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Parnian Zargham successfully defends dissertation

Feb 23 2016
Parallel transmit (PTx) systems have been proposed to compensate for radiofrequency  (RF) field non-uniformity in MR imaging. These systems require prior knowledge of the RF field (B1) of each channel in order to perform calibration and RF shimming. Moreover, measuring B1 maps of each transmit array is required for new applications of parallel transmit systems in RF safety and MRI interventions for controlling RF coupling and minimizing RF exposure. Existing B1 mapping methods suffer from a variety of issues ranging from long scan times, limited B1 dynamic range, and high specific absorption rate (SAR). Therefore, for applications such as calibration of parallel transmit system and interventional MRI, imaging work-flow would be improved if experimental B1 mapping could be avoided or minimized.

In the first part of this talk, I will present a new method for estimating transmit B1 maps by combining the transmit coil currents and orientation information in the scanner space with a previously simulated B1 library. I will then show that the 1.5T estimated B1 maps can be used in designing pulses for radiofrequency shimming instead of doing time-consuming B1 mapping. In the second part of the talk, I will describe our method for safely visualizing coupled structures inside the excitation volume by using transmit coil locators and current sensor measurements.