Intravascular ultrasound: validation and clinical application

Atherogenesis is a process with an insidious onset and course. Once clinical signs and symptoms have become manifest, the obstructive lesion is usually at an advanced stage. Arteriography is the standard method for evaluation of atherosclerotic disease and has been useful in identifying the location and approximate severity of the stenotic lesion. Although arteriography provides a silhouette of the vessel lumen, it does not provide accurate knowledge on cross-sectional lumen area, vessel area, shape and morphology of the stenotic lesion. Intravascular ultrasound (lVUS) may overcome these limitations by providing a tomographic image of the vessel. The aim of this work is to validate IVUS and to evaluate subsequent clinical application of this imaging technique. The subjects dealt with in this dissertation are categorised into 5 main topics. I) displacement sensing device; 2) validation of IVUS-derived parameters; 3) the spectrum of vascular morphology before and after intervention determined by IVUS; 4) IVUS as a research tool; 5) IVUS as a clinical too

Segmentation of Intracranial Arterial Calcification with Deeply Supervised Residual Dropout Networks

Intracranial carotid artery calcification (ICAC) is a major risk factor for stroke, and might contribute to dementia and cognitive decline. Reliance on time-consuming manual annotation of ICAC hampers much demanded further research into the relationship between ICAC and neurological diseases. Automation of ICAC segmentation is therefore highly desirable, but difficult due to the proximity of the lesions to bony structures with a similar attenuation coefficient. In this paper, we propose a method for automatic segmentation of ICAC; the first to our knowledge. Our method is based on a 3D fully convolutional neural network that we extend with two regularization techniques. Firstly, we use deep supervision (hidden layers supervision) to encourage discriminative features in the hidden layers. Secondly, we augment the network with skip connections, as in the recently developed ResNet, and dropout layers, inserted in a way that skip connections circumvent them. We investigate the effect of skip connections and dropout. In addition, we propose a simple problem-specific modification of the network objective function that restricts the focus to the most important image regions and simplifies the optimization. We train and validate our model using 882 CT scans and test on 1,000. Our regularization techniques and objective improve the average Dice score by 7.1%, yielding an average Dice of 76.2% and 97.7% correlation between predicted ICAC volumes and manual annotations.Comment: Accepted for MICCAI 201

MRI-based biomechanical parameters for carotid artery plaque vulnerability assessment.

Carotid atherosclerotic plaques are a major cause of ischaemic stroke. The biomechanical environment to which the arterial wall and plaque is subjected to plays an important role in the initiation, progression and rupture of carotid plaques. MRI is frequently used to characterize the morphology of a carotid plaque, but new developments in MRI enable more functional assessment of carotid plaques. In this review, MRI based biomechanical parameters are evaluated on their current status, clinical applicability, and future developments. Blood flow related biomechanical parameters, including endothelial wall shear stress and oscillatory shear index, have been shown to be related to plaque formation. Deriving these parameters directly from MRI flow measurements is feasible and has great potential for future carotid plaque development prediction. Blood pressure induced stresses in a plaque may exceed the tissue strength, potentially leading to plaque rupture. Multi-contrast MRI based stress calculations in combination with tissue strength assessment based on MRI inflammation imaging may provide a plaque stress-strength balance that can be used to assess the plaque rupture risk potential. Direct plaque strain analysis based on dynamic MRI is already able to identify local plaque displacement during the cardiac cycle. However, clinical evidence linking MRI strain to plaque vulnerability is still lacking. MRI based biomechanical parameters may lead to improved assessment of carotid plaque development and rupture risk. However, better MRI systems and faster sequences are required to improve the spatial and temporal resolution, as well as increase the image contrast and signal-to-noise ratio.This is the author accepted manuscript. The final version is available from Schattauer via http://dx.doi.org/10.1160/TH15-09-071

Low-Dose Computed Tomography With Two- and Three-Dimensional Postprocessing as an Alternative to Plain Radiography for Intrathecal Catheter Visualization: A Phantom Pilot Study

Objectives: In intrathecal drug delivery, visualization of the device has been performed with plain radiography. However, the visibility of the related structures can be problematic. In troubleshooting, after the contrast material injection via the cathe

Reduced cortical complexity in children with prader-willi syndrome and its association with cognitive impairment and developmental delay

Background: Prader-Willi Syndrome (PWS) is a complex neurogenetic disorder with symptoms involving not only hypothalamic, but also a global, central nervous system dysfunction. Previously, qualitative studies reported polymicrogyria in adults with PWS. However, there have been no quantitative neuroimaging studies of cortical morphology in PWS and no studies to date in children with PWS. Thus, our aim was to investigate and quantify cortical complexity in children with PWS compared to healthy controls. In addition, we investigated differences between genetic subtypes of PWS and the relationship between cortical complexity and intelligence within the PWS group.Methods: High-resolution structural magnetic resonance images were acquired in 24 children with genetically confirmed PWS (12 carrying a deletion (DEL), 12 with maternal uniparental disomy (mUPD)) and 11 age- and sex-matched typically developing siblings as healthy controls. Local gyrification index (lGI) was obtained using the FreeSurfer software suite.Results: Four large clusters, two in each hemisphere, comprising frontal, parietal and temporal lobes, had lower lGI in children with PWS, compared to healthy controls. Clusters with lower lGI also had significantly lower cortical surface area in children with PWS. No differences in cortical thickness of the clusters were found between the PWS and healthy controls. lGI correlated significantly with cortical surface area, but not with cortical thickness. Within the PWS group, lGI in both hemispheres correlated with Total IQ and Verbal IQ, but not with Performance IQ. Children with mUPD, compared to children with DEL, had two small clusters with lower lGI in the right hemisphere. lGI of these clusters correlated with cortical surface area, but not with cortical thickness or IQ.Conclusions: These results suggest that lower cortical complexity in children with PWS partially underlies cognitive impairment and developmental delay, probably due to alterations in gene networks that play a prominent role in early brain development

What have we learned from in vitro intravascular ultrasound?

In vitro studies have established that intravascular ultrasound is a reliable technique for accurate assessment of vascular anatomic structure and disease conditions before and after intervention. In addition, quantitative data from intravascular ultrasound studies correspond well with histologic findings, which serve as the gold standard. These in vitro studies permit the understanding and interpretation of ultrasound images obtained in vivo, although differences between the two settings should be taken into account. New ultrasound modalities currently being developed may enhance the diagnostic differentiation of plaque morphologic characteristics and facilitate on-line quantitative assessment of vessel structure

Noninvasive detection of a ruptured aneurysm at a basilar artery fenestration with submillimeter multisection CT angiography

The criterion standard for the detection of intracranial aneurysms is digital subtraction angiography. MR imaging and CT provide good accuracy in the evaluation of brain arteries and aneurysms. We herein report a case of a ruptured aneurysm at a basilar artery fenestration. The diagnosis was assessed with 16-row multisection CT angiography and was confirmed by using digital subtraction angiography. The patient was successfully treated with coil placement