title: Intra-coil interactions in split gradient coils in a hybrid MRI-LINAC system.
abstract: An MRI-LINAC system combines a magnetic resonance imaging (MRI) system with a medical linear accelerator (LINAC) to provide image-guided radiotherapy for targeting tumors in real-time. In an MRI-LINAC system, a set of split gradient coils is employed to produce orthogonal gradient fields for spatial signal encoding. Owing to this unconventional gradient configuration, eddy currents induced by switching gradient coils on and off may be of particular concern. It is expected that strong intra-coil interactions in the set will be present due to the constrained return paths, leading to potential degradation of the gradient field linearity and image distortion. In this study, a series of gradient coils with different track widths have been designed and analyzed to investigate the electromagnetic interactions between coils in a split gradient set. A driving current, with frequencies from 100 Hz to 10 kHz, was applied to study the inductive coupling effects with respect to conductor geometry and operating frequency. It was found that the eddy currents induced in the un-energized coils (hereby-referred to as passive coils) positively correlated with track width and frequency. The magnetic field induced by the eddy currents in the passive coils with wide tracks was several times larger than that induced by eddy currents in the cold shield of cryostat. The power loss in the passive coils increased with the track width. Therefore, intra-coil interactions should be included in the coil design and analysis process.
authors: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Fangfang
authors: F
authors: Tang
authors: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia; Department of Energy, Politecnico di Torino, Corso Duca Degli Abruzzi, 24, 10129 Torino, Italy.
authors: Fabio
authors: F
authors: Freschi
authors: Department of Electrical Engineering, Universitas Dian Nuswantoro, Jl. Imam Bonjol No. 207, Semarang, Indonesia.
authors: Hector
authors: H
authors: Sanchez Lopez
authors: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia; Department of Energy, Politecnico di Torino, Corso Duca Degli Abruzzi, 24, 10129 Torino, Italy.
authors: Maurizio
authors: M
authors: Repetto
authors: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia. Electronic address: feng@itee.uq.edu.au.
authors: Feng
authors: F
authors: Liu
authors: School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
authors: Stuart
authors: S
authors: Crozier
keywords: Eddy currents; Electromagnetic interactions; Gradient coil; MRI–LINAC