Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 16

By applying a narrow bandwidth B₁ pulse, shaped to include a limited range of frequencies, simultaneously with the slice select gradient G_ss, the excitation region is restricted to a narrow slice of the patient’s anatomy with a width or thickness:

(1.3)

The slice thickness can be controlled by changing the amplitude of the slice‐select gradient or by changing the bandwidth of the RF pulse. The slice orientation can be selected by using different gradient coils (or a combination of coils for oblique views). By changing the RF frequency images may be acquired as a series of 2D multiple slices at different locations (Figure 1.6).

Figure 1.6 Multiple slice imaging. Changing the frequency of each RF pulse whilst a gradient G_ss is applied selects a different slice position.