A method of decoupling of radio frequency coils in magnetic resonance imaging : application to MRI with ultra short echo time concurrent excitation and acquisition
Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 50-55.In this thesis, it was both experimentally and theoretically shown that decoupling
of transmit and receive coils can be achieved by using a transmit array system
such that individual currents induced from transmit coils will cancel each other
resulting in a significantly reduced coupling. A novel method for decoupling of
radio frequency (RF) coils was developed and implemented in a transmit array
system with multiple transmit coil elements driven by RF current sources of different
amplitude and phase. It was shown that this method for decoupling provides
isolation over 70dB between transmit and receive coils. Decoupling procedure
was described and its performance was analyzed in terms of obtained isolation.
It was shown that MR signal can be detected during RF excitation with the
achieved amount of decoupling. NMR spectroscopy and MRI with concurrent
excitation and acquisition (CEA) was implemented. As an alternative to existing
CEA methods, this method reduces dynamic range requirements so that CEA
sequences can be applied in standard MRI scanners with minimal hardware modification.
It was also demonstrated that this method can be used to implement
ultra-short echo time (UTE) imaging with shorter acquisition delay. For CEA
approach, acquired raw data was formulated as convolution of the free induction
decay (FID) signal and the input B1 field. First proof of concept images were reconstructed
from nonuniformly sampled k space data using both UTE and CEA
sequences. UTE and CEA were shown to be feasible to implement using the
same custom made decoupling setup in a clinical 3T MRI scanner. Significance
of imaging of samples with ultra short T2* values was discussed.Özen, Ali ÇağlarM.S