Abstract:
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Purpose: Nearly all studies of dynamic knee motion have been based either on measurements made in cadavers or tracking of externally placed markers. Cine MRI has recently been introduced to more accurately characterize the motions of the knee in vivo. However, cine MRI is severely limited as the number of motion cycles required to characterize the motion makes it infeasible to study the knee under the large loads typically generated during activities of daily living. The purpose of this study was to determine the feasibility of tracking bone motion with real-time magnetic resonance imaging.
Methods and Materials: A high resolution Spiral SSFP pulse sequence was implemented on a GE Signa 1.5T CV/i scanner with high-speed gradients. The sequence consisted of a 640 μs excitation, 2.4 ms spiral readouts, and a moment-nulled rewinding gradient. The imaging TR was 6 ms, and 70-interleaves were used to achieve 1.1 mm resolution over a 24 cm FOV every 448 ms. A bit-reversed interleaf ordering and sliding window reconstruction were used to generate and display 10 frames/s with minimal view sharing artifacts. Reconstruction and display was performed in real-time on a workstation adjacent to the scanner. A body coil was used for RF transmission, and 5-inch surface coil (strapped to the side of knee) was used for signal reception.
Results: Five healthy subjects were scanned in a supine position with knee elevated. Knee extensions were performed without guidance at a rate of roughly 1 cycle per 3 seconds. Sagittal, coronal, and axial movies of the patellofemoral joint were recorded during motion. Approximately 45 degrees of knee extension was achieved in the closed bore. SNR was measured to be 27 to 61 in the patella and 22 to 51 in the femur, with variations primarily due to coil proximity and knee size. Bone position, surface, and contact points were clearly visualized in all real-time images. An accurate representation of the three-dimensional in vivo kinematics could then be established with the use of shape-matching algorithms.
Conclusion: We have demonstrated the feasibility of tracking bone motion in real-time and with millimeter resolution using MRI. Sprial SSFP is a particularly appropriate pulse sequence for this purpose, because it is robust to motion and has high scan efficiency, SNR, and contrast. Such a method could potentially determine joint kinematics under dynamic loading conditions.
Questions about this event email: nayak@mrsrl.stanford.edu
Nayak PhD, K,
High-Resolution Real-Time MRI of Knee Kinematics. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3101925.html
