Target audience:

Clinical radiologists, technologists and scientists with a basic understanding of MR imaging techniques looking to learn the concepts of multi-sequence musculoskeletal MR imaging and who are interested in the development of rapid comprehensive MRI protocols for musculoskeletal applications.

Learning objectives:
- To review common clinical questions for musculoskeletal MR imaging and to illustrate how particular MR pulse sequences are utilized to answer these questions;
- To explain basic technical challenges to musculoskeletal MR imaging;
- To highlight advances in MR data acquisition technology and protocol optimization for a variety of musculoskeletal MRI application that could facilitate high-throughput.
- To understand for which musculoskeletal indications a 5-minute MR scan would or would not be feasible.

Outline of lecture
The purpose of this lecture is to provide a perspective on whether high-throughput MR for musculoskeletal applications is feasible. The central question will be if a 5-minute “comprehensive” MR scan will be able to address the most common clinical indications for which musculoskeletal MR imaging is performed. Since MRI is a powerful and flexible imaging modality particularly for musculoskeletal indications, musculoskeletal MR imaging constitutes a large (if not the largest) proportion of the MR workload in most clinical radiology settings. Hence, high-throughput musculoskeletal MR imaging will have major impact on the efficiency and productivity in most radiology departments.

The lecture will begin with a discussion of the most frequent clinical questions for musculoskeletal MR imaging, which include post-traumatic work-up, chronic joint complaints (overuse), and arthritis, and what information is critical for the diagnosis (and what isn’t). The most widely applied current MR approaches to address these questions, along with the MR acquisition times thereof, will be discussed. Virtually all current-day clinical MR protocols include proton-density weighted fast spin-echo (FSE) sequences with and without fat suppression, and T2-weighted fast spin-echo (FSE) images with fat suppression. Fluid-sensitive sequences with fat suppression are essential in every musculoskeletal MR protocol, as many pathologies demonstrate edema in bone marrow and soft tissues. Some protocols also contain T1-weighted sequences to assess bone marrow. A variety of gradient-recalled-echo (GRE) sequences have been proposed to evaluate articular cartilage, each with advantages and drawbacks. Contrast administration is usually reserved for imaging of musculoskeletal inflammation and tumors. MR acquisition in multiple (preferably three orthogonal) planes is necessary for accurate diagnosis. A routine clinical knee MRI protocol will be reviewed, highlighting normal anatomy and pathological conditions that can be visualized on each of the sequences and imaging planes. The most important challenges with regard to imaging of musculoskeletal tissues will also be touched upon. MR imaging of a variety of relevant tissues, in particular tendons, ligaments, and menisci, is hampered by short T2 relaxation time, which renders these tissues dark on most conventional MR sequences. The magic angle artefact can occur in musculoskeletal tissues such as articular cartilage, tendon, and menisci, and can mimic relevant pathologies. Understanding of these concepts will direct the definition of a “comprehensive” 5-minute MR examination.

Recent advances in MR data acquisition technology and protocol optimization that could facilitate high-throughput musculoskeletal MR imaging will be presented. Examples and results of comparative studies will be shown for a variety of large (knee, shoulder, hip) and smaller (ankle, wrist) joints, but emphasis will be on the knee joint, which is the most frequently imaged joint with MR imaging. Among the techniques discussed are parallel imaging, compressed sensing, and rapid isotropic 3D sequences which can be a time efficient approach to multiplanar imaging, essential for musculoskeletal MR imaging, as they allow multiplanar reconstructions. Differences between 1.5 and 3.0 Tesla MR acquisition and impact on scan time will also be reviewed.

Some time will also be spent on a discussion of previous results of studies on cost-effectiveness studies and impact on therapeutic decision making of rapid MR imaging of the knee applied in the acute stage after knee injury. Based on the knowledge of different indications, involved joints, clinical setting, novel MR technology, and results of previous research, the lecture will conclude with a statement about the musculoskeletal body parts or indications for which a 5-minute MR scan would or would not be feasible.