The Trail of Invisible Light: A Century of Medical Imaging
Introduction
1.Wide view of the UIHC Medical Museum. |
| The Trail of the Invisible Light: A Century of Medical Imaging
explores the growth of radiological methods from the discovery
of X rays to the present. Nearly a century after Wilhelm Roentgen, a
German physicist, showed that invisible rays could penetrate matter to imprint
ghostly images on photographic plates, X rays continue to engage our imagination
as well as our intellect. This is due in part to facination with a device
that makes the invisible visible. An additional source of awe is that the
X rays, like atomic radiation, embody the capacity to produce both benefit
and harm. More recently developed technologies, such as Magnetic
Resonance Imaging and Positron Emission Tomography,
which are in daily use in the University of Iowa Hospitals and Clinics,
extend and refine the X-ray experiments first made in a physics laboratory
at Wurzburg University in 1895.
Within weeks of Roentgen's announcement of his methods and results in a German
scientific journal in January 1890, the news of his discovery had been broadcast to the
world via the telegraph and the popular press. Academic interest matched the public's
enormous enthusiasm, and over the next few months scientists in Europe, the United
States and Canada raced to deuplicate Roentgen's experiments. Among them was
Professor Frank Almy, who produced "cathodic ray photographs" of frogs, keys and
coins with an apparatus in the physics laboratory of Grinnell College as early as
February 1896. A number of Almy's images are included in this exhibit. |
Although many properties of X-rays were known by the turn of the century, practical applications developed only gradually. Physicians were eager to employ X-rays to capture the exact shape of bone fractures, the location of foreign objects embedded in flesh and the study of growth abnormalities. The difficulty of using fragile and balky X-ray equipment, however, hampered the growth of medical radiology. Only when the Coolidge tube had replaced the unreliable Crookes tube in 1913 and after nitro-cellulose based photographic film supplanted glass-plate negatives around 1920 did radiology become attractive to most physicians. Examples of gas and Cooidge tubes are found in the exhibit. |
2. Fluorescing tubes, circa 1900. Courtesy
of the Department of Physics and Astronomy, UI |
Some applications of X-rays were more serious than others, and ignorance of the dangers of excess radiation dogged the spread of the new technology. Fluroscopy, for example, which substituted a screen of light-emitting crystals for the photographic plate and thus enabled viewers to seek skeletal structures and organs in motion, was a marvelous diagnostic and teaching device. Yet beginning in the 1920s floor-model fluroscopes were installed in shoe stores and induced a generation of customers to wriggle their toes and see the bones in their feet; the serious radiation risk of this theatrical marketing tool only became fully apparent in the early 1950s. |
3. Fluoroscopic examination. From Electro-Therapeutics and Roentgen Rays, Mihran Krikor Kassabian, MD, J.B. Lippincott Company. 1907 |
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Great refinements in medical imaging have been made in recent years.
Computed Axial Tomography (CAT) takes the medical
X-ray to its logical conslusion by rotating the tube entirely around the
body; this permits numerous exposures from many angles which the computer
then assembles into a cross-sectional image of the harder structures of
the whole body - a CT or CAT scan. Even more recent devices employ non-ionizing
forms of radiation that are safer than X-rays and that involve technologies
as fantastic to us as X-rays were to lay persons in 1900. For instance,
Magnetic Resonance Imaging (MRI), perfected
only in the 1980s, employs a superconducting magnet and computer-controlled
radio-waves to generate images of inaccessible soft tissues; these images
can be used to diagnose sports injuries, brain lesions, and spinal traumas.
MRI has advanced to the point where a computer-generated image of the
brain can be rotated in any direction so that all internal surfaces can
be viewed in sucession. While MRI gives access to deep structures and
tissues, another technolgy called Positron Emission
Tomography (P.E.T.) enables the visualization of chemical processes.
For example, P.E.T. studies can demonstrate the metabolism of glucose
inside heart muscle and the brain; these and similar data enable diagnoses
that had previously eluded physicians.
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Some of the most intriguing work being conducted by UIHC physicians combines
several imaging techniques to solve complex diagnostic problems. Site of brain disorder, for example, can be precisely located by three-dimensional computer reconstructions of MRI "slices"; P.E.T. images are then made of these sites to locate areas of decreased metabolism and confirm diagnoses. |
4. CT scans of brain. Courtesy of Hanna Damasio, MD,
Department of Neurology, and the Division of Nuclear Medicine,
Department of
Radiology, UIHC |
While the primary goals of medical radiology are the early diagnosis and treatment of illness, CT, MRI and P.E.T. technologies inevitably further scientists' understanding of how the body functions. UIHC health care professionals are deeply involved in research that uses state-of-the-art methods to understand fundamental processes of health and disease. |
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