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Table 2 Frequency of MRI lesions recorded by four readers jointly and percentage concordance among six possible reader pairs.

From: Can erosions on MRI of the sacroiliac joints be reliably detected in patients with ankylosing spondylitis? - A cross-sectional study

  Lesion Per subject Ilium R+L Sacrum R+L P-value Ilium versus Sacrum
AS patients (number = 30)      
Frequency: median (IQR)a ER 11.4 (9.0) 8.6 (6.9) 2.1 (2.9) < 0.0001
  BME 13.1 (15.1) 6.8 (10.4) 5.1 (7.9) 0.67
  FI 10.9 (11.7) 4.5 (5.3) 5.6 (7.0) 0.06
  EE 1.1 (1.4) 1.0 (1.0) 0.0 (0.3) < 0.0001
  BF 1.0 (1.3) 0.8 (1.3) 0.0 (0.3) < 0.0001
% Concordance six RP: total (positive/negative)b ER 73.9 (56.9/16.9) 80.0 (75.0/5.0) 67.8 (38.9/28.9) N/A
  BME 85.0 (60.4/24.6) 79.7 (60.3/19.4) 90.3 (60.6/29.7) N/A
  FI 69.7 (43.6/26.1) 66.4 (35.3/31.1) 73.1 (51.9/21.1) N/A
  EE 75.7 (19.7/56.0) 65.8 (32.5/33.3) 85.6 (6.9/78.6) N/A
  BF 80.0 (13.8/66.3) 70.3 (24.7/45.6) 89.7 (2.8/86.9) N/A
Controls (number = 30)      
Frequency: median (IQR)a ER 0 (0.4) 0 (0.3) 0 (0.0) 0.02
  BME 0.1 (0.9) 0 (0.4) 0 (0.3) 0.81
  FI 0 (2.1) 0 (0.9) 0 (0.2) 0.26
  EE 0 (0.0) 0 (0.0) 0 (0.0) N/A
  BF 0 (0.0) 0 (0.0) 0 (0.0) 0.98
% Concordance six RP: total (positive/negative)b ER 92.1 (0.8/91.3) 87.8 (1.4/86.4) 96.4 (0.3/96.1) N/A
  BME 89.3 (1.9/87.4) 88.6 (2.2/86.4) 90.0 (1.7/88.3) N/A
  FI 83.8 (2.9/80.8) 80.3 (4.7/75.6) 87.2 (1.1/86.1) N/A
  EE 100.0 (0.0/100.0) 100.0 (0.0/100.0) 100.0 (0.0/100.0) N/A
  BF 98.7 (0.2/98.5) 98.1 (0.3/97.8) 99.2 (0.0/99.2) N/A
  1. aFrequency of lesions: for ER, BME and FI the number of SIJ quadrants affected; for EE and BF the number of joint surfaces affected irrespective of the number of SIJ MRI slices; bpercentage concordance among six possible reader pairs for 60 joint surfaces (Ilium R+L; Sacrum R+L) and for 120 joint surfaces (per subject). AS, ankylosing spondylitis; BF, backfill; BME, bone marrow edema; EE, extended erosion; ER, erosion; FI, fat infiltration; IQR, interquartile range; L, left; N/A, not applicable; R, right; RP, reader pair; % Concordance six RP, percentage concordance among six possible reader pairs (100% = six concordant reader pairs); total = positive and negative concordance.