Autopsy of the living pg. 2
Supported in part by the sales of Beatles records, the EMI group, led by Godfrey Newbold Hounsfield, developed and brought the first CT scanner to market in 1971. As image resolution improved and scanning speed increased, the CT scan soon became the “standard of care” for suspected brain disorders. It has since become a powerful method for imaging the body as well.
Over the seven decades that passed between the first X-ray devices and the modern version of CT, the basis for the next wave of medical imaging—one that didn’t involve harmful radiation—was slowly taking shape.
In the late 1930s, physicists discovered that atomic nuclei containing odd numbers of protons (such as hydrogen) would align themselves with a strong magnetic field and revert to their original state, or “relax,” when the field was turned off. This change could be detected by the radiofrequency waves given off in the process.
Since bodily tissues differ in their water content (and consequently, hydrogen content), scientists realized that this “nuclear magnetic resonance,” or NMR, could be used to distinguish between soft tissues—and possibly to detect disease.
In 1971, Raymond Damadian, M.D., a physician at Downstate Medical School in Brooklyn, N.Y., used NMR to distinguish excised cancerous tissue from normal, healthy tissue.
Two years later, Paul Lauterbur, Ph.D., a chemist at the State University of New York at Stony Brook, introduced rotating magnetic field gradients and computer algorithms to assemble a two-dimensional image from NMR data. Using this technique, he produced the first NMR image of a living subject, a clam.
Damadian and colleagues followed in 1977 with the first NMR image of a human subject.
Peter Mansfield, Ph.D., a physicist at the University of Nottingham in England, developed mathematical calculations that allowed faster acquisition of the NMR image. His work led to the “fast” or “functional” MRI (fMRI), which could acquire images at the rate of 30 to 100 frames per second.
In 1989, Seiji Ogawa, Ph.D., a physicist at AT&T Bell Laboratory in New Jersey, described the phenomenon—called Blood Oxygenation Level Dependent (BOLD) effects—that forms the basis for functional MRI (fMRI). The changes in oxygenation of blood hemoglobin in “activated” brain regions perturb the local magnetic environment, serving as a natural contrast agent.
Since changes in the BOLD signal depend on the changes in blood flow and oxygenation, fMRI provided a measure of brain activity and the unparalleled ability to safely and non-invasively probe the physiological basis of neurological and psychological disorders as well as normal cognitive function.
Medical ‘Geiger counters’
Despite the attractiveness of MR as a radiation-free, and presumably safe, imaging technique, nuclear technology has spawned some of the most sensitive and powerful imaging methods to date—single photon emission computed tomography (SPECT) and positron emission tomography (PET).