MEDRADSC 2Z03 Lecture Notes - Lecture 15: Hertz, Larmor Precession, Shoulder Joint

• School: McMaster University
• Department: Medical Radiation Sciences
• Course: MEDRADSC 2Z03
• Professor: Dawn Danko

Document Summary

The radiofrequency or rf field (b1) has to be generated at the larmor precessional frequency. It is therefore a high frequency, oscillatory electromagnetic field and should be applied such that the direction of the b1 field is perpendicular to the applied field b0 for maximum efficiency and sensitivity. In mri, the frequencies used are in the megahertz (mhz) range. Rf field perpendicular to b0 exerts a torque on magnetic moments precessing with a. Larmor frequency equal to the frequency of the applied rf field. The devices that generate these rf fields are known as coils, resonators or probes. Coils that apply the rf excitation pulse are called transmit coils. The same coil that generates therf field may also be used to receive the considerably weaker mr signal. Alternatively, a separate coil, placed close to the patient, may be used as a receive coil.