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".

• 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.

Estimate g from your results.  How might you estimate this more accurately?

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 0.06 T.  The magnetic field now is no longer uniform, but is a function of position.
  Slowly bring up the frequency from 10 MHz and 110 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?