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  • 1
    In: Nanophotonics, Walter de Gruyter GmbH, Vol. 10, No. 14 ( 2021-10-28), p. 3769-3775
    Abstract: Strong-field photoemission from nanostructures and the associated temporally modulated currents play a key role in the development of ultrafast vacuum optoelectronics. Optical light fields could push their operation bandwidth into the petahertz domain. A critical aspect of their functionality in the context of applications is the impact of charge interaction effects. Here, we investigated the photoemission and photocurrents from nanometric tungsten needle tips exposed to carrier-envelope phase (CEP)-controlled few-cycle laser fields. We report a characteristic rapid increase in the intensity-rescaled cutoff energies of emitted electrons beyond a certain intensity value. By comparison with simulations, we identify this feature as the onset of charge-interaction dominated photoemission dynamics. Our results are anticipated to be relevant also for the strong-field photoemission from other nanostructures, including photoemission from plasmonic nanobowtie antennas used in CEP-detection and for PHz-scale devices.
    Type of Medium: Online Resource
    ISSN: 2192-8614
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2674162-3
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  • 2
    In: Current Directions in Biomedical Engineering, Walter de Gruyter GmbH, Vol. 7, No. 1 ( 2021-08-01), p. 106-110
    Abstract: Algorithms for automated analysis of intravascular ultrasound (IVUS) images can be disturbed by guidewires, which are often encountered when treating bifurcations in percutaneous coronary interventions. Detecting guidewires in advance can therefore help avoiding potential errors. This task is not trivial, since guidewires appear rather small compared to other relevant objects in IVUS images. We employed CNNs with additional multi-task learning as well as different guidewire-specific regularizations to enable and improve guidewire detection. In this context, we developed a network block which generates heatmaps that highlight guidewires without the need of localization annotations. The guidewire detection results reach values of 0.931 in terms of the F1-score and 0.996 in terms of area under curve (AUC). Comparing thresholded guidewire heatmaps with ground truth segmentation masks leads to a Dice score of 23.1 % and an average Hausdorff distance of 1.45 mm. Guidewire detection has proven to be a task that CNNs can handle quite well. Employing multi-task learning and guidewire-specific regularizations further improve detection results and enable generation of heatmaps that indicate the position of guidewires without actual labels.
    Type of Medium: Online Resource
    ISSN: 2364-5504
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2835398-5
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  • 3
    Online Resource
    Online Resource
    Walter de Gruyter GmbH ; 2021
    In:  Current Directions in Biomedical Engineering Vol. 7, No. 1 ( 2021-08-01), p. 96-100
    In: Current Directions in Biomedical Engineering, Walter de Gruyter GmbH, Vol. 7, No. 1 ( 2021-08-01), p. 96-100
    Abstract: Knowing the shape of vascular calcifications is crucial for appropriate planning and conductance of percutaneous coronary interventions. The clinical workflow can therefore benefit from automatic segmentation of calcified plaques in intravascular ultrasound (IVUS) images. To solve segmentation problems with convolutional neural networks (CNNs), large datasets are usually required. However, datasets are often rather small in the medical domain. Hence, developing and investigating methods for increasing CNN performance on small datasets can help on the way towards clinically relevant results. We compared two state-of-the-art CNN architectures for segmentation, U-Net and DeepLabV3, and investigated how incorporating auxiliary image data with vessel wall and lumen annotations improves the calcium segmentation performance by using these either for pretraining or multi-task training. DeepLabV3 outperforms U-Net with up to 6.3 % by means of the Dice coefficient and 36.5 % by means of the average Hausdorff distance. Using auxiliary data improves the segmentation performance in both cases, whereas the multi-task approach outperforms the pre-training approach. The improvements of the multi-task approach in contrast to not using auxiliary data at all is 5.7 % for the Dice coefficient and 42.9 % for the average Hausdorff distance. Automatic segmentation of calcified plaques in IVUS images is a demanding task due to their relatively small size compared to the image dimensions and due to visual ambiguities with other image structures. We showed that this problem can generally be tackled by CNNs. Furthermore, we were able to improve the performance by a multi-task learning approach with auxiliary segmentation data.
    Type of Medium: Online Resource
    ISSN: 2364-5504
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2835398-5
    Location Call Number Limitation Availability
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