# Frequency of RF pulse in MRI

• BobP

#### BobP

The magnetic moment of protons precesses at a frequency ω0=γB0 about the static magnetic field.

In order to move the magnetisation vector into the transverse plane the RF pulse must be applied at a frequency
ω0. However, as B1 (the field strength of the RF pulse) is << B1 how is this possible (as ω0=γB0 >> ω1=γB1)

Does this makes sense. Please can someone explain where I am going wrong
Thanks

I presume that, as with any resonant system, a small disturbance at the resonant frequency will add a little energy each cycle until the cumulative effect is large. The resonant system will store energy from the RF field over many cycles.

The magnetic moment of protons precesses at a frequency ω0=γB0 about the static magnetic field.

In order to move the magnetisation vector into the transverse plane the RF pulse must be applied at a frequency
ω0. However, as B1 (the field strength of the RF pulse) is << B1 how is this possible (as ω0=γB0 >> ω1=γB1)

Does this makes sense. Please can someone explain where I am going wrong
Thanks
I am not sure what you are asking. There are two motions that are important here. One is the precession, that is driven by B0 and so by the Larmor equation it is typically in the 100 MHz range. The other is nutation, that is driven by B1 and is typically in the 100 Hz range. This corresponds to the fact that the B0 field is in the Tesla range while the B1 field is in the micro Tesla range.

I am not sure what you are asking. There are two motions that are important here. One is the precession, that is driven by B0 and so by the Larmor equation it is typically in the 100 MHz range. The other is nutation, that is driven by B1 and is typically in the 100 Hz range. This corresponds to the fact that the B0 field is in the Tesla range while the B1 field is in the micro Tesla range.
My question was based on a misunderstanding of the difference between frequency of the RF pulse and Larmor frequency.
I foolishky assumed they were the same which is why I was confused. However problem is now fixed :)

Thanks for your help though :)