Fifty years ago a machine was tested for the first time that analyzed X-ray images of the human body taken from multiple angles. Many historians consider this to be the first example of computer tomography, an imaging method that relies on special X-ray equipment to create a series of detailed pictures, or scans, of a human body. In effect, the machine developed by physician David Kuhl and engineer Roy Edwards of the University of Pennsylvania, in Philadelphia, mapped changes in density—caused by different organs—in the path of the X-rays. They first operated the machine, the Mark II, on 14 May 1965.
CT scans radically changed doctors’ views of the human body and the practice of health care, as well as the study of anatomy. Physicians could detect serious health problems such as tiny brain tumors or damaged lung tissue as if the person had been cut open and examined, yet the method was completely noninvasive. CT scans also ushered in other imaging methods that produced clearer, more comprehensive views of the interior of the body.
A LOOK INSIDE
These breakthroughs in medical imaging were decades in the making. In 1895, German physicist Wilhelm Conrad Röntgen announced the discovery of a new, penetrating form of electromagnetic radiation. He named this by-product of the operation of the cathode ray tube X-rays. How much X-rays are attenuated depends on the density of the materials they pass through. When Röntgen’s X-rays were made to strike a photographic plate, they produced a shadow image of physical structures.
Röntgen immediately realized the potential medical application of his discovery. He reported his breakthrough to the Physical Medical Society of Würzburg, Germany, and he included in his presentation an X-ray image of his wife’s hand. The world, medical and otherwise, quickly grasped the importance of the discovery. Within two months, an X-ray photograph of a bullet still lodged in a victim’s leg was admitted as evidence at a trial in a Canadian court and led to a conviction. Within a year, the article “The Clinical Application of the Röntgen Rays” appeared in the American Journal of Medical Sciences. Only six years after his discovery, Röntgen received the 1901 Nobel Prize in Physics—the first of many such prizes to be awarded to researchers for the understanding and application of X-rays.
Thanks to Röntgen’s discovery, the inside of the human body could now be observed noninvasively, and the field of radiography was born. It was clear that the 20th century was to be the century of the X-ray.
Early radiographers worked to increase the resolution, stability, and flexibility of the image while improving the safety of X-rays and lowering costs. The main challenge was to improve the image so as to be able to focus on only one plane of the body. Because X-rays pass completely through body parts, it was necessary to remove the shadows of bones or internal organs that existed in other planes. This was accomplished in 1914, when Karol Mayer, a Polish doctor, produced the first tomogram, an image of a single plane or “slice” of the heart. By 1937, the first commercial tomographs had been produced. Now, designers of X-ray equipment had a new challenge: taking clearer images of interior slices and reconstructing 3-D images based on those slices.
In 1960, William Oldendorf patented an electronically based device that could capture image slices continuously through a solid object. He was a physician but also an inveterate tinkerer and a member of the American Institute of Electrical Engineers, one of IEEE’s predecessor societies. What Oldendorf’s device lacked was the computational power to turn those image slices into a single 3-D image.
Hearing of Oldendorf’s work, Kuhl recruited Edwards, who headed up the engineering branch of the University of Pennsylvania’s radiology department, to tackle the problem. The result was the Mark II, which used a double-headed scanner and an optical integrator—an analog optical device that sharpens fuzzy X-ray patterns into clearer images—to perform transaxial section tomography of the body.
In 1971, developments in X-rays and computing led Electrical and Musical Industries, in London, to patent and produce the first commercial computer-aided axial tomography (CAT) scanner. Computer tomography (CT) scanners, as they came to be known, used powerful electronic digital computers to take X-ray cross sections of the body and convert them into 3-D images. Godfrey Hounsfield, the lead engineer on the EMI project, was unaware of the work of Kuhl and Edwards; much of the mathematics was the same for both projects.
In recognition of the impact of CT, Hounsfield became the first engineer to receive the Nobel Prize for Physiology or Medicine, in 1979. By awarding its most prestigious scientific prize to Hounsfield, the world had recognized the convergence of electrical engineering and medicine.
But the imaging work of Kuhl and Edwards was not in vain. Their research on single-photon emission techniques led them to develop positron emission tomography (PET), an imaging technique based on gamma rays. This technology achieved commercial success and recognition in its own right (although it did not, alas, lead to a Nobel Prize).
Over the past five decades, all of these instruments have been further refined, both in their physical and computational aspects. And engineers and physicists have been able to develop forms of tomography based on other physical effects, including magnetic resonance imaging (better known as MRI), based on nuclear magnetic resonance, and ultrasound, based on ultrasonic waves. With such ongoing advances in imaging, there is no doubt that biomedical engineering will continue to transform medicine in the decades to come.