The Physics
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Magnetic Field Inside an MRI

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Bibliographic Entry Result
(w/surrounding text)
High Field Magnetic Resonance Imaging. Brookhaven National Laboratory Chemistry Department. Long Island, NY: 1996. "A nuclear magnetic resonance (NMR) instrument with a 4 tesla whole-body magnet." 4 T
Center for Magnetic Resonance Research. University of Minnesota. Minneapolis, MN: 1997. "It is the home of the world's first 4 tesla whole body imaging instruments." 4 T
Grolier Encyclopedia. USA: Grolier, 1996: 106-107. "NMR spectrometers commonly operate near the maximum field for iron, and for the ultimate in research applications, commercial units have superconducting solenoid magnets providing 12 tesla and more." 12 T
Berman, Phyllis. Forbes. 153 (1994): 112. "MRIs go up to a field of strength 15,000 gauss." 1.5 T
Cutnell, John D. & Kenneth W. Johnson. Physics Third Edition. New York: Wiley, 1995: 738-739. "Suppose that a large surface of the body through which flux passes has an area of 0.032 m2 and a normal that is parallel to a magnetic field of 1.5 T." 1.5 T

Magnetic Resonance Imaging (MRI) uses two elements: computer controlled radio waves and magnetic fields that are up to 25,000 times as strong as the earth's. Some nuclei behave like magnetic spinning tops. An MRI uses a magnetic field to position the spinning nuclei of the atoms being studied, then temporarily disturbs the orientation with a burst of energy from a radio frequency transmitter. The whole MRI procedure takes about 5 minutes. There are different MRI machines that use different field strengths. Some use 4 tesla, others use 9.4 tesla and 15 tesla.

This procedure is not dangerous compared to others that expose the patient to radiation. However, while in the machine the patient may become claustrophobic. Most MRI machines use around 1 tesla and this is considered safer than the 4 tesla very powerful machine. The MRI machine is about 2 feet by 7 feet, standard in which the nuclei of hydrogen atoms are excited by radio wave pulses.

Ms. Alla Reyfman -- 1997

Bibliographic Entry Result
(w/surrounding text)
Magnet Safety in MRI. Videocassette. GE Medical Systems Institute, 1988. " Up to 25,000 times the force of the earth's magnetic field. And how strong is that? Compare it to the power of a crane magnet, which can lift up to four tons of iron and steel. The field of the MR system magnet is even stronger." > 1 T
Smith, Michael. "Cutting Edge: Brain surgeons can now see what they're doing as they do it." New Scientist. 2153 (26 September 1998), 16. "The magnet itself is weak by MRI standards -- only 0.2 tesla -- and gives less detailed images than a standard 1.5 tesla machine." 1.5 T
0.2 T

IGMIT means Image-Guided Minimally Invasive Therapy -- a new technique using a special MRI developed in Ontario.

Editor's Supplement -- 1998, 2002