Browsing by Subject "RF pulse design"

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    Data for Detection of Exchangeable Protons in NMR Metabolomic Analysis using AI-Designed Water Irradiation Devoid Pulses
    (2025-02-06) Veliparambil Subrahmanian, Manu; Veglia, Gianluigi; Vuckovic, Ivan; Macura, Slobodan; mvelipar@umn.edu; Manu, Veliparambil Subrahmanian; Veglia Lab
    1H NMR spectroscopy has enabled the quantitative profiling of metabolites in various biofluids, emerging as a possible di-agnostic tool for metabolic disorders and other diseases. To boost the signal-to-noise ratio and detect proton resonances near the water signal, current 1H NMR experiments require solvent suppression schemes (e.g., presaturation, jump-and-return, WATERGATE, excitation sculpting, etc.). Unfortunately, these techniques affect the quantitative assessment of analytes containing exchangeable protons. To address this issue, we introduce two new1D 1H NMR techniques that eliminates the water signal, preserving the intensities of exchangeable protons. Using GENETICS-AI, a software that combines an evolutionary algorithm and artificial intelligence, we tailored new WAter irradiation DEvoid (WADE) pulses and optimized 1D 1H NOESY sequence for metabolomics analysis. When applied to human urine samples, kidney tissue extract, and plasma, the WADE technique allowed for accurate measurement of typical metabolites and direct quantification of urea, which is usually challenging to measure using standard NMR experiments. We anticipate that these new NMR techniques will significantly improve the accuracy and reliability of metabolite quantitative assessment for a wide range of biological fluids.
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    Parallel transmission for magnetic resonance imaging on a 9.4 Tesla Human System.
    (2010-01) Wu, Xiaoping
    Over recent years, researchers have been increasingly pushing towards using ultrahigh magnetic field (7 Tesla and higher) for magnetic resonance imaging in human to benefit from substantial increases in signal to noise ratio and contrast. However, at ultrahigh field, severe transmit B1 (B1+) inhomogeneity occurs, limiting applications of most conventional MR techniques. Multidimensional spatially selective RF pulses have been proposed as a method to mitigate B1+ inhomogeneity. However, those RF pulses are typically very long and are impractical at high field. Parallel transmission, an emerging technique, makes it possible to design sufficiently short selective RF pulses for use in actual experiments. In this thesis, we demonstrate the first successful implementation of parallel transmission at an ultrahigh field of 9.4 Tesla (T) in the human brain with an eight-channel transmit system, using accelerated (x 4) RF pulses designed to create arbitrarily shaped excitation profiles. To achieve satisfactory excitation accuracy, k-space errors due to gradient system imperfection had to be accurately calibrated and integrated in RF pulse calculation. In order to limit RF power deposition in tissues, an inherent concern for patient safety at very high field, we introduced and demonstrated a new 2D RF pulse design method that effectively reduces specific absorption rate (SAR) while preserving excitation pattern fidelity. SAR reduction efficiency was demonstrated with numerical simulations while excitation pattern fidelity was experimentally verified at 9.4T. Additional preliminary work relevant to B1+ manipulation at high field were also conducted through the course of this thesis, including the implementation of spoke trajectory based transmit excitation with 16 channels at 9.4T, a fast 2D B1 mapping technique and in-depth simulation of SAR in the human brain with multi transmission.