Narayanan Krishnamurthy, MS

MS in Bioengineering, University of Pittsburgh
MS Computer Engineering, George Washington University
BS Mechanical Engineering,  Kakatiya University, Regional Engineering College


BioE Thesis: “RF Studies for Ultrahigh Field MRI RF Coils and Arrays”

 Over the past few decades, different research groups have worked on different facets of Ultra-High Field (UHF) Magnetic Resonance Imaging (MRI); these developments culminated with the FDA approval of the first clinical 7 Tesla (T) MR scanner, Siemens MAGNETOM Terra in late-2017. MRI is still the preferred non-invasive multi-modal imaging technique for visualization of structural and functional correlates in-vivo and clinical diagnosis. Key issues with UHF MRI are in homogeneities in electric and magnetic fields as the size of imaged object becomes comparable with or larger than the radiofrequency (RF) wavelength. This inherent electromagnetic field inhomogeneity and elevated RF power deposition associated with UHF human imaging can have detrimental effects on the quality and safety in high field MRI.

To address these challenges, the research work presented in this study 1) evaluated different cylindrical loop receive (Rx) array geometry to establish their effect on the transmit (Tx) coil RF fields. 2) performed detailed analysis, phantom and in-vivo, comparing the performance of the Tic Tac Toe (TTT) coil with a 16-element Transverse Electromagnetic (TEM) coil using multiple anatomical head models and in-vivo.

The abovementioned areas of research included: Rx geometry model extraction from CAD models, and development of multiple anatomically detailed models and evaluation of MR coils simulations using full wave Maxwell’s equations.  Furthermore, an important part of the thesis work was bench marking of transmit coil performance for efficient and safe use in-vivo. The transmit arrays were tested for reproducibility, reliability and safe usage across multiple studies.  Finite Difference Time Domain simulations of the Tx and composite of five head models were used to optimize parameters, to obtain homogenous whole brain excitation with low RF absorption or specific absorption rate (SAR).


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