Objective: To investigate the impact of a double dose compared to a single dose of contrast material in low-field magnetic resonance imaging (MRI) on semi-quantitative scoring of synovitis in patients with rheumatoid arthritis (RA).
Methods: This prospective study included 38 RA patients (23 women and 15 men, mean age 51 years). All patients underwent low-field MRI of the hand before administration of contrast medium, after intravenous injection of 0.1 mmol/kg gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA), and after another dose of 0.1 mmol/kg Gd-DTPA. Two readers (A and B) blinded to dosage independently scored the single dose and double dose image sets for synovitis according to outcome measures in rheumatology (OMERACT) recommendations. Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were also calculated for each set.
Results: 149 metacarpophalangeal (MCP) joints were evaluated. There was good inter-reader agreement for each of the two sets (intra-class correlation coefficient of 0.75 for the single dose set and 0.83 for the double dose). Median CNR and SNR values were 5.4 and 15.9, respectively, for the single dose set and 8.5 and 16.6, respectively, for the double dose set (p<0.0001). Single dose set mean synovitis scores were 1.7 and 1.6 for readers A and B, respectively. Double dose set scores were 1.9 and 2.0, respectively. Thus, higher synovitis scores were recorded for the double dose sets than the single dose sets (p<0.005).
Conclusion: In low-field MRI, when evaluating RA, the dose of the contrast material influences synovitis scoring. Therefore, dosage of contrast material should be taken into consideration when using extremity dedicated low-field MRI.