Еволюція автокефального руху в Україні (1917 - 1936 рр.)

У статті розглядаються основні етапи становлення, розвитку та причини перших невдач відродження православної автокефалії в Україні, її наслідки щодо Української православної церкви, а також взаємини з радянською владою.В статье рассматриваются основные этапы становления, развития и причины первых неудач возрождения православной автокефалии в Украине, её последствия для Украинской православной церкви, а также взаимоотношения с советской властью.The basic stages of the foundation, the development and the causes of the first failures of orthodox autocephalous revival in Ukraine, its consequences for Ukrainian orthodox church and interrelation with Soviet regime are considered in this article

Visualization of metasurface eigenmodes with magnetic resonance imaging

The ability to control the electromagnetic near field with metasurfaces offers potential applications over the frequency range from radio frequency to optical domains. In this work, we show an essential feature of metasurfaces, subwavelength field confinement via excitation of a large number of eigenstates in a narrow frequency range, and demonstrate an innovative way of visualizing profiles of metasurface eigenmodes with the aid of a magnetic resonance imaging (MRI) system. We show that by tuning different eigenmodes of the metasurface to the Larmor frequency, we can passively tailor the near-field distribution to adjust the desired pattern of radio-frequency excitation in a MRI experiment. Our work demonstrates a practical nonperturbed rapid way of imaging metasurface eigenmodes

Dose optimisation for the MRI-accelerator (THESIS VERSION)

A combined system of a 6 MV linear accelerator and a 1.5 T MRI scanner is currently being developed. In this system, the patient will be irradiated in the presence of a 1.5 T magnetic field. This causes a strong dose increase at tissue-air interfaces. Around air cavities in the patient, these effects may become problematic. Homogeneous dose distributions can be obtained around regulary shaped symmetrical cavities using opposing beams. However, for more irregulary shaped cavities this approach may not be sufficient. This study will investigate whether IMRT can be used to cope with magnetic field dose effects, in particular for target volumes adjacent to irregulary shaped air cavities. Therefore, an inverse treatment planning approach has been designed based on pre-calculated beamlet dose distribution kernels. Using this approach, optimized dose distributions were calculated for B = 1.5 T and for B = 0 T. Investigated target sites include a prostate cancer, a laryngeal cancer and an oropharyngeal cancer. Differences in the dose distribution between B = 0 and 1.5 T were minimal; only the skin dose increased for B = 1.5 T. Homogeneous dose distributions were obtained for target structures adjacent to air cavities without the use of opposing beams. These results show that a 1.5 T magnetic field does not compromise the ability to achieve desired dose distributions with IMRT

Dose optimisation for the MRI-accelerator (ENHANCEMENT)

A combined system of a 6 MV linear accelerator and a 1.5 T MRI scanner is currently being developed. In this system, the patient will be irradiated in the presence of a 1.5 T magnetic field. This causes a strong dose increase at tissue-air interfaces. Around air cavities in the patient, these effects may become problematic. Homogeneous dose distributions can be obtained around regulary shaped symmetrical cavities using opposing beams. However, for more irregulary shaped cavities this approach may not be sufficient. This study will investigate whether IMRT can be used to cope with magnetic field dose effects, in particular for target volumes adjacent to irregulary shaped air cavities. Therefore, an inverse treatment planning approach has been designed based on pre-calculated beamlet dose distribution kernels. Using this approach, optimized dose distributions were calculated for B = 1.5 T and for B = 0 T. Investigated target sites include a prostate cancer, a laryngeal cancer and an oropharyngeal cancer. Differences in the dose distribution between B = 0 and 1.5 T were minimal; only the skin dose increased for B = 1.5 T. Homogeneous dose distributions were obtained for target structures adjacent to air cavities without the use of opposing beams. These results show that a 1.5 T magnetic field does not compromise the ability to achieve desired dose distributions with IMRT

MR-guided radiotherapy: magnetic field dose effects

At the UMC Utrecht, together with Elekta Oncology and Philips Research, we are developing a combined system of a 1.5 Tesla MRI scanner and a 6 MV linear accelerator for cancer treatment. In contrast to present online imaging methods, superior soft-tissue contrast will be achieved. The system will enable patient positioning based on the tumour itself. In the design, the patient will be irradiated in the presence of a 1.5 Tesla magnetic field. This will affect the dose distribution, due to the Lorentz force acting on the secondary electrons. These so-called magnetic field dose effects have been investigated using the Monte Carlo code GEANT4. In homogeneous media, the magnetic field causes a reduced build-up distance and a shifted, asymmetric penumbra. At tissue-air boundaries dose increase of 40% is shown, due to electrons returning into the phantom by arc-shaped trajectories. This phenomenon has been called ‘Electron Return Effect’ (ERE). The ERE will take effect at the distal side of the treatment beam and at the proximal side of interior air cavities within the patient. The ERE in the latter case can be compensated by using opposing beams. We validated the simulation results of GEANT4 by comparison to dose measurements at 0, 0.6 and 1.3 Tesla. We demonstrated that both the reduced build-up distance and the ERE are highly dependent on surface orientation. If the treatment beam extends over the edges of a phantom, the so-called lateral ERE causes a dose increase of 50% relative to the central axis dose. We showed that even for oblique incidence opposing beams still have a compensating effect. We also investigated the ERE at the distal side, the lateral ERE, ERE at air cavities and ERE at tissue-lung transitions for magnetic field values of 0.2, 0.75, 1.5 and 3 Tesla. Results show that the ERE is reduced by lower magnetic field strengths, in particular for small irradiation fields, the lateral ERE, small cavities and lung tissue. However, for large irradiation fields (10 cm) and large interior air cavities (3 cm), the ERE reaches considerable levels of exit dose increase for all magnetic field values. For air cavities within the patient near the target, multiple beams, although not necessarily opposing, do have a compensating effect on the ERE dose increase. The remaining dose inhomogeneities can be dealt with by IMRT. We designed an inverse treatment planning approach, to calculate optimized IMRT dose distributions in the presence of a magnetic field. We used this method to calculate optimized IMRT treatment plans for a prostate cancer, a laryngeal cancer and an oropharyngeal cancer at B = 0 and 1.5 Tesla. Results hardly showed any differences between B = 0 and 1.5 T in terms of target coverage and sparing of organs at risk. This thesis shows that radiotherapy treatment in the presence of a magnetic field is feasible

Dose optimisation for the MRI-accelerator (AGGREGATION CH 9)

A combined system of a 6 MV linear accelerator and a 1.5 T MRI scanner is currently being developed. In this system, the patient will be irradiated in the presence of a 1.5 T magnetic field. This causes a strong dose increase at tissue-air interfaces. Around air cavities in the patient, these effects may become problematic. Homogeneous dose distributions can be obtained around regulary shaped symmetrical cavities using opposing beams. However, for more irregulary shaped cavities this approach may not be sufficient. This study will investigate whether IMRT can be used to cope with magnetic field dose effects, in particular for target volumes adjacent to irregulary shaped air cavities. Therefore, an inverse treatment planning approach has been designed based on pre-calculated beamlet dose distribution kernels. Using this approach, optimized dose distributions were calculated for B = 1.5 T and for B = 0 T. Investigated target sites include a prostate cancer, a laryngeal cancer and an oropharyngeal cancer. Differences in the dose distribution between B = 0 and 1.5 T were minimal; only the skin dose increased for B = 1.5 T. Homogeneous dose distributions were obtained for target structures adjacent to air cavities without the use of opposing beams. These results show that a 1.5 T magnetic field does not compromise the ability to achieve desired dose distributions with IMRT

Potential Reduction of Peripheral Local SAR for a Birdcage Body Coil at 3 Tesla Using a Magnetic Shield

| openaire: EC/H2020/736937/EU//M-CUBEThe birdcage body coil, the standard transmit coil in clinical MRI systems, is typically a shielded coil. The shield avoids interaction with other system components, but Eddy Currents induced in the shield have an opposite direction with respect to the currents in the birdcage coil. Therefore, the fields are partly counteracted by the Eddy currents, and large coil currents are required to reach the desired B1+ level in the subject. These large currents can create SAR hotspots in body regions close to the coil. Complex periodic structures known as metamaterials enable the realization of a magnetic shield with magnetic rather than electric conductivity. A magnetic shield will have Eddy currents in the same direction as the coil currents. It will allow generating the same B1+ with lower current amplitude, which is expected to reduce SAR hotspots and improve homogeneity. This work explores the feasibility of a birdcage body coil at 3 T with a magnetic shield. Initially, we investigate the feasibility by designinga scale model of a birdcage coil with an anisotropic implementation of a magnetic shield at 7 T using flattened split ring resonators. It is shown that the magnetic shield destroys the desired resonance mode because of increased coil loading. To enforce the right mode, a design is investigated where each birdcage rung is driven individually. This design is implemented in a custom built birdcage at 7 T, successfully demonstrating the feasibility of the proposed concept. Finally, we investigate the potential improvements of a 3 T birdcage body coil through simulations using an idealized magnetic shield consisting of a perfect magnetic conductor (PMC). The PMC shield is shown to eliminate the peripheral regions of high local SAR, increasing the B1+ per unit maximum local SAR by 27% in a scenario where tissue is present close to the coil. However, the magnetic shield increases the longitudinal field of view, which reduces the transmit efficiency by 25%.Peer reviewe

Exploring the Relationship between Subjectively Experienced Severity of Imprisonment and Recidivism: A Neglected Element in Testing Deterrence Theory

Criminal Justice: Legitimacy, accountability, and effectivit

Combining a reduced field of excitation with SENSE-based parallel imaging for maximum imaging efficiency

PURPOSE: To show that a combination of parallel imaging using sensitivity encoding (SENSE) and inner volume imaging (IVI) combines the known benefits of both techniques. SENSE with a reduced field of excitation (rFOX) is termed rSENSE. THEORY AND METHODS: The noise level in SENSE reconstructions is reduced by removing voxels from the unfolding process that are rendered silent by using rFOX. The silent voxels need to be identified beforehand, this is done by using rFOX in the coil sensitivity maps. In vivo experiments were performed at 7 Tesla using a 32-channel receive coil. RESULTS: Good image quality could be obtained in vivo with rSENSE at acceleration factors that are higher than could be obtained using SENSE or IVI alone. With rSENSE we were also able to accelerate scans using an rFOX that was purposely designed to be imperfect or incompatible at all with IVI. CONCLUSION: rSENSE has been demonstrated in vivo with two-dimensionally selective radiofrequency pulses. Besides allowing additional scan acceleration, it offers a greater robustness and flexibility than IVI. The proposed method can be used with other field strengths, anatomies and other rFOX techniques. Magn Reson Med 78:88-96, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution Non Commercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes

A deep learning method for image-based subject-specific local SAR assessment

Purpose: Local specific absorption rate (SAR) cannot be measured and is usually evaluated by offline numerical simulations using generic body models that of course will differ from the patient's anatomy. An additional safety margin is needed to include this intersubject variability. In this work, we present a deep learning–based method for image-based subject-specific local SAR assessment. We propose to train a convolutional neural network to learn a “surrogate SAR model” to map the relation between subject-specific (Formula presented.) maps and the corresponding local SAR. Method: Our database of 23 subject-specific models with an 8–transmit channel body array for prostate imaging at 7 T was used to build 5750 training samples. These synthetic complex (Formula presented.) maps and local SAR distributions were used to train a conditional generative adversarial network. Extra penalization for local SAR underestimation errors was included in the loss function. In silico and in vivo validation were performed. Results: In silico cross-validation shows a good qualitative and quantitative match between predicted and ground-truth local SAR distributions. The peak local SAR estimation error distribution shows a mean overestimation error of 15% with 13% probability of underestimation. The higher accuracy of the proposed method allows the use of less conservative safety factors compared with standard procedures. In vivo validation shows that the method is applicable with realistic measurement data with impressively good qualitative and quantitative agreement to simulations. Conclusion: The proposed deep learning method allows online image-based subject-specific local SAR assessment. It greatly reduces the uncertainty in current state-of-the-art SAR assessment methods, reducing the time in the examination protocol by almost 25%