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MR Coils and Simulation

Research profil

Bio-effects of MRI gradient systems

Fast switching MRI gradient fields induce electric fields (E-fields) in the patient that can become strong enough to cause peripheral nerve stimulation (PNS). PNS has become a significant limitation for gradient performance, and therefore speed and resolution of MR imaging. Our group has developed and successfully validated a simulation framework to predict PNS thresholds in detailed electromagnetic body models coupled with neurodynamic models of the largest peripheral nerves. These simulations allow us to study the mechanisms underlying PNS in MRI and to evaluate various mitigation techniques such as the design of gradient coils with inherently higher PNS thresholds. Since it is a growing safety concern that very high E-field amplitudes could potentially stimulate the heart muscle, we have recently extended our simulations towards prediction of cardiac stimulation thresholds to evaluate safe limits for MRI gradients.

Human body model and nerve atlas for prediction of peripheral nerve stimulation (Davids et al., Sci Rep, 2017).
Prediction of electromagnetic cardiac stimulation in human and animal body models for investigation of safety limits for MRI gradients (Klein et al., ISMRM, 2020).

RF systems and techniques

We develop radio-frequency (RF) methods for Magnetic Resonance Imaging and Spectroscopy (MRI/MRS) and conduct electromagnetic field simulations for RF safety. Special focus is set on high-resolution proton MRI of kidneys as a pre-clinical tool at 3T and 9.4T. Furthermore, we work on improving the signal-to-noise ratio (SNR) for X-nuclei MRI in the human body at 3T, and for preclinical research at 9.4T.

Cationized-Ferritin ex-vivo mouse kidney scanned at 9.4 T with a cryogenically cooled quadrature coil (Bruker BioSpin GmbH, Germany). 25 µm isotropic resolution.
3 different stacked receive-only coils to a 3 coil base Rx array to enhance prostate MRI at 3T.

Current research projects

  • Design of gradient coils with reduced PNS
  • Development and validation of simulations of electromagnetic cardiac stimulation
  • High-resolution imaging of glomeruli in ex-vivo rodent kidneys at 9.4 and 3T
  • 35Cl/23Na/1H RF resonator systems for preclinical imaging at 9.4T
  • Human abdominal, spine and head RF resonators for X-nuclei imaging

Equipment

  • Scanners: 

    • 0.5T portable MRI system (Pure Devices GmbH, Germany)
    • 1 and  9.4T pre-clinical MRI Systems (Bruker BioSpin GmbH, Germany)
    • 1.5 and 3T clinical MRI systems (Siemens Healtcare GmbH, Germany)

  • RF laboratory (equipped with 2 NWA)
  • EM field simulation software: CST (Computer Simulation Technology AG, Germany) & Sim4Life (Zurich MedTech, Switzerland)

Recent publications

  • V. Klein, M. Davids, L. Schad, L. Wald and B. Guérin.
    Investigating cardiac stimulation limits of MRI gradient coils using electromagnetic and electrophysiological simulations in human and canine body models.
    Magn Reson Med, 85(2), p. 1047-1061 (2021).
  • M. Davids, B. Guérin, V. Klein and L. Wald.
    Optimization of MRI gradient coils with explicit peripheral nerve stimulation constraints.
    IEEE Trans Med Imag, 40(1), p. 129-142 (2021).
  • J. Chacón Caldera, A. Maunder, M. Rao, G. Norquay, O. Rodgers, M. Clemence, C. Puddu, L. Schad and J. Wild.
    Dissolved hyperpolarized Xenon-129 MRI in human kidneys.
    Magn Reson Med, 83(1), p. 262-270 (2020).
  • M. Davids, B. Guérin, V. Klein, M. Schmelz, L. Schad and L. Wald.
    Optimizing selective stimulation of peripheral nerves with arrays of coils or surface electrodes using a linear peripheral nerve stimulation metric.
    J Neural Eng, 17(1), 016029 (2020).
  • M. Davids, B. Guérin, L. Schad and L. Wald.
    Peripheral nerve stimulation modeling for MRI.
    eMagRes, 8(2), p. 87-102 (2019).
  • M. Davids, B. Guérin, A. vom Endt, L. Schad and L. Wald.
    Prediction of peripheral nerve stimulation thresholds of MRI gradient coils using coupled electromagnetic and neurodynamic simulations.
    Magn Reson Med, 81(1), p. 686-701 (2019).
  • V. Klein, M. Davids, L. Wald, L. Schad and B. Guérin.
    Sensitivity analysis of neurodynamic and electromagnetic simulation parameters for robust prediction of peripheral nerve stimulation.
    Phys Med Biol, 64(1), p. 015005 (2019).
  • M. Malzacher, J. Chacón Caldera, N. Paschke and L. Schad.
    Feasibility study of a double resonant (1 H/ 23Na) abdominal RF setup at 3T.
    Z Med Phys, 29(4), p. 359-367 (2019).
  • M. Malzacher, J. Chacón Caldera, N. Paschke and L. Schad.
    Feasibility study of a double resonant 8-channel 1H/ 8-channel 23Na receive-only head coil at 3 Tesla.
    Magn Reson Med, 59, p. 97-104 (2019).

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