Could anyone give me a basic idea of the physics principle behind the theory of MRI scanners?
What is being detected to form the image?
2006-08-01 09:24:31 · 4 answers · asked by hippoterry2005 3 in Science & Mathematics ➔ Physics
I know that a powerful magnet field and radio frequencies are used.
2006-08-01 09:25:58 · update #1
Better yet: there are usually three things going on.
1)A constant magnetic field
2)A slowly-varying magnetic field
3)An RF oscillation
The slowly-varying field is to make a signal easier to see (it's easier to pick up a periodic signal than a spike in time).
Hydrogen nuclei have a magnetic moment, think of it like a little magnet. When placed in a magnetic field, they tend to line up just like a compass needle in the earth's field. It costs energy to disalign them. This is what the RF is for. However, they can disalign only when you feed them the right amount of energy. This means that the Frequency of the RF has to match the energy difference. When it does, it puts out more power, and this "resonance" is detected.
What makes this useful is that the effective energy depends on exactly what the nucleus is doing--it could be part of a water molecule, or part of a piece of cartilege, or something else. By scanning the RF and scanning the applied field over, say, your knee, you can learn a lot about what's going on inside it.
The MRI machine is doing just this, and mapping the results to show what kind of stuff is where in the scanned volume.
2006-08-01 10:17:06 · answer #1 · answered by Benjamin N 4 · 2⤊ 0⤋
Hi. The magnetic field causes the hydrogen atoms to line up a bit. When the field is turned off the atoms snap back and give off a tiny signal.
2006-08-01 09:31:12 · answer #2 · answered by Cirric 7 · 0⤊ 0⤋
Magic.
2006-08-01 09:27:22 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Hopefully this link will help you... it goes on for a few pages though but is interesting.....
http://www.howstuffworks.com/mri.htm
2006-08-01 09:29:09 · answer #4 · answered by Anonymous · 0⤊ 0⤋