used bismuth- 214 to determine the arm -t o- arm circulation time in patients. Sodium-24, the first artificially created biomarker radioisotope, was used by Joseph Hamilton to investigate electrolyte metabolism in 1937.

Unlike x-rays, however, radiation from isotopes weak enough to be safe was not powerful enough to create an image merely by letting it fall on a photographic plate. This problem was solved when Hal Anger of the University of California, building on the efficient gamma-ray capture system using large flat crystals of sodium iodide doped with thallium developed by Robert Hofstadter in 1948, constructed the first gamma camera in 1957.

The desire for three-dimensional images that led to tomography with x-rays also influenced radioisotope imaging and drove the development of singlephoton- emission computed tomography (SPECT) by David Kuhl and Roy Edwards in 1968. Positron-emission tomography (PET) also builds images by detecting energy given off by decaying radioactive isotopes in the form of positrons that collide with electrons and produce gamma rays that shoot off in nearly opposite directions. The collisions can be located in space by interpreting the paths of the gamma rays, and this information is then converted into a three-dimensional image slice. The first PET camera for human studies was built by Edward Hoffman, Michael Ter-Pogossian, and Michael Phelps in 1973 at Washington University. The first whole-body PET scanner appeared in 1977.

Radiation, whether from x- ray tubes or from radioisotopes, came to be recognized as having dangers both for the patient and for personnel operating the equipment, and efforts were made to discover media that would produce images without these dangers. In the late 1940s, George Ludwig, a junior lieutenant at the Naval Medical Research Institute in Bethseda, Maryland, undertook experiments using industrial ultrasonic flaw - detection equipment in an attempt to determine the acoustic impedance of various tissues, including human gallstones surgically implanted into the gallbladders of dogs. His observations were detailed in a 30-page project report to the Naval Medical Research Institute dated June 16, 1949, now considered the first report of its kind on the diagnostic use of ultrasound. However, a substantial portion of Ludwig's work was considered classified information by the Navy and was not published in medical journals.

Civilian research into what became the two biggest areas of early ultrasonic diagnosis—cardiology and obstetrics—began in Sweden and Scotland, respectively, both making use of gadgetry initially designed for shipbuilding. In 1953, Inge Edler, a cardiologist at Lund University collaborated with Carl Hellmuth Hertz, a graduate student in the department of nuclear physics who was familiar with using ultrasonic reflectoscopes for nondestructive materials testing, and together they developed the idea of using this method in medicine. They made the first successful measurement of heart activity on October 29, 1953 using a device borrowed from Kockums, a Malmo shipyard. On December 16 of the same year, the method was used to generate an echo encephalogram. Edler and Hertz published their findings in 1954.

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