A novel method of high-spatial-resolution, 3D B1-field distribution measurements is presented. The method is independent of the MR-scanner, and it allows for automated acquisitions of complete maps ...of all magnetic field vector components for both proton and heteronuclear MR coils of arbitrary geometrical shapes. The advantage of the method proposed here, compared with methods based on measurements with an MR-scanner, is that a complete image of both receive and transmit B1-fields, including the phase of the B1-field, can be acquired. The B1 field maps obtained in this manner can be used for absolute quantification of metabolites in MRS experiments, as well as for intensity compensations in imaging experiments, both of which are important concepts in biological and medical MR applications. Another use might be in coil development and testing. A comparison with B1 field magnitude maps obtained with an MR-scanner was included to validate the accuracy of the proposed method.
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•Spatial distribution of a B1-field affects results•Spatial variations of the signals hampers quantitative measurements•Spatial maps of the B1-field must be obtained•B1-field maps independent from the MR-scanner are advantageous•Especially for low gamma (SNR) nuclei
We propose a method to calculate field maps from the phase of each EPI in an fMRI time series. These field maps can be used to correct the corresponding magnitude images for distortion caused by ...inhomogeneity in the static magnetic field. In contrast to conventional static distortion correction, in which one ‘snapshot’ field map is applied to all subsequent fMRI time points, our method also captures dynamic changes to B
0
which arise due to motion and respiration. The approach is based on the assumption that the non-B
0
-related contribution to the phase measured by each radio-frequency coil, which is dominated by the coil sensitivity, is stable over time and can therefore be removed to yield a field map from EPI.
Our solution addresses imaging with multi-channel coils at ultra-high field (7 T), where phase offsets vary rapidly in space, phase processing is non-trivial and distortions are comparatively large. We propose using dual-echo gradient echo reference scan for the phase offset calculation, which yields estimates with high signal-to-noise ratio. An extrapolation method is proposed which yields reliable estimates for phase offsets even where motion is large and a tailored phase unwrapping procedure for EPI is suggested which gives robust results in regions with disconnected tissue or strong signal decay.
Phase offsets are shown to be stable during long measurements (40 min) and for large head motions. The dynamic distortion correction proposed here is found to work accurately in the presence of large motion (up to 8.1°), whereas a conventional method based on single field map fails to correct or even introduces distortions (up to 11.2 mm). Finally, we show that dynamic unwarping increases the temporal stability of EPI in the presence of motion.
Our approach can be applied to any EPI measurements without the need for sequence modification.
This paper proposes a geometrical multi-satellite discontinuous-coverage analysis method for arbitrary fields that considers the J2 perturbation. First, to calculate the single-satellite ...discontinuous coverage performance, the concept of single-satellite field mapping is introduced. Additionally, based on the geometric relationship between any two satellites, relative field mapping is proposed, which can transform the double-satellite coverage problem into an equivalent single-satellite coverage problem. Furthermore, by extending the concept of the relative field mapping, the constellation field mapping and its mapping regions are presented, which can be used to analytically calculate the revisit time of the constellation. The proposed method is verified by simulations under different conditions such as altitude, inclination, target latitudes, the field parameters of the sensor, sunlight, and the constellation configuration. The simulation results show that the maximum revisit time can be accurately obtained and intuitively displayed with the proposed method, which provides a valuable reference for Earth observation constellation design.
•The analytical constellation field mapping with translation property is presented for the first time.•The proposed constellation field mapping is time-invariant and suitable for any field of view.•The discontinuous coverage can be obtained rapidly, and the sunlight constraint is considered.•Other characteristics of the constellation coverage are obtained through this analysis approach.
Purpose
To develop a robust algorithm for field‐mapping in the presence of water–fat components, large B0 field inhomogeneities and MR signal voids and to apply the developed method in body ...applications of quantitative susceptibility mapping (QSM).
Methods
A framework solving the cost‐function of the water–fat separation problem in a single‐min‐cut graph‐cut based on the variable‐layer graph construction concept was developed. The developed framework was applied to a numerical phantom enclosing an MR signal void, an air bubble experimental phantom, 14 large field of view (FOV) head/neck region in vivo scans and to 6 lumbar spine in vivo scans. Field‐mapping and subsequent QSM results using the proposed algorithm were compared to results using an iterative graph‐cut algorithm and a formerly proposed single‐min‐cut graph‐cut.
Results
The proposed method was shown to yield accurate field‐map and susceptibility values in all simulation and in vivo datasets when compared to reference values (simulation) or literature values (in vivo). The proposed method showed improved field‐map and susceptibility results compared to iterative graph‐cut field‐mapping especially in regions with low SNR, strong field‐map variations and high R2∗ values.
Conclusions
A single‐min‐cut graph‐cut field‐mapping method with a variable‐layer construction was developed for field‐mapping in body water–fat regions, improving quantitative susceptibility mapping particularly in areas close to MR signal voids.
•Electron Holography and DPC have been applied to a simple silicon pn-junction, a silicon CMOS device and an InGaN/GaN quantum well structure.•We discuss the artefacts that are present when using ...both techniques to measure fields.•We discuss the sensitivity, spatial resolution, advantages and disadvantages of each technique.•The use of a convergent beam for DPC causes additional problems with dynamical diffraction which is more easily eliminated when using a plane wave for electron holography.
To provide a direct comparison, off-axis holography and differential phase contrast have been performed using the same microscope on the same specimens for the measurement of active dopants and piezoelectric fields. The sensitivity and spatial resolution of the two techniques have been assessed through the study of a simple silicon p-n junction observed at different bias voltages applied in-situ. For an evaluation of limitations and artefacts of the methods in more complicated systems a silicon pMOS device and an InGaN/GaN superlattice with 2.2-nm In0.15Ga0.85N quantum wells is investigated. We demonstrate the effects of dynamical scattering on the electric field measurements in the presence of local strain-induced sample tilts and its dependence on parameters like the convergence angle.
This paper proposes a geometric-based method of the ground-point visibility from a satellite or satellite constellation in elliptical orbit considering the J 2 perturbation. First, the field-element ...equations describing the relationship between the elliptical satellite orbit, field parameters, and ground point are introduced and can be solved semi-analytically. Also, using a two-dimensional map composed of the mean argument of latitude and geographic longitude of the ascending node, the problem of calculating visible intervals is transformed into a simple intersection problem of a group of parallel lines and a time-invariant region generated by the field-element equations. Furthermore, based on the geometric relationship between any two satellites, the relative field mapping and constellation field mapping are described, which can simplify the multi-satellite coverage problem to a single-satellite coverage problem and can be used to obtain the coverage performance of the constellation analytically and rapidly for the target. The simulation results demonstrate that the proposed method is rapid, efficient, intuitive, and accurate, suggesting its wide applications in constellation studies .
Despite the acceptance of electric vehicles (EVs) by consumers in developed countries, consumers' intentions towards these smart devices (SD) and the steps that can be taken to expand in this market ...continue to be investigated in developing countries such as Turkey. In this study, policies and incentives for the purchase of Electric Vehicles in different countries were examined, consumer concerns before the adoption of SDs were evaluated, and then consumer intentions in adopting EVs with models such as reasoned action theory, planned behavior theory, and technology acceptance model were evaluated with bibliometric analysis through conducted studies. Data from 63 publications accessed from Scopus, Web of Science, and DergiPark databases were used in the field mapping process. The results provide insights into increasing the market share of electric vehicles, which are critical in reducing the carbon footprint, by recommending the issues that need to be highlighted to the industry and researchers.
Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data ...for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high-quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching ‘work streams’ that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.
Pulsed Field Mapping of Ventricular Tachycardia Nies, Moritz; Koruth, Jacob S.; Musikantow, Daniel R. ...
JACC. Clinical electrophysiology,
March 2024, 2024-03-00, Volume:
10, Issue:
3
Journal Article
PDF
