Applied Magnetic Resonance最新文献

An analytical approach is demonstrated for the direct calculation of the mean distance between a pair of spins from pulse dipolar spectroscopy measurements by electron paramagnetic resonance. This direct approach uses the Mellin integral transform and does not measure the spectrum of distances between spins, offering substantial increases in sensitivity. The approach provides accurate a priori prediction of the uncertainty for a mean distance measurement, based only on experimental measurement parameters and the final signal-to-noise ratio. The feasibility of this approach is confirmed by comparison with the standard indirect approaches using a set of in silico measurements. The new approach demonstrates comparable accuracy and possibilities for enhancing sensitivity.

Brain cancer represents a significant global health challenge with increasing incidence and mortality rates. Magnetic Resonance Imaging (MRI) plays a pivotal role in early detection and treatment planning. This study adopts a systematic approach across four phases: (1) Optimal Model Selection using the Adam optimizer, emphasizing accuracy metrics, weight computation, early stopping, and ReduceLROnPlateau techniques. (2) Real-world Scenario Simulation through synthetic perturbed datasets created by applying noise, blur (to simulate various magnetic field strengths: 1T, 1.5T, 3T), and patient motion artifacts (mimicking MRI scanning motion effects) to the testing data from the BT-MRI dataset, an online published brain tumor MRI dataset. (3) Optimization involving a range of optimizers (Adam, Adagrad, Nadam, RMSprop, SGD) and online augmentation techniques (AutoMix, CutMix, LGCOAMix, PatchUp). (4) Solution Exploration integrating Gaussian Noise and Blur as augmentation strategies during training to enhance model generalization under diverse conditions. Initial evaluations achieved strong performance, consistently reaching 99.45% accuracy on the BT-MRI dataset. However, testing against synthetic perturbed datasets mimicking real-world conditions revealed challenges in maintaining robust model performance. Despite employing diverse optimization methods and advanced augmentation techniques, this study identifies persistent challenges in ensuring model robustness with synthetic perturbed datasets. Notably, the integration of Gaussian Noise and Blur during training significantly improved model resilience. This research underscores the critical role of methodological rigor and innovative augmentation strategies in advancing deep learning applications for precise brain cancer diagnosis using MRI.

In this paper, we explore the robustness and sensitivity of Gd(III)-Gd(III) double electron–electron resonance (DEER) distance measurements in proteins for different spectrometer designs and three spin labels. To do this a protein was labeled at the same two positions with Gd(III) spin labels and measurements were performed on two home-built high-frequency (W-band, ~ 95 GHz) EPR spectrometers with different design approaches, and a commercial 150 W Q-band (34 GHz) spectrometer. The first W-band measurement approach uses a conventional, narrow band single mode cavity, while the second uses a broadband non-resonant induction mode sample holder. Both systems incorporate advanced arbitrary waveform generators (AWGs) that give flexibility over excitation bandwidth. We use three DOTA-like Gd(III) spin labels, Gd.C12, Gd.DO3A and Gd.L¹, conjugated to the calmodulin protein. We compare measurements taken by including or excluding the Gd(III) central transition excitation. The advantages and disadvantages of the EPR spectrometers for the measurement of Gd(III)–Gd(III) DEER are discussed in terms of the robustness of the resulting distance distribution width, absolute and concentration sensitivity, sample handling, ease of use, and flexibility of measurement.

Electron paramagnetic resonance (EPR) has been established as a unique and reliable method for quantitative in vivo oximetry applicable to a variety of preclinical and clinical studies. A recent clinical study using EPR oximetry with OxyChip from our laboratory demonstrated the feasibility of tumor oxygen measurements in cancer patients (Schaner, et al. Front. Oncol. 2021). During this study, the need to improve oxygen measurement capability in tumors at depths greater than 10 mm became apparent. This prompted us to develop new designs of resonators (RF coils) with enhanced sensitivity for measuring deep-tissue oxygen levels. In this manuscript, we report the development of a new cylindrical surface dielectric resonator (c-SDR) designed with a ceramic dielectric material for substantially enhanced sensitivity and capability for deep-tissue oximetry. The c-SDR was constructed with a cylindrical dielectric material (ϕ 27.2 × 22.2 mm; ε = 160), 6-segmented coupling loop and copper shield to provide an active surface (aperture) of 25 mm with an operating frequency of 1.16 GHz (L-band) and an unloaded Q 600. The resonator could detect OxyChip (ϕ 0.6 × 5 mm) at a surface-to-sample depth of 50 mm in water or 30 mm in a tissue-emulating phantom with a signal-to-noise ratio of 5. Further evaluations of the c-SDR using OxyChip demonstrated its capability for oxygen measurements at depths of 27 mm for 1% oxygen and 15 mm for 5% oxygen in a tissue phantom. In conclusion, the new c-SDR is a significant upgrade to the currently used resonators for in vivo EPR oximetry including clinical oximetry.

The common interpretation of magnetic resonance relaxation time distribution of liquids in porous media assumes a one-to-one relationship between the pore size and the relaxation time constants. This common conviction may not be correct in many microporous materials. Each pore size may be associated with more than one peak in the NMR relaxation time distributions: a single dominant peak and also possibly one or a few minor peaks. The appearance of minor peaks is due to the non-vanishing nonground eigenvalues of the diffusion–relaxation equation. Brownstein and Tarr (Phys Rev A 19:2446, 1979) described these features, but their solutions at conditions beyond the fast-diffusion regime are not widely adopted. We provide the derivation of Brownstein–Tarr equations for multi-exponential magnetic resonance relaxation decay for liquids in simple pore geometries. General solutions are presented for planar, cylindrical, and spherical pores—as well as two limiting cases of fast and slow diffusion for each geometry. Similar solutions are also relevant to first-order dilute reactions in porous media in heterogeneous reaction–diffusion systems. We hope that the availability of these derivations helps wider adoption of more realistic interpretation of magnetic resonance relaxation in porous media in the light of the multi-exponential Brownstein–Tarr model.

Water-soluble compositions of D-α-tocopherol (TP) as an effective antioxidant obtained by its encapsulation into amphiphilic copolymer of N-vinylpyrrolidone with hexyl methacrylate and triethylene glycol dimethacrylate (VP–HMA–TEGDM) and linear polyvinylpyrrolidone (PVP) were studied by electron absorption spectroscopy, dynamic light scattering and by ¹H high-resolution and pulsed field gradient (PFG) NMR. TP absorption band was at 292 nm in the absorption spectra of TP–VP–HMA–TEGDM and TP–PVP solutions, and the TP-loaded nanoparticles in water solution had average hydrodynamic radii, R_h, values about 65 and 57 nm, and diffusion coefficient, D_t, values were 3.7 × 10^–8 and 4.3 × 10^–8 cm²/s, respectively. The investigation of the self-diffusion by PFG NMR technique in addition reveals the presence of the phases of small sizes containing TP, which are invisible in DLS measurements. The investigation of the exchange between these phases shows that the retention time of TP in large associates is longer for TP–VP–HMA–TEGDM water solution compared to TP–PVP.

Over the last 50 years, EPR oximetry has been established as the gold standard for absolute quantitative measurement and imaging of oxygen partial pressure in the biomedical setting. In this review, the main developments in EPR oximetry through its history are discussed. The first oxygen measurement with EPR was reported approximately 50 years ago, in 1975. Since then, a wide variety of probes have been developed for various biomedical applications including preclinical and clinical study. These probes can be categorized into soluble probes including nitroxides and trityls for volumetric imaging, and solid-state probes, for long-term point measurements. Oximetry measurements range in size from a single cell to whole body rabbit imaging. The applications of preclinical EPR oximetry are still growing in scope, and include cancer, myocardial infarction, stroke, and wound healing. First studies in clinical oximetry appear promising, with discrete measurement of oxygen using injected ink or implanted OxyChip probes.

This review is directly related to the new field of biology and medicine—the biology and medicine of nitric oxide (NO)—the simplest molecule produced in all living organisms and serving as one of the universal regulators of various metabolic processes. Specifically, this review concerns dinitrosyl iron complexes (DNICs) with thiol-containing ligands, which arise in living organisms and function in them, according to our data, as a “working form” of NO.

Double spin labeling is often used to study the conformations of biomolecules using pulsed dipolar EPR spectroscopy (PDS). For spin labels based on triarylmethyl (TAM) radicals, there is a data processing problem due to the strong dipole–dipole coupling of the two spins due to the narrow EPR line. As recently shown, these problems can be overcome in a simple PDS approach based on two-pulse electron spin echo spectroscopy (2p ESE). Although the theory underlying this approach was developed by Salikhov and Zhidomirov many years ago, all of its predictions, however, have yet to be tested. Here we obtain additional arguments in favor of the applicability of this theory by investigating the dependence of the echo signal on the pulse turning angles. In addition, we show how the results obtained can be useful for data processing in PDS methods.

Diesel is the most important liquid fuel in Brazil, representing 49.6% of the total liquid fuels commercialized in the country and, therefore, is important to have simple and rapid method for diesel quality control. The Brazilian National Agency of Petroleum, Gas and Biofuels verified that 4.0% of the diesel samples did not meet the required specification in 2022. Adulterated fuel increased fuel consumption, cause engine problems, increased emission of polluting gases among others problems. This study presents the use of bench top, time domain nuclear magnetic resonance (TD-NMR) relaxometer as a simple, rapid and non-destructive analytical method to quantify the adulteration of diesel with ethanol, which is the cheapest liquid fuel available in Brazil. The results show that commercial diesel and ethanol have transverse relaxation time (T₂) equal to 0.67 s and 1.75 s, respectively. The addition of 10–90% v/v) ethanol in diesel increased the T₂ linearly. The correlation of T₂ values with the middle infrared band at 1747 cm⁻¹ shows determination coefficient (R² = 0.94). Therefore, TD-NMR relaxometry is a rapid, simple and alternative method to determine the adulteration of the commercial diesel with ethanol.