Manifestation of magic angle phenomenon: comparative study on effects of varying echo time and tendon orientation among various MR sequences.

The purpose of this study was to systematically investigate the effect of varying the echo time (TE) values and angle of the tendon to the main magnetic field (B(o)) upon the signal intensity observed with the magic angle phenomenon in tendons among most commonly used MR pulse sequences, including conventional spin echo (CSE), fast spin echo (FSE) and gradient echo (GRE) sequences. The intact bovine Achilles tendon was imaged using a clinical 1.5-T MR scanner. Magic angle phenomenon occurs in CSE, FSE and GRE sequences with different grade, appearing most severe in CSE, middle in FSE, and weakest in GRE sequence. In addition, the tendon signal changes produced by the magic angle phenomenon could be greatly reduced by increasing the TE to above a certain critical value in all three sequences. These critical TE values were different among CSE (40 msec), FSE (70 msec), and GRE (30 msec) sequences.