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Tiers analysis based on ISO/TS 10974
According to ISO/TS 10974, the safety of MRI for patients with an active implantable medical device (AIMD) is assessed through a standard four-tier procedure. Tier 1 is the most conservative approach, that determines power deposition without requiring electromagnetic modelling, but leads to overestimation of the induced voltage. Tier 2 determines the electric field in the implant volume of interest based on electromagnetic modelling of human RF exposures. Tier 3 involves electromagnetic modelling to determine the tangential electric field along a device pathway and the development and validation of an AIMD model. Tier 4 provides the least overestimation but requires the most extensive electromagnetic computational modelling by assessing the AIMD model within anatomical models, for relevant RF exposure conditions.
Hyperthermia and thermal ablation
Hyperthermia is clinical procedure during which an external medical device (electromagnetic coil), often combined with magnetic nanoparticles injected in the patient’s bloodstream, is used mainly to treat cancer. The method delivers thermal energy to malignant cells causing their selective hyperthermic death at sub-ablative temperatures. Computationally, the procedure can be simulated through a series of electromagnetic and thermal simulations, where the specific absorption rate (SAR) and temperature increase are evaluated to ensure the patient’s safety.
Electric field (EF) modeling regards the numerical calculation of the induced electric field and is a valuable complementary approach to multiple clinical implementations of bioelectromagnetic medical applications. The relevant computational techniques commonly implement the Finite Element Method (FEM) or Boundary Element Method (BEM) to numerically calculate the induced by an electromagnetic source EF on a three-dimensional regular grid of voxels or a mesh of tetrahedra. The method can be applied to various models, from simple solids to realistic anatomical models, including either well-established high-resolution phantoms or custom-made personalized models, specially segmented to meet the requirements of each specific project.
The brain or neural stimulation is determined through analyzing the results of the electromagnetic simulations and comparing them to widely accepted threshold values from the corresponding literature, during the stage of post-process. The initial results evaluation is usually followed by an optimization analysis, where the parameters of simulation are progressively re until the optimal conditions for the stimulation are sufficiently approximated.
Safety and pre-compliance tests
Humans are constantly exposed to electromagnetic fields in the environment or due to medical or telecommunication devices, while the exposure can be estimated either computationally through numerical simulations or experimentally through measurements with proper equipment. Thess S.A. is highly experienced in the field of exposure assessment for safety and pre-compliance purposes.