MRI synchronization with the IRF90

[Bayoudh101]

Hello ,

In MRI physics , I don't seem to be able to wrap my head around the synchronization in the precession of the protons after an RF90 impulse (which is an electromagnetic impulse that would deviate the precessing magnetic field axe by 90 degrees) the synchronization would give the vector length on the XY plane and that's logical , but why doesn't synchronization happen with the IRF180 pulse ? Which only seems to flip the vector ? Can someone please explain the origin of this resonance ?

Thank you .

 

[Dale]

the synchronization would give the vector length on the XY plane and that's logical , but why doesn't synchronization happen with the IRF180 pulse ? Which only seems to flip the vector ?

If you start with a vector aligned along the z axis and you rotate it by 180 deg, then how much of the vector is in the xy plane?