The success of x-ray fluoroscopy-guided coronary catheterization depends in part on the ability to obtain simultaneous and real-time visualization of the guidewire, guiding catheter, and anatomy of the chest. The hypothesis explored in this paper is that magnetic resonance imaging (MRI) could provide this ability. This hypothesis was tested with loopless antennas used as the guidewire and a guiding catheter and two surface coils, each connected to four different receiver channels of a GE 1.5-T CV/I MRI scanner. Experiments were conducted on six healthy dogs. Intravascular antennas were inserted in the right carotid artery and maneuvered in the aorta while running a fast gradient-echo sequence (TR/TE 5/1.3 msec, flip angle 7°). Real-time projection images of the chest anatomy, together with the guidewire and guiding catheter, were obtained. Positioning of the MRI guiding catheter either in the descending aorta, ascending aorta, or heart was achieved easily. This study represents a step toward MRIguided coronary catheterization.
Because of its superb temporal resolution, echo planar imaging (EPI) is widely used for functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), and monitoring dynamic processes. EPI suffers from geometric distortions caused by magnetic field inhomogeneities, and although these distortions can be corrected by field mapping, current methods require lengthy auxiliary image acquisitions and/or phase unwrapping. We present a 3-point method for field mapping that circumvents these problems and is robust to additive noise. Results demonstrate that the performance of this approach is markedly better than the standard twopoint method and is comparable to methods requiring much longer auxiliary image acquisitions.
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