This study investigates the RF-induced heating of tibial nail implants during MRI using thermal simulations. Results show that surgical state, bone adhesives, implant characteristics, and anatomical variability strongly influence temperature rise. Heating was most pronounced in surgical models with 50 mm adhesives and in cases with synovial fluid due to high conductivity, while variations were also observed with nail length across different human models. In many scenarios, rises in temperature exceeded $6^{\circ} \mathrm{C}$, raising safety concerns for post-operative MRI in patients with implants.

PURPOSE:This study presents an in-silico assessment of RF-induced heating of orthopedic implants during various stages of bone fracture healing, namely surgery, scar, and healed phases, under 1.5 T and 3.0 T MRI. METHODS:Computational human models Duke, Ella, and Fats were used to develop the stages of bone fracture healing. These models reflect clinically relevant conditions and also include assessment of the surgery model with the presence of tissue adhesive and its leakage. Two types of orthopedic implants are analyzed: (a) a tibial nail system embedded within bone, and (b) a reverse shoulder arthroplasty (RSA) implant located partially in bone and muscle. RESULTS:Results demonstrate variations in RF-induced heating across stages of bone fracture healing and anatomical models, indicating that localized tissue properties, location of the implantation as well as the presence of tissue adhesive significantly influence RF-induced heating. CONCLUSION:The findings highlight the importance of (a) integrating clinically relevant in silico models to evaluate the safety of patients undergoing MRI scans which are not included in the current testing standards for passive implantable medical devices, and (b) accurate labeling of orthopedic implants for testing in an MRI environment.

In this work, we studied the combined effects of MR emissions, including gradient-induced electric fields and radiofrequency-induced heating, on vagus nerve activation in the presence of a cuff electrode. Our approach integrates electromagnetic and thermal simulations and neurophysiological modeling to assess these interactions. Preliminary results indicate that the radiofrequency-induced heating of the cuff electrode can further alter the activation threshold in the specific configuration investigated.Clinical Relevance— This study highlights the potential for radiofrequency-induced heating to lower the activation threshold, potentially leading to unintended vagus nerve stimulation, which may have safety implications for patients with implanted cuff electrodes.

The transfer function (TF) method is crucial in assessing radio frequency induced heating in active implantable medical devices (AIMDs) during magnetic resonance imaging scans within the human body. Despite numerous implementations to develop TF models for AIMDs, a lingering question remains: TFs are typically developed in a straight pathway configuration, which may differ from TFs in the clinically relevant curved implantation pathways. This article explores the validity of TFs developed in a straight configuration for curved pathways. To address this, a robotic arm capable of three-dimensional measurements is introduced, facilitating the direct development of TFs along curved trajectories. Various curved pathways, including three clinically relevant trajectories, are selected for TF development. The results demonstrate the consistency of TFs obtained along curved and straight pathway configurations in all the cases. This indicates the applicability of TFs developed along a straight configuration for clinically relevant scenarios. Further insights into this trajectory-independent TF model are gained through numerical simulations. Additionally, the article discusses the conditions under which the straight TF remains valid for curved trajectories. For the commercially available AIMDs investigated in the article, the TFs remain consistent regardless of the trajectories, implying its invariance with respect to implantation trajectories.

Presents the recipients of (For the introduction and development of the dielectric resonator antenna and the early development of the microstrip patch antenna) awards for (2024).

W. Ross Stone, Ph.D. was a major contributor in the development of the IEEE Antennas and Propagation Society. He served both the Society and the IEEE as a whole in many capacities, including positions concerning symposia and society administration, but his contributions in the area of publications are perhaps the most significant and the ones that continue to influence the Society and the Institute today.

Objective. A bone-inclusive ASTM phantom is proposed to improve the assessment of radiofrequency electromagnetic field (RF-EMF) power deposition near orthopedic device under 1.5 T and 3 T magnetic resonance imaging (MRI). Approach. A phantom is created by introducing a cylindrical bone structure inside the American Society for Testing and Materials (ASTM) phantom. Four orthopaedic implant families-rod, nailing system, plate system, and hip replacement-are used in the study. RF-EMF power deposition (in terms of peak averaged specific absorption rate over 1 gram) near these implants are evaluated by placing these implants inside the standard ASTM phantom, the developed bone-inclusive ASTM phantom, and two anatomically representative human body phantoms, known as Duke and Ella. Numerical simulations are performed to calculate the RF-EMF power deposition near various orthopaedic devices within these phantoms. Main Results. For devices implanted inside or near bone tissue, the evaluation of RF-EMF power deposition using the developed bone-inclusive ASTM phantom shows better correlations to the human body phantoms than the ASTM phantom. This improvement is attributed to the portion of the devices implanted within the bone tissue. Significance. The bone-inclusive ASTM phantom has the different tissue of interests surrounding the implants compared to the ASTM phantom. This variation can lead to the different resonance frequency under RF-EMF exposure. This leads to better correlation of RF-EMF power deposition near orthopaedic implants inside human body, making the bone-inclusive ASTM phantom more suitable for evaluating RF-EMF power deposition than ASTM phantom in MRI scans.

Few books have had the level of impact on a field as the textbook, Antenna Theory: Analysis and Design by Professor Constantine A. Balanis has had on antenna engineering. Its share of adoptions at universities around the world is extensive, and since its first publication in 1982, it has now maintained this dominance through four editions for over 40 years.

This study examines the influence of orthopedic implants on electric field disruptions during electrosurgical procedures, along with the risk of overexposure in their vicinity. Experimental measurements were undertaken to validate a computational model of electrosurgery. Following this, numerical simulations were carried out to assess the impact of implants on induced variations in the electric field. The results suggest that the presence of implants may lead to increased energy concentration nearby, potentially creating conditions for overexposure.

This article studies the impact of strain relief loops on RF-induced heating of active implantable medical devices (AIMDs) during magnetic resonance imaging (MRI) scans at 1.5 T. Two commercially available AIMDs, a 40-cm lead length peripheral nerve stimulator (PNS) and a 60-cm lead length spinal cord stimulator (SCS), were utilized. In the in vitro study, lead-tip heating was calculated using the transfer function (TF) method and compared to direct measurement results for strain relief loops at various locations. In the human model analysis, RF-induced heating along six PNS and two SCS trajectories within the Duke, Ella, and FATS models was evaluated for strain relief loops positioned at various locations along the implantation trajectories. From the in vitro study, we can see up to a 48.3% reduction in the overall lead-tip heating. Inappropriate placement may result in doubled temperature rises. Significant temperature rise variation (up to 9 degrees C) is observed with loop position, loop diameter, number of turns, and patient landmark. Differentiation of cumulative summation analysis is necessary to comprehend the strain relief loop's effect on RF-induced heating. The findings suggest that strategically placing the loop can effectively mitigate RF-induced heating for AIMDs exposed to 1.5-T MR environments.

PURPOSE:To address the issue of RF-induced heating for partially in and partially out (PIPO) medical devices during 1.5 T MRI scans by proposing a method of minimizing the external portion. METHODS:A method of tightly winding the external segment of the PIPO device is proposed to minimize the overall device effective reception length during MRI scans to mitigate the RF-induced heating. Two commercially available PIPO medical devices and simplified solid wires were used to demonstrate the concept. RF heating results are compared between typical and minimized-length trajectories under the American Society for Testing and Materials (ASTM) testing procedure. In addition, 16 scaled and validated device models were used in conjuncture with human body numerical simulations within three virtual human models to estimate clinically relevant heating. RESULTS:The wound segments in PIPO devices functioned as a lumped element rather than a receiving antenna, reducing induced energy/heating as compared to the original PIPO devices under typical straight or loop configurations. Minimizing the lead's external portion can reduce the RF-induced heating by significant factors for all studied cases during ASTM phantom measurements and in human body simulations. CONCLUSION:Our findings show a significant reduction in RF heating by minimizing the external segment, thereby enhancing patient safety during 1.5 T MRI procedures. Although limited to four devices at 1.5 T across two applications, the extent of heating reduction may vary for others. Nonetheless, tightly winding the external segment of PIPO electrodes holds promise for improving device safety under MRI.

The 60-year history of the International Symposium on Antennas and Propagation is summarized. A list of locations, general chairs, and technical programs chairs from 1963 to the present is presented.

In this article, a convolutional neural network (CNN) model is proposed to predict the in vitro radio frequency (RF)-induced heating of complex-shaped passive implantable medical devices (PIMDs) under magnetic resonance imaging (MRI). The electromagnetic (EM) simulation meshes and incident electric field on the mesh grids are used as the input of the CNN model while the network output corresponds to the RF-induced 1-g specific absorption rate (SAR). A convergence analysis is performed to understand the effectiveness of the method. A discussion on selecting the training dataset size is presented using a principal component analysis (PCA) algorithm. Results demonstrate the robustness of the CNN model for the prediction of RF-induced heating from complex-shaped PIMDs under MR exposure.

The Radiofrequency (RF)‐induced heating for an active implantable medical device (AIMD) with dual parallel leads is evaluated in this paper. The coupling effects between dual parallel leads are studied via simulations and experiments methods. The global transfer function technique is used to assess the RF‐induced heating for dual‐lead AIMDs inside four human body models.

It has been 50 years since Professor Yahya Rahmat-Samii received his MS degree from the University of Illinois, Urbana-Champaign. The year 2023, marks the anniversary of his 75th year on earth. We highlight the many fields where Professor Rahmat-Samii has made pioneering contributions. He is a true leader in electro magnetics and antennas and has made a tremendous impact in research, on students and colleagues, in service to the greater good, and in leadership.

Almost 40 years after the initial development of the dielectric resonator antenna, a large number of variations based on the original design have been proposed, and some recently integrated into modern telecommunications equipment. As a class of radiators, they have been shown to be efficient at high frequencies with relatively large bandwidths. An early history of the design and development of this antenna is presented to document the processes which led to the original innovation.

PURPOSE:To assess RF-induced heating hazards in 1.5T MR systems caused by body-loop postures.METHODS:Twelve advanced high-resolution anatomically correct human body models with different body-loop postures are created based on poseable human adult male models. Numerical simulations are performed to assess the radiofrequency (RF)-induced heating of these 12 models at 11 landmarks. A customized phantom is developed to validate the numerical simulations and quantitatively analyze factors affecting the RF-induced heating, eg, the contact area, the loop size, and the loading position. The RF-induced heating inside three differently posed phantoms is measured.RESULTS:The RF-induced heating from the body-loop postures can be up to 11 times higher than that from the original posture. The RF-induced heating increases with increasing body-loop size and decreasing contact area. The magnetic flux increases when the body-loop center and the RF coil isocenter are close to each other, leading to increased RF-induced heating. An air gap created in the body loop or generating a polarized magnetic field parallel to the body loop can reduce the heating by a factor of three at least. Experimental measurements are provided, validating the correctness of the numerical results.CONCLUSION:Safe patient posture during MR examinations is recommended with the use of insulation materials to prevent loop formation and consequently avoiding high RF-induced heating. If body loops cannot be avoided, the body loop should be placed outside the RF transmitting coil. In addition, linear polarization with magnetic fields parallel to the body loop can be used to circumvent high RF-induced heating.

Purpose The paper presents a novel method to reduce the RF-induced heating of active implantable medical devices during MRI. Methods With the addition of an energy decoying and dissipating structure, RF energy can be redirected toward the dissipating rings through the decoying conductor. Three lead groups (45 cm-50 cm) and 4 (50 cm-100 cm) were studied in 1.5 Tesla MR systems by simulation and measurement, respectively. In vivo modeling was performed using human models to estimate the RF-induced heating of an active implantable medical device for spinal cord treatment. Result In the simulation study, it was shown that the peak 1g-averaged specific absorption rate near the lead-tips can be reduced by 70% to 80% compared to those from the control leads. In the experimental measurements during a 2-min exposure test in a 1.5 Telsa MR system, the temperature rises dropped from the original 18.3celcius, 25.8celcius, 8.1celcius, and 16.1celcius (control leads 1-4) to 5.4celcius, 6.9celcius, 1.6celcius, and 3.3celcius (leads 1-4 with the energy decoying and dissipation structure). The in vivo calculation results show that the maximum induced temperature rise among all cases can be substantially reduced (up to 80%) when the energy decoying and dissipating structures were used. Conclusion Our studies confirm the effectiveness of the novel technique for a variety of scanning scenarios. The results also indicate that the decoying conductor length, number of rings, and ring area must be carefully chosen and validated.

PURPOSE:During MR scans, abandoned leads from active implantable medical devices (AIMDs) can experience excessive heating at the lead tip, depending on the type of termination applied to the proximal contacts (proximal end treatment). The influence of different proximal end treatments (ie, [1] freely exposed in the tissue, [2] terminated with metal in contact with the tissue, or [3] capped with plastic, and thereby fully insulated, on the RF-induced lead-tip heating) are studied. A technique to ensure that MR Conditional AIMD leads remain MR Conditional even when abandoned is recommended. METHODS:Abandoned leads from three MR Conditional AIMDs ([1] a sacral neuromodulation system, [2] a cardiac rhythm management pacemaker system, and [3] a deep brain stimulator system) were investigated in this study. The computational lead models (ie, the transfer functions) for different proximal end treatments were measured and used to assess the in vivo lead-tip heating for four virtual human models (FATS, Duke, Ella, and Billie) and compared with the lead-tip heating of the complete MR Conditional AIMD system. RESULT:The average and maximum lead-tip heating for abandoned leads proximally capped with metal is always lower than that from the complete AIMD system. Abandoned leads proximally insulated could lead to an average in vivo temperature rise up to 3.5 times higher than that from the complete AIMD system. CONCLUSION:For the three investigated AIMDs under 1.5T MR scanning, our results indicate that RF-induced lead-tip heating of abandoned leads strongly depends on the proximal lead termination. A metallic cap applied to the proximal termination of the tested leads could significantly reduce the RF-induced lead-tip heating.

PURPOSE:This paper presents a method to search for the worst-case configuration leading to the highest RF exposure for a multiconfiguration implantable fixation system under MRI. METHODS:A two-step method combining an artificial neural network and a genetic algorithm is developed to achieve this purpose. In the first step, the level of RF exposure in terms of peak 1-g and/or 10-g averaged specific absorption rate (SAR1g/10g ), related to the multiconfiguration system, is predicted using an artificial neural network. A genetic algorithm is then used to search for the worst-case configuration of this multidimensional nonlinear problem within both the enumerated discrete sample space and generalized continuous sample space. As an example, a generic plate system with a total of 576 configurations is used for both 1.5T and 3T MRI systems. RESULTS:The presented method can effectively identify the worst-case configuration and accurately predict the SAR1g/10g with no more than 20% of the samples in the studied discrete sample space, and can even predict the worst case in the generalized continuous sample space. The worst-case prediction error in the generalized continuous sample space is less than 1.6% for SAR1g and less than 1.3% for SAR10g compared with the simulation results. CONCLUSION:The combination of an artificial neural network with genetic algorithm is a robust technique to determine the worst-case RF exposure level for a multiconfiguration system, and only needs a small amount of training data from the entire system.