Vol 47, No 5 (2016)

The electron paramagnetic resonance (EPR) spectrum of 24 magnetically nonequivalent Nd³⁺ centers has been found and studied in the perovskite-type crystal KZnF₃ for the first time. The problem of attributing EPR spectra of magnetically nonequivalent centers with S = 1/2 in crystals with the cubic symmetry was solved in the general form. The parameters of the spin Hamiltonian were determined.

Magnetic resonance imaging (MRI) is a non-ionizing and non-invasive imaging modality. One major limitation of MRI is its long data acquisition time. Parallel magnetic resonance imaging (PMRl) has the potential to decrease the MRI scan time by acquiring fewer k-space lines while using numerous independent receiver coils for data acquisition. SENSE reconstruction is one of the PMRI algorithms most widely used in commercial MRI scanners these days. SENSE needs accurate estimates of the receiver coil sensitivity profiles to reconstruct fully sampled images from the acquired undersampled data. This paper presents a comparison between two methods of estimating receiver coil sensitivities: (1) eigenvalue approach, in which a series of eigenvalue decompositions at the center of the acquired k-space are performed; (2) pre-scan method which uses a low-resolution image to estimate receiver coil sensitivities. In this paper, SENSE reconstruction is performed with receiver coil sensitivities estimated using both the methods. The quality of the reconstructed image is evaluated using artifact power, mean signal-to-noise ratio and line profile. The results show that the eigenvalue method to estimate sensitivity maps can be used as an alternate method for receiver coil sensitivity estimation, as it provides good reconstruction results without any compromise on the artifact power, mean signal-to-noise ratio and the line profile of the reconstructed image. Moreover, it does not require a pre-scan image to estimate receiver coil sensitivities which is required in the pre-scan method.

The electron transfer pathways in two axially bound triads based on aluminum(III) porphyrin (AlPor) are investigated using the electron spin polarization patterns of the final radical pair state. In the triads, TTF-(Ph)_n-py-AlPor-Ph-H₂Por (n = 0, 1), free-base porphyrin (H₂Por) is attached covalently to the Al(III) center, while the donor tetrathiafulvalene (TTF) coordinates to Al(III) via an appended pyridine on the opposite face of the porphyrin ring. Excitation of the triad at 532 nm leads to absorption by both AlPor and H₂Por and to two possible charge separation pathways. In the liquid crystalline solvent 5CB, spin polarized transient electron paramagnetic resonance spectra of a weakly coupled radical pair are observed and assigned to the state \({\text{TTF}}^{ \cdot+ } {\text{H}}_{2} {\text{Por}}^{ \cdot- }\). The radical pair spectra are analyzed using a structural model of the complex to determine the dipolar coupling and relative orientation of the radicals. The inertia tensor calculated from the structural model is used to derive the principal values and axes of the order matrix. It is shown that the observed polarization pattern is only consistent with ferromagnetic exchange coupling in the radical pair. The spectra can be reproduced as the sum of two contributions originating in electron transfer from the excited singlet state of AlPor and from the excited the triplet state of H₂Por. The latter is shown to account for the integral emissive net polarization observed in the spectra.

Magnetic resonance imaging (MRI) is the keystone technique to characterize the psychology and neurochemistry of human body. This imaging mechanism is advanced and with ample significances to detect the biological changes or diseases in human body. This work exploits the notable properties of compact/thin broadside coupled (BC) split ring resonator (SRR) metamaterial lens that can be use to enhance image quality of 1.5-T MRI systems. We analyzed two strongly coupled BC-SRR copper arrays attached on printed circuit board and loaded with parametric elements (capacitor and inductor). The significance of design is its compact thickness of 3.2 mm, its tunability at different working frequencies due to parametric elements and it places no restrictions on MR coil designing as proposed in previous work. The technique combining parametric elements, copper loops, and SRRs has not been used before for such lower working frequency. In addition, the designed lens persuades the radio frequency field’s rotational symmetry around the its axis due to the uniformly induced currents along its arrays which in results, improves the mutual inductance between BC-SRR arrays, and finally restores the amplitude of magnetic field (B) at the considered area, e.g., phantom and enhances the image quality. The negative resonance at 63.8 MHz was achieved with relative negative permeability, μ_r = −1.74 − j0.0063. Furthermore, image quality inside phantom was optimized in the presence or in the absence of BC-SRR lens by the analysis of thickness variations of MR coil of MRI system.