| With the advantageous characteristics of non-invasive and nonionizing radiation,magnetic resonance imaging (MRI) technology has become an important tool for modernmedical diagnosis and researches. RF coils are crucial component in MRI and playing asignificant role in image quality by directly affecting the image signal to noise ratio.Using RF coils, the MRI system launches electromagnetic waves to excite human tissuesand then the human tissues produce MR signals which can be detected by the RF coils. At thefinal stage, the signals will be sent to the computer to be imaged. In order to obtainhigh-quality MRI scanning images, it is requested that the B1field generated by thetransmitted coil has good uniformity and the signal to noise ratio of the received coil is high.Since a birdcage coil can generate a high uniform magnetic field at the center of thecylinder, we usually use birdcage coils to transmit signal. Birdcage coils can be categorizedinto three groups: high pass, low pass, and band pass. Considering the convenience in anactual operation, we generally use the high pass birdcage coil.The main contribution of this thesis is to investigate and design the high passtransmitting coils for body MRI systems. First the theory of nuclear magnetic resonance isintroduced briefly, which includes the basic structure of magnetic resonant imaging scanner.Then the principles and design requirements of RF coils is analyzed. On the basis of thetheory, body transmitting coil is proposed and studied. Several methods for measuring the Qvalue of the coils are investigated. A high pass body transmitting coil of16legs is designedand simulated. According to the theoretical analysis, a simple and quick method is proposedand applied to magnetic resonance imaging by adding lumped elements to coil. Finally thecoil is integrated into an MRI scanner. A phantom and human abdomen experiment isperformed in the3T system. It is confirmed that the coil can lead to a better imaging. |
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