Knee MR Using a Body Coil is Equivalent to CT in Measuring the TT-TG Distance: Removing the Systematic Bias.

 To compare magnetic resonance imaging (MRI) using a body coil with computed tomography (CT) in measuring the tibial tubercle-trochlear groove distance (TT-TG) and the patellar tendon-cartilaginous trochlear groove (PT-CTG) distances, and evaluate interrater reliability.  The study group consisted of 34 knees from 17 asymptomatic subjects with no history of knee pathology, trauma or surgery. A low-dose CT scan and an axial T1-weighted MRI sequence of the knees were performed with rigorous standardization of the positioning with full extension of the knees and parallel feet. Two musculoskeletal radiologists performed the measurements independently. The reliability of the TT-TG and PT-CTG distances on CT (17.1 ± 4.2 mm and 17.3 ± 4.2 mm) and of MRI (16.2 ± 3.7 mm and 16.5 ± 4.1 mm) was assessed by intraclass correlation coefficient (ICC [2,1]) and Bland-Altman graphs, as well as the interrater reliability for both methods.  Good reliability and agreement was observed between CT and MRI measurements for TT-TG and PT-CTG, with an ICC of 0.774 (  < 0.001) and 0.743 (  < 0.001), respectively, and no systematic bias was observed. The interrater reliability was excellent for all measurements on both imaging methods.  This was the first study that compared MRI using a body coil with CT in measuring the TT-TG distance, with the potential clinical implication that the CT in this clinical setting could be avoided.