Discovery and insights from DSX mission's high-power VLF wave transmission experiments in the radiation belts.

Space weather phenomena can threaten space technologies. A hazard among these is the population of relativistic electrons in the Van Allen radiation belts. To reduce the threat, artificial processes can be introduced by transmitting very-low-frequency (VLF) waves into the belts. The resulting wave-particle interactions may deplete these harmful electrons. However, when transmitting VLF waves in space plasma, the antenna, plasma, and waves interact in a manner that is not well-understood. We conducted a series of VLF transmission experiments in the radiation belts and measured the power and radiation impedance under various frequencies and conditions. The results demonstrate the critical role played by the plasma-antenna-wave interaction around high-voltage space antennae and open the possibility to transmit high power in space. The physical insight obtained in this study can provide guidance to future high-power space-borne VLF transmitter developments, laboratory whistler-mode wave injection experiments, and the interpretation of various astrophysical and optical phenomena.

[In vivo imaging of the corneal nerve plexus : From single image to large scale map]. / In-vivo-Bildgebung des kornealen Nervenplexus : Vom Einzelbild zur großflächigen Darstellung.

The sub-basal nerve plexus (SNP) of the cornea provides the possibility of in vivo and non-invasive examination of peripheral nerve structures by corneal confocal microscopy (CCM). Thus morphological alterations of the SNP can be directly detected and quantified. A single CCM image is insufficient for a well-founded diagnosis because of the inhomogeneous distribution of the nerve fibers; therefore, there is a demand for techniques for large area imaging of the SNP. This article provides an overview of published approaches to the problem. Current developmental work at the Karlsruhe Institute of Technology and the University of Rostock Eye Clinic is expected to lead to a simplified handling of the technology and a further improvement in the image quality.

[Morphometric characterization of the subbasal nerve plexus : Detection and analysis of networks of nerve fibers]. / Morphometrische Charakterisierung des subbasalen Nervenplexus : Detektion und Analyse von Nervenfasernetzwerken.

Confocal laser scanning microscopy is a versatile tool in medical research and enables noninvasive in vivo imaging of the corneal subbasal nerve plexus. The aim of this work is to provide a structured overview about the detection and quantification of nerve fibers of the subbasal nerve plexus from images acquired by confocal laser scanning microscopy. Relevant steps are explained and potential factors influencing the quality of the results are pointed out. Information obtained from the quantification of subbasal nerve fiber structure can be potentially used as clinical parameters in the context of diagnostics and therapy control of diabetic neuropathy.

Comparative quantitative assessment of the human corneal sub-basal nerve plexus by in vivo confocal microscopy and histological staining.

PurposeThis study was designed to compare and contrast quantitative data of the human corneal sub-basal nerve plexus (SBP) evaluated by two different methods: in vivo confocal microscopy (IVCM), and immunohistochemical staining of ex vivo donor corneas.MethodsSeven parameters of the SBP in large-scale IVCM mosaicking images from healthy subjects were compared with the identical parameters in ex vivo donor corneas stained by ß-III-tubulin immunohistochemistry. Corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), average weighted corneal nerve fiber tortuosity (CNFTo), corneal nerve connection points (CNCP), average corneal nerve single-fiber length (CNSFL), and average weighted corneal nerve fiber thickness (CNFTh) were calculated using a dedicated, published algorithm and compared.ResultsOur experiments showed significantly higher values for CNFL (50.2 vs 21.4 mm/mm2), CNFD (1358.8 vs 277.3 nerve fibers/mm2), CNBD (847.6 vs 163.5 branches/mm2), CNFTo (0.095 vs 0.081 µm-1), and CNCP (49.4 vs 21.6 connections/mm2) in histologically staining specimens compared with IVCM images. In contrast, CNSFL values were higher in IVCM images than in histological specimens (32.1 vs 74.1 µm). No significant difference was observed in CNFTh (2.22 vs 2.20 µm) between the two groups.ConclusionsThe results of this study have shown that IVCM has an inherently lower resolution compared with ex vivo immunohistochemical staining of the corneal SBP and that this limitation leads to a systematic underestimation of several SBP parameters. Despite this shortcoming, IVCM is a vital clinical tool for in vivo characterization, quantitative clinical imaging, and evaluation of the human corneal SBP.

[Large-scale imaging of corneal nerve fibres by guided eye movements]. / Großflächige Abbildung kornealer Nervenfasern durch geführte Augenbewegungen.

BACKGROUND: The high resolution of corneal confocal microscopy (CCM) allows in vivo imaging of the corneal sub-basal nerve plexus (SNP). The field of view of a single CCM image (0.16 mm²) is not sufficient for the reliable morphometric characterisation of the SNP. Therefore we are developing a highly automated mosaicking technique for large-area imaging of the SNP using CCM image sequences. METHODS: In order to acquire an image sequence of a larger area of the SNP, the view direction of the patient is guided by a computer-controlled moving fixation target on a display in front of the non-examined eye. The CCM image sequence is recorded with 30 fps. An online calculated mosaic image allows the medical operator to observe the acquisition process and assess the quality and size of the resulting image during the CCM recording process. Remaining image artefacts are corrected in an automated post-processing step. RESULTS: Using a first prototype system and an appropriate fixation target trajectory, a mean growth of the covered SNP area of 0.18 mm²/s could be achieved. CONCLUSION: Using the presented technology, large-area images of the SNP can be generated. The technology is characterized by a high degree of automation and short examination times.

[Image reconstruction of the corneal subbasal nerve plexus with extended field of view from focus image stacks of a confocal laser scanning microscope]. / Bildrekonstruktion des subbasalen Nervenplexus der Kornea mit erweitertem Bildfeld aus Fokusserien eines konfokalen Laser-Scanning-Mikroskops.

BACKGROUND: Confocal laser scanning microscopy (CLSM) allows the in vivo analysis of nerve structures of the human cornea. In this way, pathological alterations of the peripheral nervous system that also affect the corneal subbasal nerve plexus (SNP) can be diagnosed non-invasively and possibly earlier than with other methods. The field of view of in vivo CLSM images of the cornea (ca. 0.4 × 0.4 mm²) is not sufficient for a reliable assessment. Two phenomena make the image assessment difficult: the presence of ridge-like tissue deformations in the neighbourhood of the SNP and image distortions that are induced by involuntary and unavoidable eye movements during image acquisition. This paper presents an image processing method for generating undistorted images of the SNP with an extended field of view. METHODS: The presented method has been tested on five volunteers. Eight focus image stacks have been taken and processed from each subject using a Heidelberg Retina Tomograph with Rostock Cornea Module (HRT). An image registration scheme specifically adapted to the image acquisition system corrects the non-linear motion-induced image distortions and reconstructs a volume from each focus image stack. The epithelial basal boundary surface including the SNP appears as a distinctive hyper-reflective layer inside the reconstructed volume. Extracting this continuous layer generates a depth map and finally a two-dimensional image of the SNP. A final fusion step of the single reconstructed SNP images leads to laterally extended images. RESULTS: Out of 40 focus image stacks, 34 have been fully processed into two-dimensional SNP reconstruction images. Six focus image stacks could not be transformed into volumes because of extremely fast eye movements during the image acquisition that prevented the complete image registration of the stacks. The 34 SNP reconstruction images depict an average area of 94.7 % ( ±â€Š6.2 %) with respect to the field of view of a single HRT image. The final fusion of the reconstructed images resulted in an average increase of the image area by a factor of 2.6 (ranging from 2.2 to 3.1). CONCLUSION: The presented image processing algorithms are capable of correcting the motion-induced image distortions and of generating larger two-dimensional images of the SNP even in presence of severe tissue deformations. These images provide the basis for a more reliable assessment of the corneal nerve fibres.