A 600W on-coil Class-E RF power amplifier array with dynamic phase control for 3T MRI

Abstract

Due to their size and cooling constraints, conventional Magnetic Resonance Imaging (MRI) places radio frequency (RF) amplifiers away from the scanner. These RF amplifiers have relatively low efficiency due to the matching of 50Ω output impedance for means of transmission with cables. Switching Class-E amplifiers on the other hand, by default need a bare RLC network as their load and thus can be directly integrated with the bare unmatched coils and reduce the cost and power losses significantly. This thesis aims to build up on the previous theses’ line of work including [1, 2, 3, 4, 5]. Instead of mitigating the symptoms, chronic problems of artifacts have been fixed by focusing on their root causes in the FPGA side of the updated design.The driver has been updated, timing problems have been resolved. FPGA design is also extended to support multichannel phase control.

A dual channel imaging configuration of on-coil Class-E amplifiers with on-the-fly digital fine phase control is presented for 3T MRI. The system can control the phase with less than 2° granularity (this setting can be fine-tuned down to 0.15°). Without any mechanical intervention with the coil setup, using merely phase control, illuminated slice depth is modulated to three times its base-size during scantime. B1 field maps are also extracted for another setup.

Periodically linear switching (PLS) circuit model of the Class-E amplifier is derived and computed, yielding a simulator with fast and customizable optimization capability. The PLS model is also verified by SPICE and theoretical analysis.