Simulations and Comparative Study of Very-Low-Field MRI

Abstract

Magnetic resonance imaging (MRI) scanners are expensive, stationary, and not suitable for patients with metal implants. Low-field MRI machines, ranging from 1 mT to 100 mT, reduce these limitations. Despite high inhomogeneity and lower MR signal quality, recent improvements in low-field MRI image quality have gained attention. Very-Low-Field magnetic resonance imaging (VLF-MRI) is a project by Aalto University AMRI (accessible magnetic resonance imaging) group which designed a VLF-MRI prototype scanner.

Currently, no simulator software package has been built specifically for very-low field MRI, despite the fact that many have been created for MR imaging in the high field. Therefore, the purpose of this thesis was to customize an existing MRI simulator software package by researching processes that impact the quality of magnetic fields and making the necessary modifications to enable simulation at very low magnetic fields. This thesis focused on modelling the VLF-MRI system in MRiLab simulations as well as on comparison of the current VLF-MRI prototype with the VLF-MRI in simulations. Simulation and VLF-MRI comparison involved several stages starting with the customizing the MRiLab simulator by designing phantoms, obtaining a magnetic field from VLF-MRI prototype and using it in simulations. Furthermore free induction decay output from MR signal simulations and outputs in VLF-MRI prototype were compared and analyzed. Additionally this thesis studied the most common MRI sequences and performed simulations for future comparison and use in VLF-MRI prototype.

This thesis developed a VLF-MRI simulator using MRiLab software, comparing simulation results with the prototype. The simulator was improved and tested against free induction decay pulse responses, ensuring the prototype responses matched simulation responses. Additional MRiLab simulations were used to evaluate multiple sequences in preparation for any future comparisons.