Purpose
Compare numerically-simulated and experimentally-measured temperature increase due to Specific energy Absorption Rate (SAR) from radiofrequency fields.
Methods
Temperature increase induced in both a phantom and in the human forearm when driving an adjacent circular surface coil was mapped using the proton resonance frequency shift technique of Magnetic Resonance (MR) thermography. The phantom and forearm were also modeled from MR image data, and both SAR and temperature change as induced by the same coil were simulated numerically.
Results
The simulated and measured temperature increase distributions were generally in good agreement for the phantom. The relative distributions for the human forearm were very similar, with the simulations giving maximum temperature increase about 25% higher than measured.
Conclusion
Although a number of parameters and uncertainties are involved, it should be possible to use numerical simulations to produce reasonably accurate and conservative estimates of temperature distribution to ensure safety in MR imaging.
Purpose
To investigate the use of a new high-dielectric constant (HDC) material for improving SNR and transmission efficiency for clinical MRI applications at 3T with cervical spine imaging.
Materials and Methods
Human subjects were imaged using a commercial cervical spine receive array coil on a clinical system with and without pads containing Barium Titanate beads in deuterium water placed around the neck. Numerical electromagnetic field simulations of the same configuration were also performed.
Results
Experimental and simulated maps of transmit and receive fields showed greater efficiency for imaging the cervical spine when the pads were present. Experimental measurements showed a significant improvement in SNR with the pads present and an average input power reduction of 46%.
Conclusion
Use of HDC material can enhance SNR and transmission efficiency for clinical imaging of the cervical spine at 3.0 T.
Passive dielectric materials have been used to improve aspects of MRI by affecting the distribution of radiofrequency electromagnetic fields. Recently, interest in such materials has increased with the number of high-field MRI sites. Here, we introduce a new material composed of sintered high-permittivity ceramic beads in deuterated water. This arrangement maintains the ability to create flexible pads for conforming to individual subjects. The properties of the material are measured and the performance of the material is compared to previously used materials in both simulation and experiment at 3 T. Results show that both permittivity of the beads and effect on signal-to-noise ratio and required transmit power in MRI are greater than those of materials consisting of ceramic powder in water. Importantly, use of beads results in both higher permittivity and lower conductivity than use of powder.
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