3Established rheumatoid arthritis – new imaging modalities
Introduction
There have been extraordinary advances in medical imaging over the last 20 years and these are now having a major impact on clinical rheumatology. Whereas conventional radiography (CR) continues to have the greatest role in routine management of established rheumatoid arthritis (RA), newer modalities, including high-field and extremity magnetic resonance imaging (MRI), high-resolution ultrasound (HRUS) and multidetector CT are rapidly entering clinical practice. Other novel imaging techniques, such as high-resolution multi-pinhole single-photon-emission computed tomography (MPH-SPECT), 18F-flurorodeoxyglucose (FDG) positron emission tomography (PET) and various techniques employing molecular targeting and bioluminescence, currently remain research tools but hold considerable promise for future clinical applications. These advances in imaging have developed in tandem with the great progress in RA management afforded by the use of biologics. Now that these agents have made the goal of arresting disease progression a possibility, there is a need for more sensitive imaging modalities that can allow clinicians to carefully track the development of joint inflammation and damage, as it occurs within bone and articular soft tissues and even to follow the response to therapeutic intervention.1 This information can then be used to tailor management appropriately for the individual patient.
This chapter focuses on the role of these new imaging modalities in the management of RA in today's clinical environment and looks ahead to prospects for the future.
Section snippets
Magnetic resonance imaging
MRI is unique in terms of imaging modalities in that it employs the resonance of protons, which have been induced to oscillate in various ways by exposure to a powerful magnetic field and superimposed radiofrequency pulses, to build up an image of the tissue being examined.2 As protons are found within water molecules, and water is present in cells, blood and synovial fluid, MRI allows visualization of inflammatory change within the joint in a way that radiographic techniques cannot. It can
CT scanning
CT is a radiographic technique and incorporates the strengths of CR, which include excellent resolution of cortical bone allowing clear definition of the margins of erosions. By virtue of its tomographic capability, it can provide a 3-dimensional image, thus circumventing the primary weakness of 2-dimensional CR, which produces multiple overlapping bony shadows in complex regions such as the wrist. Multidetector helical CT provides high-quality images and, as is the case for MRI, computerized
Ultrasonography
The technological advances of the last two decades have made ultrasonography (US) a useful imaging method for the assessment of RA patients. Although previously confined to imaging large joints37, 38, high-frequency linear array transducers now allow high-resolution imaging of such superficially located structures as the small joints of the hands and feet. US has several advantages: its running costs are low, it is patient-friendly, easily accessible, portable, dynamic, interactive and quick to
Imaging using scintigraphy
Several emerging modalities indicate the directions that imaging of RA might take in the future. These include molecular imaging whereby specific molecules, identified as being crucial to the inflammatory or destructive process in RA, can be targeted and used to create an image via various signaling probes.70 Examples include localization of TNFα and interleukin (IL)-1 within rheumatoid synovium using radiolabeled anti-TNF monoclonal antibody71 and IL-1 receptor antagonist (IL-1ra)72,
Summary
In summary, the field of imaging in RA is progressing rapidly and new modalities are being developed to take advantage of recent advances in technology and the biosciences. Although CR is still the most widely accepted tool for monitoring disease progression, modalities such as MRI and ultrasonography are becoming accepted as part of clinical practice. Each form of imaging has its own special advantages. High-resolution multidetector CT provides high-definition images of complex regions as a
Acknowledgements
The authors wish to thank Dr B. Ostendorf for providing the high-resolution MPH-SPECT image shown in Figure 3.
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