La distinction entre les fœtus constitutionnellement petits de ceux qui présentent une réelle restriction de croissance liée à une insuffisance placentaire n’est pas aisée avec les mesures échographiques utilisées en pratique courante. Le retard de croissance intra-utérin (RCIU) est responsable d’une part importante de la prématurité induite, et d’une augmentation du risque de mortalité et de morbidité néonatales. C’est pourquoi, l’amélioration de la connaissance de la vascularisation placentaire est indispensable pour mieux identifier et prendre en charge les situations d’hypoxie chroniques foetales associées à l’insuffisance placentaire.Pour quantifier la vascularisation les modalités d’imagerie de perfusion disponibles sont l’échographie et l’IRM. Les études évaluant la quantification de la perfusion placentaire par échographie de contraste sont peu nombreuses. Les avantages et les limites de cet examen ont été évalués sur un modèle murin de RCIU par ligature vasculaire. Ainsi, l’échographie de contraste permettait de quantifier une baisse de la perfusion placentaire sur un modèle de RCIU sans que l’on puisse observer de passage d’agents de contraste ultrasonores au travers la barrière placentaire. Les résultats obtenus ont été comparés aux données obtenues par l’IRM de perfusion. Les paramètres quantitatifs obtenus à partir des courbes de cinétiques du contraste pour chacune des deux modalités d’imagerie étaient comparables sur un modèle identique de RCIU murin. Enfin, une méthode d’étude de l’oxygénation placentaire par imagerie photoacoustique a été évaluée. Cette modalité d’imagerie non invasive permettait d’obtenir en temps réel l’oxygénation placentaire, avec cependant une profondeur limitée d’exploration. Le placenta semblait se comporter comme une réserve en oxygène au cours de l’étude d’une séquence hypoxie – hyperoxygénation maternelle avec une désaturation moins importante que celle observée dans les autres tissus maternels. / To identify fetuses small for their gestational-age who have reached their appropriate growth potential from growth-restricted fetuses due to placental insufficiency is uneasy. Intra Uterine Growth Restriction (IUGR) increases the risk for indicated preterm delivery, neonatal mortality and morbidity. Therefore, improving the knowledge of the placental perfusion is essential to better identify and manage fetal chronic oxygen deprivation associated with placental insufficiency.Contrast Enhanced Ultrasound (CEUS) and MRI are two imaging modalities available to quantify placental perfusion. However, few studies focus on the quantification of placental perfusion with CEUS. First, the advantages and limitations of CEUS were presented in an IUGR rat model by uterine ligation. The placental perfusion observed by CEUS was significantly decreased in the ligated horn. No contrast enhancement was observed in the umbilical vein or the fetus. Then, we compared the CEUS parameters to results obtained by MRI perfusion. Perfusion parameters were obtained from the signal intensity decay curve for the two imaging modalities. Results of such perfusion parameters were comparable in the same IUGR rat model. Finally, we evaluated the response of the placenta to oxygenation by photoacoustic imaging. PA imaging is a real-time, non-invasive method to evaluate placental oxygenation without contrast agents. Our results suggesting that placenta is less affected than maternal tissue by the decline in maternal oxygenation. The placenta may play an important role in protecting the feus against hypoxia.

This diploma thesis deals with DCE-MRI (Dynamic Contrast-Enhanced Magnetic Resonance Imaging) thus one of the contrast magnetic resonance imaging methods. It describes the principle of conventional continuous DCE-MRI, which uses single bolus of contrast agent and further it focuses on the dual bolus contrast agent techniques, especially the interleaved acquisition. The graphical interface for processing Bruker systems data was made. Synthetic data were used to evaluate the influence of this method on the perfusion parameters estimation. Simulations proved that the further the second bolus is from the first one, the better results are. Simulations of acquisition interruption did not lead to the clear result. However, two statements, which are expected to lead to as good estimation of perfusion parameters as possible, were formulated

Since its introduction, contrast-enhanced ultrasonography (CEUS) has significantly extended the value of ultrasonography (US). CEUS can be used to more accurately determine pancreatic lesions compared to conventional US or to characterize lesions already detectable by US. Thus, CEUS can aid in the differential diagnosis of pancreatic tumors. Using US contrast media, it is possible to visually detect microvessels in the majority of pancreatic ductal adenocarcinomas. Thus, the use of quantitatively evaluated transabdominal CEUS can help in the differentiation of patients with mass-forming pancreatitis from patients with pancreatic adenocarcinomas. In neuroendocrine pancreatic tumors, different enhancement patterns can be observed in relation to the tumor mass: larger ones show a rapid early enhancement sometimes combined with necrotic central structures, and smaller ones disclose a capillary-blush enhancement. Pseudocysts, the most widespread cystic lesions of the pancreas, are not vascularized. They do not show any signal in CEUS and remain entirely anechoic in all phases, while true cystic pancreatic tumors usually have vascularized septa and parietal nodules. In summary, CEUS is effective for differentiating solid pancreatic tumors in most cases. CEUS is safe and cost effective and can better discriminate solid from cystic pancreatic lesions, thereby directing further imaging modalities. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Diffusion weighted imaging (DWI) and dynamic susceptibility contrast-enhanced (DSC) perfusion-weighted imaging (PWI) are commonly employed in clinical practice and in research to give pathophysiological information for patients with acute ischemic stroke. DWI is thought to roughly reflect the severely damaged infarct core, while DSC-PWI reflects the area of hypoperfusion. The volumetric difference between DWI and DSC-PWI is termed the PWI/DWI-mismatch, and has been suggested as an MRI surrogate of the ischemic penumbra. However, due to the application of a contrast agent, which has potentially severe side-effects (e.g., nephrogenic systemic fibrosis), the DSC-PWI precludes repetitive examinations for monitoring purposes. New approaches are being sought to overcome this shortcoming. BOLD (blood oxygen-level dependent) signal can reflect the metabolism of blood oxygen in the brain and hemodynamics can be assessed with resting-state fMRI. The aim of this thesis was to use resting-state fMRI as a new approach to give similar information as DSC-PWI. This thesis comprises two studies: In the first study (see Chapter 2), two resting-state fMRI methods, local methods which compare low frequency amplitudes between two hemispheres and a k-means clustering approach, were applied to investigate the functional damage of patients with acute ischemic stroke both in the time domain and frequency domain. We found that the lesion areas had lower amplitudes than contralateral homotopic healthy tissues. We also differentiated the lesion areas from healthy tissues using a k-means clustering approach. In the second study (see Chapter 3), time-shift analysis (TSA), which assesses time delays of the spontaneous low frequency fluctuations of the resting-state BOLD signal, was applied to give similar pathophysiological information as DSC-PWI in the acute phase of stroke. We found that areas which showed a pronounced time delay to the respective mean time course were very similar to the hypoperfusion area. In summary, we suggest that the resting-state fMRI methods, especially the time-shift analysis (TSA), may provide comparable information to DSC-PWI and thus serve as a useful diagnostic tool for stroke MRI without the need for the application of a contrast agent.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20564号 / 医博第4249号 / 新制||医||1022(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 増永 慎一郎, 教授 妹尾 浩, 教授 鈴木 実 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13133号 / 論医博第2137号 / 新制||医||1024(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 溝脇 尚志, 教授 妹尾 浩, 教授 鈴木 実 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

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The deep learning-based automatic segmentation methods have developed rapidly in recent years to give a promising performance in the medical image segmentation tasks, which provide clinical medicine with an accurate and fast computer-aided diagnosis method. Generative adversarial networks and their extended frameworks have achieved encouraging results on image-to-image translation problems. In this report, the proposed hybrid network combined cycle-consistent adversarial networks, which transformed contrast-enhanced images from computed tomography angiography to the conventional low-contrast CT scans, with the segmentation network and trained them simultaneously in an end-to-end manner. The trained segmentation network was tested on the non-contrast-enhanced CT images. The synthetic process and the segmentation process were also implemented in a two-stage manner. The two-stage process achieved a higher Dice similarity coefficient than the baseline U-Net did on test data, but the proposed hybrid network did not outperform the baseline due to the field of view difference between the two training data sets.

La segmentation d’images médicales est depuis longtemps un sujet de recherche actif. Cette thèse traite des méthodes de segmentation basées modèles, qui sont un bon compromis entre généricité et capacité d’utilisation d’informations a priori sur l’organe cible. Notre but est de construire un algorithme de segmentation pouvant tirer profit d’une grande variété d’informations extérieures telles que des bases de données annotées (via l’apprentissage statistique), d’autres images du même patient (via la co-segmentation) et des interactions de l’utilisateur. Ce travail est basé sur la déformation de modèle implicite, une méthode variationnelle reposant sur une représentation implicite des formes. Après avoir amélioré sa formulation mathématique, nous montrons son potentiel sur des problèmes cliniques difficiles. Nous introduisons ensuite différentes généralisations, indépendantes mais complémentaires, visant à enrichir le modèle de forme et d’apparence utilisé. La diversité des applications cliniques traitées prouve la généricité et l’efficacité de nos contributions. / Within the wide field of medical imaging research, image segmentation is one of the earliest but still open topics. This thesis focuses on model-based segmentation methods, which achieve a good trade-off between genericity and ability to carry prior information on the target organ. Our goal is to build an efficient segmentation framework that is able to leverage all kinds of external information, i.e. annotated databases via statistical learning, other images from the patient via co-segmentation and user input via live interactions. This work is based on the implicit template deformation framework, a variational method relying on an implicit representation of shapes. After improving the mathematical formulation of this approach, we show its potential on challenging clinical problems. Then, we introduce different generalizations, all independent but complementary, aimed at enriching both the shape and appearance model exploited. The diversity of the clinical applications addressed shows the genericity and the effectiveness of our contributions.

Perfusion magnetic resonance imaging is modern diagnostic method used mainly in oncology. In this method, contrast agent is injected to the subject and then is continuously monitored the progress of its concentration in the affected area in time. Correct determination of the arterial input function (AIF) is very important for perfusion analysis. One possibility is to model AIF by multichannel blind deconvolution but the estimated AIF is necessary to be scaled. This master´s thesis is focused on description of scaling methods and their influence on perfussion parameters in dependence on used model of AIF in different tissues.