Applied Magnetic Resonance

Detection of Magnetosome-Like Structures in Eukaryotic Cells Using Nonlinear Longitudinal Response to ac Field Abstract Although magnetosomes have been discovered in bacteria since several decades, until today the question remains open whether such biomineralized structures do exist in eukaryotic cells. Herein, evidence was provided for the existence of magnetosome-like Fe-based structures in different viable eukaryotic cells by the registration of second harmonic of magnetization M2(H) of longitudinal nonlinear response to weak ac field. The behavior of the field hysteresis of the M2 response from cells in suspension and/or in pellet indicated a multi-domain state of magnetosome-like structures in certain type of cells, and a single-domain state in other cell lines. The amounts of magnetosomes in cells range from ≤ 1÷2 to 5÷8 per cell. The presence of magnetosome-like structures was analyzed in normal tissue samples obtained from Wistar rats and C57/Bl6 mice. Additionally, the tumor tissue (orthotopic rat C6 glioma and mouse GL261 glioma) were assessed for magnetosomes. Detected magnetosomes in certain tissues (i.e., brain, heart, lungs) matched to a single-domain magnetite nanoparticle, whereas in other organs they exhibited characteristics attributable to a multi-domain state, better corresponding to Fe(0) composition of their magnetic cores. Subsequent studies are necessary to elucidate the role of the Fe-based magnetosome-like structures in the biology and physiology of eukaryotic cells.

Golden-Angle Radial Sparse Parallel MR Image Reconstruction Using SC-GROG Followed by Iterative Soft Thresholding Abstract Golden-angle radial sparse parallel (GRASP) magnetic resonance imaging (MRI) is a recent MR image reconstruction technique which integrates parallel imaging, compressed sensing and golden-angle radial scheme to reconstruct the dynamic contrast-enhanced MRI (DCE-MRI) data. Conventionally, GRASP exploits non-uniform fast Fourier transform to grid and de-grid the golden-angle radial data and employs nonlinear conjugate gradient method to recover the unaliased images. GRASP performs gridding and de-gridding operations of golden-angle radial data in every iteration which increases the computational complexity of the conventional GRASP and takes a long image reconstruction time. In this paper, self-calibrated GRAPPA operator gridding (SC-GROG) followed by iterative soft thresholding (IST) is proposed for faster GRASP reconstruction of the golden-angle radial DCE-MRI data. In the proposed method, firstly SC-GROG maps the undersampled golden-angle radial data to a Cartesian grid and then reconstructs the solution image using the IST technique. The proposed method does not require gridding and de-gridding in each iteration; therefore, it is computationally less expensive as compared to the conventional GRASP reconstruction approach. The proposed method is tested for undersampled DCE golden-angle radial liver perfusion data (at acceleration factors 11.8, 19.1 and 30.9). The reconstruction results are assessed visually as well as using mean square error, line profiles and reconstruction time. The reconstruction results are compared with the conventional GRASP reconstruction. The results show that the proposed method provides better quality reconstruction results in terms of reconstruction time and spatio-temporal resolution than the conventional GRASP approach.

The Inter/Intra-brain Metabolite Concentration Change as Applying the Rehabilitate Treatment in Intra-cerebral Hemorrhage Rat Models: Pilot Study Abstract If intra-cerebral hemorrhage (ICH) rehabilitation animal model studies had included processes related to imaging diagnosis, not only interim evaluation of treatment effects but also the objectification of treatment effects would have been possible. The purpose of this study was to examine the rehabilitation treatment effect on biomarkers identified on magnetic resonance imaging/spectroscopy in an animal intra-cerebral hemorrhage model. Two groups of rats were used in this study: (1) the rehabilitation treatment group, 12 6-week-old Sprague–Dawley rats with experimental hemorrhage that received rehabilitation; and (2) the control group of 12 rats with experimental hemorrhage that received no intervention. Training rehabilitation was implemented 15 min daily for 2 weeks with 55–85% of the VO2 max. We conducted MRI/MRS scans before and after ICH rat modeling to evaluate brain metabolite concentration changes. The signal intensity of T2WI was measured at the site of ICH and in a similarly sized area on the opposite side. Integration of the areas under the peaks was conducted to measure cerebral metabolite concentrations. Differences in the mean T2WI-SI ratios measured 2 weeks after ICH induction were not statistically significant (p = 0.514) between the control group and the experimental group. However, the brain tCho/tCr metabolite ratio in the control group was significantly lower than in the experimental group 2 weeks after ICH induction (0.243 ± 0.044 vs. 0.326 ± 0.061, p = 0.007). The tCho/tCr ratio might be used as a biomarker to evaluate the effect of rehabilitation treatment for ICH.

EPR and DEER Characterization of New Mixed Weakly Coupled Nitroxide Triradicals for Molecular Three-Spin Qubits Abstract Three new mixed triradicals with small exchange coupling parameters (J ≪ AN) were obtained on the base of a coupling reaction between the derivative of spirofused 2,5-dihydroimidazol-type monoradical and the two mol. equivalents of carboxylic acid derivatives of PROXYL-, TEMPO- or 2,5-dihydro-1H-pyrrol-type nitroxides. Their intramolecular magnetic interactions were characterized in terms of comparison of the CW X, Q- and W-band EPR spectra with those of the monoradical precursors. The dipole–dipole coupling parameters of the triradicals were estimated on the base of the quantum chemical calculations at UB3LYP/6-31G(d) level of theory. Two types of the spin distances were found in the triradicals: short—with the distance of 13–17 Å (D ≈ 11–24 MHz) and long—with the distance of 21–23 Å (D ≈ 4–6 MHz). The longest spin–spin as well as spin–lattice relaxation times at 50 K were detected for the triradical carrying the two TEMPO fragments, indicating the potential usage of three-spin qubit models for quantum gate operations.

Optimizing T1rho and T2 Values for Intervertebral Discs Obtained from the Combined T1rho and T2 Sequence Abstract To investigate the effect of the number of spin-lock (SL) and T2 preparation pulse using T1rho and T2 values obtained from the combined T1rho and T2 sequence. We included 30 patients who underwent magnetic resonance imaging of the lumbar spine because of low back pain and leg numbness, tingling, and pain. We used 3D turbo-field echo and the adiabatic pulse as SL pulse for T1rho mapping and the block pulse as T2 preparation pulse for T2 mapping of the combined T1rho and T2 sequence. The preparation time of T1rho and T2 was set at 0, 20, 40, 60, and 80 ms. We defined the T1rho and T2 values calculated from all SL and T2 preparation pulses as Dfull and decreased several number of SL and T2 preparation pulses from Dfull as other groups (D1, D2, and D3). We used the Bland–Altman analyses to estimate the systematic and proportional bias between Dfull and other groups. The 95% CI of the mean difference included zero in all groups. Therefore, systematic bias was not detected. The regression coefficients with D3 of the T1rho and T2 value were − 0.34 and − 0.23, respectively (p < 0.01). We detected the proportional bias in the T1rho and T2 values in only D3 (0 and 80 ms). An investigation of the T1rho and T2 values of IVDs using the combined T1rho and T2 sequence suggested that the accuracy of these values decreased with suitably adjusted three preparation pulses, facilitating the assessment of both T1rho and T2 values at approximately 10 min.

Computation of Resonance Magnetic Fields of CW-EPR Spectra by Reversion of Power Series Abstract The linear relationship between the frequency of an EPR transition and the magnetic field, valid in the presence of only the Zeeman interaction, generally becomes nonlinear, when other interactions become operative. In such cases, obtaining accurate values of the resonance magnetic fields of a given spin system for simulating their EPR spectra, recorded at a fixed frequency, is not a trivial exercise. Because of its fundamental importance in the analysis of EPR spectra, there are several methods available in the literature to address this issue. These methods either use numerical techniques to compute the resonance fields from the resonance energies computed at various magnetic fields by diagonalization of the Hamiltonian matrix, or modify the Hamiltonian appropriately and resort to perturbation calculations. In this work, we have examined a method based on a mathematical technique of reversion of a power series, by which the resonance magnetic fields at a fixed frequency can be achieved in a relatively simple and straightforward manner. We have shown that, when the energy of an EPR transition can be expressed as a power series in powers of the magnetic field, obtained either from the analytical energy expression or by fitting the calculated energies to an empirical power series, a reversed power series in powers of the transition energy can be obtained to represent the resonance magnetic field. We have derived the necessary algebraic relationships between the coefficients of these two series. We have shown the success and usefulness of this method by applying it to calculate the resonance magnetic fields of well-studied EPR spectra of hydrogen atom, naphthalene triplet, and 6S state of Fe3+ in an octahedral crystalline electric field, at different frequencies.

Towards a Model-Based Field-Frequency Lock for Fast-Field Cycling NMR Abstract Fast-field cycling nuclear magnetic resonance (FFC NMR) relaxometry allows to investigate molecular dynamics of complex materials. FFC relaxometry experiments require the magnetic field to reach different values in few milliseconds and field oscillations to stay within few ppms during signal acquisition. Such specifications require the introduction of a novel field-frequency lock (FFL) system. In fact, control schemes based only on current feedback may not guarantee field stability, while standard FFLs are designed to handle very slow field fluctuations, such as thermal derives, and may be ineffective in rejecting faster ones. The aim of this work is then to propose a methodology for the synthesis of a regulator that guarantees rejection of field fluctuations and short settling time. Experimental trials are performed for both model validation and evaluation of the closed-loop performances. Relaxometry experiments are performed to verify the improvement obtained with the new FFL. The results highlight the reliability of the model and the effectiveness of the overall approach.

EPR Characterization of the Light-Induced Negative Polaron in a Functionalized Dithienylthiazolo[5,4- d ]thiazole Acceptor for Organic Photovoltaics Abstract Functionalized 2,5-dithienylthiazolo[5,4-d]thiazole (DTTzTz) derivatives have attracted interest towards application as non-fullerene acceptors in solution-processed organic solar cells. Here, we present a combined high-field electron paramagnetic resonance and density functional theory study of the light-induced negative polaron on the novel acceptor 2,4-diCN-Ph-DTTzTz formed after charge transfer in bulk heterojunction blends with a donor polymer. Despite spectral overlap with the polymer cation, the g-anisotropy of the acceptor radical could be directly confirmed through detection of its unique 14N hyperfine couplings using electron–electron double resonance (ELDOR)-detected nuclear magnetic resonance (EDNMR) for spectral filtering. The spectral assignment is further underpinned by quantum-chemical calculations, which also provide detailed information about the spin density and charge distribution of the polaron in the DTTzTz acceptor.

1 H NMR study of the effect of cucurbit[7]uril on the aquation of carboplatin in biologically relevant media Abstract The aquation of carboplatin, a second-generation Pt(II)-based antitumor drug, in two biologically relevant media (PBS buffer solution and RPMI-1640 medium for cell growth) has been studied by means of 1H nuclear magnetic resonance spectroscopy. The effect of the macrocyclic cavitand cucurbit[7]uril on the carboplatin aquation rates in these two types of media has also been studied. Although, the cucurbit[7]uril does not form stable inclusion complex with carboplatin, it greatly affects the carboplatin aquation rates, presumably, through the two mechanisms: prevention of the carboplatin dimer formation and encapsulation of some components of the medium.

Correction to: Spin-label Order Parameter Calibrations for Slow Motion In the print published article, some equations were published incorrectly, the correct equations are given below.