No description available.

Current applied to coils wound at the tip of an endovascular catheter can be used to remotely steer a catheter tip in a clinical magnetic resonance imaging (MRI) scanner. This study focuses on (1) derivation and experimental validation of an equation that characterizes the relationship between catheter tip deflection and a number of magnetic, mechanical, and physical factors, and (2) evaluation of resistive heating in a worst-case scenario due to application of current necessary for clinically significant deflections, and radiofrequency (RF) heating due to real-time MRI pulse sequences. The derived equation was found to accurately model the behavior of the specialized catheter tip. The equation also has implications for catheter design and device implementation, including minimization of resistive heating, which was physiologically significant (> 4°C) under certain worst-case scenario conditions. This catheter steering mechanism should improve navigational control and is a unique advantage offered by MRI-guidance of endovascular procedures.

Current applied to coils wound at the tip of an endovascular catheter can be used to remotely steer a catheter tip in a clinical magnetic resonance imaging (MRI) scanner. This study focuses on (1) derivation and experimental validation of an equation that characterizes the relationship between catheter tip deflection and a number of magnetic, mechanical, and physical factors, and (2) evaluation of resistive heating in a worst-case scenario due to application of current necessary for clinically significant deflections, and radiofrequency (RF) heating due to real-time MRI pulse sequences. The derived equation was found to accurately model the behavior of the specialized catheter tip. The equation also has implications for catheter design and device implementation, including minimization of resistive heating, which was physiologically significant (> 4°C) under certain worst-case scenario conditions. This catheter steering mechanism should improve navigational control and is a unique advantage offered by MRI-guidance of endovascular procedures.

The main objective was to construct a 16-channel anterior cardiac array for 3T MRI capable of ⅓ mm pixel resolution across the right coronary artery, while achieving favourable parallel imaging characteristics. Based on FDTD simulations, improved performance relative to previous 16-channel designs was predicted by focusing small elements directly above the ROI, improving SNR behaviour, and using larger peripheral loops for maintaining overall parallel imaging characteristics, verifying the primary project hypothesis. Within the cardiac region, average simulated SNR gains of 62% and 129% were found for acceleration factors R=1 and R=4 respectively, compared to an industry design. Experimental analysis verified that ⅓ mm resolution is achievable within the right coronary artery, while also applying the benefits of parallel imaging up to R=3. This is a crucial step towards improving cardiac diagnostics. In addition, acceleration factors up to R=5 are achievable on a human torso, offering significant imaging time reductions. For an anterior section of the cardiac region, simulated results predicted an average SNR gain of 221%, where 460% gain was found experimentally. / May 2007

The main objective was to construct a 16-channel anterior cardiac array for 3T MRI capable of ⅓ mm pixel resolution across the right coronary artery, while achieving favourable parallel imaging characteristics. Based on FDTD simulations, improved performance relative to previous 16-channel designs was predicted by focusing small elements directly above the ROI, improving SNR behaviour, and using larger peripheral loops for maintaining overall parallel imaging characteristics, verifying the primary project hypothesis. Within the cardiac region, average simulated SNR gains of 62% and 129% were found for acceleration factors R=1 and R=4 respectively, compared to an industry design. Experimental analysis verified that ⅓ mm resolution is achievable within the right coronary artery, while also applying the benefits of parallel imaging up to R=3. This is a crucial step towards improving cardiac diagnostics. In addition, acceleration factors up to R=5 are achievable on a human torso, offering significant imaging time reductions. For an anterior section of the cardiac region, simulated results predicted an average SNR gain of 221%, where 460% gain was found experimentally.

Advances in fetal cardiovascular MRI have been limited by the absence of a reliable cardiac gating signal. Recently, metric optimized gating (MOG) has been proposed as a solution to this limitation. In this thesis, I have developed and validated MOG for cine imaging of the fetal heart. ECG gated cine MR data of the adult heart were acquired from a healthy volunteer to compare MOG reconstructions to conventional ECG reconstructions. The image quality of ECG and MOG reconstructions was compared as was the difference between MOG and ECG trigger times. Fetal images were also acquired, their quality evaluated by experienced radiologists, and the theoretical error in the MOG trigger times calculated. Excellent agreement between ECG and MOG reconstructions was observed. Using MOG, the world’s first gated MR images of the human fetal heart were obtained. Small moving structures were visualized during radial contraction, thus capturing normal fetal cardiac wall motion.

Advances in fetal cardiovascular MRI have been limited by the absence of a reliable cardiac gating signal. Recently, metric optimized gating (MOG) has been proposed as a solution to this limitation. In this thesis, I have developed and validated MOG for cine imaging of the fetal heart. ECG gated cine MR data of the adult heart were acquired from a healthy volunteer to compare MOG reconstructions to conventional ECG reconstructions. The image quality of ECG and MOG reconstructions was compared as was the difference between MOG and ECG trigger times. Fetal images were also acquired, their quality evaluated by experienced radiologists, and the theoretical error in the MOG trigger times calculated. Excellent agreement between ECG and MOG reconstructions was observed. Using MOG, the world’s first gated MR images of the human fetal heart were obtained. Small moving structures were visualized during radial contraction, thus capturing normal fetal cardiac wall motion.

The main objective was to construct a 16-channel anterior cardiac array for 3T MRI capable of ⅓ mm pixel resolution across the right coronary artery, while achieving favourable parallel imaging characteristics. Based on FDTD simulations, improved performance relative to previous 16-channel designs was predicted by focusing small elements directly above the ROI, improving SNR behaviour, and using larger peripheral loops for maintaining overall parallel imaging characteristics, verifying the primary project hypothesis. Within the cardiac region, average simulated SNR gains of 62% and 129% were found for acceleration factors R=1 and R=4 respectively, compared to an industry design. Experimental analysis verified that ⅓ mm resolution is achievable within the right coronary artery, while also applying the benefits of parallel imaging up to R=3. This is a crucial step towards improving cardiac diagnostics. In addition, acceleration factors up to R=5 are achievable on a human torso, offering significant imaging time reductions. For an anterior section of the cardiac region, simulated results predicted an average SNR gain of 221%, where 460% gain was found experimentally.

L’imagerie de l’angiogénèse tumorale représente actuellement un domaine majeur de la recherche pour la détection précoce des cancers et le développement de nouveaux traitements des tumeurs. Les cellules endothéliales des néovaisseaux formés surexpriment l’intégrine αvβ₃, qui se lie sélectivement aux peptides contenant la séquence Arg-Gly-Asp (RGD). Le processus angiogénique joue également un rôle dans le développement d’autres pathologies telles les maladies cardiovasculaires. Le but de ce projet est ainsi de concevoir un agent de contraste bimodal (IRM et fluorescence) ciblant les intégrines αvβ₃ pour une détection précoce de l’angiogénèse. Des nanoparticules superparamagnétiques d’oxyde de fer ont été fonctionnalisées en surface par des agents complexants de type cathécol ou bisphosphonate présentant des fonctions réactives terminales, acide carboxylique ou alcyne. L’efficacité du couplage de diverses molécules (fluorophores, PEG, RGD) par chimie des carbodiimides ou par chimie click (réactions de Huisgen ou thiol-yne) a été comparée. La stabilité des différentes sondes dans le sérum et leur potentiel en tant qu’agent de contraste IRM a été évalué. L’affinité vis-à-vis des intégrines a été étudiée par résonance plasmonique de surface et par dosage de liaisons sur support solide en présence d’un compétiteur radioactif. Dans le but d’optimiser les propriétés d’agents de contraste IRM, une étude de l’influence de la taille et de la forme des nanoparticules a été réalisée. Les premières évaluations in vitro et in vivo des nanoplateformes ont été entreprises. Parallèlement, une nanoplateforme théranostique, alliant diagnostic et thérapie, a été envisagée. / The molecular imaging of tumor angiogenesis currently represents a major field of research for the diagnostic and the development of new treatment strategy of solid tumors. Endothelial cells from tumor neovessels overexpress the αvβ₃ integrins, which selectively bind to Arg- Gly-Asp (RGD)-containing peptides. The angiogenic process plays a key role during the development of other pathologies like cardiovascular diseases. So, the aim of this project is to design a bimodal contrast agent (MRI and fluorescence) targeting αvβ₃ integrins for early angiogenesis detection. Superpamagnetic iron oxide nanoparticles were surface functionalized with cathecol and bisphosphonate as anchoring agents and bearing carboxylic acid or alkyne functions as terminal end groups. We compared the efficiency of conjugation of three different types of molecules (fluorophores, PEG and RGD peptides) using carbodiimide coupling and click chemistry (Huisgen and thio-yne reactions). The stability of the various nanoplatforms and their uses as MRI contrast agents were evaluated. The affinity towards integrins was evidenced by surface plasmon resonance and solid-phase receptor-binding assay with a radioactive competitor ligand. With the aim to improve MRI properties, nanoparticles differing by their size and shape were synthesized and the magnetic properties were studied. The first in vitro and in vivo experiments were performed. In parallel, a theranostic nanoplatform, with both properties of diagnostic and therapy, has been considered.

No description available.