MR Imaging of the Shoulder: Basic Introduction to MRI, What To Look For and Potential Problems
The purpose of the next MRI few chapters is to review the normal anatomy of the shoulder and shoulder pathology seen on MRI. This chapter will review for the shoulder surgeon important concepts about MRI that will allow this technology to be more useful b
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G. R. Applegate
8.1 lntroduction The purpose of the next MRI few chapters is to review the normal anatomy of the shoulder and shoulder pathology seen on MRI. This chapter will review for the shoulder surgeon important concepts about MRI that will allow this technology to be more useful both diagnostically and as a preparatory tool for surgery. MRI is the imaging technique of choice for the shoulder after standard roentgenogram evaluation. It offers multi-planar imaging with superb soft-tissue contrast. Radiologic interpretation varies from the experienced, MRI-musculoskeletal fellowshiptrained radiologist to the general, community radiologist. The orthopedist must view the radiologist as a consultant and give accurate and helpful clinica! history and differential diagnoses prior to the scan. In addition, sending the radiologist a copy of the operative report is very helpful in establishing long-term, consistent interpretation. Overall, the shoulder surgeon should strive to obtain the ability to read the MRI independently of the radiology report. This requires a quick, disciplined approach to reviewing an MRI of the shoulder. We recommend either reviewing each anatomic area in all three planes before evaluating the next anatomic area or reviewing each plane for all anatomic areas before evaluating the next plane. It is helpful to have an area in the clinic with multiple view boxes or a robust digital imaging workstation in order to accomplish this efficiently and with precision.
G. Lajtai et al. (eds.), Shoulder Arthroscopy and MRI Techniques © Springer-Verlag Berlin Heidelberg 2003
MR lmaging of the Shoulder: Basic lntroduction to MRI, What To Look For and Potential Problems
8.2 Principles of Magnetic Resonance lmaging Following clinica! examination, routine radiography remains the initial screening sttidy of choice when imaging the shoulder. MRI, however, is proving to be the imaging study of choice for further evaluation due to its superb ability to evaluate soft tissues of the rotator cuff, glenohumeral articulation, and tendons, as well as radiographically occult conditions. The advantages of MRI include the lack of ionizing radiation, the ability to scan clearly in a multi-planar fashion, and the superb soft-tissue contrast. MRI has the ability to distinguish between fat, ligamentous structures, tendons, bone marrow, and fluid. Excellent high-resolution imaging of the shoulder and surrounding soft tissues can be easily obtained. The magnetic resonance phenomenon involves an atomic nucleus. Usually hydrogen nuclei, consisting of a single proton, which are most abundant in water, are imaged. A strong magnetic field is used to align these protons uniformly (Fig. 8.1 ). Simplistically, as the patient enters the MRI unit, all of the protons within the patient's body are aligned along the long axis of the magnet (Bo ). Additional gradient coils slightly alter this magnetic field so that the protons being imaged may be localized in three-dimensional space. A frequency-selected pulse is then quickly applied which
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