Page 69 - Imaging of Osteoarthritis and Rheumatoid Arthritis in Hand Joints
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 Accuracy of cartilage MRI of CMC1; comparison with histology
MRI evaluation
Reading exercises were performed on the MR images from patients of whom
histology was not possible. In the first exercise we tested a scoring method
for cartilage assessment similar to the MRI osteoarthritis knee score (MOAKS).15
However, we decided not to use this scoring method as the tested cases all
received the highest score possible, even though clear differences in cartilage
damage were visible on the images. In the second exercise we tested the
currently used scoring method, which uses the same definitions as MOAKS for identification of partial-thickness cartilage loss and full-thickness cartilage loss,
but the extent of the cartilage damage is not scored on an ordinal scale from
0-3, but on a ratio scale from 0-100%. After the second exercise we decided
to score a thin layer of one or two voxels of high signal intensity (comparable
to cartilage) on the bony surface area as partial-thickness loss and not as full- 4 thickness loss. All images were evaluated by two musculoskeletal radiologists
and a hand surgeon (GM, EO and HC) together in consensus. The readers were blinded to patient data, clinical data, histological findings and other imaging results. The anonymized images were read using the open source software ClearCanvas Workstation (ClearCanvas Inc., Toronto, Canada). Using all available sequences, the articular surface of the trapezium was evaluated for grade of cartilage loss as normal cartilage thickness, partial-thickness loss of cartilage, or full-thickness loss of cartilage. On each 0.7 mm SPGR FS slice the readers indicated the surface corresponding to each grade. Measurements from all slices per patient were summed to compute the total articular surface, total area of normal thickness, total area of partial-thickness loss, total area of full-thickness loss, and total area of any thickness loss (full and partial thickness loss combined). Percentages of these were calculated for comparison with histological findings. The image quality of the SPGR images was scored as either low, sufficient for evaluation, or good. Low means that there is a reasonable chance that error was introduced because of low image quality.
The CMC1 joints were scored for presence or absence of osteophytes, erosions/ cysts and subluxation. Osteophytes were defined as abnormal bone formation in the peri-articular region on the SPGR and PD images. Erosions/cysts were considered as a single feature and were defined as sharply marginated bone lesions with increased signal intensity on SPGR images, and intermediate signal on PD images, which were visible in two planes. The joint was considered to be

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