Appendix B.

Combined results of interobserver agreement and correlation between observers and reference standard

MRI features	Significant correlation between observer and reference standard (p ≤ 0.05)			Kappa or intraclass coefficient ≥0.40			Relevant MRI feature
	Observer 1	Observer 2	Observer 3	1 vs. 2	2 vs. 3	1 vs. 3
Wall thickness	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Mesorectal lymph nodes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Obturator lymph nodes	No	No	No	No	No	No	No
Iliac lymph nodes	No	No	No	No	No	No	No
Inguinal lymph nodes	No	No	No	Yes	No	Yes	No
% of circumference involved	Yes	Yes	Yes	No	No	Yes	No
Mural T2 signal	Yes	Yes	No	No	Noa	Noa	No
Perimural T2 signal	Yes	Yes	Yes	Yes	Yes	Yes	Yes
T1 enhancement	Yes	No	Yes	No	No	No	No
T1 enhancement pattern	No	Yes	Yes	No	No	Yes	No
Perimural enhancement	Yes	Yes	Yes	Yes	No	Yes	Yes
Mural fat	Yes	No	Yes	Yes	Yes	Yes	Yes
Ulcers	No	No	Yes	Noa	No	No	No
Supralevatoric fistula	No	No	No	Yes	Yes	Yes	No
Supralevatoric abscess	No	No	No	Yes	Yes	Yes	No
Creeping fat	b	Yes	Yes	Yes	Yes	Yes	Yes
Comb sign	Yes	Yes	Yes	No	No	Yes	No

^aProportion of agreement calculated, because observed concordance is smaller than mean-chance concordance. Assuming kappa ≤0.40

^bNot calculated because of the presence of a zero in the crosstab