DOI: 10.5061/dryad.53bh1
title: Data from: Investigation of parallel radiofrequency transmission for the reduction of heating in long conductive leads in 3 tesla magnetic resonance imaging

description: Deep Brain Stimulation (DBS) is increasingly used to treat a variety of
 brain diseases by sending electrical impulses to deep brain nuclei through
 long, electrically conductive leads. Magnetic resonance imaging (MRI) of
 patients pre- and post-implantation is desirable to target and position
 the implant, to evaluate possible side-effects and to examine DBS patients
 who have other health conditions. Although MRI is the preferred modality
 for pre-operative planning, MRI post-implantation is limited due to the
 risk of high local power deposition, and therefore tissue heating, at the
 tip of the lead. The localized power deposition arises from currents
 induced in the leads caused by coupling with the radiofrequency (RF)
 transmission field during imaging. In the present work, parallel RF
 transmission (pTx) is used to tailor the RF electric field to suppress
 coupling effects. Electromagnetic simulations were performed for three pTx
 coil configurations with 2, 4, and 8-elements, respectively. Optimal input
 voltages to minimize coupling, while maintaining RF magnetic field
 homogeneity, were determined for all configurations using a Nelder-Mead
 optimization algorithm. Resulting electric and magnetic fields were
 compared to that of a 16-rung birdcage coil. Experimental validation was
 performed with a custom-built 4-element pTx coil. In simulation, 95-99%
 reduction of the electric field at the tip of the lead was observed
 between the various pTx coil configurations and the birdcage coil. Maximal
 reduction in E-field was obtained with the 8-element pTx coil. Magnetic
 field homogeneity was comparable to the birdcage coil for the 4- and
 8-element pTx configurations. In experiment, a temperature increase of
 2±0.15°C was observed at the tip of the wire using the birdcage coil,
 whereas negligible increase (0.2±0.15°C) was observed with the optimized
 pTx system. Although further research is required, these initial results
 suggest that the concept of optimizing pTx to reduce DBS heating effects
 holds considerable promise.
description: Axial Image with
 4-element PTX coil in suppression modeAxial slice through
 center of phantom obtained with GRE sequence (TR = 2000 ms, TE = 40 ms,
 slice thickness = 10 mm, in-plane resolution = 256x256, FOV = 24 cm) with
 4-Element PTX operating in suppression mode (phase shifts of 40, 16, 200
 and 301 degrees). Dicom file for image shown in
 manuscript.AxialGREwPTX.dcmCoil GeometryContains specs about the geometry of the coil configurations (including capacitance values) for the simulations.CoilGeometry.txtBirdcage HeatingTemperature probe measurements for heating at tip of wire 12 cm long copper wire in a polyacrylic acid cylindrical phantom (radius = 9 cm, height = 24 cm) using FRFSE sequence (TR = 559 ms, TE = 100 ms, echo train length = 24, 1 slice, imaging time = 4:08). Excitation with transmit/receive GE birdcage coil with transmit gain of 153.PTx Quadrature HeatingTemperature probe measurements for heating at tip of wire 12 cm long copper wire in a polyacrylic acid cylindrical phantom (radius = 9 cm, height = 24 cm) using FRFSE sequence (TR = 559 ms, TE = 100 ms, echo train length = 24, 1 slice, imaging time = 4:08). Excitation with 4-element parallel transmit coil with phase shifts of 0, 90, 180 and 270 degrees between elements with transmit gain of 195PTx Quad Heating Test 1 TX195.txtPTx Suppression Heating Test 1Temperature probe measurements for heating at tip of wire 12 cm long copper wire in a polyacrylic acid cylindrical phantom (radius = 9 cm, height = 24 cm) using FRFSE sequence (TR = 559 ms, TE = 100 ms, echo train length = 24, 1 slice, imaging time = 4:08). Excitation with 4-element parallel transmit coil with phase shifts of 40, 16, 200 and 301 degrees (suppression mode) with a transmit gain of 190PTx Suppression Heating Test 2Temperature probe measurements for heating at tip of wire 12 cm long copper wire in a polyacrylic acid cylindrical phantom (radius = 9 cm, height = 24 cm) using FRFSE sequence (TR = 559 ms, TE = 100 ms, echo train length = 24, 1 slice, imaging time = 4:08). Excitation with 4-element parallel transmit coil with phase shifts of 40, 16, 200 and 301 degrees (suppression mode) with a transmit gain of 187. Second measurement.E-field increase as function of wire positionFolder containing two files with % increase in E-field magnitude at tip of wire vs minimum in field of view for varying radial position (RposRatio.csv) and z position (ZposRatio.csv)WirePos.zipSimulation data for wire at r = 2.5 cm, z = 0 cm (E-field and H-field)Contains simulation data for wire positions r = 2.5 cm, z = 0 cm. Includes data for a 16-rung birdcage coil operating in quadrature mode and a 2-element PTX coil, 4-element PTX coil and 8-element PTX operating in suppression mode (amplitudes and phases found in manuscript). Each folder contains a folder named 'XY plane' corresponding to data in the z = 0 cm plane, x = -10 cm to x = 10 cm, y = -10 cm to 10 cm and 'YZ plane' corresponding to data in the x = 0 cm plane, z = -12 cm to 1 cm, y = -10 cm to 10 cm. Each file is named: _.txt. The files are space delimited. Header of 15 lines.Leadat25mm.zipSimulation data for wire at r = 8 cm, z = 2 cm (E-field and H-field)Contains simulation data for wire positions r = 8 cm, z = 2 cm. Includes data for a 16-rung birdcage coil operating in quadrature mode and a 2-element PTX coil, 4-element PTX coil and 8-element PTX operating in suppression mode (amplitudes and phases found in manuscript). Each folder contains a folder named 'XY plane' corresponding to data in the z = 0 cm plane, x = -10 cm to x = 10 cm, y = -10 cm to 10 cm and 'YZ plane' corresponding to data in the x = 0 cm plane, z = -12 cm to 1 cm, y = -10 cm to 10 cm. Each file is named: _.txt. The files are space delimited. Header of 15 linesLeadat80mmz2cm.zipSimulation data for wire at r = 7.5 cm, z = 0 cm (E-field and H-field)Contains simulation data for wire positions r = 7.5 cm, z = 0 cm. Includes data for a 16-rung birdcage coil operating in quadrature mode and a 2-element PTX coil, 4-element PTX coil and 8-element PTX operating in suppression mode (amplitudes and phases found in manuscript). Each folder contains a folder named 'XY plane' corresponding to data in the z = 0 cm plane, x = -10 cm to x = 10 cm, y = -10 cm to 10 cm and 'YZ plane' corresponding to data in the x = 0 cm plane, z = -12 cm to 1 cm, y = -10 cm to 10 cm. Each file is named: _.txt. The files are space delimited. Header of 15 linesLeatat75mm.zip