The Basics of NMR

B1 in the Rotating Frame


The B1 magnetic field in the laboratory frame of reference is typically described by two vectors. One vector rotates clockwise at o and the other counter clockwise at -o. In the laboratory frame of reference, the net B1 magnetic field appears as an oscillating vector along the X axis.

In a rotating frame of reference traveling clockwise about Z at o, the B1 vector component that rotates clockwise in the laboratory frame of reference will be stationary. The B1 vector component that rotates counter clockwise is traveling about the Z axis at -2o. A component that rotates about Z at -2o is so far from the resonance frequency of the spins that it can be ignored. Therefore, in the rotating frame of reference, the B1 field appears stationary.


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