Our objective was to test the hypothesis that diurnal changes occur in thickness or volume of the femoral articular cartilage of the knee in asymptomatic young adults. Fat‐suppressed three‐dimensional (3D) spoiled gradient‐echo magnetic resonance imaging (MRI) was employed. Six volunteers each were scanned early in the morning and at the end of a working day spent mainly standing. This protocol was repeated on 3 successive weeks. Femoral cartilage volumes were obtained via semiautomatic segmentation that employed a seeding algorithm. These segmentations then were regridded onto a 500‐pixel template, and differences in the resulting thickness maps were assessed. Analysis of variance showed no significant diurnal variation in overall volume or thickness. The reproducibility for volume (test‐retest coefficient of variation) was 1.6%. There were, however, statistically‐significant diurnal changes in the thickness maps. Cartilage thickness decreased by up to 0.6 mm during the day in each of the following three specific locations: the patellofemoral compartment, the lateral tibiofemoral compartment, and the medial tibiofemoral compartment. Elsewhere, cartilage thickness was unchanged or increased by up to 0.5 mm. We conclude that, in asymptomatic young adults, cartilage volume does not change during the day; however, the cartilage does become thinner in locations that encounter the greatest biomechanical force. Magn Reson Med 43:126–132, 2000. © 2000 Wiley‐Liss, Inc.

The failure to identify loss of cartilage volume over 3 years in this cohort of patients with established knee OA using MRI challenges the face validity of this endpoint to assess structural changes in OA.

Objectives-To investigate the potential of quantitative magnetic resonance imaging (MRI) to diVerentiate between therapeutically induced changes in inflammation and synovial proliferation in rheumatoid arthritis (RA) of the knee. Methods-MRI of the knee was performed on patients with RA before and one week after injection with corticosteroid (triamcinolone acetonide, TA group, n=9) and before, four, and 12 weeks after injection with yttrium-90 plus TA (TA+Y group, n=7). MRI scans were analysed by subjective visual grading by a trained observer and by computer aided quantitation for three features: synovial fluid volume, synovial pannus volume, and synovial enhancement after intravenous contrast agent. Results-All TA subjects improved clinically at one week but the eVects of TA+Y were more variable. TA significantly reduced synovial enhancement and eVusion volume, whereas TA+Y at 12 weeks tended to increase synovial enhancement and decrease pannus volume. Quantitative MRI values agreed well with subjective assessment of scans. Comparison of calculated change on MRI scan before and immediately after aspiration with actual volume aspirated showed high correlation (r=0.96). Conclusions-Quantitative MRI correlates with subjective visual assessment and, at least for synovial fluid, is accurate. MRI can diVerentiate actions of two therapeutic modalities on various pathological processes and is sensitive enough to detect change after one week. With the additional advantage of lack of observer bias, it will probably become a useful tool in the development and assessment of existing and novel treatments.

MRI is a valuable imaging modality for assessment of the articular cartilage in rheumatoid arthritis (RA) and is potentially of use in monitoring disease progression and response to therapy. In this study, we investigated the sources of error in volume measurements obtained by segmentation of MR images of knee cartilage in patients with RA and followed cartilage volume in a group of RA patients for 12 months. 23 RA patient volunteers were recruited for knee imaging. Six subjects were imaged at baseline only, six were imaged at baseline and again within an hour in the same imaging session, six subjects were imaged at baseline and 7 days, and 17 subjects were imaged at baseline, 4+/-2 months and 12 months. Imaging was performed at 1.0 T using a three-dimensional spoiled gradient-echo sequence with fat-suppression. Manual image segmentation was performed once or twice on the lateral tibial, medial tibial, patellar and femoral compartment by either one or two segmenters. Coefficients of variation (CoV) for repeated volume measurement of total cartilage were 2.2% (same segmenter, same scan), 5.2% (different segmenter, same scan), 4.9% (same segmenter, different scan, same session), and 4.4% (same segmenter, different scan, different session). Over the 12 month duration of the study there was no significant change in total cartilage volume, nor were there significant changes in volume in any individual compartment. This measurement technique is reproducible, but any net change in cartilage volume over 1 year is very small.