27 research outputs found
Evaluation of state-of-the-art segmentation algorithms for left ventricle infarct from late Gadolinium enhancement MR images
Studies have demonstrated the feasibility of late Gadolinium enhancement (LGE) cardiovascular magnetic
resonance (CMR) imaging for guiding the management of patients with sequelae to myocardial infarction,
such as ventricular tachycardia and heart failure. Clinical implementation of these developments necessitates
a reproducible and reliable segmentation of the infarcted regions. It is challenging to compare
new algorithms for infarct segmentation in the left ventricle (LV) with existing algorithms. Benchmarking
datasets with evaluation strategies are much needed to facilitate comparison. This manuscript presents
a benchmarking evaluation framework for future algorithms that segment infarct from LGE CMR of the
LV. The image database consists of 30 LGE CMR images of both humans and pigs that were acquired
from two separate imaging centres. A consensus ground truth was obtained for all data using maximum
likelihood estimation.
Six widely-used fixed-thresholding methods and five recently developed algorithms are tested on the
benchmarking framework. Results demonstrate that the algorithms have better overlap with the consensus
ground truth than most of the n-SD fixed-thresholding methods, with the exception of the FullWidth-at-Half-Maximum
(FWHM) fixed-thresholding method. Some of the pitfalls of fixed thresholding
methods are demonstrated in this work. The benchmarking evaluation framework, which is a contribution
of this work, can be used to test and benchmark future algorithms that detect and quantify infarct
in LGE CMR images of the LV. The datasets, ground truth and evaluation code have been made publicly
available through the website: https://www.cardiacatlas.org/web/guest/challenges
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NANOSCALE FUNCTIONALIZATION OF SOFC CATHODE SURFACE AND INTERFACES
In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system. In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths. To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs
Hierarchical adaptive texture conditional random field for enhanced pathology segmentation
This thesis proposes a new hierarchical Conditional Random Field (CRF) based classifier to address the task of small enhanced pathology segmentation. Specifically, a Hierarchical Adaptive Texture CRF (HAT-CRF) is developed and applied to the challenging problem of Gad-enhancing lesion segmentation in brain Magnetic Resonance Images (MRI) of patients with Multiple Sclerosis (MS). In this context, aside from the general small sizes of the enhanced lesions, the presence of many non-lesional enhancements (such as blood vessels) renders the problem more difficult. The proposed HAT-CRF model is the first automatic segmentation and detection approach for this context. In addition to voxel-wise cliques of up to size three, it exploits multiple higher order textures to discriminate the true lesional enhancements from the pool of other enhancements. Moreover, a temporal model referred to as temporal Hierarchical Adaptive Texture CRF (THAT-CRF) is also developed in this thesis which is the first work addressing the incorporation of temporal texture analysis in order to study the textures of enhanced candidates over time. Since the temporal profiles of the lesional and non-lesional enhancements are different from each other, including the temporal texture comparison increases the discrimination power of the THAT-CRF model. The two proposed models are trained on very large multi-center clinical trials consisting of 2380 scans from 247 different centers as part of multi-center clinical trials. The models are further tested on two separate clinical trials consisting of 813 scans from 27 centers and 2770 scans from 142 centers. It is shown that the incorporation of the temporal textures results in a general decrease of the false detection rate. Specifically, the THAT-CRF model achieves an over all sensitivity of 95% which ranges from 89% for very small lesions (3-5 voxels) to 100% for very large ones (101+ voxels) while the average false positive count per scan ranges from 0.27 to 0. The significance of different components of the model as well as the effect of different design choices, such as the neighborhood factorization, the registration techniques, and the parameter learning and inference approaches, are studied. Comparison with Support Vector Machine (SVM), Random Forest and variant of an MRF is also included where they are all outperformed by the proposed approach. Finally, superior performance is achieved by the reviewed labelings of the proposed model (corrected only for the false detections) compared to the fully manual labeling when applied to the context of separating different treatment arms in a real clinical trial.Cette thèse propose un nouveau classificateur basé sur la méthode de Champ Aléatoire Conditionnel (CAC) hiérarchique pour la segmentation de petite pathologie augmentée. Plus précisément, un CAC Hiérarchique de Texture Adaptive (CAC-HTA) est développé et appliqué sur le problème difficile de segmentation de lésions cérébrales augmentée par gadolinium dans les images à résonance magnétique (IRM) des patients atteints de Sclérose En Plaques (SEP). Dans ce contexte, en plus de la petite taille habituelle des lésions augmentées, la présence de nombreuses augmentations non lésionnelles (tels que les vaisseaux sanguins) rend le problème plus difficile. Le modèle CAC-HTA proposé est la première approche de segmentation et de détection automatiques pour ce contexte. En plus de groupements voxelliques allant jusqu'à de taille trois, elle exploite des textures multiples d'ordre supérieures pour discriminer les véritables augmentations lésionnelles des augmentations parasites. En outre, un modèle temporel appelé CAC Temporelle Hiérarchique de Texture Adaptative (THTA-CAC) est également développé dans cette thèse. C'est la première contribution qui s'adresse à l'incorporation de l'analyse temporelle des textures pour étudier les textures des candidats augmentés dans le temps. Etant donné que les profils temporels des augmentations lésionnelles et non lésionnelles sont différents l'un de l'autre, y compris la comparaison de texture temporelle augmente le pouvoir de discrimination du modèle THTA-CRF. Les deux modèles proposés sont formés sur de très grands essais cliniques multi centres constitués de 2380 scans de 247 centres différents dans le cadre d'essais cliniques multi centriques. Les modèles sont ensuite testés sur deux essais cliniques distincts composés de 813 scans de 27 centres et 2770 scans de 142 centres. Il est démontré que l'incorporation des textures temporelles en résulte une diminution générale du taux de fausse détection. Plus précisément, le modèle THTA-CAC réalise un taux global de sensibilité de 95% qui varie de 89% pour les très petites lésions (3-5 voxels) à 100% pour les très grandes (101+ voxels), tandis que le nombre de faux positifs moyens par scan varie de 0,27 à 0. L'importance des différentes composantes du modèle ainsi que l'effet de différents choix de conception, telles que la factorisation du voisinage, les techniques de recalage et les paramètres d'apprentissage et approches d'inférence sont étudiés. Une comparaison avec les Machines à Support de Vecteurs (MSV), les Forêts Aléatoires et variantes des MRF est également inclus, dans laquelle ils sont tous surpassé par l'approche proposée. Enfin, une performance supérieure est réalisée par le marquage supervisé du modèle proposé (corrigé uniquement pour les fausses détections) par rapport au marquage entièrement manuel lorsqu'il est appliqué au contexte de séparation des différents groupes de traitement dans un véritable essai clinique
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NANOSCALE FUNCTIONALIZATION OF SOFC CATHODE SURFACE AND INTERFACES
In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system. In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths. To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs
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Corrigendum to progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes [Journal of Power Sources 437 (2019) 226935] (Journal of Power Sources (2019) 437, (S0378775319309280), (10.1016/j.jpowsour.2019.226935))
The authors regret that a technical mistake has been discovered, which impacts the current density and power density reported in this article. Briefly, the mistake was caused by catalyst solution leaking out of the intended 1 cm2 catalyzed area and depositing catalyst over the whole cell. As a result, the calculated current and power densities (total divided by the catalyzed area) were higher than reality because the measured current and power were dividing by the intended 1 cm2 instead of the actual area including the leakage, which was approximately 5 cm2. This issue is presented, analysed, and discussed in further detail in the supporting information of Reference 1. The authors would like to apologise for any inconvenience caused
Quantification of Edematic Effects in Prostate Brachytherapy Interventions
Abstract. We present a quantitative model to analyze the detrimental effects of edema on the quality of prostate brachytherapy implants. We account for both tissue expansion and implant migration by mapping intra-operative ultrasound and post-implant CT. We pre-process the ultrasound with a phase congruency filter, and map it to the volume CT using a B-spline deformable mutual information similarity metric. To test the method, we implanted a standard training phantom with 48 seeds, imaged the phantom with ultrasound and CT and registered the two for ground truth. Edema was simulated by distorting the CT volume by known transformations. The objective was to match the distorted implant to the intra-operative ultrasound. Performance was measured relative to ground truth. We successfully mapped 100% of deformed seeds to ground truth under edematic expansion up to 40% of volume growth. Seed matching performance was 98% with random seed migration of 3mm superimposed on 10% edematic volume growth. This method promises to be clinically applicable as the first quantitative analysis tool to measure edematic implant deformations occurring between the operating room and post-operative CT imaging
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Progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes
High power density and longevity are required to commercialize solid oxide fuel cells for vehicular applications. In this work, electrochemical durability of high-performance metal-supported solid oxide fuel cells (MS-SOFCs) with infiltrated catalysts is investigated. Durability screening of various cathode and anode compositions is conducted. The Pr6O11 cathode and SDCN40 (40 vol% Ni-60 vol% SDC) anode are selected due to preferential tradeoff between performance and durability. X-ray diffraction indicates the catalyst phases are stable after prolonged thermal annealing. Electrochemical impedance and scanning electron microscopy analyses show that the evolution of SDCN40 is minimal, and coarsening and Cr poisoning of the Pr6O11 catalyst are the dominant degradation mechanisms. These degradation mechanisms are addressed by implementing three additional fabrication steps: (1) preoxidation of the metal support, (2) deposition of thin and protective atomic layer deposition (ALD) coatings throughout the cathode-side electrode and support, and (3) in situ pre-coarsening of the catalysts. A favorable tradeoff is achieved: the combination of the three fabrication steps reduces degradation rate at 0.7 V and 700 °C by two orders of magnitude to 2.3% kh−1, while sacrificing 35% of initial power density. The catalyst pre-coarsening step is primarily responsible for the loss of performance
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Corrigendum to progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes [Journal of Power Sources 437 (2019) 226935] (Journal of Power Sources (2019) 437, (S0378775319309280), (10.1016/j.jpowsour.2019.226935))
The authors regret that a technical mistake has been discovered, which impacts the current density and power density reported in this article. Briefly, the mistake was caused by catalyst solution leaking out of the intended 1 cm2 catalyzed area and depositing catalyst over the whole cell. As a result, the calculated current and power densities (total divided by the catalyzed area) were higher than reality because the measured current and power were dividing by the intended 1 cm2 instead of the actual area including the leakage, which was approximately 5 cm2. This issue is presented, analysed, and discussed in further detail in the supporting information of Reference 1. The authors would like to apologise for any inconvenience caused
Recommended from our members
Progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes
High power density and longevity are required to commercialize solid oxide fuel cells for vehicular applications. In this work, electrochemical durability of high-performance metal-supported solid oxide fuel cells (MS-SOFCs) with infiltrated catalysts is investigated. Durability screening of various cathode and anode compositions is conducted. The Pr6O11 cathode and SDCN40 (40 vol% Ni-60 vol% SDC) anode are selected due to preferential tradeoff between performance and durability. X-ray diffraction indicates the catalyst phases are stable after prolonged thermal annealing. Electrochemical impedance and scanning electron microscopy analyses show that the evolution of SDCN40 is minimal, and coarsening and Cr poisoning of the Pr6O11 catalyst are the dominant degradation mechanisms. These degradation mechanisms are addressed by implementing three additional fabrication steps: (1) preoxidation of the metal support, (2) deposition of thin and protective atomic layer deposition (ALD) coatings throughout the cathode-side electrode and support, and (3) in situ pre-coarsening of the catalysts. A favorable tradeoff is achieved: the combination of the three fabrication steps reduces degradation rate at 0.7 V and 700 °C by two orders of magnitude to 2.3% kh−1, while sacrificing 35% of initial power density. The catalyst pre-coarsening step is primarily responsible for the loss of performance