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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°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.

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 influence of the accuracy level for whole-body birdcage coil models on electromagnetic exposure estimations was evaluated using three anatomical human body models located at the head landmark position. Both generic and vendor-specific birdcage coil models were created and analyzed using a radio-frequency (RF) circuit and a three-dimensional electromagnetic (EM) co-simulation approach to evaluate EM properties of the coil used in a commercial 3T magnetic resonance imaging (MRI) scanner. The fidelity of the coil geometry and excitation, as well as consideration of permissible variations of the coil electrical components and capacitor losses, had a significant impact on the estimated electric field distributions inside the human models. Therefore, the variety of electric fields generated in humans should be carefully considered for a reliable RF safety assessment of a patient with a passive or active implant undergoing a scan in a modern MRI scanner with dual-channel transmit RF coils.

In this paper, the impact of the electrode structure on radio-frequency (RF) induced heating near an active implantable medical device implanted lead under magnetic resonance imaging exposure is investigated. The specific absorption rate (SAR) distributions and the temperature rises of the leads with different electrodes were assessed. It is shown that increasing the size of the lead electrode reduces the SAR distribution and temperature rise near the electrode. Our results indicate that a larger electrode size will reduce the magnitudes of the lead transfer function, subsequently reducing the heating effect near the electrode. Both numerical simulations and experimental measurements were performed to verify the effectiveness of a large electrode in mitigating the RF-induced heating.

This study investigates variations in radiofrequency- (RF-) induced energy absorption by orthopedic plates within the human body during 1.5T and 3T magnetic resonance imaging (MRI) scans, considering diverse postures. Using the poseable Duke model, we developed typical postures (O-posture, X-posture, Y-posture, and Z-posture) and placed anatomically correct representations of various orthopedic plates within these postures. Numerical simulations were conducted to evaluate electromagnetic fields and RF-induced energy absorption in these postures near orthopedic plates during MRI scans. Comparing RF-induced energy absorption (peak spatial averaged SAR over 1 g, pSAR1g) in postured models to the original posture reveals substantial variations. The pSAR1g differences for X-posture, Y-posture, and Z-posture reach 48%, 134%, and 32% at 1.5T, and 36%, 83%, and 101% at 3T, respectively. Changing posture can lead to higher or lower pSAR1g. These findings underscore the impact of patient posture on RF-induced energy absorption in orthopedic plates on the ulna bone. The study recommends considering representative body postures in future evaluations for MR conditional labeling of passive implants. Until then, maintaining a neutral posture during MR scans is advised to mitigate unforeseen RF-induced heating risks.

Over the past decades, significant improvements have been made in the field of computational human phantoms (CHPs) and their applications in biomedical engineering. Their sophistication has dramatically increased. The very first CHPs were composed of simple geometric volumes, e.g., cylinders and spheres, while current CHPs have a high resolution, cover a substantial range of the patient population, have high anatomical accuracy, are poseable, morphable, and are augmented with various details to perform functionalized computations. Advances in imaging techniques and semiautomated segmentation tools allow fast and personalized development of CHPs. These advances open the door to quickly develop personalized CHPs, inherently including the disease of the patient. Because many of these CHPs are increasingly providing data for regulatory submissions of various medical devices, the validity, anatomical accuracy, and availability to cover the entire patient population is of utmost importance. This paper is organized into two main sections: the first section reviews the different modeling techniques used to create CHPs, whereas the second section discusses various applications of CHPs in biomedical engineering. Each topic gives an overview, a brief history, recent developments, and an outlook into the future.

One of the major components of magnetic resonance imaging safety for patients with an active implantable medical device is the evaluation of in vivo radio frequency induced heating of tissue near a lead electrode, which can result in tissue damage. This numerical case study investigated a number of the recommendations, assumptions, and requirements of Clause 8 of the technical specification ISO/TS10974. For this, a lead electromagnetic model (LEM) of a generic coax lead at 128 MHz was evaluated with 3-D electromagnetic and thermal cosimulations of the entire lead. Two sets of 120 incident electric fields with different profiles were generated in a homogenous medium using the electrical properties of blood by an array of four antennas. Substantial dependence of power deposition and temperature profiles around lead electrodes on the incident electric field did not reduce the quotient of the variances of the fitted LEM values, observed values of power deposition, and the net temperature increase, above background, with the presence of the generic coax lead. Our results indicate that the power injection approach based only on the comparison of the temperature increase in the medium along the lead tip electrode axis can result in substantial underestimation or overestimation of power deposition around lead electrodes.

IMPORTANCE: Airline pilots and cabin crew are occupationally exposed to higher levels of cosmic and UV radiation than the general population, but their risk of developing melanoma is not yet established. OBJECTIVE: To assess the risk of melanoma in pilots and airline crew. DATA SOURCES: PubMed (1966 to October 30, 2013), Web of Science (1898 to January 27, 2014), and Scopus (1823 to January 27, 2014). STUDY SELECTION: All studies were included that reported a standardized incidence ratio (SIR), standardized mortality ratio (SMR), or data on expected and observed cases of melanoma or death caused by melanoma that could be used to calculate an SIR or SMR in any flight-based occupation. DATA EXTRACTION AND SYNTHESIS: Primary random-effect meta-analyses were used to summarize SIR and SMR for melanoma in any flight-based occupation. Heterogeneity was assessed using the χ2 test and I2 statistic. To assess the potential bias of small studies, we used funnel plots, the Begg rank correlation test, and the Egger weighted linear regression test. MAIN OUTCOMES AND MEASURES: Summary SIR and SMR of melanoma in pilots and cabin crew. RESULTS: Of the 3527 citations retrieved, 19 studies were included, with more than 266 431 participants. The overall summary SIR of participants in any flight-based occupation was 2.21 (95% CI, 1.76-2.77; P < .001; 14 records). The summary SIR for pilots was 2.22 (95% CI, 1.67-2.93; P = .001; 12 records). The summary SIR for cabin crew was 2.09 (95% CI, 1.67-2.62; P = .45; 2 records). The overall summary SMR of participants in any flight-based occupation was 1.42 (95% CI, 0.89-2.26; P = .002; 6 records). The summary SMR for pilots was 1.83 (95% CI, 1.27-2.63, P = .33; 4 records). The summary SMR for cabin crew was 0.90 (95% CI, 0.80-1.01; P = .97; 2 records). CONCLUSIONS AND RELEVANCE: Pilots and cabin crew have approximately twice the incidence of melanoma compared with the general population. Further research on mechanisms and optimal occupational protection is needed.

This paper presents the design, optimization, realization and verification of novel whole-body exposure setups for rats. The setups operating at 902 MHz and 1747 MHz provide highly efficient, National Toxicology Program (NTP) compatible and well-characterized exposures. They are compared to existing concepts of exposure setups with respect to efficiency, induced field uniformity, good laboratory practice (GLP) compatibility and cost. The novel exposure setup consists of a circular cascade of 17 sectorial waveguides excited by a novel loop antenna placed in the centre. The 70% overall efficiency of the exposure setup surpasses comparable values of existing setups. A field uniformity inside the phantom of more than 86% for the 1g cubical averaged specific absorption rate (SAR) within ±5 dB of the whole-body SAR (WB-SAR) was attained. The uniformity of the exposure inside the setup, defined as the variation of the WB-SAR between animals, was better than ±24%. Using only stainless steel, gold and polycarbonate in the vicinity of the animals ensured full GLP compatibility. The entire exposure system features fully automated computer controlled exposure and data monitoring, data storing and failure handling. Therefore, the proposed exposure system can be used to run blinded large scale, long-term exposure studies.

This paper presents new definitions for obtaining reproducible results in numerical phone dosimetry. Numerous numerical dosimetric studies have been published about the exposure of mobile phone users which concluded with conflicting results. However, many of these studies lack reproducibility due to shortcomings in the description of the phone positioning. The new approach was tested by two groups applying two different numerical program packages to compare the specific anthropomorphic mannequin (SAM) to 14 anatomically correct head models. A novel definition for the positioning of mobile phones next to anatomically correct head models is given along with other essential parameters to be reported. The definition is solely based on anatomical characteristics of the head. A simple up-to-date phone model was used to determine the peak spatial specific absorption rate (SAR) of mobile phones in SAM and in the anatomically correct head models. The results were validated by measurements. The study clearly shows that SAM gives a conservative estimate of the exposure in anatomically correct head models for head only tissue. Depending on frequency, phone position and head size the numerically calculated 10 g averaged SAR in the pinna can be up to 2.1 times greater than the peak spatial SAR in SAM. Measurements in small structures, such as the pinna, will significantly increase the uncertainty; therefore SAM was designed for SAR assessment in the head only. Whether SAM will provide a conservative value for the pinna depends on the pinna SAR limit of the safety standard considered.

Formal methods for the description of spatial relations can be based on mathematical theories of order. Subdivisions of land are represented as partially ordered sets (posets), a model that is general enough to answer spatial queries about inclusion and containment of spatial areas. After a brief introduction to the basic concepts of posets and lattices, their applications to modelling spatial relations and operations for spatial regions in terms of containment and overlay are presented. An interpretation is given for new geographical elements that are created by the completion from a poset to a lattice. It is shown that a novel approach to characterize certain topological relations based on a lattice of a simplicial complex is a model for spatial regions that combines both topological and order relations and allows spatial queries to be answered in a unified way.

A realistic model for a condenser microphone is theoretically investigated. The model consists of a rigid cylinder closed on the bottom by a membrane and on the top by a rigid plate. The cylinder is divided into two chambers by an electrode with a number of small holes. This coupled acoustic system is mathematically treated by an operator formalism. Each part of the system (outer space, membrane, electrode, two chambers) corresponds a linear operator in a Hilbert space. The interfaces (membrane, electrode with holes) correspond to state vectors in this Hilbert space. Applying Green’s integral formula leads to a system of equations in this space, corresponding conventionally to integral equations with Green’s functions as kernels. By approximating the operators of the two chambers by multiples of the identity operator (i.e., conventionally replacing the singular Green’s function by multiples of the Dirac delta function) it is possible to solve the problem analytically, taking into account exactly the pattern of the holes in the electrode, thus avoiding an approximation made in the preceding paper. The agreement with experiment is very satisfactory. © 1996 Acoustical Society of America.

In this work an analytical model for a condenser microphone with a pattern of holes in the electrode is solved approximately by applying an operator method of quantum mechanics. Essential is the replacement of the operators corresponding to the Green’s functions of the cylinder in the fundamental integral equations of the system by products of identity operators times an appropriately chosen constant. The second approximation is the averaging of the holes and by replacing the effect of the holes in the electrode by a product of the identity operator times the part of the area of the small holes in the electrode compared to the whole area of the electrode. The last approximation is the replacement of the displacement of the fluid in the small holes by their mean value and the assumption of small holes compared to the total area of the electrode. By a summation method over zeros of Bessel functions it is possible to do infinite summations exactly and to provide an analytical solution of the average displacement of the membrane as a function of the frequency of the incoming plane wave. The approximations are justified by the good agreement with experiment. © 1996 Acoustical Society of America.

The confinement in compact QED is known to be related to magnetic monopoles. Magnetic currents form a solenoid around electric flux lines between a pair of electric charges. This behaviour can be described by the dual version of Maxwell—London equations including a fluctuating string. We use a definition of magnetic monopole currents adjusted to the definition of the electric field strength on a lattice and get good agreement for field and current distributions between compact QED and the predictions of dual Maxwell—London equations. Further we show that the monopole fluctuations in the vacuum are suppressed by the flux tube.

The total product life cycle (TPLC) of medical devices has been defined by four stages: discovery and ideation, regulatory decision, product launch, and postmarket monitoring. Manufacturers of medical devices intended for use in the peripheral vasculature, such as stents, inferior vena cava (IVC) filters, and stent-grafts, mainly use computational modeling and simulation (CM&S) to aid device development and design optimization, supplement bench testing for regulatory decisions, and assess postmarket changes or failures. For example, computational solid mechanics and fluid dynamics enable the investigation of design limitations in the ideation stage. To supplement bench data in regulatory submissions, manufactures can evaluate the effects of anatomical characteristics and expected in vivo loading environment on device performance. Manufacturers might also harness CM&S to aid root-cause analyses that are necessary when failures occur postmarket, when the device is exposed to broad clinical use. Once identified, CM&S tools can then be used for redesign to address the failure mode and re-establish the performance profile with the appropriate models. The Center for Devices and Radiological Health (CDRH) wants to advance the use of CM&S for medical devices and supports the development of virtual physiological patients, clinical trial simulations, and personalized medicine. Thus, the purpose of this paper is to describe specific examples of how CM&S is currently used to support regulatory submissions at different phases of the TPLC and to present some of the stakeholder-led initiatives for advancing CM&S for regulatory decision-making.

This paper presents a novel approach for simulation validation by combining systematic, National Institute of Standards and Technology-guideline-based uncertainty assessment with the gamma dose distribution comparison method, and applies the approach to simulated and measured complicated pressure distributions in the field of focused ultrasound. Simulations require verification and validation to demonstrate that they correctly implement the underlying model and sufficiently capture the real-world behavior of the system of interest within the context-of-use. Uncertainty assessment is necessary to determine the quality (strength, success, and range) of the validation. The combined approach of systematic uncertainty evaluation and the gamma-method presented herein permits thorough validation with meaningful and reasonable tolerances (expanded uncertainty: 1.04 dB = 12.7%, 1.88 wavelengths), whereas point-wise comparison would have resulted in an unacceptably large uncertainty (>10 dB) due to the impact of distortion. The approach presented also provides a scalar agreement metric and a natural means of visualizing areas of disagreement. Verification is achieved by identifying the critical physical and numerical phenomena and ascertaining correct handling by means of analytical and numerical benchmarks. The generality of the verification and validation approach presented makes it applicable to a wide range of computational models, beyond the highlighted acoustic simulations.

Common bean (Phaseolus vulgaris L.) was introduced in Europe from both Mesoamerican and Andean centers of origin and has been cultivated in central Europe for centuries. The first objective of this study was to evaluate genetic diversity and the population structure of 167 accessions divided into four groups according to geographical origin (Slovenia and Austria) and time periods (historical and present) using 14 simple sequence repeat (SSR) markers. The second objective was to improve our understanding of the pathways of dissemination and the evolution of this species in central Europe. Great allelic polymorphism was detected in all four groups of examined accessions, indicating that Slovene and Austrian bean gerinplasm in the past possessed significant variation that has been well preserved until today. In factorial correspondence analysis, accessions from different groups clustered together indicating potential gene flow between countries. The uncovered diversity corresponded very well to the two recognized gene pools (Andean and Mesoamerican). The majority of accessions in every single group belonged to the Andean gene pool. Strong predominance of Andean genotypes classifies Slovenia among other Mediterranean countries, like Spain and Italy. The latter appears as a most probable source of first beans in Slovenia and Austria. We assume that in the beginning of the previous century after very tight relationships between Slovenia and Austria loosened, introgression of genotypes from western and northern European countries took place in Austria, which resulted in a very high proportion of Mesoamerican genotypes that we found in the present Austrian germplasm (44%). Several putative hybrids between the Andean and Mesoamerican gene pools were detected in this study. Evolutionary significance, origin, and breeding potential of these recombinants are discussed here. [ABSTRACT FROM AUTHOR]