Decoupling Methods of Magnetic Resonance Imaging Array Coils and Its Biomedical Applications

In MRI (Magnetic Resonance Imaging) system, phased-array coils have been used to have high signal-to-noise (SNR) as well as to cover big field-of-view (FOV). When the numbers of coils increases, the coupling between coils get increased also. How to decrease the mutual inductance between these coils is the main goal of this thesis. In these several years, array coils have also combine parallel imaging to reduce the acquisition time for fast imaging applications.

Overlap decoupling, capacitive decoupling, and preamplifier decoupling theories are introduced in this thesis. These decoupling methods are also verified by HFSS simulation, which can create 3D models for real coils situations, and provide rule of thumb for coil design.

In addition to theory and simulations, two channel array coils were designed with overlap and capacitive decoupling for phantom and mice at 3T MRI in National Taiwan University. Advantages and disadvantages of these two methods are also discussed. A hybrid method cover these two methods was also designed for mice anatomic imaging.

Preamplifier decoupling was also introduced due to the limitation of decoupling effects for complicated geometry coil for these two methods. We take advantage of preamplifier decoupling with low input impedance for better decoupling in complicated coil configuration. Three channel spine array coils and four channel whole body array coils was implemented with better isolated images (<-25dB) in phantom and mice study than overlap and capacitive decoupling theory (almost >-20dB) of it. These multi-channel array could successfully used to reduce sampling time to half by SENSE(Sensitivity encoding) reconstruction.

These design techniques of coils and preamplifiers could be used for large number of channels in future applications widely. IC fabrication as well wireless technology will be covered in the future studies.