Aponeuroses are the thin, sheet-like tendons that cover substantial parts of muscles. We validated measurements of the dimensions of aponeuroses from T1, mDixon and ultrashort echo time (UTE) scans by comparing to direct measurements from dissection and digitisation. We used sequences that are feasible for human studies. Aponeurosis widths and lengths, measured on 20 lamb muscles, were substantially underestimated from mDixon scans. More accurate measurements were obtained from T1 and UTE scans, which had root mean square errors of 8-10% and 5-13% of the aponeurosis width and length, respectively, and did not systematically underestimate or overestimate aponeurosis width or length.