Aortic valve stenosis impairs subendocardial perfusion with a risk of irreversible subendocardial tissue damage. A likely precursor of damage is subendocardial contractile dysfunction, expressed by the parameter TransDif, which is defined as epicardial minus endocardial myofiber shortening, normalized to the mean value. With the use of magnetic resonance tagging in two short-axis slices of the left ventricle (LV), TransDif was derived from LV torsion and contraction during ejection. TransDif was determined in healthy volunteers (control, n = 9) and in patients with aortic valve stenosis before (AVSten, n = 9) and 3 mo after valve replacement (AVRepl, n = 7). In the control group, TransDif was 0.00 ± 0.14 (mean ± SD). In the AVSten group, TransDif increased to 0.96 ± 0.62, suggesting impairment of subendocardial myofiber shortening. In the AVRepl group, TransDif decreased to 0.37 ± 0.20 but was still elevated. In eight of nine AVSten patients, the TransDif value was elevated individually ( P < 0.001), suggesting that the noninvasively determined parameter TransDif may provide important information in planning of treatment of aortic valve stenosis.

MRI sensitivity for post mortem detection of cortical lesions is low, even when a higher field-strength was used. It varies, however, for different subtypes of cortical lesions.

Perfusion of left ventricular (LV) subendocardium in valvular aortic stenosis (AS) patients is impaired. It was expected that this may lead to a reduction of subendocardial fiber contraction and, consequently, to an increase of LV torsion per amount of ejection. Using MR tagging (MRT), it was investigated whether the torsionto-shortening ratio (TSR) is elevated in valvular AS patients. Six asymptomatic children with valvular AS were investigated using echo Doppler, ECG, exercise test, and MRT. LV torsion and natural strain of the inner diameter were determined from measured tag displacements in two short-axis slices of the LV. In all AS patients TSR was ϳ40% increased (

In this study an overview of existing and planned storm surge barriers in the world is provided. A systematic analysis relates functional requirements (e.g. navigation and tidal exchange) to the main barrier characteristics (e.g. gate type, dimensions). Furthermore, as the costs of barriers are an important issue in the planning, available cost information is analyzed and related to main barrier characteristics. An approach to provide a preliminary cost estimate of new barriers is presented. Finally, some critical technical challenges are discussed and related to functional requirements and boundary conditions. Overall, the results of this study can assist in the initial design and planning phase of storm surge barriers for new locations.Keywords: storm surge barrier, coastal structures, flood risk, coastal protection. INTRODUCTIONHuman population in coastal zones is exposed to a variety of natural hazards such as erosion, salt water intrusion, subsidence, tsunamis, and floods resulting from both storm surges and high river runoff (Small and Nicholls, 2003). However, due to climate change induced effects, such as sea level rise, the likelihood of natural hazards will increase, making these areas more vulnerable. Moreover, coastal zones are associated with large and growing concentrations of human population, settlements and socio-economic activities (Small and Nicholls, 2003), intensifying their vulnerability. From an economical perspective these conditions lead to a higher demand for safety and a corresponding substantial investment in improving flood protection (Van Dantzig, 1956;Brekelmans et al., 2012). Furthermore, flood protection standards are expected to increase with enlarged prosperity (Hallegate et al. 2013). It is therefore expected that in coastal regions around the world governments will continue to invest more in coastal protection.In areas with large bays, estuaries or coastal waterways with adjacent flood defenses, constructing a barrier can be a suitable option to protect coastal zones. This type of solution is often chosen as a preferred alternative, when the required length of dike strengthening behind a barrier is significantly reduced (Jonkman et al., 2013). This measure can shorten the exposed coastline, and subsequently reduce the costs and hindrance of dike improvement in densely populated areas. In addition the construction time required to improve the dikes can be shortened considerably (Rijkswaterstaat, 1976).Although several types of barriers (e.g. closure dams, tidal barrages and storm surge barriers) exist, storm surge barriers are mainly considered as a future intervention for more developed and prosperous regions, such as many coastal cities. In such regions preserving ecology or maintaining navigation have a large value and the high costs of storm surge barriers compared to the alternative type of barriers can be afforded. For example, storm surge barriers are currently proposed at Houston, USA (De Vries, 2014); New Orleans, Mississippi, USA (van Ledden et al, 2012), New York, U...

No abstract

Abstract-Many cardiac diseases cause transmural differences in myofiber function. With the Magnetic Resonance Imaging Tagging technique a grid of magnetic tags was attached to the heart. Using a model of cardiac mechanics the motion of these tags was analyzed to deduct the transmural gradient of myofiber shortening. In normal, young healthy subjects (n=9), the transmural difference in myofiber shortening varies little, about ± ± ± ±4% (sd) of mean shortening. In patients with aortic stenosis subendocardial function is at risk. In a group of such patients (n=5) fiber shortening in the subendocardial layers was found to be decreased by 23± ± ± ±20% relative to the subepicardial layers. This finding indicates that a model of cardiac mechanics can be used as a tool to convert MRItagging motion data to clinically useful information on a transmural gradient in contractile function. Presently, no other methods are available to detect such transmural gradient noninvasively.

No abstract