DEVELOPMENT OF RF COILS AND PULSING METHODS FOR NMR/MRI

Open Access
Author:
Park, Bu Sik
Graduate Program:
Bioengineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 08, 2009
Committee Members:
  • Christopher Collins, Dissertation Advisor
  • Christopher Collins, Committee Chair
  • Michael Smith, Committee Member
  • Andrew G Webb, Committee Member
  • Qing X Yang, Committee Member
  • Mohammad Reza Tofighi, Committee Member
Keywords:
  • Pulsing Method
  • RF Coil
  • MRI
Abstract:
Radiofrequency magnetic (B1) field inhomogeneity and absorbed power in sample and RF coil have been among the main causes for image degradation in magnetic resonance imaging (MRI) since its inception. The problem becomes more pronounced at high frequencies as wavelengths in tissue become shorter. To address these problems, we present methods for design, implementation, and evaluation of RF coils considering excitation uniformity and/or specific absorption rate (SAR) for high field nuclear magnetic resonance (NMR) and MRI. Specifically, we present 1) the design of a novel radiofrequency (RF) coil for imaging of histological slices of tissue using a 7.0 T MRI system, 2) numerical model of a dielectric resonator for high field MRI, 3) a method to separate conservative and magnetically-induced electric fields from numerical calculations for MR microscopy, 4) a simple method to decrease sample heating using conductive wires, 5) a numerical analysis of conservative and magnetically-induced electric field for low-frequency human imaging, 6) numerical calculation results for the B1 field and SAR evaluation in a 3T neonate head coil, and 7) design of a slice-selective array-optimized composite pulse to improve B1 uniformity and reduce SAR using an 8-channel transmit head array loaded with a head model. The methods and results presented here can provide very useful information for designing RF coils considering excitation uniformity and SAR simultaneously in high field MRI/NMR.