A Platform for 4-Channel Parallel Transmission MRI at 3 T: Demonstration of Reduced Radiofrequency Heating in a Test Object Containing an Implanted Wire

Objective To describe a platform for 4-channel parallel transmission (pTx) integrated on a 3 T MRI system; to demonstrate utility of the platform with a pTx method to reduce localized radiofrequency (RF) heating during MRI of a test object implanted with an electrically conductive wire; and to compare the pTx results with those from a standard birdcage (BC) head coil. Methods A 4-channel pTx system with independent amplitude and phase control was added to a Siemens Prisma MRI system. Turbo spin echo pTx MRI of a homogenous tissue-mimicking head phantom, including an implanted wire to simulate a deep brain stimulation (DBS) electrode, was performed in (a) circular-polarized “quadrature” transmission mode to demonstrate localized RF heating effects, and (b) an optimized RF shim “suppression” mode to counteract RF heating at the tip of the implanted wire. Signal-to-noise ratio (SNR) and temperature results from the pTx experiment were compared with imaging using a Siemens BC head coil. Results The pTx platform provided effective control of RF amplitude and phase to minimize localized RF heating at the wire tip. No temperature elevation was detected for pTx in suppression mode, whereas maximum increases of 6.9 °C and 2.7 °C were observed for pTx quadrature mode and imaging using the BC head coil, respectively. Conclusion The platform has been adapted to a Siemens MRI system without impacting the standard RF transmission pathway, while providing accurate RF signal modulation. Demonstration of the platform showed substantial reduction of localized RF heating in a simulated DBS implant without significant SNR loss.