Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 14

What B₁ amplitude is required for a 1 ms rectangular shaped RF pulse to produce a flip angle of 90°?

Express α in radians (= ). From Equation 1.2

Figure 1.4 Excitation of the macroscopic magnetization M by the B₁ RF field.

Once excited, the magnetization recovers towards its initial equilibrium value M₀ by two independent relaxation processes: T₁ relaxation restores the longitudinal or z‐component of magnetization towards M₀; T₂ relaxation causes the transverse component, the signal, to decay to zero. T₁ and T₂ relaxation times vary by tissue type and exhibit changes due to pathology, often increasing where disease or injury is present.