Viktor Vegh

Intravenous immunoglobulin protects neurons against amyloid beta‐peptide toxicity and ischemic stroke by attenuating multiple cell death pathways

J. Neurochem. (2012) 122, 321–332.

Globally optimal superconducting magnets part I: minimum stored energy (MSE) current density map.

An optimal current density map is crucial in magnet design to provide the initial values within search spaces in an optimization process for determining the final coil arrangement of the magnet. A strategy for obtaining globally optimal current density maps for the purpose of designing magnets with coaxial cylindrical coils in which the stored energy is minimized within a constrained domain is outlined. The current density maps obtained utilising the proposed method suggests that peak current densities occur around the perimeter of the magnet domain, where the adjacent peaks have alternating current directions for the most compact designs. As the dimensions of the domain are increased, the current density maps yield traditional magnet designs of positive current alone. These unique current density maps are obtained by minimizing the stored magnetic energy cost function and therefore suggest magnet coil designs of minimal system energy. Current density maps are provided for a number of different domain arrangements to illustrate the flexibility of the method and the quality of the achievable designs.

Echo time-dependent quantitative susceptibility mapping contains information on tissue properties

Magnetic susceptibility is a physical property of matter that varies depending on chemical composition and abundance of different molecular species. Interest is growing in mapping of magnetic susceptibility in the human brain using magnetic resonance imaging techniques, but the influences affecting the mapped values are not fully understood.

Minimum Stored Energy High-Field MRI Superconducting Magnets

A globally optimum minimum stored energy optimization strategy is implemented to design actively shielded superconducting magnet configurations used in high-field applications. The current density map is first obtained and used as a foundation for the magnet configurations by placing coils at current density local extremities. Optimized current density maps based on the stored energy formulation along with final magnet arrangements are provided to illustrate the findings. In this work, the focus was on compact superconducting magnets as measured by physical size and system footprint for given magnetic field properties inside the imaging region. The process of obtaining the current density maps proposed here over the given magnet domain, where superconducting coils are laid out, suggests that peak current densities occur around the perimeter of the domain, where in the most compact designs, with the domain length less than 1 m, the current direction alternates amongst adjacent coils. To reduce the peak magnetic field to acceptable levels on the superconductors in high-field designs, the size of the magnet domain is made larger, to the extent that the current densities no longer alternate between coils.

A Variable Order Fractional Differential-Based Texture Enhancement Algorithm with Application in Medical Imaging

Texture enhancement is one of the most important techniques in digital image processing and plays an essential role in medical imaging since textures discriminate information. Most image texture enhancement techniques use classical integral order differential mask operators or fractional differential mask operators using fixed fractional order. These masks can produce excessive enhancement of low spatial frequency content, insufficient enhancement of large spatial frequency content, and retention of high spatial frequency noise. To improve upon existing approaches of texture enhancement, we derive an improved Variable Order Fractional Centered Difference (VOFCD) scheme which dynamically adjusts the fractional differential order instead of fixing it. The new VOFCD technique is based on the second order Riesz fractional differential operator using a Lagrange 3-point interpolation formula, for both grey scale and colour image enhancement. We then use this method to enhance photographs and a set of medical images related to patients with stroke and Parkinson’s disease. The experiments show that our improved fractional differential mask has a higher signal to noise ratio value than the other fractional differential mask operators. Based on the corresponding quantitative analysis we conclude that the new method offers a superior texture enhancement over existing methods.

Globally optimal superconducting magnets part II: symmetric MSE coil arrangement.

A globally optimal superconducting magnet coil design procedure based on the Minimum Stored Energy (MSE) current density map is outlined. The method has the ability to arrange coils in a manner that generates a strong and homogeneous axial magnetic field over a predefined region, and ensures the stray field external to the assembly and peak magnetic field at the wires are in acceptable ranges. The outlined strategy of allocating coils within a given domain suggests that coils should be placed around the perimeter of the domain with adjacent coils possessing alternating winding directions for optimum performance. The underlying current density maps from which the coils themselves are derived are unique, and optimized to possess minimal stored energy. Therefore, the method produces magnet designs with the lowest possible overall stored energy. Optimal coil layouts are provided for unshielded and shielded short bore symmetric superconducting magnets.

Characterization of anomalous relaxation using the time-fractional Bloch equation and multiple echo T2*-weighted magnetic resonance imaging at 7 T

To study the utility of fractional calculus in modeling gradient‐recalled echo MRI signal decay in the normal human brain.

MRI signal phase oscillates with neuronal activity in cerebral cortex: Implications for neuronal current imaging

Neuronal activity produces transient ionic currents that may be detectable using magnetic resonance imaging (MRI). We examined the feasibility of MRI-based detection of neuronal currents using computer simulations based on the laminar cortex model (LCM). Instead of simulating the activity of single neurons, we decomposed neuronal activity to action potentials (AP) and postsynaptic potentials (PSP). The geometries of dendrites and axons were generated dynamically to account for diverse neuronal morphologies. Magnetic fields associated with APs and PSPs were calculated during spontaneous and stimulated cortical activity, from which the neuronal current induced MRI signal was determined. We found that the MRI signal magnitude change (<0.1 ppm) is below currently detectable levels but that the signal phase change is likely to be detectable. Furthermore, neuronal MRI signals are sensitive to temporal and spatial variations in neuronal activity but independent of the intensity of neuronal activation. Synchronised neuronal activity produces large phase changes (in the order of 0.1 mrad). However, signal phase oscillates with neuronal activity. Consequently, MRI scans need to be synchronised with neuronal oscillations to maximise the likelihood of detecting signal phase changes due to neuronal currents. These findings inform the design of MRI experiments to detect neuronal currents.

Multi-term time-fractional Bloch equations and application in magnetic resonance imaging

Magnetic resonance imaging can reveal exquisite details about the complex structure and function of human tissue. However, magnetic resonance imaging signal behaviour at high or ultra-high field has shown increased deviation from the classically expected mono-exponential relaxation. The underlying mechanism of anomalous relaxation can contribute to a better understanding of the interaction of spins with their surroundings. The purpose of this work is to explore the utility of the multi-term time-fractional Bloch equations in relation to the anomalous relaxation processes. We proposed an effective predictor–corrector method to solve the multi-term equations. Voxel-level temporal fitting of the magnetic resonance imaging signal was performed based on the model developed from the multi-term time-fractional Bloch equations. A feasible parameter estimation method based on hybrid Nelder–Mead simplex search and particle swarm optimisation was introduced to perform the curve fitting. The extra time-fractional terms provide flexibility in the relaxation process.

Effective Protocol for Database Similarity Searching of Heteronuclear Single Quantum Coherence Spectra

The nuclear magnetic resonance (NMR) chemical shift exquisitely describes the chemical environment of the atoms in a molecule. Here we describe methods that utilize this information as an experimental probe to match 2D NMR heteronuclear single quantum coherence (HSQC) spectra of pure, unknown compounds to a database of known compounds. We implemented and compared two different approaches for similarity searching of HSQC spectra. According to our findings, our new discrete self-adaptive differential evolution method performs better than the previously published shifted grid, multiple resolution approach. The new method is provided in detail and comparisons have been performed for a set of HSQC spectra. The similarity comparison involves a peak-to-peak matching of different spectra, followed by a selection criterion and ranking to establish a level of match.