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Regularization Of Inverse Problems

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Magnetic Resonance Imaging Physical Principles And Sequence Design

Inflammatory cardiomyopathy, characterized by inflammatory cell infiltration into the myocardium and a high risk of deteriorating cardiac function, has a heterogeneous aetiology. Inflammatory cardiomyopathy is predominantly mediated by viral infection, but can also be induced by bacterial, protozoal or fungal infections as well as a wide variety of toxic substances and drugs and systemic immune-mediated diseases. Despite extensive research, inflammatory cardiomyopathy complicated by left ventricular dysfunction, heart failure or arrhythmia is associated with a poor prognosis. At present, the reason why some patients recover without residual myocardial injury whereas others develop dilated cardiomyopathy is unclear. The relative roles of the pathogen, host genomics and environmental factors in disease progression and healing are still under discussion, including which viruses are active inducers and which are only bystanders. As a consequence, treatment strategies are not well established. In this Review, we summarize and evaluate the available evidence on the pathogenesis, diagnosis and treatment of myocarditis and inflammatory cardiomyopathy, with a special focus on virus-induced and virus-associated myocarditis. Furthermore, we identify knowledge gaps, appraise the available experimental models and propose future directions for the field. The current knowledge and open questions regarding the cardiovascular effects associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are also discussed. This Review is the result of scientific cooperation of members of the Heart Failure Association of the ESC, the Heart Failure Society of America and the Japanese Heart Failure Society.

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Myocarditis and inflammatory cardiomyopathy: current evidence and future directions.

THIS interesting monograph appears in Dr. J. W. Spengel's “Ergebnisse und Fortschritte der Zoologie.” It gives an excellent account of the structure and mechanism of the central nervous system founded on morphological and physiological facts, as these have been laboriously collected by the most modern methods by which the nervous elements have been examined. The author deals with the plan of reflex mechanisms, he describes the architecture and localisation of the central ganglia and nerve-roots, and his illustrations are drawn from morphological studies of the simpler types. One of the most important sections is No. vii., in which he discusses the functions of the great divisions of the nervous system. Nowhere have we seen a better discussion of the relations and functions of the cerebellum, or a more lucid account of the remarkable deep connections of the auditory nerves. The author has evidently received illumination from the researches and constructive criticism of Sherrington, while, as indicated by a good bibliography, he is acquainted with the literature of this vast subject. The work is a valuable contribution to human and comparative neurology. The Central Nervous System of Vertebrates. By J. B. Johnston. Pp. 170. (Jena: G. Fischer, 1909.)

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The Central Nervous System of Vertebrates

This fifth edition continues the tradition of excellence with thorough coverage of recent trends and changes in the clinical diagnosis and treatment of CNS diseases, detailed relevant neuropathologic, genetic, and clinical findings, and how those changes relate to MRI findings. It remains a comprehensive, internationally acclaimed, state-of-the-art reference for all who have an interest in neuroradiology – trainees to experts in the field, basic science researchers, and clinicians.

Magnetic Resonance Imaging of the Brain and Spine

Purpose
To develop a model-based reconstruction technique for single-shot T1 mapping with high spatial resolution, accuracy, and precision using an inversion-recovery (IR) fast low-angle shot (FLASH) acquisition with radial encoding.

Methods
The proposed model-based reconstruction jointly estimates all model parameters, that is, the equilibrium magnetization, steady-state magnetization, 1/ T1*, and all coil sensitivities from the data of a single-shot IR FLASH acquisition with a small golden-angle radial trajectory. Joint sparsity constraints on the parameter maps are exploited to improve the performance of the iteratively regularized Gauss-Newton method chosen for solving the nonlinear inverse problem. Validations include both a numerical and experimental T1 phantom, as well as in vivo studies of the human brain and liver at 3 T.

Results
In comparison to previous reconstruction methods for single-shot T1 mapping, which are based on real-time MRI with pixel-wise fitting and a model-based approach with a predetermination of coil sensitivities, the proposed method presents with improved robustness against phase errors and numerical precision in both phantom and in vivo studies.

Conclusion
The comprehensive model-based reconstruction with L1 regularization offers rapid and robust T1 mapping with high accuracy and precision. The method warrants accelerated computing and online implementation for extended clinical trials. Magn Reson Med 79:730–740, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Model-based T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH.

Noradrenaline is a neurotransmitter involved in general arousal, selective attention, memory, inflammation, and neurodegeneration. The purpose of this work was to delineate noradrenergic neurons in vivo by T1-weighted MRI with magnetization transfer (MT). In the brainstem of human and mice, MRI identified the locus coeruleus, dorsal motor vagus nucleus, and nucleus tractus solitarius. Given (1) the long T1 and low magnetization transfer ratio for the noradrenergic cell groups compared to other gray matter, (2) significant correlation between MT MRI signal intensity and proton density, and (3) no correlation between magnetization transfer ratio (or R1) and iron, copper, or manganese in human brain, the high MRI signal of the noradrenergic neurons must be attributed to abundant water protons interacting with any T1-shortening paramagnetic ions in active cells rather than to specific T1-shortening molecules. The absence of a high MRI signal from the locus coeruleus of Ear2(-/-) mice lacking noradrenergic neurons confirms that cell bodies of noradrenergic neurons are the source of the bright MRI appearance. The observation of this high signal in DBH(-/-) mice, in 3-week-old mice, and in mice under hyperoxia/hypercapnia/hypoxia together with the general absence of neuromelanin (NM) in noradrenergic neurons of young rodents further excludes that it is due to NM, dopamine β-hydroxylase, their binding to paramagnetic ions, blood inflow, or hemoglobin. Instead, these findings indicate a high density of water protons whose T1 is shortened by paramagnetic ions as the relevant source of the high MRI signal. In the brain of APP/PS1/Ear2(-/-) mice, a transgenic model of Alzheimer's disease, MRI detected noradrenergic neuron loss in the locus coeruleus. Proton magnetic resonance spectroscopy revealed that a 60-75% reduction of noradrenaline is responsible for a reduction of N-acetylaspartate and glutamate in the hippocampus as well as for a shortening of the water proton T2 in the frontal cortex. These results suggest that a concurrent shortage of noradrenaline in Alzheimer's disease accelerates pathologic processes such as inflammation and neuron loss.

/pdf/magnetic-resonance-imaging-of-noradrenergic-neurons-4qsothm5ef.pdf

Magnetic resonance imaging of noradrenergic neurons

Quantitative parameter mapping in MRI is typically performed as a two-step procedure where serial imaging is followed by pixelwise model fitting. In contrast, model-based reconstructions directly reconstruct parameter maps from raw data without explicit image reconstruction. Here, we propose a method that determines T1 maps directly from multi-channel raw data as obtained by a single-shot inversion-recovery radial FLASH acquisition with a Golden Angle view order. Joint reconstruction of a T1, spin-density and flip-angle map is formulated as a nonlinear inverse problem and solved by the iteratively regularized Gauss-Newton method. Coil sensitivity profiles are determined from the same data in a preparatory step of the reconstruction. Validations included numerical simulations, in vitro MRI studies of an experimental T1 phantom, and in vivo studies of brain and abdomen of healthy subjects at a field strength of 3 T. The results obtained for a numerical and experimental phantom demonstrated excellent accuracy and precision of model-based T1 mapping. In vivo studies allowed for high-resolution T1 mapping of human brain 0.5-0.75 mm in-plane, 4 mm section thickness and liver 1.0 mm, 5 mm section within 3.6-5 s. In conclusion, the proposed method for model-based T1 mapping may become an alternative to two-step techniques, which rely on model fitting after serial image reconstruction. More extensive clinical trials now require accelerated computation and online implementation of the algorithm. © 2016 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 26, 254-263, 2016

Model-based reconstruction for T1 mapping using single-shot inversion-recovery radial FLASH

This study develops a model-based myocardial T1 mapping technique with sparsity constraints which employs a single-shot inversion-recovery (IR) radial fast low angle shot (FLASH) cardiovascular magnetic resonance (CMR) acquisition. The method should offer high resolution, accuracy, precision and reproducibility. The proposed reconstruction estimates myocardial parameter maps directly from undersampled k-space which is continuously measured by IR radial FLASH with a 4 s breathhold and retrospectively sorted based on a cardiac trigger signal. Joint sparsity constraints are imposed on the parameter maps to further improve T1 precision. Validations involved studies of an experimental phantom and 8 healthy adult subjects. In comparison to an IR spin-echo reference method, phantom experiments with T1 values ranging from 300 to 1500 ms revealed good accuracy and precision at simulated heart rates between 40 and 100 bpm. In vivo T1 maps achieved better precision and qualitatively better preservation of image features for the proposed method than a real-time CMR approach followed by pixelwise fitting. Apart from good inter-observer reproducibility (0.6% of the mean), in vivo results confirmed good intra-subject reproducibility (1.05% of the mean for intra-scan and 1.17, 1.51% of the means for the two inter-scans, respectively) of the proposed method. Model-based reconstructions with sparsity constraints allow for single-shot myocardial T1 maps with high spatial resolution, accuracy, precision and reproducibility within a 4 s breathhold. Clinical trials are warranted.

https://link.springer.com/content/pdf/10.1186/s12968-019-0570-3.pdf

Model-based myocardial T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH cardiovascular magnetic resonance

Objective:To develop a novel method for rapid myocardial T1 mapping at high spatial resolution.Methods:The proposed strategy represents a single-shot inversion recovery experiment triggered to early diastole during a brief breath-hold. The measurement combines an adiabatic inversion pulse with a real-time readout by highly undersampled radial FLASH, iterative image reconstruction and T1 fitting with automatic deletion of systolic frames. The method was implemented on a 3-T MRI system using a graphics processing unit-equipped bypass computer for online application. Validations employed a T1 reference phantom including analyses at simulated heart rates from 40 to 100 beats per minute. In vivo applications involved myocardial T1 mapping in short-axis views of healthy young volunteers.Results:At 1-mm in-plane resolution and 6-mm section thickness, the inversion recovery measurement could be shortened to 3 s without compromising T1 quantitation. Phantom studies demonstrated T1 accuracy and high precision for v...

High-resolution myocardial T1 mapping using single-shot inversion-recovery fast low-angle shot MRI with radial undersampling and iterative reconstruction.

Xiaoqing Wang

Papers

Model-based T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH.

Magnetic resonance imaging of noradrenergic neurons

Model-based reconstruction for T1 mapping using single-shot inversion-recovery radial FLASH

Model-based myocardial T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH cardiovascular magnetic resonance

High-resolution myocardial T1 mapping using single-shot inversion-recovery fast low-angle shot MRI with radial undersampling and iterative reconstruction.