Wilhelm Konrad Roentgen's (1845-1923; German physicist and winner of the first Nobel Prize for physics in 1901) discovery of X-rays in 1895 revolutionized most fields of science, including medicine. The fact that some parts of the body are more dense than others means that X-rays can be used to diagnose some medical problems. Bone fractures, for example, are easily examined using X-ray photographs.
This generalization is not true, however, for studies of the brain because the brain's density is essentially constant in all its parts. In an attempt to apply X-ray analysis to the brain, Walter E. Dandy (1886-1946) developed a technique for injecting air into brain cavities. The lower density of air made it possible to use X-rays to study normal and abnormal brain structures. The method was not very effective, however, and often involved considerable risk to the patient.
In 1927, Portuguese neurologist Antonio Egas Moniz came up with another solution to this problem. He injected opaque (inpenetrable to the passage of light) liquid solutions into the brain's arteries. Blood vessels in the brain then become clearly visible. The resulting photographs could be compared with photographs of the normal brain to see where tumors may have taken the place of blood vessels. Over the next decade, Moniz and his colleagues published more than 200 papers describing their technique, known as cerebral angiography.
Although several newer brain scanning tools have been developed over the years since Moniz created his technique, including CAT (computerized axial tomography), PET (positron emission tomography) and MRI (magnetic resonance imaging), angiography still holds its own as a technique for pinpointing injuries and abnormalities of the brain.