Aortic root sizing for transcatheter aortic valve implantation using a shape model parameterisation.

During a transcatheter aortic valve implantation, an axisymmetric implant is placed in an irregularly shaped aortic root. Implanting an incorrect size can cause complications such as leakage of blood alongside or through the implant. The aim of this study was to construct a method that determines the optimal size of the implant based on the three-dimensional shape of the aortic root. Based on the pre-interventional computed tomography scan of 89 patients, a statistical shape model of their aortic root was constructed. The weights associated with the principal components and the volume of calcification in the aortic valve were used as parameters in a classification algorithm. The classification algorithm was trained using the patients with no or mild leakage after their intervention. Subsequently, the algorithms were applied to the patients with moderate to severe leakage. Cross validation showed that a random forest classifier assigned the same size in 65 ± 7% of the training cases, while 57 ± 8% of the patients with moderate to severe leakage were assigned a different size. This initial study showed that this semi-automatic method has the potential to correctly assign an implant size. Further research is required to assess whether the different size implants would improve the outcome of those patients.

Morphological Characteristics and Calcification of the Native Aortic Valve and the Relation to Significant Aortic Regurgitation after CoreValve TAVI.

BACKGROUND AND AIM OF THE STUDY: Aortic regurgitation (AR) is a frequent and life-limiting complication after transcatheter aortic valve implantation (TAVI). The study aim was to relate post-TAVI AR, using a self-expandable stent, to detailed baseline anatomical and morphological characteristics of the native aortic valve. METHODS: A total of 82 patients (40 males, 42 females; mean age 80 ± 7 years) who received a Medtronic CoreValve implant was included. Aortic root morphology, aortic annulus and implant size mismatch, implant position, extent of aortic annulus and leaflet calcification, the connected sub-annular calcification volume, and their distribution were quantified based on computed tomography scan analysis. AR following TAVI was quantified using standardized angiography and echocardiography. RESULTS: The mean logistic EuroSCORE of all patients was 16.9 ± 11.1%. According to angiography and echocardiography, 41% and 39% respectively, of the patients had AR grade ≥2. The two methods correlated moderately (Spearman's ρ = 0.51, p <0.001). The maximal diameter of the native annulus was larger in patients with significant AR after TAVI based on echocardiography (28.0 mm versus 26.8 mm, p = 0.059). Excessive calcification, especially on the left coronary cusp, was present in patients with significant AR, based on angiography (AR ≥II 71.0 mm3 versus AR

A validated methodology for patient specific computational modeling of self-expandable transcatheter aortic valve implantation.

Leakage of blood alongside the implant is a relatively frequent and life-limiting complication after transcatheter aortic valve implantation. The aim of this study is to develop and validate a workflow to simulate the implantation prior to the intervention. Based on the simulation outcome, the amount of leakage is estimated in order to evaluate the risk of a severe complication. A finite element model of the stent implantation in 10 patients was created based on a pre-operative computed tomography scan. All 10 patients also received a follow-up computed tomography scan, after the implantation. This scan was used to extract the deformed geometry of the stent and the position of the calcifications for validation of the simulation results. The maximal average perimeter difference between the simulated stent and the post-operative stent is 2.9±2.1mm, and occurs at the bottom of the device. The sensitivity of the simulation to the soft tissue material parameters and aortic root wall thickness was tested. The maximal diameter deviation of 6% occurred when the thickness of the aortic root was doubled. The result of the leakage analysis based on the distance between the simulated stent and the surrounding aortic root corresponded well when no regurgitation was observed. The developed tools have the potential to reduce the occurrence and severity of leakage by providing the clinician with additional information prior to the intervention. The simulated geometry and estimated leakage can help decide on the best implant type, size and position before treatment.

The potential of spatially resolved spectroscopy for monitoring angiogenesis in the chorioallantoic membrane.

Over the last decade, the poultry sector has sought to develop ways to monitor chicken embryonic development as to optimize the incubation conditions. One of the parameters of development which may change under different incubation conditions is the angiogenesis in the chorioallantoic membrane (CAM). To be able to quantify these changes in the angiogenesis and detect long-term effects on health, a non-destructive technique is necessary. In this article, the first steps toward such a non-destructive technique are successfully taken. A spatially resolved spectroscopy set-up is built and tested for its potential to measure changes in angiogenesis with incubation time, and differences between a normal and hypercapnic incubation. In this first study, reflectance measurements are performed directly on the CAM as the eggshell considerably complicates the analysis. This issue should be addressed in future research to come to a really non-destructive technique. An experiment was conducted in which one group was incubated under normal conditions, and another under early prenatal hypercapnic conditions (i.e., increased CO(2) concentrations). The angiogenesis in the CAM was measured at embryonic day (ED) 10, 13, and 16. The measurements showed a clear blood spectrum with an increasing amount of blood in time, and significant differences in the reflectance as function of the source-detector distances. However, no significant differences between the hypercapnia and the control group could be detected.

The effect of early prenatal hypercapnia on the vascular network in the chorioallantoic membrane of the chicken embryo.

Over the last decade, the poultry sector has sought to develop novel ways to monitor chicken embryonic growth, health, and quality to control and optimize egg incubation conditions, particularly the concentration of dissolved gases (O(2), CO(2)). One of the parameters, which may change under different gas concentrations, is the angiogenesis in the chorioallantoic membrane (CAM), the organ for gas exchange of the chicken embryo. In this study, a newly developed methodology was used to quantify the angiogenesis in the CAM under normal and early hypercapnic conditions (i.e., increased CO(2) concentrations). Two experiments were conducted in which the same CO(2) profile was applied. The development of the vascular system was monitored from embryonic day (ED) 10 until ED 14 in Experiment 1, and until ED 16 in Experiment 2. This development was characterized by two different parameters-the vascular fraction (VF) as a measure for the density of the vascular network and the fractal dimension (FD) as a measure for the degree of branching of the vascular network. Moreover, in Experiment 2, embryo weights were compared between both groups. The proposed methodology showed that differences in the development of the vascular system could be observed across groups but also as function of the ED. Both VF and FD and the embryo weights were shown to be higher in the hypercapnia group compared to the control group.

Development of a fast, objective, quantitative methodology to monitor angiogenesis in the chicken chorioallantoic membrane during development.

Recent research investigates the role of different gas concentrations during incubation, on chicken growth, quality and health post hatch. One of the parameters of chicken development which changes under different gas concentrations is angiogenesis in the chorioallantoic membrane (CAM). To be able to perform large incubation experiments under different conditions, angiogenesis in the whole CAM must be quantified objectively and easily. In this paper, a fast, objective, quantitative methodology to assess changes in the overall vascular development in the CAM of chicken embryos is presented. Samples were taken with minimal disturbance by emptying the egg, so that the CAM stayed attached to the shell, which was then cut in pieces. We employed a commercial digital camera and a macro lens set at 5x magnification to take pictures with sufficient contrast and resolution (2.64 mm/pixel). These were processed with computer algorithms to calculate the vascular fraction (VF) and the fractal dimension (FD) automatically on binary images. The ratio of the repeatability and reproducibility variation compared to the parts variation was 0.32 for VF and 0.21 for FD. In a validation experiment (n=284), one group was incubated under hypoxic conditions and the other under normoxic conditions. It was shown that early hypoxia stimulated angiogenesis, while chronic hypoxia impeded growth with significant differences between both groups, which is in accordance with literature data. Thus, we report here a method to asses overall angiogenesis in the CAM under different incubation conditions.