Characteristic retinal atrophy pattern allows differentiation between pediatric MOGAD and MS after a single optic neuritis episode.

BACKGROUND Optic neuritis (ON) is the most prevalent manifestation of pediatric multiple sclerosis (MSped) and myelin-oligodendrocyte glycoprotein antibody-associated disease (MOGADped) in children > 6 years. In this study, we investigated retinal atrophy patterns and diagnostic accuracy of optical coherence tomography (OCT) in differentiating between both diseases after the first ON episode. METHODS Patients were retrospectively identified in eight tertial referral centers. OCT, VEP and high/low-contrast visual acuity (HCVA/LCVA) have been investigated > 6 months after the first ON. Prevalence of pathological OCT findings was identified based on data of 144 age-matched healthy controls. RESULTS Thirteen MOGADped (10.7 ± 4.2 years, F:M 8:5, 21 ON eyes) and 21 MSped (14.3 ± 2.4 years, F:M 19:2, 24 ON eyes) patients were recruited. We observed a significantly more profound atrophy of both peripapillary and macular retinal nerve fiber layer in MOGADped compared to MSped (pRNFL global: 68.2 ± 16.9 vs. 89.4 ± 12.3 µm, p < 0.001; mRNFL: 0.12 ± 0.01 vs. 0.14 ± 0.01 mm3, p < 0.001). Neither other macular layers nor P100 latency differed. MOGADped developed global atrophy affecting all peripapillary segments, while MSped displayed predominantly temporal thinning. Nasal pRNFL allowed differentiation between both diseases with the highest diagnostic accuracy (AUC = 0.902, cutoff < 62.5 µm, 90.5% sensitivity and 70.8% specificity for MOGADped). OCT was also substantially more sensitive compared to VEP in identification of ON eyes in MOGAD (pathological findings in 90% vs. 14%, p = 0.016). CONCLUSION First MOGAD-ON results in a more severe global peripapillary atrophy compared to predominantly temporal thinning in MS-ON. Nasal pRNFL allows differentiation between both diseases with the highest accuracy, supporting the additional diagnostic value of OCT in children with ON

Imaging the dynamics of dyke propagation prior to the 2000-2003 flank eruptions at Piton de La Fournaise, Reunion Island

International audienceThe relationship between shallow magma storage and flank injections in volcanic edifices is rarely documented. We analyse the time series of geodetic and seismic data collected at Piton de La Fournaise volcano (La Reunion) during 9 flank eruptions from 2000 to 2003. The data depicts how magma injections supplied flank eruptions at Piton de la Fournaise volcano, and allows to precisely determine the direction and duration of dike intrusions, indicating a two phases pattern, consistent over all the eruptions: 1) Fast vertical migration of the dyke (~2 m/s) from the magma chamber to the surface in 10 to 50 minutes, and 2) slower, lateral migration (0.2-0.8 m/s) in tens of minutes to hours controlled by the rift zone geometry

Intraoperative assessment of stapes movement

A method is described that allows, for the first time, intraoperative vibration modes assessment of the acoustically stimulated stapes by means of scanning laser Doppler interferometry (LDI). The study was designed to answer the following questions: 1) Is LDI practical for taking measurements during surgery? 2) Are the results comparable to the findings in temporal bone preparations? and 3) Do the vibration characteristics of the stapes change after the posterior incudal ligament is detached from the incus? Seven patients with profound bilateral hearing loss who were undergoing cochlear implantation were included in the study. The measurement system was easily applicable for intraoperative measurements and allowed contact-free analysis with very high accuracy. No major differences in the results from the live human subjects and temporal bone preparations were observed. The stapes movement was predominantly pistonlike at the lower frequencies and became complex at higher frequencies. Sacrificing the posterior incudal ligament had no statistically significant effect on stapes vibration

Eruption forerunners from multiparameter monitoring and application for eruptions time predictability (Piton de la Fournaise)

International audienceVolcanic eruptions impact on societal risk, and volcanic hazard assessment is a necessary ingredient for decision-makers. However, the prediction of volcanic eruptions remains challenging due to the complexity and the non-linearity of volcanic processes. Identified forerunners such as increasing seismicity or deformation of the volcanic edifice prior to eruption are not deterministic. In this study, we use statistical methods to identify and discriminate precursory patterns to eruptions, on three sets of observables of Piton de la Fournaise volcano. We analyzed the short-term (i.e. the inter-eruptive period) time series of the seismicity rate, the deformation and the seismic velocity changes (deduced from seismic noise cross-correlations) over the period 1999-2006, with two main goals. First, we characterize the average pre-eruptive time patterns before 22 eruptions using superposed epoch analysis for the three observables. Using daily rate values, we resolve (1) a velocity change within 100-50 days from the eruptions onsets, then a plateau value up to eruption onset; (2) a power law increase in seismicity rate from noise level 15-10 days before eruption time; (3) an increase of displacement rate on the eruption day. These results support a three step mechanism leading to magma transfers toward the surface. Second we use pattern recognition techniques and the formalization of error diagrams to quantify the predictive power of each forerunner either as used independently or as combined to each other. We show that when seismicity rate alone performs the best prediction in the failure to predict versus alarm duration space, the combination of the displacement and seismicity data reduces the false alarm rate. We further propose a tool which explores the prediction results in order to optimize prediction strategy for decision-makers, as a function of the risk value

Evaluation of eardrum laser doppler interferometry as a diagnostic tool

OBJECTIVES: Laser Doppler interferometry (LDI) of the eardrum allows noncontact optical analysis of its vibrations in response to sound. Although LDI has been widely used in research, it has not yet been introduced into clinical practice as an adjunctive test for otological workup. The aim of this study was to evaluate LDI as a diagnostic tool in the clinical sphere. STUDY DESIGN: Prospective. METHODS: A measurement system was developed based on a commercially available scanning He-Ne laser Doppler interferometer. The study included 129 eardrums of 79 subjects that were divided into 3 groups: 1) normal subjects and 2) patients with sensorineural and 3) conductive hearing loss (HL). All the patients suffering from conductive HL underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to the subgroups malleus fixation, incus luxation, and stapes fixation. RESULTS: The modified LDI system allowed bilateral evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural HL were found. However, it was possible to distinguish between normal subjects and patients with conductive HL. Furthermore, the system had the ability to differentiate between various middle ear diseases. These groups differed statistically significantly in terms of manubrium vibration amplitude and resonance frequency. In malleus fixation significant differences in tympanic membrane movement patterns were found. CONCLUSIONS: Our LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain

Very- and ultra-long-period seismic signals prior to and during caldera formation on La Réunion Island

International audienceearly detection of the onset of a caldera collapse can provide crucial information to understand their formation and thus to minimize risks for the nearby population and visitors. Here, we analyse the 2007 caldera collapse of piton de la Fournaise on La Réunion Island recorded by a broadband seismic station. We show that this instrument recorded ultra-long period (ULP) signals with frequencies in the range (0.003-0.01 Hz) accompanied by very-long period (VLP) signals (between 0.02 and 0.50 Hz) prior to and during the caldera formation suggesting it is possible to detect the beginning of the collapse at depth and anticipate its surface formation. Interestingly, VLP wave packets with a similar duration of 20 s are identified prior to and during the caldera formation. We propose that these events could result from repeating piston-like successive collapses occurring through a ring-fault structure surrounding a magma reservoir from the following arguments: the source mechanism from the main collapse, the observations of slow source processes as well as observations from the field and the characteristic ring-fault seismicity. Caldera collapses are rare (only seven events over the last 100 years) and particularly destructive volcanic events that can induce catastrophic changes in the shape of a volcanic edifice and its environment 1. Identifying the occurrence of the first collapse at depth is of major importance in evaluating the triggering factors and anticipating the caldera surface formation. This detection can help to predict or at least indicate early future caldera collapses and subsequent consequences such as explosive eruptions, (e.g. those that followed the major Kīlauea Caldera collapse in 1470-1510 2), or atmospheric impacts 3. In the past two decades only four caldera collapses have been monitored by dense geophysical networks: chronologically, the 2000 Miyake-jima, Japan; the 2007 Piton de la Fournaise, La Réunion/France; the 2014-2015 Bárðarbunga, Iceland; and the 2018 Kīlauea, Hawai'i 4-7. Laboratory experiments and numerical analyses predicted the occurrence of precursory collapses at depth before the onset of the surface subsidence 8-12 but observations obtained from adequate broadband seismometers were lacking. Until the present study, the Miyake-jima caldera formation was the only known case with evidence of such deep collapses before the faults reached the surface. The deep collapses were suggested from observations of VLP seismic pulses of 20 s width 13. However, the timing of the first collapse at depth was not reported. VLP signals observed at volcanoes are generally considered having frequencies between 0.01-0.5 Hz (ref. 14) and until the 2000 Miyake-jima event, they were generally considered to result from inertial forces associated with changes in the flow of magma and gases through conduits 14. The VLP signals detected during the Miyake-jima caldera formation were explained by different physical mechanisms: (i) a buried geyser model 15 , (ii) a piston-like model 4,13,16 , and (iii) ring-faulting mechanisms related to shear failure on curved or cone-shaped fault structures 17,18. 46 step-like tilt changes (TC) were observed during the Miyake-jima caldera formation and among them 39 were accompanied by the VLP seismic signals 4,19,20. The origin of these TC associated with the VLP pulses have been attributed to either a piston model with a vertical rock column intermittently sinking into a magma reservoir 4,21 or to a magma sheet model with a large sill-lik

Extension of the Spatial Autocorrelation (SPAC) Method to Mixed-Component Correlations of Surface Waves

Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations were not considered in the development of the SPAC method. The method originally addressed the vertical–vertical (ZZ), RR and TT correlations, hence the name spatial autocorrelation. The theoretical expressions we derive for the ZR and RZ correlations offer additional ways to measure Rayleigh wave dispersion within the SPAC framework. Expanding on the results for isotropic incidence, we derive the complete correlation matrix in the case of generally anisotropic incidence. We show that the ZR and RZ correlations have advantageous properties in the presence of an out-of-plane directional wavefield compared to ZZ and RR correlations. We apply the results for mixed-component correlations to a data set from Akutan Volcano, Alaska and find consistent estimates of Rayleigh wave phase velocity from ZR compared to ZZ correlations. This work together with the recently discovered connections between the SPAC method and time-domain correlations of ambient noise provide further insights into the retrieval of surface wave Green’s functions from seismic noise