Figure 18a. Magic angle effect. (a) Short-echo-time MR image obtained with the arm in neutral position shows a hyperintense focus approximately 1 cm proximal to the rotator cuff insertion (arrows). (b) On an MR image obtained with identical imaging parameters but with lateral flexion at the waist, the hyperintense region now extends to the insertion site (arrows). The change in position resulted in reorientation of the fibers in relation to the main magnetic field, causing a shift in the site of signal augmentation. (Fig 18a and 18b reprinted, with permission, from reference 21.)