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Medical Infrared Thermal Imaging Method for Rheumatoid Arthritis
In rheumatoid arthritis (RA), the early development of bone erosions is a poor prognostic indicator, and their presence both confirms the diagnosis and indicates that aggressive clinical intervention should proceed without delay. However, as bone erosions are typically irreversible, the development of imaging modalities is currently focused on new technologies that can be used to detect the earliest (reversible) biological and physiological changes that are associated with the disease.
Traditionally, structural imaging techniques were used to diagnose RA and to monitor the progression of joint damage and responses to therapy. Developments in structural imaging modalities, such as plain radiography, MRI and ultrasonography, have led to improvements in the spatial resolution of these techniques, which can now be used to detect bone erosions within weeks of onset of RA symptoms. However, anatomic imaging does not reveal the underlying biomolecular abnormalities in RA. The earliest changes in bone and cartilage are preceded by synovial inflammation, which is associated with tissue changes that can be detected early in the disease process. Persistent synovial inflammation leads to disease progression and the development of bone erosions.
Figure 1. Infrared thermal imaging of the palm.
The altered proinflammatory activity and specific molecular events that cause synovitis can be assessed by optical imaging methods, such as thermography. Moreover, the development of techniques for the detection of specific molecular changes in the joints of patients with RA is of great interest. As the number of RA therapies (particularly those involving targeted biologic agents) increases, the use of molecular imaging methods in clinical practice might become increasingly advantageous, as these techniques could enable initiation of the most efficacious therapies in the very earliest stages of the disease.
Figure 2. Infrared thermal imaging of mouse right hind paw.
In patients with RA, affected joints are typically warmer than those that are unaffected. The basis of thermography, and its utility in assessing arthritic joints, lies in the skin’s ability to efficiently dissipate heat to the atmosphere. Elevated skin surface temperature is, therefore, a reliable indicator of the heat within a joint, and an increase in the heat distribution index (HDI; the standard distribution of temperatures within a specific region) correlates well with the Ritchie articular index, erythrocyte sedimentation rate, and pain score. Clinical infrared thermography is a diagnostic imaging procedure that can be used to detect, record, and produce colour images of a patient’s skin surface temperature. Modern thermal imagers can determine temperature variations of the skin both qualitatively and quantitatively. These devices use either liquidcrystal or electronic infrared thermography technology.
Figure 3. Infrared thermal imaging of mouse right hind paw.
In a proofofconcept study, an infrared camera was used to generate a 3D model of metacarpophalangeal and wrist joints. Skin surface temperature was quantified using an electronic thermographer and specialized software was used to calculate three outcome measures. To demonstrate the quantification of clinically meaningful changes in arthritic joints using thermography, the painful, inflamed wrist of a child with seronegative polyarticular juvenile RA was imaged before and several days after an intraarticular steroid injection. At the second imaging session, the patient showed a 10% reduction in joint volume, a small decrease in SDI, a large decrease in skin temperature on the surface colour map, and a narrowing of the temperature frequency distribution. These changes correlated with clinically assessed improvement in swelling and tenderness and the patient’s report of symptom reduction. Clinical infrared thermography does not require the use of a contrast agent and is a lowcost, rapid and accurate technique for the assessment of arthritic joints.
James M. Mountz, Abass Alavi and John D. Mountz. Emerging optical and nuclear medicine imaging methods in rheumatoid arthritis. Nature Reviews. 8:719-728, 2012.
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