MATCH THE FREQUENCY
Resonance is effective energy transfer.
The scanner's transmit coil produces a brief radiofrequency magnetic field called B1. When that RF is applied at hydrogen's Larmor frequency, energy can be transferred to the hydrogen spin system. This matching interaction is called resonance.
BEFORE, DURING, AND AFTER RF
The net magnetization changes direction.
Net magnetization rests along B0.
Energy is transferred at resonance.
A transverse component is now present.
The RF pulse tips magnetization away from the longitudinal direction. It also creates greater phase coherence, so magnetic moments contribute together in the transverse plane.
FLIP ANGLE
RF strength and duration influence how far M tips.
Part of M moves toward the transverse plane.
In the idealized model, M is tipped into the transverse plane.
In the idealized model, M is inverted toward negative Z.
Flip angle affects longitudinal and transverse magnetization, signal behavior, contrast, and sequence timing. Its role changes across pulse sequence families.
THE PLAYGROUND SWING ANALOGY
Push at the matching rhythm.
A swing gains useful motion when each push arrives at the right rhythm. In the same way, RF transfers energy effectively when it matches the Larmor frequency.
Remember: match the frequency, transfer energy, tip the magnetization.
CHECK YOUR UNDERSTANDING
Follow the RF pulse from cause to effect.
What is resonance in this MRI lesson?
It is effective energy transfer when RF is applied at hydrogen's Larmor frequency.
What is B1?
It is the time-varying RF magnetic field used to excite and manipulate the net magnetization.
What influences flip angle?
In the simplified model, the strength and duration of the RF pulse influence how far the net magnetization tips.
LESSON 04 COMPLETE
You understand resonance and RF excitation.Educational references
This lesson uses simplified models. RF safety and sequence operation must follow formal training, manufacturer guidance, and institutional policy.