Page 78 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints
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                                Chapter 4
will have less damaged cartilage, but as mild thinning of the cartilage was also detectable in the less damaged areas of the joints in our patients, we expect that the imaging method can be used in patients with less severe OA.
The second limitation concerns image quality. Four out of twelve of our MRI examinations were of low image quality, which may have impacted the MRI results of these four patients. Our coil was a loop coil with a diameter of 40 mm, which was optimal for imaging the CMC1 joint in healthy volunteers. However, in our patients with CMC1 OA, the distance between the coil and the center of the joint was larger because of the presence of osteophytes and subluxation, and the inability of patients to hold the thumb in full extension for optimal coil placement, reducing signal-to-noise ratio. Motion artefacts also had a big impact on image quality. Improvements in either patient/coil positioning or the coil itself should be able to increase overall image quality.
The third limitation concerns the chosen MRI pulse sequence. We chose to assess cartilage with a 3D SPGR fat-suppressed pulse sequence for its high in-plane resolution with thin 0.7 mm slices, to be able to detect small cartilage lesions. This pulse sequence has previously shown promising results in finger joints. 11, 27 In healthy volunteers this sequence clearly delineated high signal cartilage layers. In our study population of patients with advanced OA only and with histologically proven abnormal cartilage, the signal intensity of cartilage was lower than expected based on the MRI in healthy volunteers. Our MRI readers therefore sometimes had trouble delineating the cartilage from the joint fluid, which is a known disadvantage of this pulse sequence. 28, 29 While this will have introduced some error in the results, this was often resolved after crosschecking with the PD and T2 FSE sequences to make the distinction between fluid and cartilage. In this study we did not detect any small focal areas of cartilage loss, raising the question whether such thin slices are required to evaluate cartilage damage in advanced OA. Other pulse sequences such as Duel Echo Steady State (DESS), SPGR with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL), and true fast imaging with steady state precession (TrueFISP) were found to have better cartilage to fluid contrast in the knee joints in healthy volunteers.28, 29 If these sequences can be adequately optimized for the small FOV and high resolution, they may improve accuracy for detecting cartilage damage in the small joints of the hand.

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