arXiv subjects

Frank D. Sönnichsen

Publications and source records attributed to Frank D. Sönnichsen.

3 recordsLinked to original sources

arXiv2025

Maximizing NMR Sensitivity: A Guide to Receiver Gain Adjustment

Novel methods and technology drive the rapid advances of nuclear magnetic resonance (NMR). The primary objective of developing novel hardware is to improve sensitivity and reliability (and possibly to reduce cost). Automation has made NMR much more convenient, but it may lead to trusting the algorithms without regular checks. In this contribution, we analyzed the signal and signal-to-noise ratio (SNR) as a function of the receiver gain (RG) for 1H, 2H, 13C, and 15N nuclei on five spectrometers. On a 1 T benchtop spectrometer (Spinsolve, Magritek), the SNR showed the expected increase as a function of RG. Still, the 1H and 13C signal amplitudes deviated by up to 50% from supposedly RG-independent signal intensities. On 7, 9.4, 11.7, and 14.1 T spectrometers (Avance Neo, Bruker), the signal intensity increases linearly with RG as expected, but surprisingly a drastic drop of SNR is observed for some X-nuclei and fields. For example, while RG = 18 provided a 13C SNR similar to that at a maximum RG of 101 at 9.4 T, at RG = 20.2 the determined SNR was 32% lower. The SNR figures are strongly system and resonance frequency dependent. Our findings suggest that NMR users should test the specific spectrometer behavior to obtain optimum SNR for their experiments, as automatic RG adjustment does not account for the observed characteristics. In addition, we provide a method to estimate optimal settings for thermally and hyperpolarized samples of a chosen concentration, polarization, and flip angle, which provide a high SNR and avoid ADC-overflow artefacts.

physics.ins-det↗

arXiv2020

Singlet state encoded magnetic resonance (SISTEM) spectroscopy

Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical processes non invasively and in vivo. Still, its application in clinical diagnostics is rare. Routine MRS is limited to spatial, chemical and temporal resolutions of cubic centimetres, mM and minutes. In fact, the signal of many metabolites is strong enough for detection, but the resonances significantly overlap, exacerbating identification and quantification. In addition, the signals of water and lipids are much stronger and dominate the entire spectrum. To suppress the background and isolate selected signals, usually, relaxation times, J-coupling and chemical shifts are used. Here, we propose methods to isolate the signals of selected molecular groups within endogenous metabolites by using long-lived spin states (LLS). We exemplify the method by preparing the LLSs of coupled protons in the endogenous molecules N-acetyl-L-aspartic acid (NAA). First, we store polarization in long-lived, double spin states and then apply saturation pulses and double quantum filters to suppress background signals. We show that LLS can be used to selectively prepare and measure the signals of chosen metabolites or drugs in the presence of water, inhomogeneous field and highly concentrated fatty solutions. The pH measurement presented here is one of the possible applications.

physics.chem-ph↗

arXiv2019

Continuous Radio Amplification by Stimulated Emission using Parahydrogen Induced Polarization (PHIP-RASER) at 14 Tesla

Nuclear Magnetic Resonance (NMR) is an intriguing quantum-mechanical effect that is used for daily life medical diagnostics and chemical analysis alike. Numerous advancements have contributed to the success of the technique, including hyperpolarized contrast agents that enables real-time imaging of metabolism in vivo. In physics, hyperpolarization has enabled an NMR RASER using a custom low-field setup and high-Q coils only recently. Expanding on this discovery, we report the finding of a RASER emitting 1H NMR signal continuously for more than 10 min at a high frequency of 600 MHz. Full chemical shift resolution is maintained and a linewidth of 2 ppb was achieved. A new simulation of a RASER effect in a coupled two spin-1/2 system was implemented and reproduced experimental findings. The effect was found using standard equipment only; no dedicated setup is necessary, making the NMR RASER accessible to a wide group of researchers.

physics.chem-ph↗