Структура и закономерности науки

Cardiovascular MR imaging (CVMR) has become a valuable diagnostic imaging modality for the non-invasive detection cardiovascular diseases. In this review, first key concepts and practical considerations of parallel CVMR are outlined. Next, highly accelerated CVMR applications are reviewed, ranging from cardiac anatomical and functional assessment to myocardial perfusion and viability to MR angiography of the coronary arteries and the large vessels. Finally, current trends, including the broad move towards high field imaging, and future directions in highly parallel CVMR are considered..

The (un)conscious mouse as a model for human brain functions: key principles of anesthesia and their impact on translational neuroimaging

In recent years, technical and procedural advances have brought functional magnetic resonance imaging (fMRI) to the field of murine neuroscience. Due to its unique capacity to measure functional activity non-invasively, across the entire brain, fMRI allows for the direct comparison of large-scale murine and human brain functions. This opens an avenue for bidirectional translational strategies to address fundamental questions ranging from neurological disorders to the nature of consciousness. The key challenges of murine fMRI are: (1) to generate and maintain functional brain states that approximate those of calm and relaxed human volunteers, while (2) preserving neurovascular coupling and physiological baseline conditions. Low-dose anesthetic protocols are commonly applied in murine functional brain studies to prevent stress and facilitate a calm and relaxed condition among animals. Yet, current mono-anesthesia has been shown to impair neural transmission and hemodynamic integrity. By linking the current state of murine electrophysiology, Ca(2+) imaging and fMRI of anesthetic effects to findings from human studies, this systematic review proposes general principles to design, apply and monitor anesthetic protocols in a more sophisticated way. The further development of balanced multimodal anesthesia, combining two or more drugs with complementary modes of action helps to shape and maintain specific brain states and relevant aspects of murine physiology. Functional connectivity and its dynamic repertoire as assessed by fMRI can be used to make inferences about cortical states and provide additional information about whole-brain functional dynamics. Based on this, a simple and comprehensive functional neurosignature pattern can be determined for use in defining brain states and anesthetic depth in rest and in response to stimuli. Such a signature can be evaluated and shared between labs to indicate the brain state of a mouse during experiments, an important step toward translating findings across species

Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond

Objective: This work investigates electrodynamic constraints, explores RF antenna concepts and examines the transmission fields (B 1 + ) and RF power deposition of dipole antenna arrays for 1H magnetic resonance of the human brain at 1 GHz (23.5 T). Materials and methods: Electromagnetic field (EMF) simulations are performed in phantoms with average tissue simulants for dipole antennae using discrete frequencies [300 MHz (7.0 T) to 3 GHz (70.0 T)]. To advance to a human setup EMF simulations are conducted in anatomical human voxel models of the human head using a 20-element dipole array operating at 1 GHz. Results: Our results demonstrate that transmission fields suitable for 1H MR of the human brain can be achieved at 1 GHz. An increase in transmit channel density around the human head helps to enhance B 1 + in the center of the brain. The calculated relative increase in specific absorption rate at 23.5 versus 7.0 T was below 1.4 (in-phase phase setting) and 2.7 (circular polarized phase setting) for the dipole antennae array. Conclusion: The benefits of multi-channel dipole antennae at higher frequencies render MR at 23.5 T feasible from an electrodynamic standpoint. This very preliminary finding opens the door on further explorations that might be catalyzed into a 20-T class human MR system

Solving the time- and frequency-multiplexed problem of constrained radiofrequency induced hyperthermia

Targeted radiofrequency (RF) heating induced hyperthermia has a wide range of applications, ranging from adjunct anti-cancer treatment to localized release of drugs. Focal RF heating is usually approached using time-consuming nonconvex optimization procedures or approximations, which significantly hampers its application. To address this limitation, this work presents an algorithm that recasts the problem as a semidefinite program and quickly solves it to global optimality, even for very large (human voxel) models. The target region and a desired RF power deposition pattern as well as constraints can be freely defined on a voxel level, and the optimum application RF frequencies and time-multiplexed RF excitations are automatically determined. 2D and 3D example applications conducted for test objects containing pure water (r(target) = 19 mm, frequency range: 500–2000 MHz) and for human brain models including brain tumors of various size (r(1) = 20 mm, r(2) = 30 mm, frequency range 100–1000 MHz) and locations (center, off-center, disjoint) demonstrate the applicability and capabilities of the proposed approach. Due to its high performance, the algorithm can solve typical clinical problems in a few seconds, making the presented approach ideally suited for interactive hyperthermia treatment planning, thermal dose and safety management, and the design, rapid evaluation, and comparison of RF applicator configurations

Development and evaluation of a small and mobile Magneto Alert Sensor (MALSE) to support safety requirements for magnetic resonance imaging

OBJECTIVE: The purpose of this study is to (i) design a small and mobile Magnetic field ALert SEnsor (MALSE), (ii) to carefully evaluate its sensors to their consistency of activation/deactivation and sensitivity to magnetic fields, and (iii) to demonstrate the applicability of MALSE in 1.5 T, 3.0 T and 7.0 T MR fringe field environments. METHODS: MALSE comprises a set of reed sensors, which activate in response to their exposure to a magnetic field. The activation/deactivation of reed sensors was examined by moving them in/out of the fringe field generated by 7TMR. RESULTS: The consistency with which individual reed sensors would activate at the same field strength was found to be 100% for the setup used. All of the reed switches investigated required a substantial drop in ambient magnetic field strength before they deactivated. CONCLUSIONS: MALSE is a simple concept for alerting MRI staff to a ferromagnetic object being brought into fringe magnetic fields which exceeds MALSEs activation magnetic field. MALSE can easily be attached to ferromagnetic objects within the vicinity of a scanner, thus creating a barrier for hazardous situations induced by ferromagnetic parts which should not enter the vicinity of an MR-system to occur

Cyclic behavior and microstructural stability of ultrafine-grained AA6060 under strain-controlled fatigue

AbstractThe strain-controlled fatigue behavior of AA6060, a precipitation hardening aluminum alloy, was investigated in ultrafinegrained (UFG) conditions after severe plastic deformation (SPD) by equal-channel angular pressing (ECAP). Two as-processed conditions, representing different stages of strain hardening and grain refinement as well as a ductility-optimized condition, achieved by a combined ECAP and aging treatment were considered. Low-voltage scanning transmission electron microscopy on samples stopped at characteristic stages of the fatigue process was applied to investigate the microstructural development. The as-processed as well as the optimized condition showed cyclic softening, which was found to be dependent on the amount of prestrain induced by ECAP processing. This is linked to dynamic recovery processes in the microstructure, indicated by a clearer distinction of grain boundaries and a reduction of dislocations in the grain interior. For all applied plastic strain amplitudes, ranging from Δεpl/2=1×10−3 to 5×10−3, the fatigue life of the ductility-optimized condition did not reach that of the severely work-hardened counterpart. For explaining this unexpected result, the differing (size-dependent) effectiveness of precipitates for the pinning of dislocations during cyclic loading was considered

From ultrahigh to extreme field magnetic resonance: where physics, biology and medicine meet

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On the Impact of Texture and Grain Size on the Pseudoelastic Properties of Polycrystalline Fe–Ni–Co–Al–Ti Alloy

The effects of thermomechanical treatments on crystallographic texture and grain size evolution and their impact on the pseudoelastic properties in Fe41–Ni28–Co17–Al11.5–Ti2.5 (at.%) were studied in the present paper. The results show that cold rolling leads to brass-type texture in this alloy, which is typical for low stacking fault energy materials. Thermal treatments up to 1300 °C were conducted and it is shown that the presence of β-phase helps to control grain growth. After the dissolution of the secondary phase induced by heat treatment at higher temperatures, a strong {230}〈001〉 recrystallization texture evolves in cold rolled samples already upon imposing medium reduction ratios. Finally, good pseudoelastic properties are found in conditions being characterized by adequate texture and grain sizes spanning over the entire thickness of the samples tested.Fil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lauhoff, C.. University of Kassel; AlemaniaFil: Wegener, T.. University of Kassel; AlemaniaFil: Niendorf, T.. University of Kassel; AlemaniaFil: Krooß, P.. University of Kassel; Alemani

Performance of compressed sensing for fluorine-19 magnetic resonance imaging at low signal-to-noise ratio conditions

PURPOSE: To examine the performance of compressed sensing (CS) in reconstructing low signal-to-noise ratio (SNR) (19)F MR signals that are close to the detection threshold and originate from small signal sources with no a priori known location. METHODS: Regularization strength was adjusted automatically based on noise level. As performance metrics, root-mean-square deviations, true positive rates (TPRs), and false discovery rates were computed. CS and conventional reconstructions were compared at equal measurement time and evaluated in relation to high-SNR reference data. (19)F MR data were generated from a purpose-built phantom and benchmarked against simulations, as well as from the experimental autoimmune encephalomyelitis mouse model. We quantified the signal intensity bias and introduced an intensity calibration for in vivo data using high-SNR ex vivo data. RESULTS: Low-SNR (19)F MR data could be reliably reconstructed. Detection sensitivity was consistently improved and data fidelity was preserved for undersampling and averaging factors of α = 2 or = 3. Higher α led to signal blurring in the mouse model. The improved TPRs at α = 3 were comparable to a 2.5-fold increase in measurement time. Whereas CS resulted in a downward bias of the (19)F MR signal, Fourier reconstructions resulted in an unexpected upward bias of similar magnitude. The calibration corrected signal-intensity deviations for all reconstructions. CONCLUSION: CS is advantageous whenever image features are close to the detection threshold. It is a powerful tool, even for low-SNR data with sparsely distributed (19)F signals, to improve spatial and temporal resolution in (19)F MR applications