High fidelity triangular sweep of the magnetic field for millisecond scan EPR imaging
Autor: | Hiroshi Hirata, Jay L. Zweier, Alexandre Samouilov, Denis A. Komarov |
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Jazyk: | angličtina |
Rok vydání: | 2021 |
Předmět: |
Diagnostic Imaging
Nuclear and High Energy Physics Frequency response Field (physics) Magnetometer Biophysics 010402 general chemistry 01 natural sciences Biochemistry Article 030218 nuclear medicine & medical imaging law.invention 03 medical and health sciences 0302 clinical medicine Optics law Group delay and phase delay Physics business.industry Electron Spin Resonance Spectroscopy Linearity Condensed Matter Physics 0104 chemical sciences Magnetic field Magnetic Fields Electromagnetic coil Magnet business |
Zdroj: | J Magn Reson |
Popis: | Linearity of the magnetic field sweep is important for high resolution continuous wave EPR imaging. Driving the field with triangular wave function is the most efficient way to scan EPR projections. However, the magnetic field sweep profile can be significantly distorted during fast millisecond projection scan. In this work, we introduce a method to generate highly linear and properly symmetrical triangular sweeps of the magnetic field using calibrated harmonics of the triangular wave function. First, the frequency response function of the EPR magnet and its power circuitry was obtained. For this, the field sweeping coil was driven with sinusoidal signals of different frequencies and the actual magnetic field inside the magnet was recorded. To cover wide range of frequencies, the measurements were carried out independently using gaussmeter, Hall-effect linear sensor integrated circuit, and an inductance coil. For each frequency, the system gain and the phase delay were determined. These data were used to adjust the amplitudes and the phases of individual harmonics of the triangular wave function. After the calibration, the maximum deviation of the magnetic field from the linear function was 0.05% of sweep width for 4 ms scan. The maximum discrepancy between the forward and the reverse scan was less than 0.04%. Sweep overhead time for changing the scan direction was 5%. The proposed approach allows generation of high fidelity triangular magnetic field sweeps with accuracy better than 0.1% for the range of the magnetic field sweep widths up to 48 G and scan duration from 10 s down to 1 ms. |
Databáze: | OpenAIRE |
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