Axial/coronal incoherent (spoiled) GRE/SE/FSE T1

Acts as a localizer if three-plane localization is unavailable and ensures that there is adequate signal return from the whole joint. Medium slices/gaps are prescribed relative to the horizontal alignment light so that the supraspinatus muscle is included in the image.

Axial localizer: I 0 mm to S 25 mm

Axial SE/FSE T2 or coherent GRE T2* (Figure 13.2)

Thin slices/gaps are prescribed from the top of the acromio-clavicular joint to below the inferior edge of the glenoid (Figure 13.3). The bicipital groove on the lateral aspect of the humerus to the distal supraspinatus muscle is included in the image. The axial projection displays joint cartilage and glenoid labrum, intra-osseous changes associated with Hills–Sachs deformity, and the condition of muscles and tendons of the rotator cuff.

Coronal/oblique SE/FSE T1 (Figure 13.4)

Thin slices/gaps are prescribed from the infra-spinatus posteriorly to the supraspinatus anteriorly and angled parallel to the supraspinatus muscle (Figures 13.5 and 13.6). This is best seen on a superior axial view, but coverage is easier to assess on an axial image through the lower third of the humeral head. The superior edge of the acromion to the inferior aspect of the subscapularis muscle (about 1 cm below the lower edge of the glenoid), and the deltoid muscle laterally, and the distal third of the supraspinatus muscle medially are included on the image.

Sagittal/oblique SE/FSE T1

As for coronal/oblique T1, except slices are prescribed from medial to the glenoid cavity to the bicipital groove laterally. The area from the distal portion of the joint capsule to the superior border of the acromion is included in the image (Figure 13.9).

Technical issues

The TE influences the signal of the muscle in musculoskeletal imaging. A very long TE produces T2-weighted images in which muscle is hypo-intense. The SNR is therefore reduced, but fluid detection is improved. Tissue suppression techniques can also be used to enhance the signal from fluid even further; however, larger voxels may be required to compensate for the inherent drop in SNR. By choosing a moderate TE, muscle still retains signal (a grey-level intensity) and the images are PD weighted. The SNR is however higher, and the spatial resolution can be better than a T2-weighted image. This kind of contrast is used to detect fluid and retain an anatomical image. Tissue suppression techniques are recommended with this kind of weighting because signal from fluid is reduced. Cartilage lesions can be better detected when TE is high (at least 30–40 ms) because the signal from normal cartilage decreases.

The SNR of the shoulder is largely dependent on the quality and type of coil used. Generally, dedicated shoulder coils return a much higher and more uniform signal than a surface coil, and therefore, the technique is adapted accordingly. If using a dedicated coil, thin slice thickness and higher matrices can be used to achieve the necessary spatial resolution without unduly lengthening the scan time. If the signal not high enough, some resolution may have to be sacrificed in order to maintain the SNR and keep the scan time within reasonable limits. Newly developed surface coils, with a high number of coil elements, can be configurated as high performance shoulder coils. However, spatial resolution is the key to accuracy in shoulder imaging, and the resolution must be as high as possible (pixel size below 0.8 mm). SE and FSE are usually the sequences of choice, but coherent GRE and STIR are useful to visualize joint fluid. STIR may provide better results than fat-suppressed FSE if magnet shimming is suboptimal.