Summary
Knowledge of the electrical properties (EP, conductivity and permittivity) of human tissues is required to estimate, by numerical simulation, the heating of tissues during an MRI examination in the presence of implanted or accessory medical devices. Currently, simulations assume that EP values in a given tissue are the same for each patient (values obtained from ex-vivo studies on animals), regardless of age or sex.
The aim of ELECTRA is to develop new MRI tools for imaging EP in-vivo. Our original approach relies on new reconstruction methods which are robust to transitions of EP at interfaces between tissues. By creating a database of 120 subjects with marked differences in age, we will be able to validate those measures, to establish reference values in humans as a function of age, and to interpret the observed variations across the population. Finally those results will be applied to MRI safety investigations for medical devices (Healtis company).
The consortium comprises three academic teams who have already worked together to develop MRI of EP, with complementary expertise in MRI reconstruction (IADI), acquisition and MRI signal modelling (ICUBE) and solving inverse problems associated with Maxwell equations (LMR). The Healtis company will bring its expertise in MR-compatibility (simulation and testing) and will transfer the results to new services. CIC-IT will provide support for constituting the volunteer database and for its dissemination.
The economic impact of ELECTRA affects the market of implanted medical devices, in particular active devices (cardiac and neurologic stimulators, cochlear implants etc…), which is growing fast. The issue of MR-compatibility of these devices is now essential. International standards regarding the assessment of heating risks in the case of passives devices (ASTM F2182) and active devices ((ISO/TS 10974) are evolving rapidly, and Healtis is actively participating in the workgroups of these standards. Electromagnetic simulation is increasingly present. The main challenge is to standardize the methods for validating patient models (the precise EP values for tissues, and their variability across the population, are still an open question), device models, and simulation results in terms of specific absorption rate (SAR) or temperature elevation in the patient.
The scientific ambition of ELECTRA is to make MR imaging of EP a new potential biomarker for diagnostic imaging. The new expected results in EP reconstruction (mathematics and applied methods) will be key to improve the technique, and to validate it in more and more realistic phantoms. The volunteer study will allow reference in-vivo PE values to be established for a wide range of tissues (head and trunc). This study is intended to be the first one to show in-vivo, in humans, age-related changes of conductivity in white matter, associated with structural changes.
The developments in ELECTRA will have many implications for diagnostic imaging (EP measurements as a new marker of fibrosis, inflammation, lesion severity etc…) and for the implementation of personalized SAR models. The latter will be useful for developing high-field MRI, but also for optimizing clinical MRI in general. Indeed, all MRI systems are currently restrained, based on SAR estimation in a worst-case scenario from generic patient models. A personalized SAR model, based on a patient-specific EP map, would allow these constraints to be relaxed. This would result in a gain in image quality and/or acquisition duration and ultimately an improvement in cost-efficiency of MRI.