The evolution of medical imaging and its human significance.
Editor's Note: The following is an excerpt from X-Ray Vision: The Evolution of Medical Imaging and Its Human Significance, a book by Richard B. Gunderman, MD, FACR, about the remarkable physicians, scientists, and patients who were involved in the development of the groundbreaking imaging technologies that many now take for granted. The book also discusses how these technologies have influenced both the world and humanity's self-perception.
Early Days of Neuroimaging
To understand fully what the CT scanner meant to the practice of medicine, it is helpful to know what patients went through in the years preceding its introduction. While it touched nearly every medical discipline and the diagnosis and treatment of diseases in every part of the body, its effects were perhaps nowhere more dramatic than the imaging of the central nervous system. While an X-ray image of the chest provides considerable anatomic detail and can reveal many pathological conditions, an X-ray image of the head is generally quite uninformative. But in the early days after the discovery of the X-ray, physicians did not yet know this.
Soon after the introduction of the X-ray into medical practice, physicians began making images of the human head in an effort to diagnose brain tumors and other abnormalities. Skull X-ray images featured in early publications showed vague opacities that were though to prepresent tumors but in fact probably represented hair braids. In 1919, however, neuroimaging took its first leap forward when a Johns Hopkins neurosurgeon named Walter Dandy described a technique of injecting air into the spaces in and around the brain that are normally filled with cerebrospinal fluid (CSF). He called this procedure pneumoencephalography, Greek for "air brain pictures."
A normal adult produced about half a liter of CSF each day. Because there is only about 150 milliliters of CSF in the body at any one time, the total volume must be resorbed and secreted three or four times every 24 hours. In addition to cushioning the brain and spinal cord from trauma, CSF performs a number of additional important functions. It provides buoyancy. Because the brain is floating in fluid, its 1,500 gram weight seems like only 25 grams. This enables blood to circulate easily through lower parts of the brain that would otherwise be compressed by the weight of the higher portions. The circulation of the CSF also carries away waste products that tend to accumulate in the brain. And by decreasing the amount of CSF inside the skull, the body can also provide extra space for expansion if the brain swells, thereby enabling blood to continue flowing into it. One of the signs of serious brain injury is shrinkage of the CSF spaces in and around the brain, indicating an increase in pressure within the skull. In some cases, a neurosurgeon may actually remove part of the skull to give the swollen brain room to expand.
Dandy and other physicians performed pneumoencephalography by removing small quantities of CSF through a needle inserted in the lower back (a "spinal tap"), and then replacing it with small quantities of air or another gas. When the patient was placed upright, the air tended to travel up the spinal cord and around the brain. After a sufficient amount of gas had been introduced, the patient was then rotated or even somersaulted to get the gas to travel into the CSF spaces inside the brain, called the ventricles. In the mid-1960s, a special chair was developed, rather like the chairs used to test astronauts for susceptibility to motion sickness. This made it easier to turn the patient and move the gas up and around the brain. Then X-ray images were made of the head. Depending on how the gas was displaced, radiologists could diagnose brain tumors, blockages to the flow of CSF, and abnormal enlargement of the ventricles.
In general, when patients undergo spinal taps, they are encouraged to lie down for six hours or so to prevent "spinal headache." By contrast, pneumoencephalography patients were turned in every direction, including upside down. As a result, it proved to be a very uncomfortable procedure to endure. Patients often experienced severe headache, nausea and vomiting, neck stiffness, fever, and other neurological conditions that could persist for as long as a week or more after the procedure.
An improvement in brain imaging occurred when the Portuguese neurologist Egas Moniz (1874-1955) introduced cerebral angiography. Moniz trained in neurology in France. Soon after returning to Portugal, he entered politics, serving in the parliament for 14 years and becoming an ambassador to Spain. Yet he never stopped practicing medicine, and in 1920 he returned to medicine full time. In 1927, Moniz inserted a needle into the cartoid artery and injected a solution of sodium iodide, which blocks X-rays, then made X-ray images that revealed the arteries and veins in and around the brain. Later, instead of inserting a needle directly into the neck, radiologists began to insert a catheter into a leg artery and then advance it up through the aorta and into the cartoid artery. At the time of the injection, X-ray images of the neck and head could be obtained, showing the branches of the cartoid artery in the brain. This technique revolutionized the diagnosis of brain diseases, as well as surgical planning for their treatment.
On cerebral angiograms, a brain tumor would often show up as an abnormally dense collection of blood vessels. If no such abnormal blood vessels were seen, it was unlikely that the patient was suffering from a brain tumor. If the abnormal vessels arose from vessels around the brain, then the tumor of the membranes that cover and protect the brain. The technique could also be used to diagnose other types of disorders, such as bleeding from blood vessels outside the brain. For example, a subdural hematoma, an abnormal collection of blood between the skull and the brain due to trauma, caused the blood vessels in the meninges to be pushed away from the skull and down toward the brain.
Moniz played another important role in the history of neurologic diseases. In 1936, he introduced a new surgical procedure, known as prefrontal leucotomy or lobotomy. This procedure, which was refined so that it could be performed through the nose, involved severing the connections between the frontal lobes and the remainder of the brain. This procedure became a mainstay in the care of patients suffering from psychoses, such as schizophrenia. It was widely performed in the 1940s and 1950s, with nearly 20,000 lobotomies in the US during the first decade. Moniz coined the term psychosurgery, and during this time it seemed likely that surgery would play an important role in the treatment of severe psychiatric disorders. In recognition of Moniz's work on the lobotomy, he received the Nobel Prize for Physiology or Medicine in 1949.
One of the most important portrayals of lobotomy in popular culture is the film One Flew Over the Cuckoo's Nest, based on Ken Kesey's 1962 novel. Produced in 1975, the film was only the second in history to win all five major Academy Awards, including best picture, best actor and actress in a lead role, best director, and best screenplay. Jack Nicholson plays Randall Patrick McMurphy, a prisoner convicted of statutory rape who arranges to be transferred to a mental institution. There he battles the institution's tyrannical leader, Nurse Ratched. McMurphy arranges various experiences for the inmates aimed at liberating them, for which he first receives electroconvulsive therapy and later a frontal lobotomy. Both procedures are presented as brutal and dehumanizing. Though electroconvulsive therapy remains one of the most effective treatments for severe depression, lobotomy was abandoned in the 1960s after the introduction of antipsychotic medications.
Patients today who require brain imaging should be exceedingly grateful that the CT scanner was introduced in the early 1970s. It brought pneumoencephalography to an abrupt halt, because CT imaging made it possible to visualize not only the CSF spaces but the brain itself, something the older technique could never do. Moreover, it required no injection into the spine. CT has also eliminated the need for most cerebral angiograms, although the procedure is still performed. Today it is used to diagnose and treat some vascular problems such as aneurysms, abnormal outpouchings in arteries that are prone to rupture and bleed. When a cerebral angiogram shows an aneurysm, a radiologist can advance a catheter up to the aneurysm and inject tiny metallic coils that cause a blood clot to form in the aneurysm, a procedure called embolization. Because blood is no longer flowing into the aneurysm, it can no longer bleed. This spares the patient a complex surgical procedure in which the skull and brain would be opened to reach the aneurysm and repair it surgically.
The introduction of the CT scan heralded a revolution in neuroimaging. Instead of subjecting the patients to invasive and uncomfortable procedures such as pnemoencephalography, physicians could simply ask the patient to lie down on a table and remain still while CT scan images were obtained. There was no risk of developing a severe headache, nausea, or infection of the brain or spinal cord. Moreover, physicians no longer needed to infer the appearance of the brain based on the shape of its ventricles or its blood supply. Instead, they could visualize the brain directly. Yet the early CT scanners were also slow and cumbersome; they required about 30 minutes to acquire the data and hours of computer processing to produce images. Today the entire scan takes a few seconds, and the images are available instantaneously (Figure 8.10a, b, c).