Joint MRI

What it does

Joint MRI reads non-knee joint studies: shoulder, hip, ankle, wrist and other joints imaged with fat-suppressed fluid-sensitive and T1-weighted sequences, with or without arthrography. For every joint, the run segments the bones and muscles in the field of view and measures muscle volumes, adding fat fraction when a Dixon acquisition is present.

For the shoulder, the most frequently ordered of these exams, it reads the rotator cuff tendon by tendon. Supraspinatus, infraspinatus and subscapularis each get a tear grade, tendon retraction is measured, and the fatty infiltration of the corresponding muscle bellies is graded: the three factors surgeons weigh when planning a repair.

Intended use

Decision support for physicians reporting shoulder MRI and for teams who need muscle quantification: a consistent cuff read that states tear extent, retraction and muscle quality in one place, and volumetric muscle and fat measurements that are impractical to draw by hand. Findings come with their masks and measurements.

Who it is for

Musculoskeletal and general radiologists, orthopaedic and shoulder surgeons deciding between repair, rehabilitation and arthroplasty, and sports-medicine physicians. Developers and researchers use the bone and muscle segmentation for body composition, sarcopenia and rehabilitation studies.

Accepted input

• DICOM MR study of one joint: MR Image, Enhanced MR or Legacy Converted Enhanced MR objects, zipped or sent by DICOMweb STOW-RS. NIfTI with a BIDS-style sidecar is accepted on the API.
• MR arthrography with intra-articular contrast is read for the shoulder.
• The joint, plane and fat suppression of each series are recognised from acquisition tags and the images.

Requirements

Requirement	Why
Shoulder PD or T2 fat-sat, ± MR arthrography	Tendon continuity, tear grade and retraction
Any MSK sequence	Bone and muscle segmentation
Dixon fat and water images (optional)	Muscle fat fraction

Studies outside these requirements still receive bone and muscle segmentation; the rotator cuff section is computed only for shoulder studies.

Optional context

Age, the side, symptoms (pain, weakness, trauma), prior surgery such as cuff repair, and the clinical question go in clinical_context.

The result

Section	Content
Rotator cuff	Supraspinatus, infraspinatus and subscapularis tear grade, tendon retraction, muscle fatty infiltration grade
Bones and muscles	Bone and muscle masks, per-muscle volumes, fat fraction where Dixon is available
Draft report	Opt-in (options.report): an English narrative that interprets the result for the reader (findings, impression, limitations); every number is checked against the findings

Standards

• DICOM: SEG for bones and muscles on the source series; SR TID 1500 for volumes, retraction and fat fraction; KOS key images and Encapsulated PDF.
• Grading: Goutallier/Fuchs grade for fatty infiltration of the rotator cuff muscles.
• Terminology: findings coded with RadLex and SNOMED CT; measurements in millimetres, millilitres and percent.

Scope of the read

The cuff section answers the surgical questions for shoulder pain: which tendons are torn, how far each has retracted and how much fat has replaced the muscle. Outside the rotator cuff, findings such as labral tears, cartilage defects, ligament injuries or osteonecrosis are not graded by this model.