Comparison of Methods to Improve the Transmit Efficiency for MRgFUS Systems

Transcranial MRI-guided focused ultrasound is used in clinical treatment of essential tremor. It requires an array of ultrasound transducers within an MRI system. The transducers are arranged in a dome around the head and require the presence of a fluid transfer medium, usually water, to transmit the ultrasonic energy from the transducers into the human tissues. The transfer medium impacts the distribution of the radiofrequency field used in MRI to detect the signal, and it lowers the quality of the images. Some approaches have been proposed to solve this issue. In this work we have compared the distribution of the MRI signal of three configurations: the most common used geometry with a bowl-shaped common ground and water as transfer medium, a proposed solution with the addition of two crossed wires, and a proposed solution using a slotted ground for the transducers and a fluid having a low relative electric permittivity as transfer medium. We have compared the MRI transmit efficiency of these three solutions in the center of the brain and the averaged over the brain. The last solution has provided the best performance, providing a 3.5-fold improvement over to the other solutions.