Figure 7
From: Cardiovascular magnetic resonance physics for clinicians: part I
Image formation, Step 1 - Selecting a slice. For step 1 of image formation process, a slice of tissue is selected by applying a magnetic field gradient GS at the same time as the rf excitation pulse. The position along the gradient (in this example along the z axis) determines the Larmor frequency and resonance only occurs where this matches the frequency of the rf pulse, f0, defining a plane (slice) of tissue perpendicular to the z axis. In practice the rf pulse is applied over a small range of frequencies, thus defining the thickness of the slice.