MRI Sag STIR
An artifactual T2 bright signal seen in tendons and ligaments that are oriented at about a 55 degree angle to the main magnetic field, not to be mistaken for tear.
Signal from water molecules associated with the tendon collagen fibers not normally seen because of dipolar interactions that result in very short T2 Times. At an angle of about 55 degrees to the main magnetic field, the dipolar interactions become zero, resulting in an increase of the T2 Times about 100 fold. This results in signal being visible in tendons. A bright signal from this artifact is commonly seen in the rotator cuff and distal patellar tendon.
Reference : http://www.mritutor.org/mritutor/magica.htm