Demystifying ABER (ABduction and External Rotation) sequence in shoulder MR arthrography.

ABduction and External Rotation (ABER) sequence in magnetic resonance (MR) arthrography of the shoulder is particularly important to better depict abnormal conditions of some glenohumeral joint structures and surrounding tissues by making imaging possible under a stress position relevant to pathologic conditions. Among the structures and tissues better depicted in this position are articular surface of the supraspinatus tendon, anteroinferior portion of the glenoid labrum, and anterior band of the inferior glenohumeral band. Despite these benefits of the ABER sequence, it is either not being used extensively as part of shoulder MR arthrograms or, when utilized, not properly assessed, mostly due to some practical difficulties in setting up the sequence and unfamiliarity with the alignment of structures displayed on MR images. In this technical note, we aimed to explain the ABER sequence planning in a step-by-step manner with emphasis on scout series set-up, and also present an outline of anatomic landmarks seen on ABER images.