Recording date: October 18, 2018
Magnetic Resonance Imaging (MRI) devices enjoy a good reputation as they can provide very detailed images of the human body without applying any ionizing x-ray dose. Behind the scenes, MRI requires an advanced interaction of various electromagnetic (EM) fields: a very strong, typically superconducting, static magnet together with strong gradient fields for the positioning and RF fields for the excitation of the molecular spins. All three field components have extreme requirements on homogeneity and precision. This level of simulation accuracy for the static and low freuquency (LF) fields can be best obtained by a numerical solver based on the Biot-Savart method as applied in the Opera tool. A multi-channel system is typically used for the RF coils. This can be simulated in CST Studio Suite, either with volumetric time or frequency domain solvers, coupled by a circuit simulator for tuning, matching and decoupling the individual coils.
The power-applied multi-physics effects also need to be considered, as thermal effects may occur at all levels. Superconducting coil overheating may result in the quenching of the coil, potentially leading to large stresses and deformation from Lorentz forces. Opera provides a special solver to analyze these effects. There are also many types of heating within the human body, which is typically not accessible to measurement. These need to be monitored with the Bioheat solver in CST Studio Suite as part of assessing the safety of the device.
The gradient fields also apply strong mechanical forces which need to be known in order to design the structure support of the coils and to avoid acoustic noise. Coupling the EM results to a numerical spin simulator based on the Bloch equation rounds off the MRI multi-physics multi-scale simulation environment, which is the topic of this eSeminar.’
Dr. Tilmann Wittig is a principal engineer with a focus on antennas, bio-medical simulations and computational dosimetry. Wittig was born in Leverkusen, Germany in 1972 and joined CST in 2004. He received his Dipl.-Ing. degree in telecommunications and his Ph.D. in electromagnetic simulation technology from the Technical University of Darmstadt, Germany
Mike Hook is a solution consultant at Dassault Systemes UK Ltd., working with Opera software since 2005. Hook received his degrees in physics and microwave technology from Imperial and University College in London. He specializes in applications that involve magnetic, charged-particle and high frequency analyses.