873 research outputs found

    MR thermometry for hyperthermia in the head and neck

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    The persistent shadow of the supermassive black hole of M 87

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    In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3−3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5 × 109 M⊙. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet

    Image Reconstruction and Motion Compensation Methods for Fast MRI Chaoping

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    Simultaneous Multiparametric and Multidimensional Cardiovascular Magnetic Resonance Imaging

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    Development and validation of novel and quantitative MRI methods for cancer evaluation

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    Quantitative imaging biomarkers (QIB) offer the opportunity to further the evaluation of cancer at presentation as well as predict response to anti-cancer therapies before and early during treatment with the ultimate goal of truly personalised medical care and the mitigation of futile, often detrimental, therapy. Few QIBs are successfully translated into clinical practice and there is increasing recognition that rigorous methodologies and standardisation of research pipelines and techniques are required to move a theoretically useful biomarker into the clinic. To this end, I have aimed to give an overview of what I believe to be some of key elements within the research field beginning with the concept of imaging biomarkers, introducing concepts in development and validation, before providing a summary of the current and future utility of a range of quantitative MR imaging biomarkers techniques within the oncological imaging field. The original, prospective, research moves from the technical and analytical validation of a novel QIB use (T1 mapping in cancer), first in vivo qualification of this biomarker in cancer patient response assessment and prediction (sarcoma and breast cancer as well as prostate cancer separately), and then moving on to application of more established QIBs in cancer evaluation (R2*/BOLD imaging in head and neck cancer) as well as how existing MR data can be post-processed to improved cancer evaluation (further metrics derived from diffusion weighted imaging in head and neck cancer and textural analysis of existing clinical MR images utility in prostate cancer detection)

    Recommended Implementation of Quantitative Susceptibility Mapping for Clinical Research in The Brain: A Consensus of the ISMRM Electro-Magnetic Tissue Properties Study Group

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    This article provides recommendations for implementing quantitative susceptibility mapping (QSM) for clinical brain research. It is a consensus of the ISMRM Electro-Magnetic Tissue Properties Study Group. While QSM technical development continues to advance rapidly, the current QSM methods have been demonstrated to be repeatable and reproducible for generating quantitative tissue magnetic susceptibility maps in the brain. However, the many QSM approaches available give rise to the need in the neuroimaging community for guidelines on implementation. This article describes relevant considerations and provides specific implementation recommendations for all steps in QSM data acquisition, processing, analysis, and presentation in scientific publications. We recommend that data be acquired using a monopolar 3D multi-echo GRE sequence, that phase images be saved and exported in DICOM format and unwrapped using an exact unwrapping approach. Multi-echo images should be combined before background removal, and a brain mask created using a brain extraction tool with the incorporation of phase-quality-based masking. Background fields should be removed within the brain mask using a technique based on SHARP or PDF, and the optimization approach to dipole inversion should be employed with a sparsity-based regularization. Susceptibility values should be measured relative to a specified reference, including the common reference region of whole brain as a region of interest in the analysis, and QSM results should be reported with - as a minimum - the acquisition and processing specifications listed in the last section of the article. These recommendations should facilitate clinical QSM research and lead to increased harmonization in data acquisition, analysis, and reporting

    Dual-encoded magnetization transfer and diffusion imaging and its application to tract-specific microstructure mapping

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    We present a novel dual-encoded magnetization transfer (MT) and diffusion-weighted sequence and demonstrate its potential to resolve distinct properties of white matter fiber tracts at the sub-voxel level. The sequence was designed and optimized for maximal MT contrast efficiency. The resulting whole brain 2.6 mm isotropic protocol to measure tract-specific MT ratio (MTR) has a scan time under 7 minutes. Ten healthy subjects were scanned twice to assess repeatability. Two different analysis methods were contrasted: a technique to extract tract-specific MTR using Convex Optimization Modeling for Microstructure Informed Tractography (COMMIT), a global optimization technique; and conventional MTR tractometry. The results demonstrate that the tract-specific method can reliably resolve the MT ratios of major white matter fiber pathways and is less affected by partial volume effects than conventional multi-modal tractometry. Dual-encoded MT and diffusion is expected to both increase the sensitivity to microstructure alterations of specific tracts due to disease, ageing or learning, as well as lead to weighted structural connectomes with more anatomical specificity.Comment: 26 pages, 7 figure

    First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass

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    In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching ∼\sim100\% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full dataset using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8±2.351.8 \pm 2.3 μ\muas (68\% credible intervals), with the ring thickness constrained to have an FWHM between ∼\sim30\% and 50\% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8−0.7+1.44.8_{-0.7}^{+1.4} \mathrm{\mu as}, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0−0.6+1.1×1064.0_{-0.6}^{+1.1} \times 10^6 M⊙_{\odot}.Comment: 65 pages, 35 figures, published in The Astrophysical Journal Letters on May 12, 2022. See the published paper for the full authors lis

    The food quality schemes of the European Union and their implications on the Hungarian market [védés előtt]

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    It is becoming increasingly important for consumers to know exactly what kind of foods they consume, while it is increasingly vital for food producers to excel from the competition in the global market. This requires a great deal of information exchange between these two market players. The most common way to do this is through various food labels. I have focused on one group of such labels in my research, trying to find out as much useful information as possible about the geographical indications (GI) of the European Union. I was looking for answers to the following questions: 1, How well-known are the labels of EU GI products among Hungarian consumers, and how well do they know their meaning? The awareness of the GI labels in Hungary is definitely low (in the best case, it was 31%), even if this number is not much lower than the average in the EU. This number is probably too low for these labels to be effective marketing tools for producers. It also includes the fact that only 50% of those who said they know the label know at least approximately the meaning of the label. Can you build a marketing campaign currently on these markings? Probably not an effective one, but what gives hope is that awareness of the labels compared to previous surveys is constantly increasing. The EU focuses on GI products, so this growth is expected to be continued. So far, the EU has completed more than 30 international agreements, which allow the recognition of many EU GI outside the boundaries of the EU and the recognition of non-EU GI inside the territories of the EU. GIs represent an increasingly important aspect of trade negotiations between the EU and other countries. The Commission separates around €50 million year after year to support quality products in the EU and all over the world. Taking this into account, these labels can play an important role in the food markets in the near future. 2, What is the level of trust in the labelling of EU GI products, and what influences this trust? About half of the respondents said that they trust the logo. When we analysed the possible variables, which can influence trust, we concluded that knowledge of logos is important because if someone knows the label, they have more than three times the chance to trust them, while in terms of meaning, the chance is almost double. Based on the research, we can say that gender, education, and age do not affect trust in EU GI labels. In the case of place of residence, it can be said that someone who lives in a more urban environment trusts less in GI labels. All in all, consumer education is most needed to build confidence in GI, as those who recognize the labels on food packaging or are aware of what those labels mean will treat these products with much greater confidence. 3, How often do consumers buy EU GI certified products, and what affects it? More than 35% of those surveyed are regular customers of GI-labelled products. The frequency of purchases is mostly determined by consumer confidence (the result is not significant for the PDO). Women become much fewer regular customers (not significant for the PGI). In terms of age, the older a consumer is, the less likely it is to become a regular buyer (not significant for PDO), while residents of rural, smaller settlements are more loyal buyers of PGI products. The highest level of education has no detectable effect here either. So, in this topic also, we have to repeat that the most important thing is to inform consumers as widely as possible. 4, In the Hungarian market, what is the market size of products with geographical indication, examining the example of discount stores? The number of GI products available in Hungarian discount stores is limited, with an average of 11 products per store. The supply is fairly constant; however, even though there are only a limited number of GI products on the shelves, they are at least always available to consumers and are part of the chains ’core product portfolio. However, the number of GI products usually increases during the thematic days (e.g., Greek days). We can see that the supply is very limited for GI products, so buyers rarely meet face to face with the label, they are even less likely to find out about the meaning of the markings on their own. Targeted information on GI labels is needed for consumers, and for that they start to appreciate them. 5, In Hungarian discount stores, what is the price premium of products with a geographical indication compared to their direct substitutes, estimated from below? The average price premium for GI products is 29% in the Aldi, 46% in the Penny Market and the highest was in Lidl with 54%. Overall, the average premium was around 43%. It is also important to mention that in addition to supply, prices did not really change during the observations. Although the price of some products may also change during promotional periods, consumers can plan to purchase GI products in advance. On the other hand, discount stores provide a continuous market for producers as well. 6, Are geographical indications positively related to comparative advantages in the beer market? Our results show that the number of GI-registered beers is positively related to comparative advantages. Countries with traditional beer products closely linked to their place of origin are usually with a higher level of comparative advantages as the number of GI beers positively determines SRCA indices. From this, it can be concluded that it is not pointless to promote the increase in the number of GI products and devote resources to GI labels

    HyperSLICE: HyperBand optimized spiral for low-latency interactive cardiac examination

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    PURPOSE: Interactive cardiac MRI is used for fast scan planning and MR-guided interventions. However, the requirement for real-time acquisition and near-real-time visualization constrains the achievable spatio-temporal resolution. This study aims to improve interactive imaging resolution through optimization of undersampled spiral sampling and leveraging of deep learning for low-latency reconstruction (deep artifact suppression). METHODS: A variable density spiral trajectory was parametrized and optimized via HyperBand to provide the best candidate trajectory for rapid deep artifact suppression. Training data consisted of 692 breath-held CINEs. The developed interactive sequence was tested in simulations and prospectively in 13 subjects (10 for image evaluation, 2 during catheterization, 1 during exercise). In the prospective study, the optimized framework-HyperSLICE- was compared with conventional Cartesian real-time and breath-hold CINE imaging in terms quantitative and qualitative image metrics. Statistical differences were tested using Friedman chi-squared tests with post hoc Nemenyi test (p < 0.05). RESULTS: In simulations the normalized RMS error, peak SNR, structural similarity, and Laplacian energy were all statistically significantly higher using optimized spiral compared to radial and uniform spiral sampling, particularly after scan plan changes (structural similarity: 0.71 vs. 0.45 and 0.43). Prospectively, HyperSLICE enabled a higher spatial and temporal resolution than conventional Cartesian real-time imaging. The pipeline was demonstrated in patients during catheter pull back, showing sufficiently fast reconstruction for interactive imaging. CONCLUSION: HyperSLICE enables high spatial and temporal resolution interactive imaging. Optimizing the spiral sampling enabled better overall image quality and superior handling of image transitions compared with radial and uniform spiral trajectories
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