USING CINE PHASE-CONTRAST MAGNETIC-RESONANCE-IMAGING TO NONINVASIVELYSTUDY IN-VIVO KNEE DYNAMICS

We tested the accuracy and feasibility of using cine phase contrast ma gnetic resonance imaging (cine-PC MRI) to non-invasively measure three -dimensional, in vivo, skeletal velocity. Bone displacement was estima ted by integrating the velocity measurements. Cine-PC MRI was original ly developed to directly and non-invasively measure in vivo blood and heart velocity. Since no standard of reference exists for in vivo meas urement of trabecular bone motion, a motion phantom (consisting of a s eries of paired gears that moved a sample box containing a human femor al bone sample) was built to assess the accuracy of tracking trabecula r bone with cine-PC MRT. The in-plane, average absolute displacement e rrors were 0.55 +/- 0.38 and 0.36 +/- 0.27 mm in the x- and gamma-dire ction, respectively. Thus, estimates of bone position based on the int egration of bone velocity measurements are affected little by the magn etic properties of bone [Majumdar and Genant (1995) Osteoporos Interna tional 5, 79-92]. The velocity profiles of the patella, femur and tibi a were measured in five healthy subjects during leg extensions. Extens ion was resisted by a 34 N weight. Subjects maintained a consistent mo tion rate (35 +/- 0.5 cycles min(-1)) and motion artifacts were minima l. Our results indicate that patellar flexion lags knee flexion and th e patella tilts laterally and then medially as the knee extends. We co nclude cine-PC MRI is a promising technique for the non-invasive measu rement of in vivo skeletal dynamics and, based on our previous work, m uscular dynamics as well. Published by Elsevier Science Ltd.