Ph.D. Dissertation Defense YUJIE QIU A Dynamic Magnetic Resonance Imaging (MRI) Phantom Based on Electric Field Induced Residual Dipolar

ChesterF Carlson Center for Imaging Science

Ph.D. Dissertation Defense

Yujie Qiu

A Dynamic Magnetic Resonance Imaging (MRI) Phantom Based on Electric Field Induced Residual Dipolar Couplings

Advisor: Dr. Joseph P. Hornak

Wednesday, 22 May 2013, 10am

Carlson Room76-1275

Abstract

Multi-center functional MRI (fMRI) research studies are advantageous but unavoidably introduce variations in the results due to differences in imager vendor, magnetic field strength, imaging pulse sequences, and many other aspects. These variations make combining data from different MRI centers risky. Even for a single MRI center, temporal variations over the course of a study can make combining data problematic.  Therefore, it is necessary in both situations to perform quality assurance (QA) measurements on a regular basis.  Unfortunately, there are no dynamic standards or phantoms as they are called in the MRI community, which can mimic the small, rapidly changing fMRI signal at a relatively large field-of-view (FOV) and number of magnetic field strengths. 

The goal of this research was to develop a dynamic phantom which mimics the signal change in fMRI and hence could be used for QA procedures related to fMRI.  A phantom was developed with a rapidly switchable MRI signal.  This phantom consisted of a geometric grid, eight vials with solutions of known proton spin-spin relaxation time (T₂) values, and a cylindrical electrical cell filled with a polar liquid, all surrounded by water. An electrical circuit was built to interface the phantom to an imager through the pulse sensor and produce pulsed electric (E) fields during the imaging sequence. The results of spin echo, echo planar imaging (SE-EPI) imaging sequence show that the signal changes by approximately 8% with the application of a 11.8 kV/m electric field. This change was found to be based on the residual dipolar couplings induced by the applied electric field, directly related to the size of the field, and switchable in 50 ms. 

This dissertation focuses on the underling physics and measurements made to discover the relationship between an applied electric field and the MRI signal, as well as the design and construction of a working, switchable signal phantom based on these findings.  The current working phantom has applications as a spin-spin relaxation time standard in quantitative MRI.  With higher electric fields, the phantom can also test the gradient echo-echo planar imaging (GR-EPI) imaging sequence used in fMRI.