124 research outputs found
Medical image registration by neural networks: a regression-based registration approach
This thesis focuses on the development and evaluation of a registration-by-regression approach for the 3D/2D registration of coronary Computed Tomography Angiography (CTA) and X-ray angiography. This regression-based method relates image features of 2D projection images to the transformation parameters of the 3D image by a nonlinear regression. It treats registration as a regression problem, as an alternative for the traditional iterative approach that often comes with high computational costs and limited capture range.
First we presented a survey of the methods with a regression-based registration approach for medical applications, as well as a summary of their main characteristics (Chapter 2). Second, we studied the registration methodology, addressing the input features and the choice of regression model (Chapter 3 and Chapter 4). For that purpose, we evaluated different options using simulated X-ray images generated from coronary artery tree models derived from 3D CTA scans. We also compared the registration-by-regression results with a method based on iterative optimization. Different image features of 2D projections and seven regression techniques were considered. The regression approach for simulated X-rays was shown to be slightly less accurate, but much more robust than the method based on an iterative optimization approach. Neural Networks obtained accurate results and showed to be robust to large initial misalignment.
Third, we evaluated the registration-by-regression method using clinical data, integrating the 3D preoperative CTA of the coronary arteries with intraoperative 2D X-ray angiography images (Chapter 5). For the evaluation of the image registration, a gold standard registration was established using an exhaustive search followed by a multi-observer visual scoring procedure. The influence of preprocessing options for the simulated images and the real X-rays was studied. Several image features were also compared. The coronary registrationâby-regression results were not satisfactory, resembling manual initialization accuracy.
Therefore, the proposed method for this concrete problem and in its current configuration is not sufficiently accurate to be used in the clinical practice. The framework developed enables us to better understand the dependency of the proposed method on the differences between simulated and real images. The main difficulty lies in the substantial differences in appearance between the images used for training (simulated X-rays from 3D coronary models) and the actual images obtained during the intervention (real X-ray angiography). We suggest alternative solutions and recommend to evaluate the registration-by-regression approach in other applications where training data is available that has similar appearance to the eventual test data
Recalage rigide 3D-2D par intensité pour le traitement percutané des cardiopathies congénitales
Les cardiopathies congĂ©nitales cyanogĂšnes sont des malformations cardiaques infantiles qui, dans leurs formes les plus complexes, sont aggravĂ©es par des artĂšres morbides partant de lâaorte et appelĂ©es collatĂ©rales aorto-pulmonaires majeures (MAPCAs). Pour corriger ces malformations, les cardiologues insĂšrent un cathĂ©ter dans une artĂšre du patient puis, le guident jusquâĂ atteindre la structure vasculaire dâintĂ©rĂȘt. Le cathĂ©ter est visualisĂ© grĂące Ă des angiographies acquises lors de lâopĂ©ration.
NĂ©anmoins, ces interventions, dĂźtes percutanĂ©es, sont dĂ©licates Ă rĂ©aliser. Lâemploi des angiographies 2D limite le champ de vision des cardiologues et les oblige Ă mentalement reconstruire la structure vasculaire en mouvement. Afin dâamĂ©liorer les conditions dâintervention, des techniques dâimagerie mĂ©dicale exploitant des donnĂ©es tomographiques acquis avant lâintervention sont dĂ©veloppĂ©es. Les donnĂ©es tomographiques forment un modĂšle 3D fiable de la structure vasculaire qui, une fois prĂ©cisĂ©ment alignĂ© avec les angiographies, dĂ©finit un outil de navigation virtuel 3D qui augmente le champ de vision des cardiologues. Dans ce mĂ©moire, une nouvelle mĂ©thode automatique de recalage rigide 3D-2D par intensitĂ© de donnĂ©es tomographiques 3D avec des angiographies 2D est prĂ©sentĂ©e. Aussi, une technique dâalignement semi-automatique permettant dâaccĂ©lĂ©rer lâinitialisation de la mĂ©thode automatique est dĂ©veloppĂ©e. Les rĂ©sultats de la mĂ©thode de recalage proposĂ©e, obtenus avec deux jeux de donnĂ©es de patient atteints de malformations cardiaques, sont prometteurs.
Un alignement prĂ©cis et robuste des donnĂ©es tomographique de lâartĂšre aorte et des MAPCAs (0;265ïżœ0;647mm et 99 % de succĂšs) Ă partir dâun dĂ©placement rigide dâamplitude maximale (20mm et 20°) est obtenu en un temps de calcul raisonnable (13,7 secondes)
Malformation artério-veineuses cérébrales : d'une amélioration des techniques d'imagerie vers un changement de paradigme des traitements
Brain arteriovenous malformations (bAVMs) are aggressive vascular malformations presenting a haemorrhagic complication risk that may lead to severe consequences in terms of morbi-Ââmortality. Available imaging tools poorly help in understanding their angio-Ââarchitecture. We have developed two imaging tools improving our understanding of the anatomy of these malformations: a semi-Ââautomated segmentation algorithm and a convex spherical anamorphosis algorithm. These algorithms have been elaborated for use on 3D rotational angiography acquisitions; they provide a better visualisation of the bAVMsâ main draining vein, especially for venous stenosis or for focal ectasia. They also help in depicting accurately intranidal aneurysms. These improvements in the analysis of the bAVMsâ angioarchitecure may help in reducing the therapeutic risk for these malformations. For a further testing of the potential of anti-Ââangiogenic agents for the treatment of bAVMs, we have elaborated a simplified swine AVM model consisting in the occlusion of a common carotid artery by endovascular means. The comparison between the volume of the rete mirabile at D0 and 3 months and those measured in a control group showed a significant increasing of the retia in the occlusion group. Moreover, a tendency was observed concerning an increase in VEGF (vascular endothelial growth factor) serum levels close to the rete mirabile in the occlusion group. Finally, pathological changes close to those seen in human bAVMs were observed on autopsy samples in the occlusion group.Les malformations artĂ©rio-Ââveineuses cĂ©rĂ©brales (MAVc) sont des pathologies vasculaires agressives prĂ©sentant un risque hĂ©morragique lourd de consĂ©quence en terme de morbi-ÂâmortalitĂ©. Les outils dâimagerie disponibles actuellement ne permettent de comprendre que difficilement leur angio-Ââ architecture. Nous avons dĂ©veloppĂ© dans notre travail deux outils dâimagerie permettant dâaffiner la comprĂ©hension de lâanatomie des ces malformations : un algorithme de segmentation semi-ÂâautomatisĂ© et un algorithme dâanamorphose sphĂ©rique convexe. Ces algorithmes ont Ă©tĂ© Ă©laborĂ©s pour ĂȘtre utilisĂ©s sur les acquisitions dâangiographie rotationnelle 3D ; ils permettent de mieux visualiser la veine de drainage principale des MAVc, notamment dâidentifier une stĂ©nose ou une ectasie focale sur cette veine, et Ă©galement de dĂ©celer de façon plus fiable la prĂ©sence dâun anĂ©vrysme intra-Âânidal. Ces amĂ©liorations dans lâanalyse de lâangio-Ââarchitecture des MAVc permettront vraisemblablement de rĂ©duire le risque thĂ©rapeutique pour ces malformations. En vue de tester le potentiel des agents anti-ÂâangiogĂ©niques pour le traitement des MAVc, nous avons Ă©laborĂ© un modĂšle porcin simplifiĂ© de MAVc consistant en une occlusion unilatĂ©rale dâartĂšre carotide primitive par voie endovasculaire. La comparaison entre le volume de rete mirabile Ă J0 et Ă 3 mois et les valeurs obtenues pour un groupe tĂ©moin a montrĂ© une augmentation significative du volume du rete mirabile chez les porcs ayant eu lâocclusion carotidienne. Dâautre part, une tendance nette Ă lâaugmentation des taux de VEGF (vascular endothelial growth factor) Ă proximitĂ© du rete mirabile Ă©tait observĂ©e dans le groupe occlusion. Enfin, des modifications anatomopathologiques proches de celles des MAVc humaines Ă©taient visualisĂ©es sur les piĂšces autopsiques des rete mirabile dans le groupe occlusion
Spatio-temporal data fusion in cerebral angiography
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 153-167).This thesis provides a framework for generating the previously unobtained high resolution time sequences of 3D images that show the dynamics of cerebral blood flow. These sequences allow image feedback during medical procedures that can facilitate the detection and observation of stenosis, aneurysms, and clots. The 3D time series is constructed by fusing together a single static 3D image with one or more time sequence of 2D projections. The fusion process utilizes a variational approach that constrains the volumes to have both smoothly varying regions separated by edges and sparse regions of non-zero support. Results are presented on both clinical and simulated phantom data sets. The 3D time series results are visualized using the following tools: time series of intensity slices, synthetic X-rays from an arbitrary view, time series of isosurfaces, and 3D surfaces that show arrival times of contrast using color. This thesis also details the different steps needed to prepare the two classes of data. In addition to the spatio-temporal data fusion algorithm, three new algorithms are presented: a single pass groupwise registration algorithm for registering the time series, a 2D-3D registration algorithm for registering the time series with respect to the 3D volume, and a modified adaptive version of the Cusum algorithm used for determining arrival times of contrast within the 2D time sequences.by Andrew David Copeland.Ph.D
Automatic Spatiotemporal Analysis of Cardiac Image Series
RĂSUMĂ
Ă ce jour, les maladies cardiovasculaires demeurent au premier rang des principales causes de
dĂ©cĂšs en AmĂ©rique du Nord. Chez lâadulte et au sein de populations de plus en plus jeunes,
la soi-disant Ă©pidĂ©mie dâobĂ©sitĂ© entraĂźnĂ©e par certaines habitudes de vie tels que la mauvaise
alimentation, le manque dâexercice et le tabagisme est lourde de consĂ©quences pour les personnes
affectées, mais aussi sur le systÚme de santé. La principale cause de morbidité et de
mortalitĂ© chez ces patients est lâathĂ©rosclĂ©rose, une accumulation de plaque Ă lâintĂ©rieur des
vaisseaux sanguins à hautes pressions telles que les artÚres coronaires. Les lésions athérosclérotiques
peuvent entraĂźner lâischĂ©mie en bloquant la circulation sanguine et/ou en provoquant
une thrombose. Cela mĂšne souvent Ă de graves consĂ©quences telles quâun infarctus. Outre les
problÚmes liés à la sténose, les parois artérielles des régions criblées de plaque augmentent la
rigidité des parois vasculaires, ce qui peut aggraver la condition du patient. Dans la population
pédiatrique, la pathologie cardiovasculaire acquise la plus fréquente est la maladie de
Kawasaki. Il sâagit dâune vasculite aigĂŒe pouvant affecter lâintĂ©gritĂ© structurale des parois des
artĂšres coronaires et mener Ă la formation dâanĂ©vrismes. Dans certains cas, ceux-ci entravent
lâhĂ©modynamie artĂ©rielle en engendrant une perfusion myocardique insuffisante et en activant
la formation de thromboses.
Le diagnostic de ces deux maladies coronariennes sont traditionnellement effectuĂ©s Ă lâaide
dâangiographies par fluoroscopie. Pendant ces examens paracliniques, plusieurs centaines de
projections radiographiques sont acquises en sĂ©ries suite Ă lâinfusion artĂ©rielle dâun agent de
contraste. Ces images révÚlent la lumiÚre des vaisseaux sanguins et la présence de lésions
potentiellement pathologiques, sâil y a lieu. Parce que les sĂ©ries acquises contiennent de lâinformation
trĂšs dynamique en termes de mouvement du patient volontaire et involontaire (ex.
battements cardiaques, respiration et dĂ©placement dâorganes), le clinicien base gĂ©nĂ©ralement
son interprĂ©tation sur une seule image angiographique oĂč des mesures gĂ©omĂ©triques sont effectuĂ©es
manuellement ou semi-automatiquement par un technicien en radiologie. Bien que
lâangiographie par fluoroscopie soit frĂ©quemment utilisĂ© partout dans le monde et souvent
considĂ©rĂ© comme lâoutil de diagnostic âgold-standardâ pour de nombreuses maladies vasculaires,
la nature bidimensionnelle de cette modalitĂ© dâimagerie est malheureusement trĂšs
limitante en termes de spécification géométrique des différentes régions pathologiques. En effet,
la structure tridimensionnelle des stĂ©noses et des anĂ©vrismes ne peut pas ĂȘtre pleinement
appréciée en 2D car les caractéristiques observées varient selon la configuration angulaire de
lâimageur. De plus, la prĂ©sence de lĂ©sions affectant les artĂšres coronaires peut ne pas reflĂ©ter
la véritable santé du myocarde, car des mécanismes compensatoires naturels (ex. vaisseaux----------ABSTRACT
Cardiovascular disease continues to be the leading cause of death in North America. In adult
and, alarmingly, ever younger populations, the so-called obesity epidemic largely driven by
lifestyle factors that include poor diet, lack of exercise and smoking, incurs enormous stresses
on the healthcare system. The primary cause of serious morbidity and mortality for these
patients is atherosclerosis, the build up of plaque inside high pressure vessels like the coronary
arteries. These lesions can lead to ischemic disease and may progress to precarious blood
flow blockage or thrombosis, often with infarction or other severe consequences. Besides
the stenosis-related outcomes, the arterial walls of plaque-ridden regions manifest increased
stiffness, which may exacerbate negative patient prognosis. In pediatric populations, the
most prevalent acquired cardiovascular pathology is Kawasaki disease. This acute vasculitis
may affect the structural integrity of coronary artery walls and progress to aneurysmal lesions.
These can hinder the blood flowâs hemodynamics, leading to inadequate downstream
perfusion, and may activate thrombus formation which may lead to precarious prognosis.
Diagnosing these two prominent coronary artery diseases is traditionally performed using
fluoroscopic angiography. Several hundred serial x-ray projections are acquired during selective
arterial infusion of a radiodense contrast agent, which reveals the vesselsâ luminal
area and possible pathological lesions. The acquired series contain highly dynamic information
on voluntary and involuntary patient movement: respiration, organ displacement and
heartbeat, for example. Current clinical analysis is largely limited to a single angiographic
image where geometrical measures will be performed manually or semi-automatically by a
radiological technician. Although widely used around the world and generally considered
the gold-standard diagnosis tool for many vascular diseases, the two-dimensional nature of
this imaging modality is limiting in terms of specifying the geometry of various pathological
regions. Indeed, the 3D structures of stenotic or aneurysmal lesions may not be fully appreciated
in 2D because their observable features are dependent on the angular configuration of
the imaging gantry. Furthermore, the presence of lesions in the coronary arteries may not
reflect the true health of the myocardium, as natural compensatory mechanisms may obviate
the need for further intervention. In light of this, cardiac magnetic resonance perfusion
imaging is increasingly gaining attention and clinical implementation, as it offers a direct
assessment of myocardial tissue viability following infarction or suspected coronary artery
disease. This type of modality is plagued, however, by motion similar to that present in fluoroscopic
imaging. This issue predisposes clinicians to laborious manual intervention in order
to align anatomical structures in sequential perfusion frames, thus hindering automation o
Automatic Spatiotemporal Analysis of Cardiac Image Series
RĂSUMĂ
Ă ce jour, les maladies cardiovasculaires demeurent au premier rang des principales causes de
dĂ©cĂšs en AmĂ©rique du Nord. Chez lâadulte et au sein de populations de plus en plus jeunes,
la soi-disant Ă©pidĂ©mie dâobĂ©sitĂ© entraĂźnĂ©e par certaines habitudes de vie tels que la mauvaise
alimentation, le manque dâexercice et le tabagisme est lourde de consĂ©quences pour les personnes
affectées, mais aussi sur le systÚme de santé. La principale cause de morbidité et de
mortalitĂ© chez ces patients est lâathĂ©rosclĂ©rose, une accumulation de plaque Ă lâintĂ©rieur des
vaisseaux sanguins à hautes pressions telles que les artÚres coronaires. Les lésions athérosclérotiques
peuvent entraĂźner lâischĂ©mie en bloquant la circulation sanguine et/ou en provoquant
une thrombose. Cela mĂšne souvent Ă de graves consĂ©quences telles quâun infarctus. Outre les
problÚmes liés à la sténose, les parois artérielles des régions criblées de plaque augmentent la
rigidité des parois vasculaires, ce qui peut aggraver la condition du patient. Dans la population
pédiatrique, la pathologie cardiovasculaire acquise la plus fréquente est la maladie de
Kawasaki. Il sâagit dâune vasculite aigĂŒe pouvant affecter lâintĂ©gritĂ© structurale des parois des
artĂšres coronaires et mener Ă la formation dâanĂ©vrismes. Dans certains cas, ceux-ci entravent
lâhĂ©modynamie artĂ©rielle en engendrant une perfusion myocardique insuffisante et en activant
la formation de thromboses.
Le diagnostic de ces deux maladies coronariennes sont traditionnellement effectuĂ©s Ă lâaide
dâangiographies par fluoroscopie. Pendant ces examens paracliniques, plusieurs centaines de
projections radiographiques sont acquises en sĂ©ries suite Ă lâinfusion artĂ©rielle dâun agent de
contraste. Ces images révÚlent la lumiÚre des vaisseaux sanguins et la présence de lésions
potentiellement pathologiques, sâil y a lieu. Parce que les sĂ©ries acquises contiennent de lâinformation
trĂšs dynamique en termes de mouvement du patient volontaire et involontaire (ex.
battements cardiaques, respiration et dĂ©placement dâorganes), le clinicien base gĂ©nĂ©ralement
son interprĂ©tation sur une seule image angiographique oĂč des mesures gĂ©omĂ©triques sont effectuĂ©es
manuellement ou semi-automatiquement par un technicien en radiologie. Bien que
lâangiographie par fluoroscopie soit frĂ©quemment utilisĂ© partout dans le monde et souvent
considĂ©rĂ© comme lâoutil de diagnostic âgold-standardâ pour de nombreuses maladies vasculaires,
la nature bidimensionnelle de cette modalitĂ© dâimagerie est malheureusement trĂšs
limitante en termes de spécification géométrique des différentes régions pathologiques. En effet,
la structure tridimensionnelle des stĂ©noses et des anĂ©vrismes ne peut pas ĂȘtre pleinement
appréciée en 2D car les caractéristiques observées varient selon la configuration angulaire de
lâimageur. De plus, la prĂ©sence de lĂ©sions affectant les artĂšres coronaires peut ne pas reflĂ©ter
la véritable santé du myocarde, car des mécanismes compensatoires naturels (ex. vaisseaux----------ABSTRACT
Cardiovascular disease continues to be the leading cause of death in North America. In adult
and, alarmingly, ever younger populations, the so-called obesity epidemic largely driven by
lifestyle factors that include poor diet, lack of exercise and smoking, incurs enormous stresses
on the healthcare system. The primary cause of serious morbidity and mortality for these
patients is atherosclerosis, the build up of plaque inside high pressure vessels like the coronary
arteries. These lesions can lead to ischemic disease and may progress to precarious blood
flow blockage or thrombosis, often with infarction or other severe consequences. Besides
the stenosis-related outcomes, the arterial walls of plaque-ridden regions manifest increased
stiffness, which may exacerbate negative patient prognosis. In pediatric populations, the
most prevalent acquired cardiovascular pathology is Kawasaki disease. This acute vasculitis
may affect the structural integrity of coronary artery walls and progress to aneurysmal lesions.
These can hinder the blood flowâs hemodynamics, leading to inadequate downstream
perfusion, and may activate thrombus formation which may lead to precarious prognosis.
Diagnosing these two prominent coronary artery diseases is traditionally performed using
fluoroscopic angiography. Several hundred serial x-ray projections are acquired during selective
arterial infusion of a radiodense contrast agent, which reveals the vesselsâ luminal
area and possible pathological lesions. The acquired series contain highly dynamic information
on voluntary and involuntary patient movement: respiration, organ displacement and
heartbeat, for example. Current clinical analysis is largely limited to a single angiographic
image where geometrical measures will be performed manually or semi-automatically by a
radiological technician. Although widely used around the world and generally considered
the gold-standard diagnosis tool for many vascular diseases, the two-dimensional nature of
this imaging modality is limiting in terms of specifying the geometry of various pathological
regions. Indeed, the 3D structures of stenotic or aneurysmal lesions may not be fully appreciated
in 2D because their observable features are dependent on the angular configuration of
the imaging gantry. Furthermore, the presence of lesions in the coronary arteries may not
reflect the true health of the myocardium, as natural compensatory mechanisms may obviate
the need for further intervention. In light of this, cardiac magnetic resonance perfusion
imaging is increasingly gaining attention and clinical implementation, as it offers a direct
assessment of myocardial tissue viability following infarction or suspected coronary artery
disease. This type of modality is plagued, however, by motion similar to that present in fluoroscopic
imaging. This issue predisposes clinicians to laborious manual intervention in order
to align anatomical structures in sequential perfusion frames, thus hindering automation o
Optimisation of planning and delivery methods for Gamma Knife Stereotactic Radiosurgery
The work presented in this dissertation is the response to a series of technical and clinical challenges encountered during the first four years of operations in the Gamma Knife Centre at Queen Square. These challenges, which are common to most contemporary Gamma Knife centres, were prospectively addressed and practical solutions were developed for the questions they posed. The dosimetric differences between the new convolution algorithm and the standard TMR 10 algorithm traditionally used for prediction of dose distribution in Gamma Knife Radiosurgery (GKR) were explored. It was demonstrated that inhomogeneity correction with the convolution algorithm results in a considerable but consistent dose shift compared to TMR 10. No significant difference in relative dose distribution was noted and it was concluded that a reduction of the prescription dose is necessary to obtain the same absolute dosimetric effect with the convolution algorithm. The stability of the stereotactic Leksell frame G in GKR was demonstrated using a comprehensive study design that involved repeated measurements of landmarks by two observers. The study provided reliable and realistic evidence of submillimetre stability of the stereotactic frame throughout the treatment procedure which is important for evaluation and development of new frameless radiosurgery systems. The technical feasibility of using a combination of three magnetic resonance angiography sequences (triple-MRA), instead of digital subtraction angiography (DSA), for visualisation and delineation of brain Arteriovenous Malformations (AVMs) for GKR targeting was demonstrated. Target volumes obtained using triple-MRA are on average 10% smaller than AVM targets obtained with the standard DSA planning method and this can potentially reduce the risk of adverse radiation effects (ARE). The treatment planning method described here has laid the way for a change in clinical practice that favours a less invasive treatment planning approach. The same principle of less invasive AVM imaging with triple-MRA was used at the post-GKR stage, when a DSA is performed to confirm AVM obliteration. Triple-MRA was found to consistently confirm or rule out residual AVMs in patients who had undergone GKR for brain AVMs, compared to DSA, and it can also be reliably used for characterisation of residual AVMs. The use of triple-MRA as a first line for assessment of obliteration after GKR is recommended
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