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Showing 1 to 2 of 2 (0.081 seconds)Spelling suggestions: "subject:"ultrahigh field MR"" "subject:"trahigh field MR""
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Computational Analysis of Clinical Brain Sub-cortical Structures from Ultrahigh-Field MRIKim, Jinyoung January 2015 (has links)
<p>Volumetric segmentation of brain sub-cortical structures within the basal ganglia and thalamus from Magnetic Resonance Image (MRI) is necessary for non-invasive diagnosis and neurosurgery planning. This is a challenging problem due in part to limited boundary information between structures, similar intensity profiles across the different structures, and low contrast data. With recent advances in ultrahigh-field MR technology, direct identification and clear visualization of such brain sub-cortical structures are facilitated. This dissertation first presents a semi-automatic segmentation system exploiting the visual benefits of ultrahigh-field MRI. The proposed approach utilizes the complementary edge information in the multiple structural MRI modalities. It combines optimally selected two modalities from susceptibility-weighted, T2-weighted, and diffusion MRI, and introduces a tailored new edge indicator function. In addition to this, prior shape and configuration knowledge of the sub-cortical structures are employed in order to guide the evolution of geometric active surfaces. Neighboring structures are segmented iteratively, constraining over-segmentation at their borders with a non-overlapping penalty. Experiments with data acquired on a 7 Tesla (T) MRI scanner demonstrate the feasibility and power of the approach for the segmentation of basal ganglia components critical for neurosurgery applications such as Deep Brain Stimulation (DBS) surgery. </p><p>DBS surgery on brain sub-cortical regions within the Basal ganglia and thalamus is an effective treatment to alleviate symptoms of neuro-degenerative diseases. Particularly, the DBS of subthalamic nucleus (STN) has shown important clinical efficacy for Parkinson’s disease (PD). While accurate localization of the STN and its substructures is critical for precise DBS electrode placement, direct visualization of the STN in current standard clinical MR imaging (e.g., 1.5-3T) is still elusive. Therefore, to locate the target, DBS surgeons today often rely on consensus coordinates, lengthy and risky micro-electrode recording (MER), and patient’s behavioral feedback. Recently, ultrahigh-field MR imaging allows direct visualization of brain sub-cortical structures. However, such high fields are not clinically available in practice. This dissertation also introduces a non-invasive automatic localization method of the STN which is one of the critical targets for DBS surgery in a standard clinical scenario (1.5T MRI). The spatial dependency between the STN and potential predictor structures from 7T MR training data is first learned using the regression models in a bagging way. Then, given automatically detected such predictors on the clinical patient data, the complete region of the STN is predicted as a probability map using learned high quality information from 7T. Furthermore, a robust framework is proposed to properly weight different training subsets, estimating their influence in the prediction accuracy. The STN prediction on the clinical 1.5T MR datasets from 15 PD patients is performed within the proposed approach. Experimental results demonstrate that the developed framework enables accurate prediction of the STN, closely matching the 7T ground truth.</p> / Dissertation
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Detailing radio frequency controlled hyperthermia and its application in ultrahigh field magnetic resonanceWinter, Lukas 06 August 2014 (has links)
Die vorliegende Arbeit untersucht die grundsätzliche Machbarkeit, Radiofrequenzimpulse (RF) der Ultrahochfeld (UHF) Magnetresonanztomographie (MRT) (B0≥7.0T) für therapeutische Verfahren wie die RF Hyperthermie oder die lokalisierte Freigabe von Wirkstoffträgern und Markern zu nutzen. Im Rahmen der Arbeit wurde ein 8-Kanal Sened/Empfangsapplikator entwickelt, der bei einer Protonenfrequenz von 298MHz operiert. Mit diesem weltweit ersten System konnte in der Arbeit experimentell bewiesen werden, dass die entwickelte Hardware sowohl zielgerichtete lokalisierte RF Erwärmung als auch MR Bildgebung und MR Thermometrie (MRTh) realisiert. Mit den zusätzlichen Freiheitsgraden (Phase, Amplitude) eines mehrkanaligen Sendesystems konnte aufgezeigt werden, dass der Ort der thermischen Dosierung gezielt verändert bzw. festgelegt werden kann. In realitätsnahen Temperatursimulationen mit numerischen Modellen des Menschen, wird in der Arbeit aufgezeigt, dass mittels des entwickelten Hybridaufbaus eine kontrollierte und lokalisierte thermische Dosierung im Zentrum des menschlichen Kopfes erzeugt werden kann. Nach der erfolgreichen Durchführung dieser Machbarkeitsstudie wurden in theoretischen Überlegungen, numerischen Simulationen und in ersten grundlegenden experimentellen Versuchen die elektromagnetischen Gegebenheiten von MRT und lokal induzierter RF Hyperthermie für Frequenzen größer als 298MHz untersucht. In einem Frequenzbereich bis zu 1.44GHz konnte der Energiefokus mit Hilfe spezialisierter RF Antennenkonfigurationen entscheidend weiter verkleinert werden, sodass Temperaturkegeldurchmesser von wenigen Millimetern erreicht wurden. Gleichzeitig konnte gezeigt werden, dass die vorgestellten Konzepte ausreichende Signalstärke der zirkular polarisierten Spinanregungsfelder bei akzeptabler oberflächlicher Energieabsorption erzeugen, um eine potentielle Machbarkeit von in vivo MRT bei B0=33.8T oder in vivo Elektronenspinresonanz (ESR) im L-Band zu demonstrieren. / The presented work details the basic feasibility of using radiofrequency (RF) fields generated by ultrahigh field (UHF) magnetic resonance (MR) (B0≥7.0T) systems for therapeutic applications such as RF hyperthermia and targeted drug delivery. A truly hybrid 8-channel transmit/receive applicator operating at the 7.0T proton MR frequency of 298MHz has been developed. Experimental verification conducted in this work demonstrated that the hybrid applicator supports targeted RF heating, MR imaging and MR thermometry (MRTh). The approach offers extra degrees of freedom (RF phase, RF amplitude) that afford deliberate changes in the location and thermal dose of targeted RF induced heating. High spatial and temporal MR temperature mapping can be achieved due to intrinsic signal-to-noise ratio (SNR) gain of UHF MR together with the enhanced parallel imaging performance inherent to the multi-channel receive architecture used. Temperature simulations in human voxel models revealed that the proposed hybrid setup is capable to deposit a controlled and localized RF induced thermal dose in the center of the human brain. After demonstrating basic feasibility, theoretical considerations and proof-of-principle experiments were conducted for RF frequencies of up to 1.44GHz to explore electrodynamic constraints for MRI and targeted RF heating applications for a frequency range larger than 298MHz. For this frequency regime a significant reduction in the effective area of energy absorption was observed when using dedicated RF antenna arrays proposed and developed in this work. Based upon this initial experience it is safe to conclude that the presented concepts generate sufficient signal strength for the circular polarized spin excitation fields with acceptable specific absorption rate (SAR) on the surface, to render in vivo MRI at B0=33.8T or in vivo electron paramagnetic resonance (EPR) at L-Band feasible.
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