62 Balancing these issues, 15 fps true-FISP cardiac imaging with 128 phase encode lines can be performed using an 8-channel receive coil array and optimized reconstruction hardware.63

Commercial MRI systems now commonly have multichannel receivers and see more parallel imaging options. The performance of these systems is currently in the range of what is needed to perform CMR-guided EP procedures at 5 fps with acceptable image quality.61 While the current imaging rates are adequate for a single 2-D image plane, ideal visualization Inhibitors,research,lifescience,medical of the device, target anatomy, and surrounding reference anatomy may require multiple 2-D image planes or even 3-D imaging. Other techniques that can improve imaging speed while balancing imaging quality include non-Cartesian k-space sampling, temporal data sharing between images, and adjusting the

trade-off between temporal and spatial resolution.59 These techniques may be particularly useful to accelerate imaging of reference anatomy views that are not depended on for device tracking. Use of 32-channel Inhibitors,research,lifescience,medical receive arrays to perform more rapid 3-D cardiac imaging and parallel transmission techniques to Inhibitors,research,lifescience,medical permit more efficient parallel data collection are also under active investigation.63–65 DEVICE VISUALIZATION AND NAVIGATION While fluoroscopy provides projection images where the entire catheter body and tip are easily visualized, 2-D MR images typically depict a slice through the body that is around 5–10 mm thick. Curved devices such as catheters may pass in and Inhibitors,research,lifescience,medical out of the MR imaging plane leading to mis-interpretation of the device tip position. We have noted in preclinical studies that poor delineation of the tip position can result in tissue

contact trauma, such as local hemorrhage. In addition, for electrophysiology ablation procedures the device tip contains the energy source. Misestimating the Inhibitors,research,lifescience,medical tip/tissue contact region can lead to inaccurate placement of ablation lesions. During our feasibility studies, tip location has mostly been performed using interactive real-time sequences with a user interface that permits adjustment of the scan plan during many image acquisition. Part of the catheter is first identified on some imaging plane, and the plane is manually adjusted until the tip is located. For vascular procedures where the device is constrained to a co-planar segment of blood-vessel, manual plane manipulation is acceptable since only minor image plane translations are needed to visualize the device tip and relevant anatomy. For navigation in cardiac chambers where the device tip location is less constrained, the frequent need for manual plane manipulation necessitates a skilled operator for image plane manipulation and can distract from efficient procedure work flow. One approach to this problem is to automatically direct imaging to the device location using position sensors located in the catheter. Fifteen years ago Dumolin et al.