Bone motion analysis from dynamic MRI: acquisition and tracking

RATIONALE AND OBJECTIVES: For diagnosis, preoperative planning and postoperative guides, an accurate estimate of joint kinematics is required. It is important to acquire joint motion actively with real-time protocols. MATERIALS AND METHODS: We bring together MRI developments and new image processing methods in order to automatically extract active bone kinematics from multi-slice real-time dynamic MRI. We introduce a tracking algorithm based on 2D/3D registration and a procedure to validate the technique by using both dynamic and sequential MRI, providing a gold standard bone position measurement. RESULTS: We present our technique for optimizing jointly the tracking method and the acquisition protocol to overcome the trade-off in acquisition time and tracking accuracy. As a case study, we apply this methodology on a human hip joint. CONCLUSION: The final protocol (bFFE, TR/TE 3.5/1.1 ms, Flip angle 80 degrees , pixel size 4.7 x 2.6 mm, partial Fourier reduction factor of 0.65 in read direction, SENSE acceleration factor of 2, frame rate = 6.7 frames/s) provides sufficient morphological data for bone tracking to be carried out with an accuracy of 3 degrees in terms of joint angle.