Clinical stratification of rupture risk is limited to criteria based on geometry (diameter) which is not always accurate. We propose an image transformer approach applying neural networks for focused attention on abdominal aortic aneurysms (AAAs), which doesn’t require explicit segmentation, for predicting rupture risk, starting with CT angiography images. Our image dataset consisted of 16 cases with high rupture risk and 14 cases with low rupture risk. Our study reveals that 3D ResNet classifiers trained with neural embeddings from a 3D U-Net trained on images of any one rupture risk class produced an accuracy of 90% (83% sensitivity, 100% specificity). Our representation learning pipeline, AAA-Net, could be adapted to reduce the amount of time and clinical expertise required to identify AAA rupture risk, enabling efficient and automated aneurysm monitoring.
The goal of this study is to demonstrate the classification value of the latent encodings of a neural network trained for image segmentation of the lung region. In order to achieve this, the gold standard of semantic segmentation, a 3D U-Net was used to extract the encodings for 20 thoracic CT images (10 COVID-19 and 10 Control), and a random forest classifier was trained based on the encodings developed from two training experiments. Performance was analyzed in terms of the independent classification value of each voxel of the U-Net’s latent encoding layer in distinguishing COVID-19 v/s control images.
Left atrial appendage (LAA) is the source of 91% of the thrombi in patients with atrial arrhythmias (~2.3 million US adults), turning this region into a potential threat for stroke. LAA geometries have been clinically categorized into four appearance groups viz. Cauliflower, Cactus, Chicken-Wing and WindSock, based on visual appearance in 3D volume visualizations of contrast-enhanced computed tomography (CT) imaging, and have further been correlated with stroke risk by considering clinical mortality statistics. However, such classification from visual appearance is limited by human subjectivity and is not sophisticated enough to address all the characteristics of the geometries. Quantification of LAA geometry metrics can reveal a more repeatable and reliable estimate on the characteristics of the LAA which correspond with stasis risk, and in-turn cardioembolic risk. We present an approach to quantify the appearance of the LAA in patients in atrial fibrillation (AF) using a weighted set of baseline eigen-modes of LAA appearance variation, as a means to objectify classification of patient-specific LAAs into the four accepted clinical appearance groups. Clinical images of 16 patients (4 per LAA appearance category) with atrial fibrillation (AF) were identified and visualized as volume images. All the volume images were rigidly reoriented in order to be spatially co-registered, normalized in terms of intensity, resampled and finally reshaped appropriately to carry out principal component analysis (PCA), in order to parametrize the LAA region’s appearance based on principal components (PCs/eigen mode) of greyscale appearance, generating 16 eigen-modes of appearance variation. Our pilot studies show that the most dominant LAA appearance (i.e. reconstructable using the fewest eigen-modes) resembles the Chicken-Wing class, which is known to have the lowest stroke risk per clinical mortality statistics. Our findings indicate the possibility that LAA geometries with high risk of stroke are higher-order statistical variants of underlying lower risk shapes.
Pulmonary vein isolation (PVI) is an established procedure for atrial fibrillation (AF) patients. Pre-procedural screening is necessary prior to PVI in order to reduce the likelihood of AF recurrence and improve overall success rate of the procedure. However, current reliable methods to determine AF triggers are invasive. In this paper, we present an approach to relate the regional characteristics of left atrial (LA) shape to existence of low-voltage areas (LVA) which indicate the presence of scar in invasive exams. A cohort of 29 AF patient-specific clinical images were each segmented into 3D surface bodies representing the LA. Iterative closest point based similarity transformation was used to find the best fit sphere to each patient-specific LA and the mean deviation of LA wall to this sphere of best fit was determined using a signed point-to-surface regional distance metric. Regional departure from the best-fit sphere was reduced into a metric of global LA sphericity. Next, the LA was divided into six regions to perform an analysis of regional sphericity. Regional sphericity analysis revealed that sphericity of the inferior-posterior LA region was found to be related to several clinical variables, including a direct correlation with body mass index (BMI) and an inverse correlation with left ventricular ejection fraction (EF), which presents a diseased heart that has been asymmetrically inflated. Our observations therefore demonstrate promise in being leveraged as a non-invasive patient selection tool to increase the success rate of PVI procedures.
Endovascular aneurysm repair (EVAR) of juxtarenal aortic aneurysms (JAA) is particularly challenging owing to the
requirement of suprarenal EVAR graft fixation, which has been associated with significant declines in long term renal
function. Therefore, the ability to design fenestrated EVAR grafts on a personalized basis in order to ensure visceral and
renal perfusion, is highly desirable. The objectives of this study are: a) To demonstrate novel 3D geometric methods to
virtually design and deploy EVAR grafts into a virtually designed JAA, by applying a custom surface mesh deformation
tool to a patient-specific descending aortic model reconstructed from computed tomographic (CT) images; and b) To
virtually evaluate patient-specific renal flow and wall stresses in these patient-specific virtually EVAR geometries, using
computational fluid dynamics (CFD). The presented framework may provide the modern cardiovascular surgeon the ability
to leverage non-invasive, pre-operative imaging equipment to personalize and guide EVAR therapeutic strategy. Our CFD
studies revealed that virtual EVAR grafting of a patient-specific JAA, with optimal fenestration sites and renal stenting,
led to a 179.67±15.95% and 1051.43±18.34% improvement in right and left renal flow rates, respectively, when compared
with the baseline patient-specific aortic geometry with renal stenoses, whereas a right and left renal flow improved by
36.44±2.24% and 885.93±12.41%, respectively, relative to the equivalently modeled JAA with renal stenoses, considering
averages across the three simulated inflow rate cases. The proposed framework have utility to iteratively optimize
suprarenal EVAR fixation length and achieve normal renal wall shear stresses and streamlined juxtarenal hemodynamics.
Catheter ablation is a safe and effective therapy for drug-refractory patients symptomatic of atrial fibrillation (AF), with up to 80% of patients experiencing long-term arrhythmia-free survival. However, up to 20–40% of patients require more than one procedure in order to become arrhythmia-free. Therefore, appropriate patient selection is paramount to the effective implementation and long-term success of ablation therapy for patients with atrial fibrillation (AF). In this study, as a precursor to evaluating clinical significance of specific LA shape metrics as pre-procedural predictors of AF recurrence following ablative pulmonary vein isolation therapy, we report on a computational geometric analysis in a pilot cohort evaluating relationships between various patient-specific metrics of LA shape which might have such predictive value. This study specifically is focused on establishing the relationship between LA volume and sphericity, using a novel methodology for computing atrial sphericity based on regional shape.
KEYWORDS: Blood circulation, Heart, In vivo imaging, Two photon confocal microscopy, Genetics, Data acquisition, Image processing, Green fluorescent protein, Image enhancement, Image analysis, Image filtering, 3D image processing, Digital filtering, Confocal microscopy, 3D acquisition
The mechanism of endothelial cell migration as individual cells or collectively while remaining an integral component of a functional blood vessel has not been well characterized. In this study, our overarching goal is to define an image processing workflow to facilitate quantification of how endothelial cells within the first aortic arch and are proximal to the zebrafish heart behave in response to the onset of flow (i.e. onset of heart beating). Endothelial cell imaging was conducted at this developmental time-point i.e. ~24-28 hours post fertilization (hpf) when flow first begins, using 3D+time two-photon confocal microscopy of a live, wild-type, transgenic, zebrafish expressing green fluorescent protein (GFP) in endothelial cell nuclei. An image processing pipeline comprised of image signal enhancement, median filtering for speckle noise reduction, automated identification of the nuclei positions, extraction of the relative movement of nuclei between consecutive time instances, and finally tracking of nuclei, was designed for achieving the tracking of endothelial cell nuclei and the identification of their movement towards or away from the heart. Pilot results lead to a hypothesis that upon the onset of heart beat and blood flow, endothelial cells migrate collectively towards the heart (by 21.51±10.35 μm) in opposition to blood flow (i.e. subtending 142.170±21.170 with the flow direction).
Computed tomography (CT) imaging is a sensitive and specific lung cancer screening tool for the high-risk population and shown to be promising for detection of lung cancer. This study proposes an automatic methodology for detecting and segmenting lung nodules from CT images. The proposed methods begin with thorax segmentation, lung extraction and reconstruction of the original shape of the parenchyma using morphology operations. Next, a multi-scale hessian-based vesselness filter is applied to extract lung vasculature in lung. The lung vasculature mask is subtracted from the lung region segmentation mask to extract 3D regions representing candidate pulmonary nodules. Finally, the remaining structures are classified as nodules through shape and intensity features which are together used to train an artificial neural network. Up to 75% sensitivity and 98% specificity was achieved for detection of lung nodules in our testing dataset, with an overall accuracy of 97.62%±0.72% using 11 selected features as input to the neural network classifier, based on 4-fold cross-validation studies. Receiver operator characteristics for identifying nodules revealed an area under curve of 0.9476.
The Fontan procedure for single-ventricle heart disease involves creation of pathways to divert venous blood from the superior & inferior venacavae (SVC, IVC) directly into the pulmonary arteries (PA), bypassing the right ventricle. For optimal surgical outcomes, venous flow energy loss in the resulting vascular construction must be minimized and ensuring close to equal flow distribution from the Fontan conduit connecting IVC to the left & right PA is paramount. This requires patient-specific hemodynamic evaluation using computational fluid dynamics (CFD) simulations which are often time and resource intensive, limiting applicability for real-time patient management in the clinic. In this study, we report preliminary efforts at identifying a new non-invasive imaging based surrogate for CFD simulated hemodynamics. We establish correlations between computed hemodynamic criteria from CFD modeling and cumulative wall displacement characteristics of the Fontan conduit quantified from cine cardiovascular MRI segmentations over time (i.e. 20 cardiac phases gated from the start of ventricular systole), in 5 unique Fontan surgical connections. To focus our attention on diameter variations while discounting side-to-side swaying motion of the Fontan conduit, the difference between its instantaneous regional expansion and inward contraction (averaged across the conduit) was computed and analyzed. Maximum Fontan conduit-average expansion over the cardiac cycle correlated with the anatomy-specific diametric offset between the axis of the IVC and SVC (r2=0.13, p=0.55) – a known factor correlated with Fontan energy loss and IVC-to-PA flow distribution. Investigation in a larger study cohort is needed to establish stronger statistical correlations.
Characterization of regional left ventricular (LV) function may have application in prognosticating timely response and informing choice therapy in patients with ischemic cardiomyopathy. The purpose of this study is to characterize LV function through a systematic analysis of 4D (3D + time) endocardial motion over the cardiac cycle in an effort to define objective, clinically useful metrics of pathological remodeling and declining cardiac performance, using standard cardiac MRI data for two distinct patient cohorts accessed from CardiacAtlas.org: a) MESA – a cohort of asymptomatic patients; and b) DETERMINE – a cohort of symptomatic patients with a history of ischemic heart disease (IHD) or myocardial infarction. The LV endocardium was segmented and a signed phase-to-phase Hausdorff distance (HD) was computed at 3D uniformly spaced points tracked on segmented endocardial surface contours, over the cardiac cycle. An LV-averaged index of phase-to-phase endocardial displacement (P2PD) time-histories was computed at each tracked point, using the HD computed between consecutive cardiac phases. Average and standard deviation in P2PD over the cardiac cycle was used to prepare characteristic curves for the asymptomatic and IHD cohort. A novel biomarker of RMS error between mean patient-specific characteristic P2PD over the cardiac cycle for each individual patient and the cumulative P2PD characteristic of a cohort of asymptomatic patients was established as the RMS-P2PD marker. The novel RMS-P2PD marker was tested as a cardiac function based feature for automatic patient classification using a Bayesian Rule Learning (BRL) framework. The RMS-P2PD biomarker indices were significantly different for the symptomatic patient and asymptomatic control cohorts (p<0.001). BRL accurately classified 83.8% of patients correctly from the patient and control populations, with leave-one-out cross validation, using standard indices of LV ejection fraction (LV-EF) and LV end-systolic volume index (LV-ESVI). This improved to 91.9% with inclusion of the RMS-P2PD biomarker and was congruent with improvements in both sensitivity for classifying patients and specificity for identifying asymptomatic controls from 82.6% up to 95.7%. RMS-P2PD, when contrasted against a collective normal reference, is a promising biomarker to investigate further in its utility for identifying quantitative signs of pathological endocardial function which may boost standard image makers as precursors of declining cardiac performance.
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