Quadrature RF Coil for In Vivo Brain MRI of a Macaque Monkey in a Stereotaxic Head Frame.

We present a quadrature volume coil designed for brain imaging of a macaque monkey fixed in a sphinx position (facing down the bore) within a stereotactic frame at 3 T, where the position of the monkey and presence of the frame preclude use of existing coils. Requirements include the ability to position and remove the coil without disturbing the position of the monkey in the frame. A saddle coil and a solenoid were combined on a modified cylindrical former and connected in quadrature as to produce a homogeneous circularly polarized field throughout the brain.

Faraday shields within a solenoidal coil to reduce sample heating: numerical comparison of designs and experimental verification.

A comparison of methods to decrease RF power dissipation and related heating in conductive samples using passive conductors surrounding a sample in a solenoid coil is presented. Full-Maxwell finite difference time domain numerical calculations were performed to evaluate the effect of the passive conductors by calculating conservative and magnetically-induced electric field and magnetic field distributions. To validate the simulation method, experimental measurements of temperature increase were conducted using a solenoidal coil (diameter 3 mm), a saline sample (10 mM NaCl) and passive copper shielding wires (50 microm diameter).

Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms and in vivo.

It is important to accurately characterize the heating of tissues due to the radiofrequency energy applied during MRI. This has led to an increase in the use of numerical methods to predict specific energy absorption rate distributions for safety assurance in MRI. To ensure these methods are accurate for actual MRI coils, however, it is necessary to compare to experimental results.

A method to separate conservative and magnetically-induced electric fields in calculations for MRI and MRS in electrically-small samples.

This work presents a method to separately analyze the conservative electric fields (E(c), primarily originating with the scalar electric potential in the coil winding), and the magnetically-induced electric fields (E(i), caused by the time-varying magnetic field B1) within samples that are much smaller than one wavelength at the frequency of interest. The method consists of first using a numerical simulation method to calculate the total electric field (E(t)) and conduction currents (J), then calculating E(i) based on J, and finally calculating E(c) by subtracting E(i) from E(t). The method was applied to calculate electric fields for a small cylindrical sample in a solenoid at 600MHz.

Direct magnetic resonance imaging of histological tissue samples at 3.0T.

Direct imaging of a histological slice is challenging. The vast difference in dimension between planar size and the thickness of histology slices would require an RF coil to produce a uniform RF magnetic (B1) field in a 2D plane with minimal thickness. In this work a novel RF coil designed specifically for imaging a histology slice was developed and tested.