Table 1 Intramodality and intermodality agreements of single erosion and total erosion volume in RA MCP-joints, measured on CT and MRI. Values on intermodality agreement are comparisons between CT and MRI erosions volumes.
 Reading A (mm3), mean (median; range) Reading B (mm3), mean (median; range) Mean reading A and B (mm3), mean (median; range) Spearman’s rho Absolute difference (mm3),* mean (median; range) Absolute numerical difference (mm3),† mean (median; range) Relative difference (%) mean (median; range) Coefficient of variation, mean (median; range) Intramodality agreement (CT (A) vs. CT (B) and MRI (A) vs. MRI (B)) Volume per erosion CT (n = 77) 27 (10; 0 to 272;) 24 (11; 0 to 224) 26 (10; 0 to 248) 0.96‡ 3 (0; ÷71 to 56) 6 (2; 0 to 71) 22 (15; 0 to 93) 0.11 (0.08; 0 to 0.47) MRI (n = 62) 29 (18; 1 to 159) 30 (20; 1 to 166) 30 (18; 1 to 163) 0.95‡ 0 (0; ÷62 to 43) 7 (3; 0 to 62) 26 (20; 0 to 82) 0.13 (0.10; 0 to 0.41) Volume per patient (n = 17) CT 127 (35; 5 to 510) 113 (35; 6 to 460) 120 (33; 6 to 485) 0.99‡ 13 (0; ÷56 to 144) 24 (5; 0 to 144) 19 (13; 0 to 75) 0.09 (0.07; 0 to 0.38) MRI 112 (52; 5 to 391) 111 (57; 6 to 397) 111 (58; 6 to 389) 0.97‡ 2 (÷3; ÷33 to 110) 16 (9; 1 to 110) 18 (18; 2 to 67) 0.09 (0.09; 0.01 to 0.33) Intermodality agreement (CT vs. MRI)** Volume per erosion of all concordant erosions (n = 51) CT 36 (13; 2 to 272) 33 (12; 2 to 224) 35 (12; 2 to 248) 0.64‡ ÷1 (÷6; ÷47 to 113) 18 (11; 0 to 113) 68 (61; 0 to 164) 0.34 (0.30; 0 to 0.82) MRI 36 (25; 1 to 159) 36 (24; 1 to 166) 36 (25; 1 to 163) Total volume per patient of all concordant erosions (n = 17) CT 109 (22; 4 to 507) 98 (19; 3 to 457) 104 (21; 4 to 482) 0.89‡ ÷4 (÷15; ÷102 to 117) 37 (24; 2 to 117) 67 (67; 1 to 147) 0.33 (0.36; 0.01 to 0.73) MRI 109 (52; 5 to 380) 107 (57; 6 to 397) 108 (54; 6 to 389) Total volume per person of all erosions (n = 21) CT 102 (27; 0 to 510) 92 ( 30; 0 to 460) 97 (29; 0 to 485) 0.89‡ 10 (0; ÷39 to 113) 21 (8; 0 to 113) 50 (43; 0 to 142) 0.25 (0.21; 0 to 071) MRI 91 (44; 0 to 391) 90 (46; 0 to 389) 90 (46; 0 to 389)
• CT, Computed tomography; MCP, Metacarpophalangeal; MRI, Magnetic resonance imaging; RA, Rheumatoid arthritis.

• *Intramodality agreement: reading A minus reading B; intermodality agreement: CT erosion volume minus MRI erosion volume; **For intermodality agreement values in the five right columns refer to the relation between erosion volumes on CT and erosion volumes on MRI; †For intermodality agreement: CT erosion volume minus MRI erosion volume; ‡p<0.01.

• Reading A and reading B denote volumes obtained at the first (A) and second (B) volume measurements, done by the same observer 1 week apart. The mean value of volumes obtained at reading A and B was used for the comparison of CT and MRI volumes.