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Comprehensive Chemical Exchange Saturation Transfer Magnetresonanztomographie Bildgebung bei 7T
Get PDFPurpose:
Chemical exchange saturation transfer (CEST) is a MR imaging method providing molecular image contrasts based on indirect detection of low concentrated solutes. Previous CEST studies focus predominantly on the imaging of single CEST exchange regimes, e.g. slow, intermediate or fast exchanging groups. In this work, the aim is to establish a so called comprehensive CEST protocol for 7T, covering the different exchange regimes by three saturation B1 amplitude regimes.
Methods:
Results of previous publications and own simulations in pulseq-CEST were used to come up with a 7T CEST protocol, that has sensitivity to these three B1 regimes. With post-processing optimization (WASABI B0-fitting, MIMOSA B1 correction), neural network employment (deepCEST) and analytic input feature reduction, the initial 40 minutes protocol was shortened to 15 minutes. It generates 6 CEST contrast maps simultaneously. With this protocol, healthy subjects as well as patients with cerebral diseases were measured after written informed consent and approval of the local ethics comittee.
Results:
A comprehensive CEST protocol for clinical 7T MRI, covering three different B1 amplitude regimes, was established and applied in a clinical setting. The acquisition time was significantly by more than 50% reduced, while still maintaining decent image quality and contrast in healthy subjects and patients. Data of different high-grade tumor patients showed CEST signal changes beyond areas, where clinical imaging would outline the tumor area.
Conclusion:
Comprehensive 7T CEST paves the way for comprehensive CEST studies in clinical scan times for hypothesis generation regarding molecular properties of certain pathologies, e.g. ischemic stroke, relapsing remitting multiple sclerosis or high-grade brain tumors
Akquisitions- und Rekonstruktionsmethoden für Multidimensionale und Quantitative Magnetresonanztomographie
Get PDFMagnetic Resonance Imaging (MRI) is a tomographic imaging technique using the principles of nuclear magnetism of mostly the 1H nuclei, which are largely contained in the human body. This allows for insights to the interior tissue distributions. While its non-ionizing nature is advantageous compared to, e.g., Computed Tomography (CT), standard MRI only yields qualitative data allowing to discriminate different tissue boundaries without providing quantitative values. To enable quantitative MRI, multiple dimensions, i.e., spatial voxels and different physiological modes, e.g., cardiac and/or different contrast phases, have to be acquired simultaneously for a comprehensive diagnosis. From such data, dynamically resolved volumes can be reconstructed, allowing the assessment of quantitative biomarkers from different imaging contrasts. In this thesis, we investigated novel and extended solutions for multidimensional and quantitative MRI. The proposed methods were trained and evaluated on phantom data, as well as on several acquired in-vivo data sets from in total 49 volunteers.
First, we devised a Deep Learning (DL)-based reconstruction approach for Magnetic Resonance Fingerprinting (MRF) acquisitions. MRF acquires several highly undersampled imaging contrasts of the same slice by randomly changing the sampling parameters, resulting in temporal sequences for each spatial position. Our proposed framework uses spatial patches of these sequences as input and regresses them to quantitative relaxation T1 and T2 values. The results showed that the DL-based reconstruction yields accurate results well comparable to the State-of-the-Art (SOTA) reconstruction while reducing the computational effort during runtime.
We extended a 3-D cardiac sequence to sample single-contrast (SC) data with cardiac and respiratory phases continuously. Repetitive Inversion Recovery (IR) preparation pulses were further inserted to enable the sampling of multi-contrast (MC) continuous data on the T1 relaxation curve. A Cartesian pseudo-spiral sampling was used to enforce a pseudo-random undersampling pattern for the subsequent Compressed Sensing (CS)-based reconstruction. We proposed a pipeline which binned acquired data samples into different anatomic and contrast phases prior to the CS reconstruction. The T1 relaxation values fitted from different contrast bins were shown to be well comparable with the ground-truth (GT) values, as well as with a SOTA T1 mapping sequence in a quantitative phantom.
Lastly, we proposed motion extraction and binning pipelines towards an in-vivo application of the continuous SC and MC sequences for cardiac MRI. A DL-based classifier was used to determine the R-waves directly from the acquired imaging data to bin all samples into different cardiac phases. The extracted R-waves were comparable to the R-waves from the SOTA Electrocardiogram (ECG)-sensor for both SC and MC in-vivo data, but without the use of an additional sensor. Moreover, our DL-based approach recognized R-waves that were not detected by the ECG-sensor due to its interference with the magnetic field. Further, we proposed frameworks for extracting the respiratory motion directly from the acquired data, either from central 1-D projections, or from low-resolution 2-D images with an adapted version of the sampling scheme. Our results showed that the pipelines can be used for both types of cardiac in-vivo SC and MC data with the same set of parameters. Further, the image quality for all reconstructions could be improved with the utilization of the pipelines and the reconstruction of data samples from one respiratory phase.Die Magnetresonanztomographie (MRT) ist ein Bildgebungsverfahren, das sich die Prinzipien des Kernmagnetismus und vor allem der 1H-Kerne zunutze macht, die im menschlichen Körper weitgehend enthalten sind. Dies ermöglicht Einblicke in die inneren Gewebeverteilungen. Während die nicht-ionisierende Natur von MRT im Vergleich zu z.B. Computertomographie (CT) von Vorteil ist, erfasst das Standard-MRT nur qualitative Daten, die es erlauben, verschiedene Gewebegrenzen zu unterscheiden, ohne quantitative Werte zu liefern. Um ein quantitatives MRT zu ermöglichen, müssen für eine umfassende Diagnose mehrere Dimensionen, d.h. räumliche Voxel
und verschiedene physiologische Modi, z.B. kardiale und/oder verschiedene Kontrastphasen, gleichzeitig erfasst werden. Aus solchen Daten können dynamisch aufgelöste Volumina rekonstruiert werden, die eine Bewertung von quantitativen Biomarkern aus verschiedenen Bildgebungskontrasten ermöglichen. In dieser Arbeit haben wir neuartige und erweiterte Lösungen für multidimensionale und quantitative MRT untersucht. Die vorgeschlagenen Methoden wurden sowohl an Phantomdaten als auch an verschiedenen in-vivo-Daten von insgesamt 49 Probanden trainiert und evaluiert.
Zunächst haben wir einen Rekonstruktionsansatz basierend auf Deep Learning (DL) für Magnetic Resonance Fingerprinting (MRF)-Akquisitionen entwickelt. MRF erfasst mehrere stark unterabgetastete Bildgebungskontraste derselben Schicht durch zufällige Änderung der Abtastparameter, was zu zeitlichen Sequenzen für jede räumliche Position führt. Der von uns vorgeschlagene Ansatz verwendet räumliche Ausschnitte dieser Sequenzen als Eingabe und regressiert sie zu quantitativen Relaxationswerten T1 und T2. Die Ergebnisse zeigten, dass die DL-Rekonstruktion genaue Ergebnisse liefert, die mit der Rekonstruktion nach dem Stand der Technik gut vergleichbar sind, während der Rechenaufwand zur Laufzeit reduziert wird.
Wir erweiterten eine 3-D Herzsequenz, um Einzelkontrast (EK)-Daten mit kardialen und respiratorischen Phasen kontinuierlich zu erfassen. Weiterhin wurden repetitive Inversion Recovery (IR)-Präparationsimpulse eingefügt, um die Abtastung von kontinuierlichen Multikontrast (MK)-Daten auf der T1-Relaxationskurve zu ermöglichen. Ein kartesisches Pseudo-Spiral-Abtastschema wurde verwendet, um ein pseudozufälliges Unterabtastungsmuster für die anschließende Compressed Sensing (CS)-basierte Rekonstruktion zu erzwingen. Wir haben ein Verfahren vorgeschlagen, die die aufgenommenen Daten vor der CS-Rekonstruktion in verschiedene anatomische und Kontrastphasen ordnet. Es konnte gezeigt werden, dass die T1-Relaxationswerte, die aus verschiedenen Kontrastbins abgeleitet wurden, gut mit den wahren Werten sowie mit einer T1-Mapping-Sequenz nach dem Stand der Technik in einem quantitativen Phantom vergleichbar waren.
Schließlich haben wir Bewegungsextraktions- und Binning-Verfahren für eine invivo-Anwendung der kontinuierlichen EK- und MK-Sequenzen für kardiale MRT vorgeschlagen. Ein auf dem DL basierter Klassifikator wurde verwendet, um die R-Wellen direkt aus den erfassten Bilddaten zu bestimmen und alle Datenpunkte in verschiedene kardiale Phasen einzuteilen. Die extrahierten R-Wellen waren mit den R-Wellen des Elektrokardiogramm (EKG)-Sensors nach dem Stand der Technik sowohl für EK- als auch für MK-in-vivo-Daten vergleichbar, jedoch ohne die Verwendung eines zusätzlichen Sensors. Außerdem erkannte unser DL-Ansatz R-Wellen, die vom EKG-Sensor aufgrund seiner Interferenz mit dem Magnetfeld nicht detektiert wurden. Des Weiteren haben wir Verfahren vorgeschlagen, um die Atmungsbewegung direkt aus den erfassten Daten zu extrahieren, entweder aus zentralen 1-D Projektionen oder aus niedrig aufgelösten 2-D Bildern mit einer angepassten Version des Abtastschemas. Unsere Ergebnisse zeigten, dass die Verfahren für beide Arten von kardialen in-vivo EK- und MK-Daten mit dem gleichen Parametersatz verwendet werden können. Außerdem konnte die Bildqualität für alle Rekonstruktionen durch
die Verwendung der Verfahren verbessert werden, indem Datenpunkten aus einer Atmungsphase rekonstruiert wurden
Normofraktionierte Bestrahlung, nicht aber Temozolomid, moduliert den immunogenen und onkogenen Phänotyp menschlicher Glioblastom-Zelllinien
Get PDFIm Rahmen unserer Arbeit wurden menschliche Glioblastomzellen unter anderem auf die Expression sowohl immunsuppressiver als auch immunstimulierender Checkpoint Moleküle sowie des onkogenen Faktors EGFR nach Behandlung mit Radio- und/oder Chemotherapie untersucht.
Zusammenfassend zeigte sich, dass Temozolomid keinen signifikanten Einfluss auf die Oberflächenexpression von Checkpoint-Molekülen oder des EGF-Rezeptors hat. Der Einfluss normofraktionierter Radiotherapie auf die Expression von Immun-Checkpoint- Molekülen auf der Oberfläche von GBM-Zellen nach hingegen deutlich nachweisbar, jedoch äußerst heterogen. Insbesondere die Expression von PD-L1, PD-L2, HVEM und EGFR wurde durch die durchgeführte Strahlentherapie an den untersuchten GBM-Zellen signifikant herauf reguliert. Ein signifikanter Unterschied zwischen RT- und RCT Behandlung konnte nicht festgestellt werden
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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