3 MRI Intuition (2 pts). > A spin makes an angle 9 with respect to a static eld BO, as shown below. a. _> Does the static eld Bo exert a torque on this spin? If so, what is the direction of this torque? In what direction will the spin rotate as a result? . You now wish to rotate the spin 90, so that it precesses in the .1: 3.} plane. To do so, you apply a second > > magnetic eld, B1. In what direction should you apply Bl? What is the direction of the resulting torque? > > . In order for Bl to rotate the spin into the m y plane, Bl must oscillate at the spin's Larmor frequency. Explain why a time-varying magnetic eld must be used to rotate the spin. Why must this eld oscillate at the Larmor frequency? Z