THE MAGIC-ANGLE EFFECT IN MUSCULOSKELETAL MR-IMAGING

The ''magic angle'' effect in magnetic resonance (MR) imaging is cause d by changes in the dipolar interactions between water hydrogen proton s that are loosely bound along collagen fibrils in organized tissue su ch as tendon or articular cartilage. When tendons are aligned at 55 de grees to the main magnetic field, the T2 relaxation time is lengthened , causing focal increased signal on short echo time MR images. Tendons in the ankle, wrist, and rotator cuff of the shoulder are common site s to observe this effect. Distinguishing magic angle effect from patho logic signal abnormalities due to degeneration or partial tears requir es close comparison between T1- and T2-weighted images, as well as eva luation for secondary signs of injury such as tendon thickening or ass ociated fluid.