Page 113 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints
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 Accuracy of low field MRI in early arthritis
for this difference is that the cortical defects in our patient group were overall smaller than in RA patients, and that these smaller defects are harder to detect with low field MRI. While 50% of our patients had an MRI detected erosion, almost no erosions were found with the US scoring methods, and zero erosions were found with radiography. This difference between imaging methods is in line with previous studies in RA patients, 2, 3, 15 were it has been shown that ultrasound is more sensitive for erosions than radiography and MRI is far more sensitive than the other two methods. CT studies show that these MRI detected erosions are true cortical breaks.33 While radiographic erosions were once considered pathognomic for RA, these MRI detected cortical breaks are also found in healthy controls 23, 24, 34 and not specific for RA. Future studies should investigate the clinical relevance of these MRI detected cortical breaks for patients with possible inflammatory arthritis.
0.2T MRI showed poor diagnostic performance in detecting BME, as it only
detected 8 bones with BME in contrast to 42 with 1.5T MRI. Other studies with
the same low field MRI machine found that it is also not sensitive in detecting
BME in RA patients (sensitivity 0.39 and varying agreement with high field
MRI (ICC 0.05-0.94)).13, 29 The proportion of undetected BME in our study was
higher than previously reported for RA patients.11. Our arthralgia and early RA
patients probably had less severe BME, and this less severe BME is missed more 6 often with our low field MRI. A recent study with different field strength MRI
units showed that BME detection is better with newer low field scanners, but also showed that reliability was lower for BME detection with a 0.23T MRI in comparison with 0.6T and higher field strength scanners 35, favouring scanners from 0.6T and higher.
This cross sectional analysis has several limitations and strengths, An advantage of extremity MRI is improved patient comfort.12 Out of the 32 patients that declined participation in our study, 9 patients indicated that they did not want to undergo an MRI in a whole body scanner. An extremity MRI may therefore be a good alternative for detecting synovitis and erosions in patients with claustrophobia. Imaging examinations were mostly performed on subsequent days, but an interval of maximal 6 days was present. As no medical interventions were started before or during the interval, we do not expect a large biological variation between imaging examinations. However, nineteen patients were

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