Office‐based low‐field extremity magnetic resonance imaging: Is the glass half empty or half full?

Abstract

The American College of Rheumatology Extremity Magnetic Resonance Imaging Task Force has provided a timely focus on the growing importance of magnetic resonance imaging (MRI) for rheumatologists (1). The report of the task force identifies many of the key publications in this area and emphasizes the need for more research to advance the utility of this tool. The report provides clear descriptions of terminology and distinguishes between high-field extremity scanners ( 1.0T), to which most currently published MRI literature would apply, and the low-field (0.2T) extremity scanners. We wish to expand on some of the points raised by the task force and support the call for further research. That MRI provides superior assessment of structural damage in rheumatoid arthritis (RA) comes as no surprise. What is surprising, as the task force notes, is how little rheumatologists have used this technology to benefit their patients. Are rheumatologists less aggressive adopters of technological innovation than their medical colleagues? At least part of the answer stems from the fact that, until very recently, rheumatologists had little ability to prevent the progression of structural damage in RA. Without this capability, information about joint structure on the level that MRI can provide wasn’t needed for management of RA. The introduction of tumor necrosis factor inhibition and recognition of the benefits of early intervention shifted the focus from controlling pain to early, intensive treatment to prevent irreversible functional disability. Implementation, however, is not straightforward, since a significant proportion of patients with early RA do not have rapid structural progression (2,3). Treating all cases of RA with biologic agents would incur excessive costs and unnecessary risks. Determining which newly presenting patients have the potential for progression has therefore become an important concern, creating a new demand for imaging to detect the earliest evidence of structural damage and features predicting erosion. MRI offers a unique solution. Not only has it been shown to detect bone erosions more sensitively and earlier than radiography, but it can also be used to visualize pre-erosive inflammation in synovium and bone (4,5). This has led to increasing use of MRI in RA clinical research and to the emergence of specialized MRI systems specifically designed for office-based rheumatology practice. These low-field extremity MRI units provide images of the hands and feet at a fraction of the cost and inconvenience of conventional 1.5T whole-body MRI. The question is whether the low-field MRI systems still offer a substantial advantage over conventional radiography for diagnosing and/or monitoring erosive disease in RA. Although the volume of data on low-field extremity MRI is less than that available on high-field MRI, published data show a high correlation between results obtained with these systems with respect to erosion detection. In direct comparisons, low-field extremity MRI showed approximately twice the sensitivity of radiography for detecting erosions (6). With regard to progression of disease, a recent study demonstrated that low-field MRI of a single wrist and the second through the fifth metacarpophalangeal joints was more sensitive to change than were standard radiographs of both hands, wrists, and feet (7). We therefore believe that there would be a great deal to be gained by rheumatologists and their patients if extremity MRI were to be assimilated into routine clinical practice.