Abstract
Abstract. Nuclear magnetic resonance imaging (MRI) has became an unavoidable medical tool in spite of its poor sensitivity. This fact motivates the efforts to enhance the nuclear magnetic resonance (NMR) probe performance. Thus, the nuclear spin excitation and detection, classically performed using radio-frequency coils, are required to be highly sensitive and homogeneous. The space harmonics suppression (SHS) method, already demonstrated to construct coil producing homogenous static magnetic field, is used in this work to design radio-frequency coils. The SHS method is used to determine the distribution of the electrical conductive wires which are organized in a saddle-coil-like configuration. The theoretical study of these SHS coils allows one to expect an enhancement of the signal-to-noise ratio with respect to saddle coil. Coils prototypes were constructed and tested to measure 1H NMR signal at a low magnetic field (8 mT) and perform MRI acquired at a high magnetic field (3 T). The signal-to-noise ratios of these SHS coils are compared to the one of saddle coil and birdcage (in the 3 T case) of the same size under the same pulse sequence conditions demonstrating the performance enhancement allowed by the SHS coils.
Highlights
When nuclei having a nuclear spin are immersed in a magnetic field (B0), an aligned magnetization (M), resulting from the balance between parallel and anti-parallel magnetic moments, occurs
The homogeneity of quadrature SHS4 coil proven by image acquiring is roughly comparable to the one of birdcage, making the saddle-like space harmonics suppression (SHS) coil a relevant magnetic resonance imaging (MRI) probe competitor
The SHS method allows one to determine the position of electrical conductor favoring the production of a homogenous magnetic field
Summary
When nuclei having a nuclear spin are immersed in a magnetic field (B0), an aligned magnetization (M), resulting from the balance between parallel and anti-parallel magnetic moments, occurs. Besides this net magnetization, the nuclear spins precess at the Larmor angular frequency: ω0 = −γ B0, where γ is the gyromagnetic ratio of a given nucleus. High signal-to-noise ratio (SNR) and homogeneity remain the main desirable features of these NMR/MRI probes. Research in this area remains active, and various MRI probe configurations have been proposed to address this need (Mispelter et al, 2006): solenoid, saddle coil, birdcage, Bolinger coil, etc
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