Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

Abstract

Goal-This study aims at a systematic assessment of five computational models of a birdcage coil for magnetic resonance imaging (MRI) with respect to accuracy and computational cost.Methods-The models were implemented using the same geometrical model and numerical algorithm, but different driving methods (i.e., coil "defeaturing"). The defeatured models were labeled as: specific (S2), generic (G32, G16), and hybrid (H16, H16 fr-forced ). The accuracy of the models was evaluated using the "Symmetric Mean Absolute Percentage Error" ("SMAPE"), by comparison with measurements in terms of frequency response, as well as electric (||E ⃗ ||) and magnetic (||B ⃗ ||) field magnitude. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptResults-All the models computed the ||B ⃗ || within 35 % of the measurements, only the S2, G32, and H16 were able to accurately model the ||E ⃗ || inside the phantom with a maximum SMAPE of 16 %. Outside the phantom, only the S2 showed a SMAPE lower than 11 %. Conclusions-Resultsshowed that assessing the accuracy of ||B ⃗ || based only on comparison along the central longitudinal line of the coil can be misleading. Generic or hybrid coils -when properly modeling the currents along the rings/rungs -were sufficient to accurately reproduce the fields inside a phantom while a specific model was needed to accurately model ||E ⃗ || in the space between coil and phantom.Significance-Computational modeling of birdcage body coils is extensively used in the evaluation of RF-induced heating during MRI. Experimental validation of numerical models is needed to determine if a model is an accurate representation of a physical coil.

RF Safety Evaluation of a Breast Tissue Expander Device for MRI: Numerical Simulation and Experiment

“…The first coil model (“750 mm coil,” 128 MHz) had an ID of 750 mm and with an RF shield (ID = 825mm, L = 850 mm) [24]. The inner length of the coil (i.e., length without width of the end-ring rod) was 520 mm, whereas the outer length was 600 mm (MITS1.5, Zurich Med Tech, Zurich, Switzerland).…”

Improvement of Electromagnetic Field Distributions Using High Dielectric Constant (HDC) Materials for CTL-Spine MRI: Numerical Simulations and Experiments

“…The dimensions of the coil model were: coil internal diameter (ID) = 746 mm, inner length = 570 mm, outer length=650 mm, RF shield ID=827 mm, and RF shield length = 845 mm. Tuning capacitors of 73 pF were selected to obtain a resonance frequency of 64 MHz [28]. …”

“…The body coil was driven in quadrature by two AN8102-08 RF power amplifiers (Analogic Co., Peabody, MA, USA) [28]. Measurements were performed with the coil loaded with an ASTM phantom, without and with an additional pad made of distilled water or conductive gel, positioned underneath the phantom [see Fig.…”

“…The body coil was tuned at 63.5 MHz and the measurements of S -parameters were: S 11 = − 10.3 dB, S 22 = − 9.3 dB, and S 12 = − 9.6 dB. The values of || B xy || and || E || were measured by means of a robotic measurement system (DASY system, DASY 5NEO, with the E field probe ER3DV6 and the H -field probe H3DV7, Schmid & Partner Engineering AG, Zurich, Switzerland) [28]. The probes were not aligned perfectly in Fig.…”

RF induced energy for partially implanted catheters: A computational study

“…Currently, there is no methodology to assess RF-induced heating in patients with partially implanted devices during MRI. Safety evaluation of the procedure is further complicated because a portion of the catheter is outside of the body, where the electric fields are high in magnitude and strongly affected by the coil design [5]. In addition, in commercial 1.5 T MRI scanners used in clinical applications, the position of feed excitation and orientation of the polarization with respect to the patient are often unknown.…”