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Ibrahim Traore,1 Guillaume Eberst,1– 3 Fréderic Claudé,1 Lucie Laurent,1 Aurelia Meurisse,2,3 Sophie Paget-Bailly,2,3 Pauline Roux-Claudé,1 Pascale Jacoulet,1 Cindy Barnig,1 Rachel Martarello,1 Bastien Poirson,4 Kevin Bouiller,5 Catherine Chirouze,5 Julien Behr,6 Franck Grillet,6 Ophélie Ritter,1 Sébastien Pili-Floury,7 Hadrien Winiszewski,8 Emmanuel Samain,7,9 Gilles Capellier,8– 10 Virginie Westeel1– 3 1Respiratory Medicine Department, University Hospital of Besançon, Besançon, France; 2Methodology and Quality of Life in Oncology Unit, University Hospital, Besançon, France; 3UMR 1098, University of Franche-Comté, Besançon, France; 4Department of Geriatrics, University Hospital of Besançon, Besançon, France; 5Department of Infectious Disease, University Hospital of Besançon, Besançon, France; 6Department of Radiology, University Hospital of Besançon, Besançon, France; 7Anesthesia and Intensive Care Unit, University Hospital of Besançon, Besançon, France; 8Medical Intensive Care Unit, University Hospital of Besançon, Besançon, France; 9Research Unit EA3920, Université de Franche Comté, Besançon, France; 10Australian and New Zealand Intensive Care Research Center, Department of Epidemiology and Preventive Medicine, Monash University, Monash, AustraliaCorrespondence: Ibrahim Traore, Respiratory Medicine Department, University Hospital of Besançon, Besançon, France, Email traore.ibrahim180@gmail.comBackground: Sleep apnea (SA) was reported as possibly exacerbating symptoms of COVID-19, a disease induced by SARS-CoV-2 virus. The same comorbidities are common with both pathologies. This study aimed to estimate the prevalence, characteristics of SA and variation in AHI three months after severe COVID-19 requiring intensive care unit (ICU) admission.Methods: A prospective cohort of patients admitted to ICU for severe COVID-19 underwent an overnight home polygraphy 3 months after onset of symptoms, as part of a comprehensive follow-up program (pulmonary function tests, 6-minute walk tests and chest CT-scan). Patients with an apnea hypopnea index (AHI) ≥ 5 were considered as having SA. We performed a comparative descriptive analysis of 2 subgroups according to the existence, severity of SA and indication for effective SA treatment: patients with absent or mild SA (AHI < 15) vs patients with moderate to severe SA (AHI ≥ 15).Results: Among 68 patients included, 62 (91%) had known comorbidities (34 hypertension, 21 obesity, 20 dyslipidemia, 16 type 2 diabetes). It has been observed a preexisting SA for 13 patients (19.1%). At 3 months, 62 patients (91%) had SA with 85.5% of obstructive events. Twenty-four patients had no or a mild SA (AHI < 15) and 44 had moderate to severe SA (AHI ≥ 15). Ischemic heart disease exclusively affected the moderate to severe SA group. Except for thoracic CT-scan which revealed less honeycomb lesions, COVID-19 symptoms were more severe in the group with moderate to severe SA, requiring a longer curarization, more prone position sessions and more frequent tracheotomy.Conclusion: SA involved 91% of patients in our population at 3 months of severe COVID-19 and was mainly obstructive type. Although SA might be a risk factor as well as consequences of ICU care in severe COVID-19 infection, our results underline the importance of sleep explorations after an ICU stay for this disease.Keywords: SARS-CoV-2, pneumonia, obstructive sleep apnea syndrome, intensive care unit

BackgroundExercise training increases high-density lipoprotein (HDL) cholesterol, but its effect on HDL function is unclear. In hypertensives, exercise improves endothelial dysfunction, which is related to HDL function. In the present study, we assess for the first time the effects of different exercise modalities on two cell-free assays of HDL function.DesignThe study was conducted as a prospective randomized controlled trial in 75 hypertensive patients.MethodsPatients were randomized in three groups: (a) handgrip isometric training five times weekly; (b) placebo-handgrip; and (c) aerobic exercise training at least three times per week. HDL function was assessed in serum samples at baseline and after 12 weeks of training by two independent assays that determine the proinflammatory phenotype (haptoglobin content) of a specific amount of HDL (Haptoglobin-HDL [HPHDL]) and oxidized HDL (HDLox) as a measure of reduced antioxidant function of HDL. HDL function measures were normalized by the measures of a pooled control of sera from healthy participants and by HDL-C levels (normalized ratio, no units).ResultsAerobic exercise led to significant reduction of the HDLox from 0.99 ± 0.27 to 0.90 ± 0.29 (no units, p = 0.03). The HPHDL did not change in any training group. Changes of HDLox correlated with reduction of the systolic blood pressure only after aerobic exercise (R = 0.64, p = 0.03).ConclusionsAerobic but not isometric exercise improves the antioxidant function of HDL in patients with hypertension. This improvement correlates positively with reductions of blood pressure.

This article discusses the prevalence and characteristics of Enterococcus faecalis in endocarditis, a serious infection of the heart valves. The study, conducted in the Brandenburg Endocarditis Registry, analyzed data from 324 endocarditis patients and found that E. faecalis was the second most common pathogen, after Staphylococcus aureus. Patients with E. faecalis endocarditis were more likely to have prosthetic valves or pacemakers, and the infection was often caused by urogenital sepsis. Compared to other bacteria, E. faecalis endocarditis was associated with older age, pre-existing conditions, and acute renal failure, but had lower mortality rates. The authors suggest that the rise in E. faecalis may be due to demographic changes and recommend identifying high-risk patients for preventive measures or early treatment. [Extracted from the article]

Background and Aim. Chronic kidney disease (CKD) is an emerging problem in both clinical and ambulatory medicine. Much effort in terms of managing CKD must be put into the control of so-called progression factors. In the current investigation, we evaluated the CKD-associated health care quality in all in-hospital subjects that were treated in a newly founded university hospital for a period of 1 year. Methods. The study was performed in a retrospective and observational manner. All adult (age 18 years or older) in-hospital subjects treated from January until December 2019 were included. CKD was diagnosed according to the KDIGO 2012 CKD Guideline. The following variables were assessed: CKD stage, quantification/analysis (yes/no) of blood pressure, proteinuria, serum phosphate, serum 25-OH-D3, ferritin and transferrin saturation, and blood gas analysis. In addition, recommendations of the following medicines were analyzed (given/not given): ACE inhibitor or sartan, phosphate binder, vitamin D3 (activated or native), iron, erythropoietin, and bicarbonate. It was also evaluated whether discharge letters contained CKD-related diagnoses or not. Results. In total, 581 individuals were included in the study. The majority of aspects related to the monitoring and therapeutic management of CKD were either considered in only a small proportion of affected individuals (e.g., quantification of PTH − 5.5%/25-OH-D3 − 6%/transferrin saturation − 13.6%) or avoided nearly at all (e.g., recommendation of erythropoietin—1%, documentation of CKD-MBD diagnosis—0.3%). A reasonable quality of care was identified concerning the blood pressure monitoring (performed in 100%) and blood gas analysis (55% of the patients received analysis). Serum phosphate was measured in 12.9%, particularly in subjects at higher CKD stages. Conclusions. The current investigation revealed poor quality of care in CKD patients treated at the Brandenburg University Hospital over the period of one year. Quality improvement must be achieved, most likely via a standardized educational program for physicians and a directer access to CKD management guidelines. [ABSTRACT FROM AUTHOR]

Background. Acute kidney injury substantially worsens the prognosis of hospitalized patients. The Brandenburg Medical School was founded in 2014, and a nephrology section was opened in summer 2017. The aim of the study was to analyze AKI epidemiology and outcomes in one of two university hospitals belonging to the medical school. The period of interest dated from January to December 2015. Methods. The investigation was designed as a single-center, retrospective cohort study at the Brandenburg Hospital of the Brandenburg Medical School. All in-hospital patients treated between January and the end of December 2015 were included. AKI was defined as specified in the 2012 published KDIGO criteria (criteria 1 and 2). Four parameters were evaluated in particular: AKI incidence, in-hospital mortality, frequency of renal replacement therapy, and renal recovery during the stay at the hospital. Results. A total number of 5,300 patients were included in the analysis. AKI was diagnosed in 490 subjects (10.1%). The in-hospital mortality was 26%. The following conditions/parameters significantly differed between survivors (s) and nonsurviving (ns) subjects: duration of in-hospital treatment (s > ns), AKI onset (outpatient vs. in-hospital) (outpatient in s > ns), dialysis due to AKI (s < ns), vasopressor administration (s < ns), and invasive ventilation (s < ns). 5.6% received dialysis therapy, and renal recovery occurred in 31% of all surviving AKI subjects. Conclusion. Both, the AKI incidence and the frequency of dialysis were lower than reported in the literature. However, fewer subjects recovered from AKI. These discrepant findings possibly result from the lack of prehospitalization creatinine values, the lack of follow-up data, and a generally lower awareness for the need to perform renal replacement therapy in AKI. [ABSTRACT FROM AUTHOR]

Introduction. Acute kidney injury (AKI) significantly worsens the prognosis of hospitalized patients. In recent years, cell-based strategies have been established as a reliable option for improving AKI outcomes in experimental AKI. Our previous studies focused on the so-called proangiogenic cells (PACs). Mechanisms that contribute to PAC-mediated AKI protection include production/secretion of extracellular vesicles (MV, microvesicles). In addition, the cells most likely act by paracrinic processes (secretome). The current study evaluated whether AKI may be preventable by the administration of either PAC-derived MV and/or the secretome alone. Methods. AKI was induced in male C57/Bl6N mice (8–12 weeks) by bilateral renal ischemia (IRI-40 minutes). Syngeneic murine PACs were stimulated with either melatonin, angiopoietin-1 or -2, or with bone morphogenetic protein-5 (BMP-5) for one hour, respectively. PAC-derived MV and the vesicle-depleted supernatant were subsequently collected and i.v.-injected after ischemia. Mice were analyzed 48 hours later. Results. IRI induced significant kidney excretory dysfunction as reflected by higher serum cystatin C levels. The only measure that improved AKI was the injection of MV, collected from native PACs. The following conditions worsened after ischemic renal function even further: MV + Ang-1, MV + BMP-5, MV + melatonin, and MV + secretome + Ang-1. Conclusion. Together, our data show that PAC-mediated AKI protection substantially depends on the availability of cell-derived MV. However, since previous data showed improved AKI-protection by PACs after cell preconditioning with certain mediators (Ang-1 and -2, melatonin, BMP-5), mechanisms other than exclusively vesicle-dependent mechanisms must be involved in PAC-mediated AKI protection. [ABSTRACT FROM AUTHOR]

The Caribbean and South American tectonic plates bound the north-eastwards expulsion of the North Andean Block in western Venezuela. This complex geodynamic setting resulted in the formation of major strike-slip fault systems and sizeable mountain chains. The 100-km-wide Mérida Andes extend from the Colombian/Venezuelan border to the Caribbean coast. To the north and south, the Mérida Andes are bound by hydrocarbon-rich sedimentary basins. Knowledge of lithospheric structures, related to the formation of the Mérida Andes, is limited though, due to a lack of deep geophysical data. In this study, we present results of the first broad-band magnetotelluric profile crossing the Mérida Andes and the Maracaibo and Barinas–Apure foreland basins on a length of 240 km. Geoelectrical strike and dimensionality analysis are consistent with 1-D or 2-D subsurface structures for the sedimentary basins but also indicate a strong 3-D setting for the Mérida Andes. Using a combination of 2-D and 3-D modelling we systematically examined the influence of 3-D structures on 2-D inversions. Synthetic data sets derived from 3-D modelling allow identification and quantification of spurious off-profile features as well as smoothing artefact due to limited areal station coverage of data collected along a profile. The 2-D inversion models show electrically conductive basins with depths of 2–5 km for the Barinas-Apure and 2–7 km for the Maracaibo basins. A number of resistive bodies within the Maracaibo basin could be related to active deformation causing juxtaposition of older geological formations and younger basin sediments. The most important fault systems of the area, the Boconó and Valera Faults, cross-cut the Mérida Andes in NE–SW direction along its strike on a length 400 km and N–S direction at its centre on a length 60 km, respectively. Both faults are associated with subvertical zones of high electrical conductivity and sensitivity tests suggest that they reach depths of up to 12 km. A sizeable conductor at 50 km depth, which appears consistently in the 2-D sections, could be identified as an inversion artefact caused by a conductor east of the profile. We speculate the high conductivity associated with the off-profile conductor may be related to the detachment of the Trujillo Block. Our results partially support the 'floating orogen hypothesis' developed to explain the geodynamic evolution of western Venezuela and they highlight the relevance of the Trujillo Block in this process. [ABSTRACT FROM AUTHOR]

We present a model of the electrical resistivity structure of the lithosphere in the Central Andes between 20° and 24°S from 3‐D inversion of 56 long‐period magnetotelluric sites. Our model shows a complex resistivity structure with significant variability parallel and perpendicular to the trench direction. The continental forearc is characterized mainly by high electrical resistivity (>1,000 Ωm), suggesting overall low volumes of fluids. However, low resistivity zones (LRZs, <5 Ωm) were found in the continental forearc below areas where major trench‐parallel faults systems intersect NW‐SE transverse faults. Forearc LRZs indicate circulation and accumulation of fluids in highly permeable fault zones. The continental crust along the arc shows three distinctive resistivity domains, which coincide with segmentation in the distribution of volcanoes. The northern domain (20°–20.5°S) is characterized by resistivities >1,000 Ωm and the absence of active volcanism, suggesting the presence of a low‐permeability block in the continental crust. The central domain (20.5°–23°S) exhibits a number of LRZs at varying depths, indicating different levels of a magmatic plumbing system. The southern domain (23°–24°S) is characterized by resistivities >1,000 Ωm, suggesting the absence of large magma reservoirs below the volcanic chain at crustal depths. Magma reservoirs located below the base of the crust or in the backarc may fed active volcanism in the southern domain. In the subcontinental mantle, the model exhibits LRZs in the forearc mantle wedge and above clusters of intermediate‐depth seismicity, likely related to fluids produced by serpentinization of the mantle and eclogitization of the slab, respectively. Key Points: This paper presents a three-dimensional model of the electrical resistivity structure of the Central Andes subduction zone (20°–24°S)Resistivity of the mantle wedge suggests along‐margin variability in the amount of fluids released by eclogitization of the slabResistivity structure below the arc shows distinctive domains that coincide with segmentation in the distribution of active volcanoes [ABSTRACT FROM AUTHOR]

We investigate seismoelectric (SE) signals accompanying seismic waves radiated from earthquake sources. SE signals are mostly generated from compressional portions of seismic waves by electrokinetic coupling. They contain coseismic electric fields travelling with seismic wave velocity and interface response (IR) waves, which originate at layer interfaces and travel with electromagnetic wave speed. IR wave amplitudes are sensitive to contrasts in poroelastic and electric rock parameters. We introduce SE spectral ratios (SESRs) as a tool to evaluate the influence of IRs on the overall SE signal independently of the earthquake source–time function. Based on data from Northern Chile we show that SESRs show a site specific frequency dependence with a trend of decreasing amplitudes towards increasing frequency. Modelling results reveal that the specific frequency dependence of the SESRs is caused by IRs excited at depths of some hundred metres underneath the recording stations. We analyse the SESR sensitivity towards porosity, permeability, fluid salinity and the depth of the interfaces. We verify that observed SESRs can be reproduced through forward modelling and linearized inversion based on realistic subsurface parameters. [ABSTRACT FROM AUTHOR]

Para la determinación del potencial de producción agrícola (PG) con base en índices climáticos, se analizaron los valores históricos de producción por hectárea en seis localidades de diferentes latitudes de la República Mexicana (Chihuahua, Chih.; Hermosillo, Son.; Durango, Dgo.; Morelia, Mich.; Chilpancingo, Gro. y Mérida, Yuc.) ajustándose por mínimos cuadrados con sus respectivos valores climáticos de índice de aridez (lA), en función de las disponibilidades de energía y precipitación. De esta forma se encontró la siguiente relación: PG = 2063(1ª)- 7206, por medio de la cual se obtienen valores similares a los registrados para los sistemas naturales, deduciéndose una potencialidad climática intrínseca en cada uno de los ecosistemas en estudio. Para determinar la estabilidad de producción y su vulnerabilidad a los factores climáticos de las diferentes zonas en estudio, se compara en magnitud el máximo eigenvalor negativo de la matriz de producción agrícola y natural (A) (indicador de la dinámica de interacción biológica) con la varianza del índice de aridez (a2) (indicador del efecto adverso ambiental). Se considera que la condición necesaria para que exista estabilidad es: A> a2. Se observa que las zonas del norte (Chihuahua, Durango y Hermosillo) presentan una mayor inestabilidad que las del sur (Morelia y Chilpancingo). Mérida es la que presenta una mayor discrepancia con el patrón de comportamiento respecto de las otras localidades. doi: https://doi.org/10.22201/igeof.00167169p.1988.27.2.786

Acute kidney injury (AKI) occurs frequently in hospitals worldwide, but the therapeutic options are limited. Diabetes mellitus (DM) affects more and more people around the globe. The disease worsens the prognosis of AKI even further. In recent years, cell-based therapies have increasingly been applied in experimental AKI. The aim of the study was to utilize two established autophagy inducers for pharmacological preconditioning of so-called proangiogenic cells (PACs) in PAC treatment of diabetic AKI. Insulin-dependent DM was induced in male C57/Bl6N mice by intraperitoneal injections of streptozotocine. Six weeks later, animals underwent bilateral renal ischemia for 45 min, followed by intravenous injections of either native or zVAD (benzyloxycarbonyl-Val-Ala-Asp-fluoro-methylketone)- or Z-Leu-Leu-Leu-al (MG132)-pretreated syngeneic murine PACs. Mice were analyzed 48 h (short term) and 6 wk (long term) later, respectively. DM worsened postischemic AKI, and PAC preconditioning with zVAD and MG132 resulted in a further decline of excretory kidney function. Injection of native PACs reduced fibrosis in nondiabetic mice, but cell preconditioning promoted interstitial matrix accumulation significantly. Both substances aggravated endothelial-tomesenchymal transition (EndoMT) under diabetic conditions; these effects occurred either exclusively in the short (zVAD) or in the short and long term (MG132). Preconditioned cells stimulated the autophagocytic flux in intrarenal endothelial cells, and all experimental groups displayed increased endothelial abundances of senescenceassociated β-galactosidase, a marker of premature cell senescence. Pharmacological autophagy activation may not serve as an effective strategy for improving PAC competence in diabetic AKI in general. On the contrary, several outcome parameters (excretory function, fibrosis, EndoMT) may even be worsened. [ABSTRACT FROM AUTHOR]

Production from oil fields requires the monitoring of hydrocarbon saturation in the reservoir. In the Bockstedt oil field there exists a substantial difference in resistivity between an oil-filled (approximately 100-16 Ω·m) and a brine-filled (0.6 Ω·m) reservoir. Controlledsource electromagnetics (CSEM) is chosen to test whether sufficient resistivity differences can be observed by means of surface measurements. The target is a Lower Cretaceous clastic interval at an approximate depth of 1200 m. Forward modeling demonstrates that the expected resistivity changes at reservoir level cannot be resolved with a survey setup of only surface electrical sources and sensors. Therefore a borehole-to-surface technique has been developed, whereby the metal casing of an abandoned production well serves as an input electrode. CSEM surveys were acquired in 2014 and 2015 as a time-lapse baseline and monitor for both horizontal electric (Ex and Ey) components. A four-transmitter and 25-receiver configuration was deployed for these surveys. Forward modeling indicates that induction effects from metal objects, such as casings of production wells, cannot be ignored in the electromagnetics (EM) modeling. A shallow observation well was drilled in 2015 to make the collection of vertical electric field (Ez) data sets possible. A new downhole sensor was developed for this purpose. Numerical simulations suggest Ez data are more sensitive to the anticipated resistivity changes in the reservoir. Because Ez is two orders of magnitude smaller than the horizontal components, verticality is of great importance to avoid masking the Ez signal by interference from unwanted horizontal components. Similar acquisition parameters are adopted for 2014 baseline and 2015 monitor surveys to facilitate the comparisons. The repeatability is good, generating comparable response functions. A new, computationally efficient approach considers the effect of the metal casings, and is implemented in the 3D modeling and inversion codes. Preliminary resistivity models obtained from 3D CSEM inversion explain the observed data, and are in agreement with results from a 3D-seismic survey and resistivity logs in the calibration wells. Incorporation of the metal casings in the EM-modeling scheme increases the lateral continuity of inverted resistivity bodies. In November 2016, a new time-lapse acquisition campaign was undertaken to collect a second Ex/Ey monitor and the first monitor survey for the Ez component. [ABSTRACT FROM AUTHOR]

Contrast-induced nephropathy (CIN) is a frequent and severe complication in subjects receiving iodinated contrast media for diagnostic or therapeutic purposes. Several preventive strategies were evaluated in the past. Recent clinical studies and meta-analyses delivered some new aspects on preventive measures used in the past and present. We will discuss all pharmacological and nonpharmacological procedures. Finally, we will suggest individualized recommendations for CIN prevention. [ABSTRACT FROM AUTHOR]

We present the crustal resistivity structure of the Pamir and Southern Tian Shan orogenic belts at the northwestern promontory of the India–Asia collision zone. The magnetotelluric (MT) data were recorded along a roughly north–south trending, 350 km long corridor from the Pamir Plateau in southern Tajikistan across the Pamir frontal ranges, the Alai Valley and the southwestern Tian Shan to Osh in the Kyrgyz part of the Fergana Basin. In total, we measured at 178 sites, whereof 26 combine broad band and long period recordings. One of the most intriguing features of the 2-D and 3-D inversion results is a laterally extended zone of high electrical conductivity below the Pamir Plateau, with resistivities below 1 Ωm, starting at a depth of ∼10–15 km. The high conductivity can be explained with the presence of partially molten rocks at middle to lower crustal levels, possibly related to ongoing migmatization and/or middle/lower crustal flow underneath the Southern Pamir. This interpretation is consistent with a low velocity zone found from local earthquake tomography, relatively high vp/vs ratios, elevated surface heat flow, and thermomechanical modelling suggesting that melting temperatures are reached in the felsic middle crust. In the upper crust of the Pamir and Tian Shan, the Palaeozoic–Mesozoic suture zones appear as electrically conductive, whereas the compact metamorphic rocks of the Muskol-Shatput Dome of the Central Pamir are highly resistive. The intra-montane basin of the Alai Valley—sandwiched between the Pamir and Tian Shan—exhibits a generally conductive upper crust that bifurcates into two conductors at depth. One of them connects to the active Main Pamir Thrust, which is absorbing most of today's convergence between the Pamir and the Tian Shan. Several deeper zones of high conductivity in the middle and lower crust of Central and Northern Pamir likely record fluid release due to metamorphism associated with active continental subduction/delamination. [ABSTRACT FROM PUBLISHER]

For 3-D inversion of controlled-source electromagnetic (CSEM) data, increasing availability of high-performance computers enables us to apply inversion techniques that are theoretically favourable, yet have previously been considered to be computationally too demanding. We present a newly developed parallel distributed 3-D inversion algorithm for interpreting CSEM data in the frequency domain. Our scheme is based on a direct forward solver and uses Gauss–Newton minimization with explicit formation of the Jacobian. This combination is advantageous, because Gauss–Newton minimization converges rapidly, limiting the number of expensive forward modelling cycles. Explicit calculation of the Jacobian allows us to (i) precondition the Gauss–Newton system, which further accelerates convergence, (ii) determine suitable regularization parameters by comparing matrix norms of data- and model-dependent terms in the objective function and (iii) thoroughly analyse data sensitivities and interdependencies. We show that explicit Jacobian formation in combination with direct solvers is likely to require less memory than combinations of direct solvers and implicit Jacobian usage for many moderate-scale CSEM surveys. We demonstrate the excellent convergence properties of the new inversion scheme for several synthetic models. We compare model updates determined by solving either a system of normal equations or, alternatively, a linear least-squares system. We assess the behaviour of three different stabilizing functionals in the framework of our inversion scheme, and demonstrate that implicit regularization resulting from incomplete iterative solution of the model update equations helps stabilize the inversion. We show inversions of models with up to two million unknowns in the forward solution, which clearly demonstrates applicability of our approach to real-world problems. [ABSTRACT FROM AUTHOR]

Determining the MR compatibility of medical implants and devices is becoming increasingly relevant. In most cases, the heating of conductive implants due to radiefrequency (RF) excitation pulses is measured by fluoroptic temperature sensors in relevant tests for approval. Another common method to determine these heating effects is MR thermometry using the proton resonance frequency. This method gives good results in homogeneous phantoms. However in many cases, technical shortcomings such as susceptibility artifacts prohibit exact proton resonance frequency thermometry near medical implants. Therefore, this work aimed at developing a fast T1- based method which allows controlled MR-related heating of a medical implant while simultaneously quantifying the spatial and temporal temperature distribution. To this end, an inversion recovery snapshot Fast Low-Angle Shot (FLASH) sequence was modified with additional off-resonant heating pulses. With an accelerated imaging method and a sliding-window technique, every 7.6 s a new temperature map could be generated with a spatial in-plane resolution of 2 mm. The temperature deviation from calculated temperature values to reference fluoroptic probe was found to be smaller than 1 K. [ABSTRACT FROM AUTHOR]

Electrical conductivity is a key parameter for the exploration and characterization of geothermal reservoirs as hot mineralized formation water of active geothermal areas usually exhibits significantly higher conductivity than the surrounding host rock. Here we present results of a magnetotelluric (MT) exploration experiment carried out in the vicinity of the Groß Schönebeck geothermal test site in Northern Germany, where a doublet system of two 4.3-km deep boreholes was drilled to establish an in situ laboratory to investigate the potential for geothermal energy production. Classical 2-D smooth inversion of the MT data, recorded along two profiles, reveals a shallow conductive structure in good agreement with information from regional geology and seismic images. However, at the northernmost part of the profiles, the conductivity models reveal deep-reaching conductive structures, which appear uncorrelated with existing (geophysical or geological) data. Incorporating information from seismics as independent constraints for MT inversions allows us to examine the model space rigorously but target oriented. Employing so-called tear-zone inversions we can effectively derive an alternative class of models, which are consistent with the MT observations but also with the other data sets. We speculate that the zones of high conductivity imaged at reservoir depth are related areas of reduced thickness of the overlaying evapourite layer. The enhanced conductivity can be explained by a higher fracture density in anhydritic layers and/or generally lower resistivity of the pore fluid. [ABSTRACT FROM AUTHOR]

Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being wide and reaching to depths , in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity SW of the SAF and likely represents a deep-reaching fault zone. [ABSTRACT FROM AUTHOR]

Magnetotelluric (MT) responses in complex, 3-D terrains are in general characterized by (i) elliptical polarization states of horizontal electric and magnetic fields; (ii) the non-orthogonality of electric and magnetic fields and (iii) a coupling of the anomalous tangential-electric (TE) and tangential-magnetic (TM) modes, giving rise to a mode-mixed anomalous electric field at the surface. These 3-D effects are propagated into the MT impedance tensor, which is derived from horizontal electric and magnetic fields, recorded at the earth's surface. The impedance tensor is in general fully occupied, and each of its elements is a mode-mixed quantity. To study 3-D effects of MT (impedance) data, the TE and TM mode contributions must be separated. This becomes possible with the inclusion of the single-mode vertical magnetic transfer function (the ratio of vertical to horizontal magnetic fields). Then, the individual modes can be resolved without prior knowledge of the underlying 3-D conductivity structure. For this purpose, we consider (i) the spatial relations between electromagnetic field components recorded in an array of sites (Faraday's law) and (ii) that the magnetic TE mode and electric TM mode fields are potential fields within the insulating air half-space above the earth's surface. Based on these two dependencies, it is possible to reconstruct the entire electromagnetic field from (measured) mixed-mode impedances and vertical magnetic transfer functions and to separate it into TE and TM modes, and into normal and anomalous parts. Hereby, we cannot only study the contribution of the two modes on the observed impedance tensor but also quantify the influence of 3-D effects at each location and frequency of a particular data set. Results of a modelling study suggest, that (i) none of the elements of a 3-D impedances tensor can be regarded as favourable for a 2-D interpretation (only 3-D models can explain 3-D data), (ii) a heterogeneous crust can strongly obscure identification of responses originating from the lower crust or upper mantle even at very long periods and (iii) the TE mode magnetic transfer functions are most important for sensing deep anomalies. [ABSTRACT FROM AUTHOR]

Magnetotelluric and seismic methods provide complementary information about the resistivity and velocity structure of the subsurface on similar scales and resolutions. No global relation, however, exists between these parameters, and correlations are often valid for only a limited target area. Independently derived inverse models from these methods can be combined using a classification approach to map geologic structure. The method employed is based solely on the statistical correlation of physical properties in a joint parameter space and is independent of theoretical or empirical relations linking electrical and seismic parameters. Regions of high correlation (classes) between resistivity and velocity can in turn be mapped back and re-examined in depth section. The spatial distribution of these classes, and the boundaries between them, provide structural information not evident in the individual models. This method is applied to a 10 km long profile crossing the Dead Sea Transform in Jordan. Several prominent classes are identified with specific lithologies in accordance with local geology. An abrupt change in lithology across the fault, together with vertical uplift of the basement suggest the fault is sub-vertical within the upper crust. [ABSTRACT FROM AUTHOR]

Magnetotelluric (MT) response function estimates can be severely disturbed by the effects of cultural noise. Methods to isolate and remove these disturbances are typically based on time-series editing, robust statistics, remote reference processing, or some combination of the above. Robust remote reference processing can improve the data quality at a local site, but only if synchronous recordings of at least one additional site are available and if electromagnetic noise between these sites is uncorrelated. If these prerequisites are not met, we suggest an alternative approach for noise removal, based on a combination of frequency domain editing with subsequent single site robust processing. The data pre-selection relies on a thorough visual inspection of a variety of statistical parameters such as spectral power densities, coherences, the distribution of response functions and their errors, etc. Extreme outliers and particularly noisy data segments are excluded from further data processing by setting threshold values for individual parameters. Examples from Namibia and Jordan illustrate that this scheme can improve data quality significantly. However, the examples also suggest that it is not possible to establish generally valid rules for selection as they depend strongly on the local noise conditions. High coherence, for example, can indicate a good signal-to-noise ratio or strongly correlated noise. However, we found that strong polarization of the magnetic field channels and the distribution of response function errors are two important parameters for noise detection. [ABSTRACT FROM AUTHOR]