The overall aim of this project is to apply advances in finite/discrete element modelling techniques to analyse stress distributions in magnets used in Magnetic Resonance Imaging (MRI).
Figure 1 below shows a typical MRI apparatus. Figure 2 shows a typical coil configuration of a magnet with four coils supported by coil formers.
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| Figure 1: A typical
MRI apparatus, showing the magnet. |
Figure 2: Cross-section of a typical coil configuration,
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Dr Riyu Wei of the University of Queensland, working with Magnetica Ltd, a Brisbane-based company specializing in the design and development of high performance magnets for use in advanced magnetic resonance imaging (MRI) equipment, has developed a stress analysis program for MRI magnets using ANSYS Parametric Design Language and the C language. More than 50 cases of thermal and mechanical stress analysis have been studied for magnets of varying field strengths (1.5 - 9.5 Tesla). This analysis simulated the processes of cooling down the magnets from room temperature (300K) to the liquid helium working temperature (4K), and the substantial thermal stresses in the structure; and charging up of the field coils to the full current (100-500 Amp). Varying levels of analysis ranging from preliminary/macro to detail/micro scales have been performed. The analysis outputs include deformations, stresses and strains as well as strain energies in coils and formers (see progress report below). Figure 3 below shows the meshes of a magnet and the deformation of the magnet due to Lorentz forces. This analysis is similar to that performed for blast modelling.
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Figure 3a: Mesh grid of the magnet |
Figure 3b: Deformation of the magnet due to the
strong magnetic field. |
Figure 4 shows typical results of stress analysis performed on the magnets.
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| Figure 4a: Stress distribution in coils and formers of the magnet. | Figure 4b: Stress distribution in rectangular wires of a coil. |
Based on the stress analysis results, magnetic, structural and winding optimizations of magnets have been undertaken to improve product designs in both cost effectiveness and performance.
As a result of this work, Magnetica with its partners successfully tendered for design of a new type of MRI magnet and development of a new specialist MRI magnet. The prototype for the first product is in development and expected to be completed by December 2006; the first manufacturing run is expected to commence June 2007.
Participants
Dr Riyu Wei
ACMC, University
of Queensland
Industry Participant
Reports
Final Report - November 2007
(209 KB PDF)
2nd Extension Proposal - (59 KB
PDF)
Final Report - August 2007 (28 KB
PDF)
Progress Report - March 2007
(66 KB PDF)
Progress Report - November 2006
(565 KB PDF)
Extension Proposal - July 2006 (57
KB PDF)
Final Report - August 2006 (509
KB PDF)
Progress Report - Dec 2005
(62 KB PDF)
Project Proposal (62 KB PDF)