Reference images (Canada-Denmark International MRI Group) of STIR MRI, illustrating the sagittal view of the cervico-thoracic spine. (Reference images are also available at .) The arrow in the left image at T5 upper shows a vertebral corner inflammatory lesion (CIL) at the threshold of detection. The bone marrow signal in the center of the vertebral body, if normal, constitutes the reference for designation of normal signal . The arrow in the central image shows a CIL at the anterior corner of C4 lower. The large field of view necessary to scan the entire spine in AS impairs detailed assessment of cervical vertebrae. The right image shows increased STIR signal in a vertical pattern across the anterior portions of the lumbar vertebrae simulating inflammation but indicative of blood flowing through the great vessels (phase encoding artifact). STIR, short tau inversion recovery.