| dc.description.abstract | In Magnetic Resonance Imaging (MRI) as the field strength is increased in order to achieve a higher signal to noise ratio (SNR), it becomes more difficult to image, requiring more advanced & expensive hardware, complicated pulse sequences, and different imaging techniques. 7 Tesla(T) MRI scanner are becoming more commonly used for clinical work and easier to access. The goal of this project was to build a control system capable of control a set of phase shifter dynamically in order to perform B1 steering at 7T. B1 steering refers to focusing the energy to a point in space to ensure a strong B1 at that point. This is different than shimming, where the field is made more homogenous. However, in this thesis, the term B1 shimming will be used as it is more common. The control system as well needs to perform diagnostics in order to guarantee correct operation. B1 shimming requires the ability to change phase for transmit power (TX) on each channel of a parallel transmit coil. While a simple approach to this problem would be to use a collection of coaxial cables of various lengths, this is very cumbersome and limits the functionality of the system. Therefore, a set of nonmagnetic digitally controllable phase shifters with 17 unique states were built in order to manipulate the phase on an 8- element dipole array coil designed by others in the lab. While the phase shifters and the coil, compose the front end of the system, an additional control system was still required.
Therefore, a third system was developed in order to control 16 phase shifters modules (8 low bit modules, and 8 high bit modules), measuring gain and phase on each channel of the coil, and exercising the system in the lab, and to run diagnostics. The system will be developed so it can be tested & verify on the bench at the Magnetic Resonance System Lab (MRSL) at Texas A&M University(TAMU) in order to verify the results and experiments that were conducted at the University of Texas Southwestern medical center (UTSW) in Dallas, Texas. The system was built using a microcontroller, evaluation boards, system onboard computer, and a host computer. The system can supply a DC load of up to 26A into the magnet room in order to power the entire system. The system is able to set the state of all the phase shifter in less than 10ms suitable for most multi-slice applications. | en |
