Commercial 1.5T MRI scanners used in clinical applications are typically driven with a dual port excitation for which the position of the feeding sources and the orientation of the polarization (i.e., clockwise CW vs. counterclockwise CCW) with respect to the patient is often unknown. For partially implanted leads (e.g., interventional cardiac ablation catheters), the radiofrequency (RF) induced heating of tissue near the lead tip depends on the magnitude and phase of the tangential electric field component ($$$ \overrightarrow{E}_{tan}$$$) along the lead. This study aims to answer the question on how position of feeding sources and field polarization affect $$$ \overrightarrow{E}_{tan}$$$. The study was based on electromagnetic (EM) measurements and simulations inside an ellipsoidal phantom and on simulations with an anatomical human body model.The MITS1.5 for 1.5 Tesla RF Safety Evaluation (ZurichMedTech) was used for the measurements. The system consists of a high-pass 64 MHz birdcage body coil [1]. The coil was driven at two ports (I and Q in Figure1a) physically shifted at 90^o. The EM fields were measured with the DASY52NEO robotic measurement system (SPEAG) [2]. The computational model was geometrically equivalent to the physical coil (Figure 1b) and it was implemented with Sim4Life software (ZurichMedTech). Both coil and shield were modeled as perfect electric conductors. Four different positions of the feed points were studied (Figure 1d): starting from the one implemented in the physical coil (“left” position) the pair of sources were turned 90^o. Feeding phase was imposed such to have opposite quadrature setup (i.e., 0^o-90^o CW and 90^o-0^o CCW polarization). Both the physical and the numerical coil was loaded with a superellipse-shaped phantom (Figure 1b). Three different planes inside the phantom were measured for comparison. The measured and numerical dataset were normalized to the same magnetic field magnitude for a location inside the phantom. Additionally, the coil model and source configuration were used with an anatomical human female model (“Ella” Figure1c [3]). The $$$ \overrightarrow{E}_{tan}$$$ profile was studied along the extraction lines shown in Figures 3a and 4a. The extraction line in the phantom was along a device mount track for evaluation of a partially inserted catheter, whereas in the “Ella” model was based on a typical path of MR-interventional ablation catheters. Data with “Ella” were normalized to a whole body average SAR of 2 W/kg.Figure 2 shows the electric field magnitude for the physical vs the numerical model in one plane of the phantom. The results with the sources in “left” and same polarization (CW) of the physical coil were closer to measurements with a 15.3 % Symmetric Mean Absolute Percent Error (SMAPE)[4] . When using a CCW polarization the field distribution was mirrored with respect to the central line compared to CW. When comparing CW vs. CCW in the phantom (Figure 3b) the highest difference of $$$\parallel \overrightarrow{E}_{tan}\parallel$$$ was found around the exit point (x=1579 in Figure 3a), with up to 14 % higher $$$\parallel \overrightarrow{E}_{tan}\parallel$$$ in the left and top position. Spikes in the profile were due to the pins of the device mount track made of plexiglass. With respect to the $$$\angle \overrightarrow{E}_{tan}$$$ inside the phantom, the top and right positions showed variations less than 0.5 rad, and the left and bottom positions changed by a mean of 4.5 rad and 3 rad, respectively; conversely, outside the phantom the profile of the phase was the opposite with a change of up to 3.5 rad for top/right and less than 1.3 rad for left/bottom. In the “Ella” model (Figure 4b) differences of up to 40% were observed (e.g., $$$\parallel \overrightarrow{E}_{tan}\parallel$$$ 40 % less with CCW vs. CW near the exit point, x=786 in Figure 4b). Additionally, when changing sources positions the phase had qualitatively comparable trends, but differences in values up to 4.8 rad (CW).Accurate modeling of both the magnetic and electric fields is important when evaluating RF-induced heating medical devices that are partially implanted or have external components in contact with the body. Information about field polarization and source position with respect to the patient undergoing an MRI scan can be essential in the determination of RF safety. Future work is needed to develop a systematic exposure procedure for RF heating evaluations of partially implanted leads in phantoms. These procedures must be able to mimic worst-case exposure in the patient.The mention of commercial products, their sources, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products by the Department of Health and Human Services.