The Pearls and Pitfalls of Magnetic Resonance Imaging of the Upper Extremity

Abstract

Magnetic resonance imaging (MRI), like computed tomography, can produce images in any anatomical plane, visualize and analyze a variety of tissue characteristics, as well as quantify blood flow and metabolic functions. It does not use ionizing radiation but, rather, utilizes an apparently safe interaction between static magnetic fields, radio waves, and atomic nuclei. Randomly oriented tissue nuclei are aligned by a powerful, uniform magnetic field. Properly tuned radiofrequency (RF) pulses then disrupt this magnetization and, as the nuclei recover their alignment by relaxation processes, they produce radio signals that are proportional to the magnitude of the initial alignment. is capable of producing images in any anatomical plane, visualizing and analyzing a variety of tissue characteristics, as well as quantifying blood flow and metabolic functions. Although MRI details of compact bone and calcium are poor when compared to those taken with plain radiography or computed tomography, its high soft tissue contrast discrimination and multiplanar imaging capabilities are significant advantages. Musculoskeletal anatomy and neurovascular bundles are well delineated. The advent of MRI has revolutionized the clinician's ability to confirm a proper diagnosis for musculoskeletal problems, which has led to more directed, specific rehabilitative protocols. However, the value of MRI to rehabilitative professionals has been even greater in its ability to identify serious, more uncommon pathologies, such as in those with underlying infection, fracture, or tumor, that require immediate care and are considered to be beyond their scope of practice. Furthermore, MRI, with its precise delineation of fat, muscle, and bone, is an ideal candidate for imaging of muscle disease or injury and has emerged as the method of choice for the detection of early cartilage wear in young patients, such as osteoarthritis. Finally, this imaging modality can avoid radiation exposure in a predominantly younger patient cohort commonly affected by musculoskeletal diseases. The aim of this paper is to consider how physical therapists may take advantage of the diagnostic value of MRI of the upper limb, while avoiding the pitfalls of misinterpretation of images as a result of technical issues, pathological changes, or normal variants. Ther 2011;41(11):861-872. doi:10.2519/jospt.2011 J Orthop Sports Phys T T KEY WORDS: MRI, musculoskeletal, radiology Image ContrastTissue contrast (differences in signal, T1 and T2) develops as a result of the rates at which nuclei realign with the main magnetic field. T1 is the time constant that describes how magnetization returns to its original state of equilibrium after the RF perturbation (T1 relaxation). It is an exponential process that depends on the interaction of the nucleus with its surroundings. T2 is the time constant that describes the process whereby the nuclear spins go out of phase with each other, losing their initial synchronization (T2 relaxation). 2 These processes occur together and cannot be separ...

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