Increasing temporal resolution of DSC perfusion MRI using the analytic image concept

Object  

Dynamic susceptibility contrast MRI (DSC-MRI) is increasingly being used to evaluate cerebral microcirculation. In this study, the use of the analytic image reconstruction (AIR), with the aim to increase the temporal resolution, is evaluated for DSC-MRI in small animals.     

Ultra-high field diffusion tensor imaging of articular cartilage correlated with histology and scanning electron microscopy

Object

To investigate the relationship of the different diffusion tensor imaging (DTI) parameters (ADC, FA, and first eigenvector (EV)) to the constituents (proteoglycans and collagen), the zonal arrangement of the collagen network, and mechanical loading of articular cartilage.

Material and methods

DTI of eight cartilage-on-bone samples of healthy human patellar cartilage was performed at 17.6 T. Three samples were additionally imaged under indentation loading. After DTI, samples underwent biomechanical testing, safranin-O staining for semiquantitative proteoglycan estimation, and scanning electron microscopy (SEM) for depicting collagen architecture.

Results

From the articular surface to the bone–cartilage interface, ADC continuously decreased and FA increased. Cartilage zonal heights calculated from EVs strongly correlated with SEM-derived zonal heights (P r ²=0.87). Compression reduced ADC in the superficial 30% of cartilage and increased FA in the superficial 5% of cartilage. Reorientation of the EVs indicative of collagen fiber reorientation under the indenter was observed. No significant correlation was found between ADC, FA, and compressive stiffness.

Conclusions

Correlating ADC and FA with proteoglycan and collagen content suggests that diffusion is dominated by different depth-dependent mechanisms within cartilage. Knowledge of the spatial distribution of the DTI parameters and their variation contributes to form a database for future analysis of defective cartilage.     

Parallel imaging in non-bijective, curvilinear magnetic field gradients: a concept study

Objectives The paper presents a novel and more generalized concept for spatial encoding by non-unidirectional, non- bijective spatial encoding magnetic fields (SEMs). In combination with parallel local receiver coils these fields allow one to overcome the current limitations of neuronal nerve stimulation. Additionally the geometry of such fields can be adapted to anatomy. Materials and methods As an example of such a parallel imaging technique using localized gradients (PatLoc)- system, we present a polar gradient system consisting of 2 × 8 rectangular current loops in octagonal arrangement, which generates a radial magnetic field gradient. By inverting the direction of current in alternating loops, a near sinusoidal field variation in the circumferential direction is produced. Ambiguities in spatial assignment are resolved by use of multiple receiver coils and parallel reconstruction. Simulations demonstrate the potential advantages and limitations of this approach. Results and conclusions The exact behaviour of PatLoc fields with respect to peripheral nerve stimulation needs to be tested in practice. Based on geometrical considerations SEMs of radial geometry allow for about three times faster gradient switching compared to conventional head gradient inserts and even more compared to whole body gradients. The strong nonlinear geometry of the fields needs to be considered for practical applications.     

一种适用于激光磁共振成像的磁场补偿装置

提出了一种适用于激光磁共振成像的磁场补偿装置,该装置可以与磁场循环系统集成在一起,实现对静止样品成像。文中首先根据实验要求对线圈产生的磁场进行了仿真,并制作出了实际的线圈,然后搭建了一种反馈型高精度恒流源,其长期工作时的稳定性优于2×10-4A。该补偿装置可将目标区域的地磁场抵消到100nT以内,基本满足激光磁共振成像的要求。     

Multimodal nonlinear endomicroscopic imaging probe using a double-core double-clad fiber and focus-combining micro-optical concept

Multimodal non-linear microscopy combining coherent anti-Stokes Raman scattering, second harmonic generation, and two-photon excited fluorescence has proved to ...     

Subjective acceptance of 7 Tesla MRI for human imaging

Objective One prerequisite for transferring ultra-high-field magnetic resonance imaging (MRI) (>3T) into clinical diagnostic workup is a low rate of side effects. To our knowledge, publications of subjective acceptance and willingness to undergo examinations at >3T are rare. We present first results from our research site. Materials and methods Exposure to 7T whole-body MRI of head, extremities, or breast was assessed in 102 subjects. They judged sources of discomfort (examination duration, room temperature) and physiological sensations (vertigo, light flashes) on a 10-point scale, differentiating between examination phases: table stationary or moving. For comparison, the same questionnaire was completed by 43 of these subjects after undergoing a 1.5T examination. Vertigo was the most pronounced sensation at 7T with 5% rating it as very unpleasant (none at 1.5T). This should be compared with the fact that the lengthy exam duration was regarded as even more uncomfortable. Compared to 1.5T, average study duration at 7T was roughly doubled, and 7T elicited a wider range of complaints. Conclusion Although the number of side effects is increased at 7T compared to 1.5T, 7T was well tolerated by the majority of subjects. Further data collection is necessary for better understanding of these effects.     

MR venography of the human brain using susceptibility weighted imaging at very high field strength

Objective We investigate the implications of high magnetic field strength on MR venography based on susceptibility-weighted imaging (SWI) and estimate the optimum echo time to obtain maximum contrast between blood and brain tissue. Materials and methods We measured tissue contrast and relaxation times at 7 T of gray matter, white matter, and venous blood in vivo. Results relaxation times of gray matter, white matter, and venous blood in vivo yielded 32.9 ± 2.3, 27.7 ± 4.3, and 7.4 ± 1.4 ms, respectively. Optimum TE was found to be 15 ms which is supported by theoretical considerations. Using this optimum TE, we acquired 3D high resolution datasets with a large volume coverage in a short measurement time that show very detailed microanatomical structures of the human brain such as intracortical veins and laminar cortical substructures. Conclusions By applying optimised vessel filters (vesselness filter and vessel enhancing diffusion) whole brain MR venograms can be obtained at 7 T with a significantly reduced measurement time compared to 3 T.     

Simplified dipole concept for the assessment of transient electromagnetic field in the vicinity of grounding grid

The objective of this work is to provide a simplified model to analyse the electromagnetic emission of the grounding grid thus enabling engineers to perform parametric studies rapidly without greater loss of accuracy. The proposed approach is based on the use of the transmission line theory and the concept of dipole radiation in the presence of a lossy half‐space including the Sommerfeld integral approach. The model proposes to determine the electromagnetic fields (soil and air) and current distribution in a grounding system. The proposed model is described and illustrated with applications. The limitations and advantages are also discussed and compared against antenna theory counter parts. Copyright © 2014 John Wiley & Sons, Ltd.     

对超高压输电网络建设的几点建议

概述了我国超高压输电网络的现状与未来发展的形势,从电源布局、电压等级、电网结线及塔型和杆塔材料等方面提出了一些改进的建议。     

Progress in high field MRI at the University of Florida

In this article we report on progress in high magnetic field MRI at the University of Florida in support of our new 750MHz wide bore and 11.7T/40cm MR instruments. The primary emphasis is on the associated rf technology required, particularly high frequency volume and phased array coils. Preliminary imaging results at 750MHz are presented. Our results imply that the pursuit of even higher fields seems warranted.     

US regulatory considerations for low field magnetic resonance imaging systems

Although there has been a resurgence of interest in low field magnetic resonance imaging (MRI) systems in recent years, low field MRI is not a new concept. FDA has a long history of evaluating the safety and effectiveness of MRI systems encompassing a wide range of field strengths. Many systems seeking marketing authorization today include new technological features (such as artificial intelligence), but this does not fundamentally change the regulatory paradigm for MR systems. In this review, we discuss some of the US regulatory considerations for low field magnetic resonance imaging (MRI) systems, including applicability of existing laws and regulations and how the U.S. Food and Drug Administration (FDA) evaluates low field MRI systems for market authorization. We also discuss regulatory considerations in the review of low field MRI systems incorporating novel AI technology. We foresee that MRI systems of all field strengths intended for general diagnostic use will continue to be evaluated for marketing clearance by the metric of substantial equivalence set forth in the premarket notification pathway.

     

Comparative analysis of high field MRI and histology for ex vivo whole organ imaging: assessment of placental functional morphology in a murine model

Magnetic Resonance Materials in Physics, Biology and Medicine - The purpose of our study was to evaluate MRI as a tool to examine placental morphology in a murine model in comparison to classical...     

Progress in high field MRI at the University of Florida.

In this article we report on progress in high magnetic field MRI at the University of Florida in support of our new 750MHz wide bore and 11.7T/40cm MR instruments. The primary emphasis is on the associated rf technology required, particularly high frequency volume and phased array coils. Preliminary imaging results at 750MHz are presented. Our results imply that the pursuit of even higher fields seems warranted.     

An integrated target field framework for point-of-care halbach array low-field MRI system design

Objective

Low-cost low-field point-of-care MRI systems are used in many different applications. System design has correspondingly different requirements in terms of imaging field-of-view, spatial resolution and magnetic field strength. In this work an iterative framework has been created to design a cylindrical Halbach-based magnet along with integrated gradient and RF coils that most efficiently fulfil a set of user-specified imaging requirements.

Methods

For efficient integration, target field methods are used for each of the main hardware components. These have not been used previously in magnet design, and a new mathematical model was derived accordingly. These methods result in a framework which can design an entire low-field MRI system within minutes using standard computing hardware.

Results

Two distinct point-of-care systems are designed using the described framework, one for neuroimaging and the other for extremity imaging. Input parameters are taken from literature and the resulting systems are discussed in detail.

Discussion

The framework allows the designer to optimize the different hardware components with respect to the desired imaging parameters taking into account the interdependencies between these components and thus give insight into the influence of the design choices.

     

A straightforward method for incorporating mutually-coupledcircuits into the bus admittance matrix using the concept of artificialbranches

A method is presented for demonstrating the effects of mutual inductive coupling to students which only requires inspection. The method, which is computationally stable for all practical cases investigated by the authors, produces no additional buses and retains the topological structure of the prototype except for the addition of some artificial lines. It is demonstrated that the procedure is applicable to a variety of situations and, once the basic principle is understood, can be immediately applied to yield a coupling-free equivalent network whose parameters are directly amenable to inclusion in the bus admittance matrix     

Presurgical brain mapping in epilepsy using simultaneous EEG and functional MRI at ultra-high field: feasibility and first results

Magnetic Resonance Materials in Physics, Biology and Medicine - The aim of this study was to demonstrate that eloquent cortex and epileptic-related hemodynamic changes can be safely and reliably...     

High resolution imaging of the intracranial vessel wall at 3 and 7 T using 3D fast spin echo MRI

Magnetic Resonance Materials in Physics, Biology and Medicine - High resolution MRI of the intracranial vessel wall provides important insights in the assessment of intracranial vascular disease....     

Magnetic resonance imaging of iron-oxide labeled SK-Mel 28 human melanoma cells in the chick embryo using a clinical whole body MRI scanner

Purpose: To evaluate advantages and limitations of magnetic resonance imaging (MRI) to monitor the migration of superparamagnetic iron oxide (SPIO) labeled cells in the chick embryo. Materials and methods: Labeled human SK-Mel 28 melanoma cells were injected into the E2 chick embryo neural tube. Embryos were examined with a clinical 3 T MRI whole body system using 3D -weighted sequences with isotropic spatial resolutions of 0.3–1.0 mm. MR-measurements of embryos were performed 2 – 16 days after cell injection. MRI findings were verified by dissection and histology. Results: After injection, melanoma cells formed aggregations that were detectable in the neural tube as signal voids in MR images from day 2 after injection. Emigrating cells later left MRI detectable tracks. Aggregates that remained in the neural tube left label that was absorbed by glia cells. In E18 chick embryos, signals of haematopoiesis interfered with signals from cell labeling. Conclusion: It was shown that SK-Mel 28 cells will resume the neural crest pathways after injection into the embryonic micro-environment. SPIO cell labeling allows monitoring of transplanted melanoma cells during embryonic development. MRI using the standard clinical equipment promises to be valuable for high-sensitive monitoring of ex-vivo labeled cells in the chick embryo.     

Semi-analytical approach for electromagnetic field diffusion using hertz potential

(Paper written in French) This paper contains two parts: In the first part the Hertz vectorial potential is introduced and its possible use in solving electromagnetic diffusion problems common in electrical engineering is considered. Links between this potential and other commonly used potentials are established, and a formulation procedure using three vectorial equations is proposed. This approach has several advantages due to its simplicity and the fact that it requires only a few values for computation. This method is next applied efficiently to the interaction in the static regime between a line conductor crossed by a sine-shaped current and a finite-thickness metallic plate. In the second part, a specific field quadrature method is employed in integral form. This allows the confirmation of the methods accuracy and good numerical stability.     

The concept of global space system for supplying the earth with the electric power using the lunar resource

The concept of global space system for supplying the Earth with electric power using lunar resources is presented. The places of assembly and arrangement are the stable Lagrangian libration points (L4 or L5) of the Earth-Moon gravitational field. The main freight traffic from the Moon to the libration point is performed by Moon-based electromagnetic catapults. The energy is transported from space to the Earth by means of the laser beam. The power of the space power system is several dozens of terawatts. A part of this power is used for supporting the lunar industrial infrastructure.