Open design and flat cross sectional RF transmit coil for transverse magnet based MRI systems

MRI has become a widely used and indispensable component of diagnosis, and over 5000 units are operational world wide. As cost containment becomes a priority, the utilization of MRI becomes limited by its high acquisition, siting and operating costs. Because cost reduction is a major determinant of system design, attention was paid to reducing the cost of each component. One such component is the RF power transmitter used to excite the hydrogen nuclei in the body. The decision was made to provide a separate transmitter coil, as opposed to the alternative of transmitter/receive coils. A separate transmitter coil reduces the cost and complexity of the many RF coils (10 to 12) used for reception. To minimize RF power transmitter cost the coil needs to be as small as possible, consistent with the need to accommodate the largest receiver coils in use. This led to design described here, where the transmitter coil has an arch shape with maximum width of 71 cm and height above the bed pallet of 43 cm. This coil permits imaging of patients that could not fit any available superconducting magnet MR imager. Nevertheless, even though the patient population that can be imaged in the ACCESS (Toshiba America MRI, Inc., South San Francisco) system has expanded, experience demonstrated that there was a significant population component that exceeded even the aperture provided by the arch-shaped transmitter. Also, there was a benefit in placing extra axial anatomy in the center of magnet. In large subjects the transmitter coil impedes the necessary lateral displacement. This led to the exploration of an alternative transmitter configuration that would have a minimal impact on patient access. Because the volume of such a coil would be large and its conductor would be close to the magnet structures, such a coil would require increased RF transmitter power inputs to achieve equivalent power delivery to the patient. The design of the open transmitter sought to minimize this unavoidable increase.<
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