Browsing by Subject "B0 Shimming"

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    A Combined, Fine-Tune B0 Shimming and RF Receive Array using Transmission Line Resonators for Functional Imaging of the Human Temporal Lobe at 7 Tesla
    (2020-08) Bratch, Alexander
    Functional MRI has become a one of the most powerful tools for non-invasive investigation of brain function. Increases in the magnetic field strength of these systems have yielded improvements in SNR that enable the investigation of fine-scale neural systems. However, with this increase in field strength comes an increase in artifacts arising from magnetic field homogeneity. Specifically, artifacts which occur near air-tissue boundaries (e.g., ear canals and frontal sinuses) become dramatically worse with higher field strengths, limiting the ability to derive useful information from brain areas adjacent to these regions. In recent years, a number of attempts have been made to develop technology which can help mitigate the artifacts arising in these areas. Such approaches make use of either fully external shim arrays, or shimming circuity integrated within standard array technology. Here, the use of transmission line resonators (TLRs) is proposed for use as a combined receive-only/B0 shimming element for imaging and local shimming of the ventral temporal lobe. Simulations were conducted and initial evaluations showed both good bench and in-scanner performance of prototypes. Further design refinements led to the development of an array structure and proposed shimming routine. The resulting TLR coil array structure was integrated into a larger 32 channel RF head array, and associated hardware for selectively driving the shim elements was built. Preliminary results demonstrated strong convergence with simulated shim performance, suggesting the viability of this array design and for the use of TLRs in this application.