Twenty-five years ago, researchers hoping to study brain function were limited to autopsies and electroencephalograms and the study of brain legions. Since then, however, there has been a revolution in imaging technology that has increased exponentially our understanding of the brain. The key technologies are as follows: Computer Axial Tomography (CT or CAT) Scans: This technique relies on old-fashioned X-rays but with a modern twist. Invented in the 1970s by British engineer Godfrey Hounsfield and South African physicist Allan Cormack, who shared the 1979 Nobel Prize in Physiology and Medicine, the technique employs a beam of X-rays rotated around the patient. Hundreds of electronic x-ray detectors surround the patient and measure the attenuation of the X-rays passing through the individual. A computer then analyzes the pattern and reconstructs cross-sectional images of the relevant organs that can be viewed on a computer screen. Positron Emission Tomography (PET): The first technology for actually imaging brain function, the ideas behind PET were pioneered in the 1950s at Washington University in Saint Louis, and ultimately developed in 1974 by Dr. Michael Phelps, UCLA chair of Molecular and Medical Pharmacology, along with Dr. Edward Hoffman. In PET, chemicals are injected into the bloodstream that are "labeled" by radioactive isotopes of carbon or nitrogen. As these disintegrate in the bloodstream, they emit positrons which promptly annihilate with electrons in the body, producing gamma rays. The gamma rays, which are safer than X-rays, are detected by electronic cameras surrounding the body and an image is reconstructed using a technique similar to that for CT scans. The result in the brain, for instance, is vivid images of blood flow and how it changes during different behavior. Using PET, it's also possible to image brain-energy metabolism and transmitter-receptor systems.   Magnetic Resonance Imaging (MRI): This technology was developed thanks to key breakthroughs made in the early 1970s by Pittsburgh chemist Paul Lauterbur and Brooklyn physician Raymond Damadian. The technology depends on the fact that different atomic nuclei can be induced by an external magnetic field to selectively absorb radio waves of a distinctive frequency. In Magnetic Resonance Imaging, this phenomenon is used to image living tissue by measuring the nuclear magnetic moment of the protons that constitute the nuclei of hydrogen atoms in water. These can provide a density map of water molecules in the body which changes with different tissues. It provides a noninvasive, completely safe technology to create high-contrast, two-dimensional images of tumors and necrotic tissues when used in the guise of a high-speed technology known as "functional MRI." the technology can even produce images of the working brain.