Magnetic Resonance Imaging of the Elbow

Introduction

Magnetic resonance imaging (MRI) has gained wide acceptance as a complementary tool in the diagnosis of disorders of the musculoskeletal system, largely due to its excellent depiction of soft tissues. Within the past decade, MRI at 3 T has become widely available and has shown promise in increasing diagnostic accuracy because of its inherently increased spatial resolution.

Technique

Although a detailed review of the technical parameters utilized when imaging the elbow is beyond the scope of this discussion, it is important to understand the fundamental aspects of a standard elbow MRI protocol. Optimal imaging of the small anatomic structures of the elbow necessitates the use of a dedicated multichannel (typically eight-channel) elbow coil, positioned as close as possible to the isocenter of the magnetic field. Usually the patient is prone with the arm above the head, the so-called superman position. For optimal anatomic coverage, the field of view should be approximately 12 cm, extending from the distal humeral metaphysis through the radial tuberosity. Imaging is typically performed in three planes: axial, coronal, and sagittal. Coronal images are particularly useful to visualize the common flexor and extensor tendon origins as well as the medial and lateral ligamentous structures. The plane of imaging can also be manipulated to align with the anatomic structure, such as the biceps tendon.

The selection of imaging sequences used to evaluate the elbow differs among institutions and typically includes a combination of T1, T2, proton density (PD), and short tau inversion recovery sequences. Fat saturation is often used on T2 and proton density sequences to improve conspicuity of bone marrow or soft tissue edema, which may indicate the presence of acute disease. Use of intravenously administered gadolinium-based contrast material is indicated to identify a suspected mass, infection, or inflammatory process. MRI following intraarticular injection of dilute gadolinium-based contrast material (MR arthrogram) may be beneficial in cases where there is suspicion of a ligament tear, loose body, or unstable osteochondral fragment.

MRI at higher field strengths (1.5–3 T) is preferable because of the superior signal-to-noise ratio (SNR). Higher SNRs improve spatial resolution, enhance contrast-to-noise ratio, and improve spatial resolution with thinner slice thickness. Higher SNRs increase the speed of imaging, theoretically allowing a fourfold decrease in scan time at 3 T in comparison with 1.5 T. Faster imaging lessens motion artifact and improves patient tolerance and throughput. Unfortunately, imaging artifacts such as chemical shift, metallic susceptibility, and pulsation artifact are accentuated at higher field strengths (particularly 3 T). Hence if metallic hardware is in the region of interest, it is preferable to perform imaging at lower field strengths. Additionally, the amount of energy transferred to the patient increases with the square of the field strength. The specific absorption rate must be monitored to avoid the production of heat or other undesirable biological effects.

Magnetic Resonance Imaging of the Elbow: Clinical Applications

MRI is a valuable tool, particularly in cases where the diagnosis remains clinically uncertain or symptoms are refractory to standard therapy. In the discussion that follows, the MRI appearance of some of the more common elbow injury patterns will be reviewed.