In 1971, Paul Lauterbur of SUNY conceived the idea of making the magnetic field non-uniform so that the rate at which it increased (its gradient) could be used to separate the record of the resonating nuclei spatially, that is, produce a two-dimensional image. Instead of merely registering what was contained in the sample, the record would show what is where, which is the essence of any picture.
In 1973, Lauterbur produced the first NMR image, a crude image of two test tubes of water. It consisted of two irregular dark blots that not even Picasso advised by Freud would have interpreted as tubes of water, but it was a start. One year later a British team published the first crude medical image
¾that of a human finger. Soon a number of improvements were made in the technique itself while exploiting the advances in computer technology (especially computer graphics and "false color" enhancement, in which areas of different response levels are painted in different colors on the screen). NMR scans have now become a mature technique that is both safer and superior to X-rays, and rapid advances are taking place with no slowing of the rate of improvement yet in sight.NMR is safer than X-rays because it involves no ionizing radiation (radioactivity). A single chest X-ray will administer a dose of 50 to 70 mrems, thousands of times higher than the average citizen gets from nuclear plants, and fifty times higher than even the near neighbors of TMI got in the Grand Disaster.
The reason why NMR is far superior to X-rays is that it works by source, not by attenuation. What X-rays do is exploit the varying degrees of transparency of different parts of the body: bones are less transparent to X-rays than flesh, so that they darken the flow of the rays (on the negative, they appear fighter). This is analogous to shining a fight through an aquarium: the silhouette of the fish and the plants can be projected onto the wall behind it. But NMR makes the points of the investigated body visible as individual sources, not as obstacles. This is analogous to shining a fight into an aquarium and observing the details as they reflect the light. That is why the image of a human head shown below, already much better than an X-ray, still has much improvement ahead of it, whereas X-raying has in essence reached perfection.
GRAPHIC: A12_8401.TIF
The OTA has recently published a 156-page report on the subject (Nuclear Magnetic Resonance Imaging Technology: A Clinical, Industrial and Policy Analysis, Report OTA-HCS-27, Sept. 1984, $5.50 from Govt. Printing Office, Wash., DC 20402). Its first three chapters on the technical basics are well written and interesting, the other six are a discussion on how to provide funds, and mainly how the government can help by three contributions: regulate, regulate, and regulate.
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Vol. 12, No. 4
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 12, No. 4 Date: November 29, 2004 01:03 PM Title: Good riddance
Copyright © 2004 - Access to Energy Newsletter Archive
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