Contrast-enhanced MR imaging of hand and finger joints in patients with early rheumatoid arthritis: do we really need a full dose of gadobenate dimeglumine for assessing synovial enhancement at 3 T?

To investigate the diagnostic value of a half dose compared with a full dose of gadobenate dimeglumine in the assessment of synovitis or tenosynovitis in the wrist and finger joints in patients with early rheumatoid arthritis (RA) and a disease activity score greater than 3.2. With institutional review board approval and informed consent, 57 patients with early RA underwent 3-T magnetic resonance (MR) imaging with two different doses of contrast media. The contrast enhancement was measured in inflamed synovial tissue at half dose (0.05 mmol per kilogram of body weight) and at full dose (0.1 mmol/kg) by using T1-weighted sequences with fat saturation. The differences and the correlation of signal intensities (SIs) at half- and full-dose sequences were compared by using the paired t test and Pearson correlations. Image quality, Rheumatoid Arthritis MRI Score (RAMRIS), and tenosynovitis score on half- and full-dose images were compared by two observers using the Wilcoxon test. Interrater agreement was assessed by using κ statistics. A significant difference in SI was found between half-dose and full-dose gadobenate dimeglumine-enhanced synovial tissue (mean: 914.35 ± 251.1 vs 1022 ± 244.5, P < .001). Because the SI showed high correlation between the ratio at half dose and full dose (r = 0.875), the formula, ratio of synovial enhancement to saline syringe at full dose = 0.337 + 1.070 × ratio of synovial enhancement to saline syringe at half dose, can be used to convert the normalized value of half dose to full dose. However, no difference in RAMRIS (score 0 in 490 of 1026 joints; score 1 in 344; score 2 in 158; and score 3 in 34) or tenosynovitis scores in grading synovitis or tenosynovitis in image quality and in assessment of synovial enhancement was detected between half-dose and full-dose images (P = 1). Postcontrast synovial SIs showed high correlation between half dose and full dose, and image quality was rated identically. Therefore, half-dose gadobenate dimeglumine at 3-T MR imaging may be sufficient for assessing synovitis or tenosynovitis in early RA.