Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Master's) -- Bilkent University, 2010.Includes bibliographical references leaves 36-38.Magnetic resonance imaging (MRI) is widely used diagnosis technique. During
MRI radio frequency (RF) fields are utilized to excite the spins. If these RF fields
incidence on metallic implants, currents will be induce on the metallic parts of
implants. Inside the body these induced currents on metallic implants cause
heating of tissue and sometimes cause severe burning of tissue. This phenomena
makes MRI hazardous for patients with metallic implants. Much work has been
done to understand this phenomena. However, most of these work based on
purely experimental or numerical methods. So to understand and to obtain a
good intuition on this problem a lot of cases must be solved computationally or
tested experimentally.
In this study lumped element model of the transmission line is modified in
order to model the conductive wires of implants inside the body. This model is
based on the similarity between the damped oscillatory behavior of transmission
line currents and induced currents on wires inside the body. A voltage source is
added to model the effect of the incident electric field. Voltages and currents on a
infinitesimally small portion of wire are solved. Solving currents and voltages simultaneously
on the modified lumped element model lead to a non-homogeneous
differential equation for the current. The solution of this differential equation
gives the analytical solution for the induced current on the implant lead. To
test the validity of this solution, wire under the uniform incident electric field is
solved with the Modified Transmission Line Method (MoTLiM) and compared to
Methods of Moment (MoM) solution. The results are also verified using phantom
experiments. For experimental verification, the distorted flip angle distribution
due to induced currents are measured using flip angle imaging techniques. In
addition to this, the flip angle distribution around the wire is calculated using
results obtained from MoTLiM. Finally these results are compared and an error
analysis is carried out.Açıkel, VolkanM.S