In-class group activity 12:
Use an on-line simulation from the University of
Colorado PhET group to explore a simplified version of NMR and MRI.
Link to the simulation:
http://phet.colorado.edu/en/simulation/mri
Click "Run Now!" or "Download".
Open a Microsoft Word document to keep a log of your
results and conclusions.
Start with the simplified NMR simulation.
- Familiarize yourself with the interface.
- Adjust the magnetic field to 2 T.
- Power up the radio wave source.
- Find the resonance frequency for hydrogen atoms and verify the g = B/f
(MHz/T) given in the notes
and below.
- Find the resonance frequency for sodium atoms and verify the g (MHz/T)
for sodium atoms given in the notes.
- Find g (MHz/T) for sulfur atoms and the unknown atoms. You may
want to increase the field to 3 T.
|
Nuclei
|
g (MHz/T)
from notes |
g = f/B
from your measurements |
|
1H |
42.58
|
|
|
23Na |
11.27
|
|
|
S |
|
|
|
unknown |
|
|
Paste your table into your word document and briefly
discuss your results.
Switch to the MRI simulation.
- Familiarize yourself with the interface.
- Set the main field to 2 T, power up the radio source, and find the
resonance frequency. It should be very close to the resonance
frequency for hydrogen you found above. Record
the resonance frequency.
- Add a tumor. Adjust the resonance frequency slightly to produce
the strongest signal from the tumor. Record the tumor resonance
frequency. Is there a shift?
- Remove the tumor, but add a horizontal and a vertical gradient field of
0.6 T. The magnetic field now is no longer uniform, but is a function
of position.
Slowly bring up the frequency from 10 MHz and 130 MHz and observe that MRI
signals are only generated in selected regions of the head.
What are the approximate resonance frequencies for the
upper left and the lower right portion of the head? Record your
values.