Portable, bedside, low-field magnetic resonance imaging for evaluation of intracerebral hemorrhage.

Radiological examination of the brain is a critical determinant of stroke care pathways. Accessible neuroimaging is essential to detect the presence of intracerebral hemorrhage (ICH). Conventional magnetic resonance imaging (MRI) operates at high magnetic field strength (1.5-3 T), which requires an access-controlled environment, rendering MRI often inaccessible. We demonstrate the use of a low-field MRI (0.064 T) for ICH evaluation. Patients were imaged using conventional neuroimaging (non-contrast computerized tomography (CT) or 1.5/3 T MRI) and portable MRI (pMRI) at Yale New Haven Hospital from July 2018 to November 2020. Two board-certified neuroradiologists evaluated a total of 144 pMRI examinations (56 ICH, 48 acute ischemic stroke, 40 healthy controls) and one ICH imaging core lab researcher reviewed the cases of disagreement. Raters correctly detected ICH in 45 of 56 cases (80.4% sensitivity, 95%CI: [0.68-0.90]). Blood-negative cases were correctly identified in 85 of 88 cases (96.6% specificity, 95%CI: [0.90-0.99]). Manually segmented hematoma volumes and ABC/2 estimated volumes on pMRI correlate with conventional imaging volumes (ICC = 0.955, p = 1.69e-30 and ICC = 0.875, p = 1.66e-8, respectively). Hematoma volumes measured on pMRI correlate with NIH stroke scale (NIHSS) and clinical outcome (mRS) at discharge for manual and ABC/2 volumes. Low-field pMRI may be useful in bringing advanced MRI technology to resource-limited settings.

A Synergistic Approach to Data-Driven Response Planning.

Public health practitioners face challenging, potentially high-consequence, problems that require computational support. Available computational tools may not adequately fit these problems, thus forcing practitioners to rely on qualitative estimates when making critical decisions. Scientists at the Center for Computational Epidemiology and Response Analysis and practitioners from the Texas Department of State Health Services (TXDSHS) have established a participatory development cycle where public health practitioners work closely with academia to foster the development of data-driven solutions for specific public health problems and to translate these solutions to practice. Tools developed through this cycle have been deployed at TXDSHS offices where they have been used to refine and enhance the region's medical countermeasure distribution and dispensing capabilities. Consequently, TXDSHS practitioners planning for a 49-county region in North Texas have achieved a 29% reduction in the number of points of dispensing required to complete dispensing to the region within time limitations. Further, an entire receiving, staging, and storing site has been removed from regional plans, thus freeing limited resources (eg, personnel, security, and infrastructure) for other uses. In 2018, planners from Southeast Texas began using these tools to plan for a multi-county, full-scale exercise which was scheduled to be conducted in October 2019.

Whales in warming water: Assessing breeding habitat diversity and adaptability in Oceania's changing climate.

In the context of a changing climate, understanding the environmental drivers of marine megafauna distribution is important for conservation success. The extent of humpback whale breeding habitats and the impact of temperature variation on their availability are both unknown. We used 19 years of dedicated survey data from seven countries and territories of Oceania (1,376 survey days), to investigate humpback whale breeding habitat diversity and adaptability to climate change. At a fine scale (1 km resolution), seabed topography was identified as an important influence on humpback whale distribution. The shallowest waters close to shore or in lagoons were favored, although humpback whales also showed flexible habitat use patterns with respect to shallow offshore features such as seamounts. At a coarse scale (1° resolution), humpback whale breeding habitats in Oceania spanned a thermal range of 22.3-27.8°C in August, with interannual variation up to 2.0°C. Within this range, both fine and coarse scale analyses of humpback whale distribution suggested local responses to temperature. Notably, the most detailed dataset was available from New Caledonia (774 survey days, 1996-2017), where encounter rates showed a negative relationship to sea surface temperature, but were not related to the El Niño Southern Oscillation or the Antarctic Oscillation from previous summer, a proxy for feeding conditions that may impact breeding patterns. Many breeding sites that are currently occupied are predicted to become unsuitably warm for this species (>28°C) by the end of the 21st century. Based on modeled ecological relationships, there are suitable habitats for relocation in archipelagos and seamounts of southern Oceania. Although distribution shifts might be restrained by philopatry, the apparent plasticity of humpback whale habitat use patterns and the extent of suitable habitats support an adaptive capacity to ocean warming in Oceania breeding grounds.

Analysis of eddy currents induced by transverse and longitudinal gradient coils in different tungsten collimators geometries for SPECT/MRI integration.

PURPOSE: We investigated the temporal variation of the induced magnetic field due to the transverse and the longitudinal gradient coils in tungsten collimators arranged in hexagonal and pentagonal geometries with and without gaps between the collimators. METHODS: We modeled x-, y-, and z-gradient coils and different arrangements of single-photon emission computed tomography (SPECT) collimators using FEKO, a three-dimensional electromagnetic simulation tool. A time analysis approach was used to generate the pulsed magnetic field gradient. The approach was validated with measurements using a 7T MRI scanner. RESULTS: Simulations showed an induced magnetic field representing 4.66% and 0.87% of the applied gradient field (gradient strength = 500 mT/m) for longitudinal and transverse gradient coils, respectively. These values can be reduced by 75% by adding gaps between the collimators for the pentagonal arrangement, bringing the maximum induced magnetic field to less than 2% of the applied gradient for all of the gradient coils. CONCLUSION: Characterization of the maximum induced magnetic field shows that by adding gaps between the collimators for an integrated SPECT/MRI system, eddy currents can be corrected by the MRI system to avoid artifact. The numerical model was validated and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.

Encoding methods for B1(+) mapping in parallel transmit systems at ultra high field.

Parallel radiofrequency (RF) transmission, either in the form of RF shimming or pulse design, has been proposed as a solution to the B1(+) inhomogeneity problem in ultra high field magnetic resonance imaging. As a prerequisite, accurate B1(+) maps from each of the available transmit channels are required. In this work, four different encoding methods for B1(+) mapping, namely 1-channel-on, all-channels-on-except-1, all-channels-on-1-inverted and Fourier phase encoding, were evaluated using dual refocusing acquisition mode (DREAM) at 9.4 T. Fourier phase encoding was demonstrated in both phantom and in vivo to be the least susceptible to artefacts caused by destructive RF interference at 9.4 T. Unlike the other two interferometric encoding schemes, Fourier phase encoding showed negligible dependency on the initial RF phase setting and therefore no prior B1(+) knowledge is required. Fourier phase encoding also provides a flexible way to increase the number of measurements to increase SNR, and to allow further reduction of artefacts by weighted decoding. These advantages of Fourier phase encoding suggest that it is a good choice for B1(+) mapping in parallel transmit systems at ultra high field.

Methods for pulse artefact reduction: experiences with EEG data recorded at 9.4 T static magnetic field.

BACKGROUND: The feasibility of recording electroencephalography (EEG) at ultra-high static magnetic fields up to 9.4 T was recently demonstrated and is expected to be incorporated into functional magnetic resonance imaging (fMRI) studies at 9.4 T. Correction of the pulse artefact (PA) is a significant challenge since its amplitude is proportional to the strength of the magnetic field in which EEG is recorded. NEW METHOD: We conducted a study in which different PA correction methods were applied to EEG data recorded inside a 9.4 T scanner in order to retrieve visual P100 and auditory P300 evoked potentials. We explored different PA reduction methods, including the optimal basis set (OBS) method as well as objective and subjective component rejection using independent component analysis (ICA). RESULTS: ICA followed by objective rejection of components is optimal for retrieving visual P100 and auditory P300 from EEG data recorded inside the scanner. COMPARISON WITH EXISTING METHODS: Previous studies suggest that OBS or OBS followed by ICA are optimal for retrieving evoked potentials at 3T. In our EEG data recorded at 9.4 T OBS performed alone was not fully optimal for the identification of evoked potentials. OBS followed by ICA was partially effective. CONCLUSIONS: In this study ICA has been shown to be an important tool for correcting the PA in EEG data recorded at 9.4 T, particularly when automated rejection of components is performed.

Convex optimisation of gradient and shim coil winding patterns.

Gradient and shim coils were designed using boundary element methods with convex optimisation. The convex optimisation framework permits the prototyping of many different cost functions and constraints, for example ℓ(p)-norms of the current density. Several examples of gradients and shims were designed and simulated to demonstrate this, as well as to investigate the behaviour of new cost functions. A mixture of ℓ(1)- and ℓ(∞)-norms of the current density, when used as a regularisation term in the field synthesis problem, was found to produce coils with bunches of equally spaced windings that do not take up all of the available surface. This is thought to be beneficial in the design of coils that will be manufactured from wire with a fixed cross-section.

Theoretical design of gradient coils with minimum power dissipation: accounting for the discretization of current density into coil windings.

Gradient coil windings are typically constructed from either variable width copper tracks or fixed width wires. Excessive power dissipation within these windings during gradient coil operation limits the maximum drive current or duty cycle of the coil. It is common to design gradient coils in terms of a continuous minimum power current density and to perform a discretization to obtain the locations of the coil tracks or wires. However, the existence of finite gaps between these conductors and a maximum conductor width leads to an underestimation of coil resistance when calculated using the continuous current density. Put equivalently, the actual current density within the tracks or wires is higher than that used in the optimization and this departure results in suboptimal coil designs. In this work, a mapping to an effective current density is proposed to account for these effects and provide the correct contribution to the power dissipation. This enables the design of gradient coils that are genuinely optimal in terms of power minimization, post-discretization. The method was applied to the theoretical design of a variety of small x- and z-gradient coils for use in small animal imaging and coils for human head imaging. Computer-driven comparisons were made between coils designed with and without the current density mapping, in terms of simulated power dissipation. For coils to be built using variable width tracks, the method provides slight reductions in power dissipation in most cases and substantial gains only in cases where the minimum separation between track centre-lines is less than twice the gap size. However, for coils to be built using fixed width wires, very considerable reductions in dissipated power are consistently attainable (up to 60%) when compared to standard approaches of coil optimization.

Minimum maximum temperature gradient coil design.

Ohmic heating is a serious problem in gradient coil operation. A method is presented for redesigning cylindrical gradient coils to operate at minimum peak temperature, while maintaining field homogeneity and coil performance. To generate these minimaxT coil windings, an existing analytic method for simulating the spatial temperature distribution of single layer gradient coils is combined with a minimax optimization routine based on sequential quadratic programming. Simulations are provided for symmetric and asymmetric gradient coils that show considerable improvements in reducing maximum temperature over existing methods. The winding patterns of the minimaxT coils were found to be heavily dependent on the assumed thermal material properties and generally display an interesting "fish-eye" spreading of windings in the dense regions of the coil. Small prototype coils were constructed and tested for experimental validation and these demonstrate that with a reasonable estimate of material properties, thermal performance can be improved considerably with negligible change to the field error or standard figures of merit.

Simulation and analysis of the interactions between split gradient coils and a split magnet cryostat in an MRI-PET system.

Splitting a magnetic resonance imaging (MRI) magnet into two halves can provide a central region to accommodate other modalities, such as positron emission tomography (PET). This approach, however, produces challenges in the design of the gradient coils in terms of gradient performance and fabrication. In this paper, the impact of a central gap in a split MRI system was theoretically studied by analysing the performance of split, actively-shielded transverse gradient coils. In addition, the effects of the eddy currents induced in the cryostat on power loss, mechanical vibration and magnetic field harmonics were also investigated. It was found, as expected, that the gradient performance tended to decrease as the central gap increased. Furthermore, the effects of the eddy currents were heightened as a consequence of splitting the gradient assembly into two halves. An optimal central gap size was found, such that the split gradient coils designed with this central gap size could produce an engineering solution with an acceptable trade-off between gradient performance and eddy current effects. These investigations provide useful information on the inherent trade-offs in hybrid MRI imaging systems.

Minimax current density gradient coils: analysis of coil performance and heating.

Standard gradient coils are designed by minimizing the inductance or resistance for an acceptable level of gradient field nonlinearity. Recently, a new method was proposed to minimize the maximum value of the current density in a coil additionally. The stated aim of that method was to increase the minimum wire spacing and to reduce the peak temperature in a coil for fixed efficiency. These claims are tested in this study with experimental measurements of magnetic field and temperature as well as simulations of the performance of many coils. Experimental results show a 90% increase in minimum wire spacing and 40% reduction in peak temperature for equal coil efficiency and field linearity. Simulations of many more coils indicate increase in minimum wire spacing of between 50 and 340% for the coils studied here. This method is shown to be able to increase coil efficiency when constrained by minimum wire spacing rather than switching times or total power dissipation. This increase in efficiency could be used to increase gradient strength, duty cycle, or buildability.

Simulation and analysis of split gradient coil performance in MRI.

Split magnet systems for hybrid imaging, such as positron emission tomography-magnetic resonance imaging (PET-MRI) and Radiotherapy-MRI, require gradient coils designed with similar shapes as their corresponding main magnet. This introduces challenges in the gradient coil design of good performance and manufacturing. In this paper the effect of the gap size in shielded transverse split gradient coils and split cryostat "warm" bore over the coil efficiency, shielding efficiency, wire spacing, cryostat ohmic power loss and mechanical vibration have been simulated and studied. A "free-surface" gradient coil design method was used to design the split, actively-shielded transverse gradient coils with an axial gap. A network method was used to calculate the eddy currents induced in the split cryostat "warm" bore. The shielding efficiency and the minimum wire spacing were found to decrease when the size of the central gap is increased. The ohmic power loss and the amplitude of the radial vibrations in the split cryostat "warm" bore increases when the gap size in the gradient coil and "warm" bore is increased. It is hoped that these investigations will be useful for the development of new hybrid imaging modalities involving MRI.

Eddy current simulation in thick cylinders of finite length induced by coils of arbitrary geometry.

Eddy currents are inevitably induced when time-varying magnetic field gradients interact with the metallic structures of a magnetic resonance imaging (MRI) scanner. The secondary magnetic field produced by this induced current degrades the spatial and temporal performance of the primary field generated by the gradient coils. Although this undesired effect can be minimized by using actively and/or passively shielded gradient coils and current pre-emphasis techniques, a residual eddy current still remains in the MRI scanner structure. Accurate simulation of these eddy currents is important in the successful design of gradient coils and magnet cryostat vessels. Efficient methods for simulating eddy currents are currently restricted to cylindrical-symmetry. The approach presented in this paper divides thick conducting cylinders into thin layers (thinner than the skin depth) and expresses the current density on each as a Fourier series. The coupling between each mode of the Fourier series with every other is modeled with an inductive network method. In this way, the eddy currents induced in realistic cryostat surfaces by coils of arbitrary geometry can be simulated. The new method was validated by simulating a canonical problem and comparing the results against a commercially available software package. An accurate skin depth of 2.76 mm was calculated in 6 min with the new method. The currents induced by an actively shielded x-gradient coil were simulated assuming a finite length cylindrical cryostat consisting of three different conducting materials. Details of the temporal-spatial induced current diffusion process were simulated through all cryostat layers, which could not be efficiently simulated with any other method. With this data, all quantities that depend on the current density, such as the secondary magnetic field, are simply evaluated.

Split gradient coils for simultaneous PET-MRI.

Combining positron emission tomography (PET) and MRI necessarily involves an engineering tradeoff as the equipment needed for the two modalities vies for the space closest to the region where the signals originate. In one recently described scanner configuration for simultaneous positron emission tomography-MRI, the positron emission tomography detection scintillating crystals reside in an 80-mm gap between the 2 halves of a 1-T split-magnet cryostat. A novel set of gradient and shim coils has been specially designed for this split MRI scanner to include an 110-mm gap from which wires are excluded so as not to interfere with positron detection. An inverse boundary element method was necessarily employed to design the three orthogonal, shielded gradient coils and shielded Z0 shim coil. The coils have been constructed and tested in the hybrid positron emission tomography-MRI system and successfully used in simultaneous positron emission tomography-MRI experiments.

An improved equivalent magnetization current method applied to the design of local breast gradient coils.

Magnetic resonance imaging (MRI) is an important tool in the diagnosis of breast cancer. Increased gradient strengths and slew rates assist in terms of the potential to image with increased spatial and/or temporal resolution. Strong gradients also facilitate diffusion studies; one well-known method of increasing gradient strength is to design local gradient coils, those with reduced diameter where the gradient conductors are closer to the region of interest. In the case of breast imaging, this necessitates the use of coil geometries that lack the symmetry (e.g. cylindrical) required by some standard coil design techniques. Therefore a symmetry-free, inverse boundary element method (BEM) was employed to design a set of local breast gradient coils which would allow simultaneous imaging of both breasts. This BEM is a modified version of a previously reported equivalent magnetisation current method that now incorporates a piecewise-linear magnetisation rather than piecewise-constant. It is demonstrated that coil geometries more closely encompassing the sample shape, hence possessing wire windings located close the sample, produce superior coil performances. The use of two regions of interest instead one that covers the two samples produces superior high performance breast gradient coils. Additionally, it was demonstrated that this inverse BEM produced standard cylindrical coils with comparable properties and that the method is robust when challenged with difficult coil design problems in two other examples.

Volume parcellation for improved dynamic shimming.

INTRODUCTION: The need for a homogeneous magnetic field in magnetic resonance imaging is well established, especially at high static magnetic field strengths where susceptibility-induced image distortions and signal losses become excessively large. Dynamic shim updating, where the optimal set of shim currents is applied for each slice during a multi-slice acquisition, has been shown to improve magnetic field homogeneity to a greater extent than conventional global shimming. METHODS: Here, in an initial feasibility study, we show via simulation that improved efficacy of shimming can be achieved by using the novel parcellated dynamic shimming method. RESULTS: The results of these simulations indicate that parcellated dynamic shimming based on just linear shim terms can perform approximately as well as slice-based dynamic shimming with up to third-order shim terms. CONCLUSIONS: This work shows that the effective magnetic field inhomogeneity can be further reduced if shimming and image data acquisition are sequentially performed over a series of compact, cuboidal sub-volumes rather than planes. Further work is needed to develop an imaging approach that can be used for the optimal implementation of parcellated dynamic shimming.

Missing steps in the STAIR case: a Translational Medicine perspective on the development of NXY-059 for treatment of acute ischemic stroke.

The continued failure in approving new drugs for treatment of acute stroke has been recently set back by the failure of the NXY-059 (Stroke-Acute Ischemic NXY Treatment (SAINT) II) trial. The disappointment was heightened by the latter study being viewed as a most promising compound for stroke drug development program based on the preclinical data. Since the SAINT I/II development program included many of the STAIR (Stroke Therapy Academic Industry Round table) guidelines, yet have still failed to achieve the expected efficacy, there is a clear need to continue and analyze the path forward for stroke drug discovery. To this end, this review calls for a consortium approach including academia, government (FDA/NIH), and pharmaceutical industry partnerships to define this path. It is also imperative that more attention is given to the evolving discipline of Translational Medicine. A key issue in this respect is the need to devote more attention to the characteristics of the drug candidate nature-target interaction, and its relationship to pharmacodynamic treatment end points. It is equally important that efforts are spent to prove that phenotypic outcomes are linked to the purported mechanism of action of the compound. Development of technologies that allows a better assessment of these parameters, especially in in vivo models are paramount. Finally, rational patient selection and new outcome scales tailored in an adaptive design model must be evaluated.

Visual manifestations of craniofrontonasal dysplasia.

In this sample of craniofrontonasal dysplasia, a 44.4% prevalence of visual impairment was observed, with more than half being due to potentially correctable causes of visual loss, including amblyopia and anisometropia. High prevalences of strabismus (88.9%) and V-pattern (55.5%) in craniofrontonasal dysplasia were also demonstrated. All three patients who underwent strabismus surgery showed improvement in ocular alignment postoperatively. This group needs regular eye examinations to assess for visual impairment and provide timely intervention for modifiable causes of visual loss.

Pharmacokinetically enhanced amoxicillin/clavulanate (2,000/125 mg) in acute bacterial rhinosinusitis caused by Streptococcus pneumoniae, including penicillin-resistant strains.

We evaluated the efficacy of a new pharmacokinetically enhanced formulation of amoxicillin/clavulanate (2,000/125 mg) twice daily for the treatment of acute bacterial rhinosinusitis (ABRS) caused by Streptococcus pneumoniae, particularly penicillin-resistant S pneumoniae (PRSP; penicillin minimum inhibitory concentrations [MICs]: > or = 2 microg/ml. A total of 2,482 patients received study medication (safety population). Of these, 2,324 were clinically evaluable (efficacy population), and 1,156 of them had at least one pathogen isolated at screening (bacteriology population). S pneumoniae was isolated from 371 patients in the bacteriology population, including 37 with PRSP. Follow-up in the bacteriology population on days 17 through 28 revealed that amoxicillin/clavulanate therapy was successful in 345 of 371 patients with S pneumoniae infection (93.0%) and in 36 of 37patients with PRSP infection (97.3%), including 7 of 8 patients (87.5%) whose amoxicillin/clavulanic acid MICs were 4/2 microg/ml or higher. Pharmacokinetically enhanced amoxicillin/clavulanate was generally well tolerated, as only 2.2% of patients withdrew because of adverse events. This agent represents a valuable new therapeutic option for the empiric treatment of ABRS, particularly in areas where antimicrobial-resistant pathogens (including beta-lactamase-positive organisms) are prevalent, and for the treatment of patients who are at increased risk of infection with PRSP.