Fast quantitative susceptibility mapping with L1-regularization and automatic parameter selection

Purpose To enable fast reconstruction of quantitative susceptibility maps with total variation penalty and automatic regularization parameter selection. Methods ℓ[subscript 1]-Regularized susceptibility mapping is accelerated by variable splitting, which allows closed-form evaluation of each iteration of the algorithm by soft thresholding and fast Fourier transforms. This fast algorithm also renders automatic regularization parameter estimation practical. A weighting mask derived from the magnitude signal can be incorporated to allow edge-aware regularization. Results Compared with the nonlinear conjugate gradient (CG) solver, the proposed method is 20 times faster. A complete pipeline including Laplacian phase unwrapping, background phase removal with SHARP filtering, and ℓ[subscript 1]-regularized dipole inversion at 0.6 mm isotropic resolution is completed in 1.2 min using MATLAB on a standard workstation compared with 22 min using the CG solver. This fast reconstruction allows estimation of regularization parameters with the L-curve method in 13 min, which would have taken 4 h with the CG algorithm. The proposed method also permits magnitude-weighted regularization, which prevents smoothing across edges identified on the magnitude signal. This more complicated optimization problem is solved 5 times faster than the nonlinear CG approach. Utility of the proposed method is also demonstrated in functional blood oxygen level–dependent susceptibility mapping, where processing of the massive time series dataset would otherwise be prohibitive with the CG solver. Conclusion Online reconstruction of regularized susceptibility maps may become feasible with the proposed dipole inversion

Accelerated mapping of magnetic susceptibility using 3D planes-on-a-paddlewheel (POP) EPI at ultra-high field strength

With the advent of ultra-high field MRI scanners in clinical research, susceptibility based MRI has recently gained increasing interest because of its potential to assess subtle tissue changes underlying neurological pathologies/disorders. Conventional, but rather slow, three-dimensional (3D) spoiled gradient-echo (GRE) sequences are typically employed to assess the susceptibility of tissue. 3D echo-planar imaging (EPI) represents a fast alternative but generally comes with echo-time restrictions, geometrical distortions and signal dropouts that can become severe at ultra-high fields. In this work we assess quantitative susceptibility mapping (QSM) at 7T using non-Cartesian 3D EPI with a planes-on-a-paddlewheel (POP) trajectory, which is created by rotating a standard EPI readout train around its own phase encoding axis. We show that the threefold accelerated non-Cartesian 3D POP EPI sequence enables very fast, whole brain susceptibility mapping at an isotropic resolution of 1mm and that the high image quality has sufficient signal-to-noise ratio in the phase data for reliable QSM processing. The susceptibility maps obtained were comparable with regard to QSM values and geometric distortions to those calculated from a conventional 4min 3D GRE scan using the same QSM processing pipeline

Quantitative fat and R2* mapping in vivo to measure lipid-rich necrotic core and intraplaque hemorrhage in carotid atherosclerosis

Purpose: The aim of this work was to quantify the extent of lipid-rich necrotic core (LRNC) and intraplaque hemorrhage (IPH) in atherosclerotic plaques. Methods: Patients scheduled for carotid endarterectomy underwent four-point Dixon and T1-weighted magnetic resonance imaging (MRI) at 3 Tesla. Fat and R2* maps were generated from the Dixon sequence at the acquired spatial resolution of 0.60 × 0.60 × 0.70 mm voxel size. MRI and three-dimensional (3D) histology volumes of plaques were registered. The registration matrix was applied to segmentations denoting LRNC and IPH in 3D histology to split plaque volumes in regions with and without LRNC and IPH. Results: Five patients were included. Regarding volumes of LRNC identified by 3D histology, the average fat fraction by MRI was significantly higher inside LRNC than outside: 12.64 ± 0.2737% versus 9.294 ± 0.1762% (mean ± standard error of the mean [SEM]; P < 0.001). The same was true for IPH identified by 3D histology, R2* inside versus outside IPH was: 71.81 ± 1.276 s−1 versus 56.94 ± 0.9095 s−1 (mean ± SEM; P < 0.001). There was a strong correlation between the cumulative fat and the volume of LRNC from 3D histology (R2 = 0.92) as well as between cumulative R2* and IPH (R2 = 0.94). Conclusion: Quantitative mapping of fat and R2* from Dixon MRI reliably quantifies the extent of LRNC and IPH

Consumo consciente de água: a criança como agente de transformação

Educar é desafio diário, tanto para os pais quanto para os professores. Uma função que deve ser desempenhada com atenção, cuidado e, acima de tudo, dedicação. A troca de experiências entre o mestre e o aluno pode gerar um ciclo saudável de influência e aprendizado. Sob esta plataforma, a perpetuação do pensamento crítico acontecerá de forma natural, despertando e fixando o conceito de cidadania, o qual será aplicado na sociedade e nos demais relacionamentos que o homem consolidar. O respeito ao meio ambiente, por exemplo, é uma alternativa efetiva para a propagação da empatia e coletividade. Em especial, o consumo consciente da água, a fonte da vida, e matéria prima indispensável para os três setores da economia. Assunto este que deveria estar presentes no cotidiano do brasileiro. Na busca por compreender tal problema e desenvolver novos valores para a sociedade moderna, a comunicação e o marketing são as ferramentas oportunas para alavancar o processo de conscientização da criança. Se o processo ocorrer de forma concreta, em um futuro próximo, os impactos ambientais do homem sob a natureza serão amenizados e a qualidade de vida uma realidade coletiva. Neste estudo, o qual usou pesquisa qualitativa e grupo focal, a coleta de dados possibilitou a reflexão acerca de métodos adequados para conscientizar o cidadão quanto à importância do uso consciente da água desde a infância. A partir da pequena amostra escolhida, foi observada a realidade da capital federal, o valor e custo beneficio em relação a natureza e que atitudes pró natureza, principalmente por parte de instituições privadas e não governamentais, já estão sendo executadas

Iron and Neurodegeneration in Multiple Sclerosis

Increased iron deposition might be implicated in multiple sclerosis (MS). Recent development of MRI enabled to determine brain iron levels in a quantitative manner, which has put more interest on studying the role of iron in MS. Evidence for abnormal iron homeostasis in MS comes also from analyses of iron and iron-related proteins in CSF and blood and postmortem MS brain sections. However, it is not yet clear if iron accumulation is implicated in MS pathology or merely reflects an epiphenomenon. Further interest has been generated by the idea of chronic cerebrospinal venous insufficiency that might be associated with brain iron accumulation due to a reduction in venous outflow, but its existence and etiologic role in MS are currently controversially debated. In future studies, combined approaches applying quantitative MRI together with CSF and serum analyses of iron and iron-related proteins in a clinical followup setting might help to elucidate the implication of iron accumulation in MS

Magnetization transfer imaging identifies basal ganglia abnormalities in adult ADHD that are invisible to conventional T1 weighted voxel-based morphometry

In childhood, Attention Deficit Hyperactivity Disorder (ADHD) is reliably associated with reduced volume of the striatum. In contrast, striatal abnormalities are infrequently detected in voxel-based morphometry (VBM) neuroimaging studies of adults with ADHD. This discrepancy has been suggested to reflect normalisation of striatal morphology with age and prolonged treatment of symptoms. If so, this would indicate that while striatal abnormalities are linked to symptom expression in childhood, they cannot explain the persistence of these symptoms in adulthood. However, this may not be case. Instead, we hypothesized that the lack of evidence for striatal abnormalities in adult ADHD may reflect poor sensitivity of typical (T1-weighted) neuroimaging to detect subcortical differences. To address this, we acquired both magnetisation transfer (MT) saturation maps optimised for subcortical contrast, and conventional T1-weighted images in 30 adults with ADHD and 30 age, IQ, gender and handedness-matched controls. Using VBM of both datasets, we demonstrate volumetric reductions within the left ventral striatum on MT that are not observed on identically pre-processed T1-weighted images from the same participants. Nevertheless, both techniques reported similar sensitivity to cortical abnormalities in the right inferior parietal lobe. Additionally, we show that differences in striatal iron may potentially explain this reduced sensitivity of T1-weighted images in adults. Together, these findings indicate that prior VBM studies reporting no abnormalities in striatal volume in adult ADHD might have been compromised by the methodological insensitivity of T1-weighted VBM to subcortical differences, and that structural abnormalities of the striatum in ADHD do indeed persist into adulthood

In-situ Polymerization of Polyaniline on Cellulose Nanofibers: Effects on Electrical Conductivity and Tensile Properties

Faculty advisor: Prof. William TzeSamples of aqueous cellulose nanofibers were combined with an acidic aniline solution and an oxidizer to achieve in-situ polymerization of aniline. To obtain a higher degree of flexibility, a plasticizer was added in some instances. Samples with varying mass ratios of nanofibers and PANI were prepared. Tensile tests and four-probe electrical conductivity measurements were performed. Results showed that samples with the most nanofibers were strong and quite rigid, while samples with more polyaniline (PANI) displayed a higher degree of conductivity, but were very brittle. The samples with a mix of nanofibers, polyaniline and plasticizer displayed a combination of conductivity and some flexibility, but future studies are needed to optimize the formulations.This research was supported by the Undergraduate Research Opportunities Program (UROP)

Estimating the apparent transverse relaxation time (R2*) from images with different contrasts (ESTATICS) reduces motion artifacts

Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2*, which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2* from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2* maps and reduced the coefficient of variation for both types of data—with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting

Eklektik - Verantwortung - Glück

Adorno – so die These der vorliegenden Arbeit – war – gleich den meisten Philosophen – ein Eklektiker. Er hat sich bewusst beeinflussen und anregen lassen von anderen Denkern, Dichtern und Künstlern, wählte aus deren Werk so manches, das er in sein Werk und seine Schriften aufnahm, um daraus etwas Eigenes, Neues zu schaffen und zu gestalten. Adornos Herangehensweise entwuchs seiner zwar systematischen, aber offenen Philosophie, die sich eben nicht als geschlossenes System begriff, sondern vielmehr als eine in Essays dargestellte dialektisch verwobene Konstellation von Begriffen, vergleichbar einem verlinkten Hypertext oder einer Enzyklopädie: die Begriffe beziehen sich aufeinander, bedingen einander und verweisen darüber hinaus oftmals noch auf ein Drittes, worin auch die methodische Vorgabe für vorliegende Arbeit zu sehen ist. Tritt etwas Neues hinzu oder eine Veränderung innerhalb der Konstellation ein, so verändert und verschiebt sich das Gesamtbild gleich dem Gewebe eines Teppichs oder dem Gefüge eines Mosaiks: die Gesamtheit der Elemente ist deutlich mehr und etwas anderes als die Summe der Teile. Viele dieser Elemente sind nun, in eklektischer Manier, entliehen aus dem Werk anderer. Dies zu zeigen und darzustellen, wurde in vorliegender Arbeit das Begriffspaar „Entscheidung – Verantwortung“ herangezogen. Das Moment der Entscheidung liegt zunächst in der Auswahl derer, über die Adorno schrieb, auf die er sich bezog und anhand derer er seine eigenen Gedanken entwickelte und seine Philosophie zur Darstellung brachte; im Weiteren in einem bestimmten Verhältnis gegenüber der Praxis, wie er sie verstand und die einen solchen Namen verdiente. Je eigene reflektierte Entscheidungen und die daraus entwachsenen Erfahrungen führen – so wäre mit Adorno zu hoffen – in Folge zu einem Denken, das sich der eigenen Verantwortung bewusst ist; einem Denken, das um die eigene Bedingtheit, Naturhaftigkeit und Eingeschränktheit weiß, das den Widersprüchen der Gesellschaft, in die es verflochten ist, sich stellt und dem es um eine echte Versöhnung geht. Einer Versöhnung, die das Glück des je Einzelnen insofern zum Ziel hat, als das wahre Glück des Einzelnen immer auf jenes einer geglückten, versöhnten Gesellschaft verweist, in der jegliche dialektische Spannung gehalten wird: das je Andere muss nicht dem eigenen Denken angeglichen und solcherart zurecht gebogen werden, vielmehr soll ihm Gerechtigkeit widerfahren. Das Tauschverhältnis, dem Adorno nachspürte, und das er als Grundstruktur rationalistischen Denkens erkannte, wird solcherart durchbrochen. Das Ich – nach Adorno – bildet sich nicht dort, wo es sich setzt, sondern erst dort, wo es den Anfordernissen des Denkens standhält und zurücktritt vom Beharren auf den eigenen Standpunkt, wo es sich verschenkt und wo es Gnade vor Recht ergehen lässt, das Gleich um Gleich durchbricht, ohne entsagen zu müssen.Adorno, like most philosophers, was an eclectic. This fact forms the theory of this thesis. He purposely let himself be influenced by other thinkers, poets and artists. He chose parts of their works which he absorbed into his own, to create something new and individual. Adorno’s approach grew out of his systematic but open philosophy. His philosophy was not an enclosed system but a dialectic and interweaved constellation of terms illustrated in essays. It can be compared to a linked hypertext or an encyclopedia: the terms reference each other, determine each other and beyond this often refer to something else. This is the origin of the methodological basis of this thesis. The whole picture changes or shifts like the weave of a carpet or an arrangement of a mosaic if something new appears or if a change within the constellation occurs: the entity of the elements is considerably more than the total of all parts. Many of these elements are, in an eclectic way, borrowed from someone else’s work. In the following thesis the pair of terms “decision” and “responsibility” are used to show this. The first decision is made in the selection of those who Adorno wrote about, those he referred to and those through whom he developed his own thoughts and philosophy. Furthermore, his philosophy is founded in the relation to practice, as he understood the term practice, and which deserved this term. According to Adorno, self reflected decisions and the experiences resulting from them, hopefully lead to a way of thinking in conscious responsibility. They lead to a way of thinking that is aware of its own conditionality, natural manner and limitation. This way of thinking faces antagonism in the society in which it is embedded. It longs for reconciliation in the hope of finding happiness for everyone, as true happiness is always indicative of a reconcile society. In such a society every dialectic strain is kept: what is different does not have to be adjusted and formed. In fact, justice prevails. The concept of thinking in terms of exchange values which Adorno exposed as a basis for rational thinking has to be shattered. The ego, according to Adorno, is not formed where it settles but where it resists the challenges of thinking, where it steps back to its own position, where it gives itself away, where it allows mercy instead of legal doctrine and where it breaks the concept of an eye for an eye without renouncement

Hybrid data fidelity term approach for quantitative susceptibility mapping

PURPOSE: Susceptibility maps are usually derived from local magnetic field estimations by minimizing a functional composed of a data consistency term and a regularization term. The data-consistency term measures the difference between the desired solution and the measured data using typically the L2-norm. It has been proposed to replace this L2-norm with the L1-norm, due to its robustness to outliers and reduction of streaking artifacts arising from highly noisy or strongly perturbed regions. However, in regions with high SNR, the L1-norm yields a suboptimal denoising performance. In this work, we present a hybrid data fidelity approach that uses the L1-norm and subsequently the L2-norm to exploit the strengths of both norms. METHODS: We developed a hybrid data fidelity term approach for QSM (HD-QSM) based on linear susceptibility inversion methods, with total variation regularization. Each functional is solved with ADMM. The HD-QSM approach is a two-stage method that first finds a fast solution of the L1-norm functional and then uses this solution to initialize the L2-norm functional. In both norms we included spatially variable weights that improve the quality of the reconstructions. RESULTS: The HD-QSM approach produced good quantitative reconstructions in terms of structural definition, noise reduction, and avoiding streaking artifacts comparable with nonlinear methods, but with higher computational efficiency. Reconstructions performed with this method achieved first place at the lowest RMS error category in stage 1 of the 2019 QSM Reconstruction Challenge. CONCLUSIONS: The proposed method allows robust and accurate QSM reconstructions, obtaining superior performance to state-of-the-art methods