Functional MRI of the patellofemoral joint: comparison of ultrafast MRI, motion-triggered cine MRI and static MRI

In recent years ultrafast gradient echo sequences have been used in MRI that allow functional MRI studies of the joints during active motion in an acquisition time of seconds. To evaluate the feasibility and usefulness of ultrafast MRI (u), patellar tracking from 30° of flexion to knee extension (0°) was analysed and compared with motion-triggered cine MRI (m) and a static MRI technique (s). The different imaging methods were compared in respect of the patellofemoral relationship, the examination time and image quality. Eight healthy subjects and four patients (in total 18 joints) with patellar subluxation or luxation were examined. Significant differences between the static MRI series without quadriceps contraction and the functional MRI studies (motion-triggered cine MRI and ultrafast MRI) were found for the patellar tilt angle (PTA: P_m/s = 0.01; P_u/s < 0.01). In the dynamic joint studies there was no statistical difference of the regression coefficients between the motion-triggered cine MRI studies and the ultrafast MRI studies (P_m/u = 0.8). The findings of the functional MRI studies compared with the static MRI images were significantly different for the lateralisation of the patella, expressed by the lateral patellar displacement (LPD: P_m/s < 0.01; P_u/s = 0.01) and bisect offset (BSO: P_m/s = 0.01; P_u/s < 0.05). No significant differences in patellar lateralisation were found between motion-triggered cine MRI and ultrafast MRI (LPD: P_m/u = 0.89; BSO: P_m/u = 0.33). Ultrafast MRI was superior to motion-triggered cine MRI in terms of the reduction in imaging time and improvement of the image quality.