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Design of a Parallel Transmit System for TRASE Radiofrequency-Encoded MRI

H Sun*, J Sharp, University of Alberta - Cross Cancer Institute, Edmonton, Alberta, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: TRASE (Transmit Array Spatial Encoding) encodes MR data using an array of radiofrequency (RF) phase gradients. The functionality of TRASE needs no standard magnetic field gradient system and is well-suited to use at low-field magnets, promising a low-cost and portable MRI system. To obtain 2D high resolution images, three independent RF phase gradients are needed, while any crosstalk among fields result in image artifacts. Geometric decoupling method was applied to significantly minimize fields interactions; however, further coupling reduction requires a parallel transmit system (PTX), which generally is only equipped with high-field MRI system. Here, we will show recent developments on the design of a PTX architecture for low-field TRASE MRI.

Methods: our 2D TRASE encoding, three RF phase gradients were individually generated by three coaxial cylindrical coils (two twisted solenoids and one saddle coil). The new PTX system was developed based upon Terasic Cyclone System on Chip (SoC) board and AD9106 quad DAC waveform generator chip. New PTX was implemented together with geometric decoupling techniques to mitigate the crosstalk.

Results: Bench measurements indicated that four independent arbitrary shape waveforms can be generated with new PTX. All pulse characteristics including durations, amplitudes and phases can be updated within 12 microseconds, making a design of highly efficient MR sequence possible. For TRASE MR application, the phase of each RF pulse is of most concern. The new PTX allowed fine tuning of RF pulse phase with a resolution of 0.005 degree.

Conclusion: This project describes a practically scalable design of a parallel transmit console for low-field MR system. The combination of geometric decoupling and PTX for coil drive eliminates the need for switched elements (e.g. PIN diodes). This fast updating PTX architecture demonstrates a simple MR system without extra electronics complications, promising higher spatial resolution 2D TRASE MR images to be obtained.

Funding Support, Disclosures, and Conflict of Interest: Funding: 1. 2018/2019 Alberta Cancer Foundation Antoine Noujaim Scholarship, Grant/Award Number: 27228; 2. 2019/2020 Alberta Graduate Excellence Scholarship; 3. Natural Sciences and Engineering Research Council of Canada, Grant/Award Number: RGPIN-2016-05183;


MRI, Low-field MRI, Crosstalk


IM- MRI : Development (New technology and techniques)

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