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Cardiac resynchronization therapy (CRT) has recently emerged as an effective treatment option for heart failure patients with dyssynchrony. Patients have traditionally been chosen for CRT based on a prolonged QRS interval. However, this selection method is far from ideal, as approximately 30% of those receiving CRT do not show any clinical improvement. Tissue Doppler imaging (TDI) suggests that one of the best predictors of response to CRT is the underlying level of mechanical dyssynchrony in the myocardial wall prior to CRT. As a result, there has been growing interest in direct imaging of the myocardial wall. Because myocardial contraction is a complex, three-dimensional movement, providing an accurate picture of myocardial wall motion can be challenging. Echocardiography initially emerged as the modality of choice, but the long list of limitations (limited echocardiographic windows, one direction of motion, poor reproducibility) has fostered interest in exploring the use of MR for myocardial wall imaging. Although MR presents some unique drawbacks (expensive equipment, longer imaging times), it is able to overcome many of the limitations of TDI. In particular, Phase Velocity Mapping (MR PVM) can provide a complete, three-directional description of motion throughout the entire myocardial wall at high spatial and temporal resolution. The overall goal of this project was to develop a patient-selection method for CRT based on myocardial wall velocities acquired with MR PVM. First the image acquisition and post-processing protocols for MR PVM imaging of myocardial tissue were developed. A myocardial motion phantom was used to verify the accuracy of, and optimize the acquisition parameters for, the developed MR PVM sequence. Excellent correlation was demonstrated between longitudinal myocardial velocity curves acquired with the optimized MR PVM sequence and Tissue Doppler velocities. A database describing the normal myocardial contraction pattern was constructed. A small group of dyssynchrony patients was compared to the normal database, and several areas of delayed contraction were identified in the patients. Furthermore, significantly higher levels of dyssynchrony were detected in the patients than the normal volunteers. Finally, a method for computing transmural, endocardial, and epicardial, radial strains and strain rates from MR PVM velocity data was developed |
