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Previous studies have revealed the importance of short-term bed-level change on the long-term development of intertidal ecosystems. One of the recent advancements in the short-term bed dynamics observation is the developments of laser-based surface elevation dynamics (LSED) and acoustic surface elevation dynamics (ASED) sensors. These two sensors are developed to automatically monitor tidally induced bed-level changes, and their measuring windows are during emergent and submerged periods, respectively. So far, there is no direct comparison or joint application of these two sensors. Therefore, in the current study, we first compare their observation precision in both laboratory and field conditions. Results show that both sensors' measurements are in good agreement with the manual measurements in the flume (R20.99) and field (R2 ~0.70), indicating the applicability of each sensor in natural environment. Finally, a coupled system (i.e., combining LSED and ASED) is established in a mangrove wetland and both sensors show good agreement with each other (R2 = 0.69). Results also demonstrate that the coupled observation system can well capture the bed-level change during emergent and submerged conditions, which provides detailed continuous data sets to study the bed-level dynamics within a tidal cycle. Furthermore, large-scale monitoring systems can also be established via mobile network module embedded in the sensor, providing real-time monitoring for bed-level changes, which is valuable to coastal morphological research and vital for detecting deterioration of coastal ecosystems and the services they provide to be able to apply adaptive management.

Coastal vegetation can reduce extreme water levels during storm events, but the controlling factors and processes in complex estuary or delta systems are still unclear. This limits an effective implementation of nature-based coastal defences in delta mega-cities in low-lying coastal areas.To explore the effects of vegetation on storm surge dynamics and currents, we used a Finite Volume Community Ocean Model implementation for the South China Sea and the Pearl River Delta. We numerically modelled how mangroves can offer coastal protection to the large coastal cities located in the delta, such as Guangzhou and Shenzhen, during strong typhoons, like Hato (2017).Additionally, we analyzed how the effectiveness of mangroves changes under different sea level rise scenarios.Water level attenuation by mangroves is effective during extreme water level conditions and differences in mangrove forests' properties drive their coastal protection function. The local (within-wetland) attenuation of extreme water levels is more effective with wide vegetation patches and higher vegetation drag. Narrower vegetation patches can still provide non-local (upstream) water level attenuation if located in the upper estuary channels, but their design needs to avoid amplification of water levels in other delta areas.

Coastal flood risk will increase over the coming decades as sea level rise accelerates, storm patterns change and coastal populations grow. This will likely lead to a surge in costs to build and maintain reliable flood safety infrastructure. Hence, innovative nature-based solutions that use coastal ecosystems are gaining attention. Nature-based flood defence is a potentially sustainable and cost-effective solution to reduce coastal flood risk, that can be carried out with ecosystems such as mangrove forests, saltmarshes or coral reefs. Mangrove forests are increasingly studied for nature-based flood defence across the subtropical and tropical latitudes, as their sturdy vegetation can effectively attenuate flow energy from waves – surge attenuation with mangroves remains less well understood. Wider and denser forests provide more wave attenuation. As mangroves naturally fluctuate in size, so does their wave attenuation capacity. Consequently, to reliably estimate the safety of a mangrove-based flood defence, it is necessary to understand the long-term development of the mangrove forest. The studies presented in this thesis contribute important datasets and mechanistic principles that can be used to advance mangrove forest development models and estimate long-term flood protection capacity with coastal mangroves.

4D phase contrast magnetic resonance imaging (PC-MRI) allows for the visualization and quantification of the cerebral blood flow. A drawback of software that is used to quantify the cerebral blood flow is that it oftentimes assumes a static arterial luminal area over the cardiac cycle. Quantifying the lumen area pulsatility index (aPI), i.e. the change in lumen area due to an increase in distending pressure over the cardiac cycle, can provide insight in the stiffness of the arteries. Arterial stiffness has received increased attention as a predictor in the development of cerebrovascular disease. In this study, we introduce software that allows for measurement of the aPI as well as the blood flow velocity pulsatility index (vPI) from 4D PC-MRI. The internal carotid arteries of seven volunteers were imaged using 7 T MRI. The aPI and vPI measurements from 4D PC-MRI were validated against measurements from 2D PC-MRI at two levels of the internal carotid arteries (C3 and C7). The aPI and vPI computed from 4D PC-MRI were comparable to those measured from 2D PC-MRI (aPI: mean difference: 0.03 (limits of agreement: −0.14 – 0.23); vPI: 0.03 (−0.17–0.23)). The measured blood flow rate for the C3 and C7 segments was similar, indicating that our proposed software correctly captures the variation in arterial lumen area and blood flow velocity that exists along the distal end of the carotid artery. Our software may potentially aid in identifying changes in arterial stiffness of the intracranial arteries caused by pathological changes to the vessel wall.

The intracranial arteries play a major role in cerebrovascular disease, but arterial remodeling due to hypertension has not been well described in humans. We aimed to quantify this remodeling for: the basilar artery, the vertebral, internal carotid, middle/anterior (inferior)/posterior cerebral, posterior communicating, and superior cerebellar arteries of the circle of Willis. Ex vivo circle of Willis specimens, selected from individuals with (n=24) and without (n=25) a history of hypertension, were imaged at 7T magnetic resonance imaging using a 3-dimensional gradient-echo sequence. Subsequently, histological analysis was performed. We validated the vessel wall thickness and area measurements from magnetic resonance imaging against histology. Next, we investigated potential differences in vessel wall thickness and area between both groups using both techniques. Finally, using histological analysis, we investigated potential differences in arterial wall stiffness and atherosclerotic plaque severity and load. All analyses were unadjusted. Magnetic resonance imaging and histology showed comparable vessel wall thickness (mean difference: 0.04 mm (limits of agreement:−0.12 to 0.19 mm) and area (0.43 mm 2 [−0.97 to 1.8 mm 2 ]) measurements. We observed no statistically significant differences in vessel wall thickness and area between both groups using either technique. Histological analysis showed early and advanced atherosclerotic plaques in almost all arteries for both groups. The arterial wall stiffness was significantly higher for the internal carotid artery in the hypertensive group. Concluding, we did not observe vessel wall thickening in the circle of Willis arteries in individuals with a history of hypertension using either technique. Using histological analysis, we observed a difference in vessel wall composition for the internal carotid artery.

Mechanical disturbance from waves and sediment dynamics is a key bottleneck to mangrove seedling establishment. Yet, how species vary in tolerance to sediment dynamics has not been quantified. We identified how tolerance to sediment dynamics differs for three mangrove propagule traits: propagule size, successional stage, and type of embryo development. We selected eight mangrove species growing in south China that vary from small seeds to large elongated propagules, pioneer to climax species, and non-viviparous to viviparous. In a mesocosm set-up, we applied bed level treatments to establishing seedlings: erosion, control, or accretion, by removing 2 cm, 0 cm, or adding 1 cm of sediment per week over 3 weeks. We measured seedling survival, shoot, and root lengths, and the critical erosion depth that leads toppling or dislodgement. We identified five relationships between seedling morphology and accretion and erosion thresholds: (1) tall (viviparous) propagules likely had highest accretion thresholds; (2) small pioneer propagules grew relatively fast to increase accretion thresholds; (3) there was a strong correlation between the erosion threshold and root length; and (4) climax species grew longest roots overall, (5) while pioneer species grew longer roots fast in response to sediment erosion. We identify distinct strategies for successful establishment in sediment dynamics that contribute to understanding mangrove zonation and underpin the importance of restoring diverse forests containing not just robust climax species, but also adaptable pioneers. Furthermore, this study reveals maximum shoot and root length as key determinants for seedling stability across species, providing a simple proxy for modeling establishment events.

Use of mangrove ecosystems for coastal flood protection requires reliable predictions of mangrove wave attenuation, especially if this capacity lessens due to storm-induced forest damage. Quantifying and understanding the variation in drag forces and mechanical properties of mangrove vegetation can improve assessment of mangrove protective capacity. We studied five mangrove species common in the subtropical Pearl River Delta, south China. The studied species range from typically landward-occurring to more seaward-occurring pioneer species. We sampled across seven sites in the delta to study the impact of salinity on mechanical properties. We quantified strength and flexibility of branches (branch strength and flexibility related to branch diameter, modulus of rupture and modulus of elasticity), leaf strength (leaf attachment strength related to leaf size, and leaf mass per area) and drag properties (drag force related to surface area and drag coefficient). For all tested species, larger branch diameters resulted in higher mechanical strength. Larger leaf size resulted in larger peak pulling forces and larger branch surface area resulted in stronger drag forces. Notably, species that generally occur lower in the intertidal zone, where exposure to wind and waves is higher, had relatively stronger branches but more easily detachable leaves. This may be regarded as a damage-avoiding strategy. Across the seven field sites, we found no clear effect of salinity on mangrove mechanical properties. This study provides a mechanistic insight in the storm damage process for individual mangrove trees and a solid base for modeling storm (surge) damage at the forest scale.

Cerebrovascular disease results in morphological and functional alterations in the intracranial macro- and microvasculature. Early detection of such alterations is key for better understanding of cerebrovascular disease mechanisms, and in taking preventative measures against cerebrovascular disease development. In this thesis, we aimed to quantify alterations in the vessel walls, brain parenchyma, and blood flow using both high-resolution post-mortem 7T magnetic resonance imaging (MRI), histopathological analysis, and in vivo MRI in volunteers, and in patients with a history of cerebrovascular disease. High-resolution post-mortem 7T MRI and histopathological analysis of circle of Willis specimens was performed in Chapter 2, where we investigated arterial remodeling caused by hypertension. We observed no significant differences in vessel wall area and thickness, between hypertensive patients and normotensive controls. Histological analysis showed early and advanced atherosclerotic plaques for almost all vessels of the circle of Willis for both groups. The collagen to smooth muscle ratio, as a measure for arterial stiffness, was significantly higher for the internal carotid artery in the hypertensive group. In Chapter 3, we investigated the limitations of vessel wall MRI regarding the accuracy of vessel wall thickness measurements. Using high-field 7T MRI of post-mortem circle of Willis specimens, we have shown that with conventional measurement methods accurate thickness measurements are possible for vessel walls with a thickness larger than 1.25 times the acquired voxel size. For thinner vessel walls, measurements were ambiguous and inaccurate. Because the vessel wall for all arteries of the circle of Willis is thinner than the acquired voxel size, early vessel wall thickening cannot be quantified from vessel wall images acquired with commonly used in vivo MR sequences. Using the vessel wall image intensity allows for measurements for vessel walls thinner than the acquired voxel size (Chapter 4). However, such measurements are uncalibrated and qualitative, and are therefore only usable for visualizing relative differences in vessel wall thickness within a subject. We therefore proposed a neural network for measuring the subvoxel vessel wall thickness. Hereto, we imaged post-mortem circle of Willis specimens with a clinically-used sequence, and an ultra-high-resolution sequence. The neural network was trained to measure the vessel thickness from the clinically-used images. Thickness measurements on the ultra-high-resolution image, which were performed prior to training of the network, were used as reference for the network. Results showed that accurate subvoxel vessel wall thickness measurements are possible. In addition, we showed its feasibility on three in vivo vessel wall MR images of intracranial aneurysms. In Chapter 5, we introduced software that allows for the measurement of the arterial diameter pulsatility and blood flow velocity pulsatility over the cardiac cycle, as measure for the arterial stiffness, from 4D phase contrast (velocity) MR (PC-MRI) images. Measurements on the arterial diameter pulsatility and blood flow velocity pulsatility using our software were validated against measurements from 2D PC-MRI for two locations of the internal carotid artery in 7 volunteers. Our software may potentially aid in identifying changes in arterial stiffness of the intracranial arteries caused by pathological changes to the vessel wall. Lastly, we investigated the use of anomaly detection for the automated detection of brain pathology (Chapter 6). We evaluated the performance of our anomaly detection method on the detection of chronic brain infarcts. Besides the detection of brain infarcts, our proposed method also detected white matter hyperintensities, and image infarcts. Most interestingly, it also detected brain infarcts that were initially missed by the radiologist during radiological reading of the MR images. Anomaly detection is a powerful tool for the detection of brain pathology, and may aid diagnostic radiology by highlighting locations in the image that likely contain pathology.

The performance of current machine learning methods to detect heterogeneous pathology is limited by the quantity and quality of pathology in medical images. A possible solution is anomaly detection; an approach that can detect all abnormalities by learning how ‘normal’ tissue looks like. In this work, we propose an anomaly detection method using a neural network architecture for the detection of chronic brain infarcts on brain MR images. The neural network was trained to learn the visual appearance of normal appearing brains of 697 patients. We evaluated its performance on the detection of chronic brain infarcts in 225 patients, which were previously labeled. Our proposed method detected 374 chronic brain infarcts (68% of the total amount of brain infarcts) which represented 97.5% of the total infarct volume. Additionally, 26 new brain infarcts were identified that were originally missed by the radiologist during radiological reading. Our proposed method also detected white matter hyperintensities, anomalous calcifications, and imaging artefacts. This work shows that anomaly detection is a powerful approach for the detection of multiple brain abnormalities, and can potentially be used to improve the radiological workflow efficiency by guiding radiologists to brain anomalies which otherwise remain unnoticed.

Until recently, Dutch merchant ships could not rely on privately contracted maritime security staff to protect themselves against pirates. On the one hand, the argument prevailed that the State had to retain the monopoly on the use of force and, on the other hand, one also feared for the escalation of violence or international incidents. Nowadays, however, more and more European countries allow for the use of privately contracted armed security personnel on board merchant ships. As a result, the Dutch Parliament has adopted a bill containing rules for the use of armed private security guards on board Dutch maritime merchant ships (Law to Protect Merchant Shipping 2019 (published in the Dutch official Gazette on June 7th, 2019)). The author addresses the question whether because of the new law a level playing field will emerge with the Merchant Navies from the neighboring Flag States of Belgium, the United Kingdom, Spain and Denmark, presenting a comparative analysis of their domestic legislation. The Dutch law clearly regulates the use of force and the master has the final responsibility for everything that happens under his authority. In principle, the security guards may only apply violence as the master has determined that it is necessary. Innovative is that there is a reporting obligation whereby every incident should be reported with images and sound recordings. It seems, however, that the law is especially made to protect and secure and not necessarily to provide a solution for situations in which pirates come on board. It is clear that the intention of the legislator is to leave the monopoly on the use of force in the hands of the State. However, the adoption of this law to protect merchant shipping could constitute a first step in enabling the use of force by other actors than the State, which in itself is groundbreaking. Before being able to go on this road, there are still countless political (mainly related to the sovereignty of a State) and legal challenges (mainly concerning the use of force and respect for human rights) to be addressed.

Monitoring is an essential component of adaptive management, and a carefully designed program is needed to ensure high-quality data and inferences over realistic time scales. Co-operation among agencies and incorporating citizen science may help enhance learning while reducing the financial costs of monitoring. We seek to realise this potential while conserving the Australian malleefowl (Leipoa ocellata). An established network of citizen scientists provide low-cost, sustainable annual monitoring data, yet the most effective actions for conserving malleefowl remain highly uncertain. The continent-wide species' distribution presents significant challenges, including multiple environmental strata to sample and numerous management jurisdictions. We outline an adaptive management framework that aims to unify malleefowl conservation priorities nationally, and target monitoring efforts. We elicited a model structure for the drivers of, and threats to, malleefowl persistence in a workshop with land managers and advocates. We parameterised 80 uncertain interactions within this structure using novel ensemble modelling techniques and identified the effectiveness of predator control as a critical uncertainty affecting malleefowl persistence. We developed a classical, spatially replicated experimental design to test whether malleefowl breed more frequently where predators are suppressed. The proposed monitoring design will rely on the contributions of several dozen land managers and 200–300 citizen scientists annually. We have developed a broad stakeholder base, a proactive communication strategy, and an agile approach to accessing resources to foster resilience and longevity in the monitoring program. If malleefowl conservation successfully adapts in response to monitoring outcomes, it will become one of the largest adaptive management programs on the planet.

We present a new laboratory setup for photoacoustic, transmission ultrasound and reflection ultrasound tomography. The system is based on a pair of independently rotating hemisphere segments on which are mounted acoustic transmitters and detectors. The interchangeability of the elements, as well as the ability to fully customise the acquisition protocol, allows for a considerable amount of flexibility in testing out different imaging approaches in both 2D and 3D. The current focus is the development of laser-induced ultrasound (LIUS) transmitters for use in tomographic imaging. We propose a transmitter design tuned for speed-of-sound mapping with a 1MHz centred response.