Refine
Document Type
- Article (2)
- Conference Proceeding (2)
Language
- English (4)
Has Fulltext
- yes (4)
Is part of the Bibliography
- no (4)
Keywords
- 3‐D inversion (1)
- Antidepressant (1)
- Depression (1)
- Prediction (1)
- Primary care (1)
- Treatment (1)
- apparent resistivity tensor (1)
- electromagnetic field theory (1)
- forward modeling (1)
- magnetotellurics (1)
Institute
- Geowissenschaften (3)
- Medizin (1)
The Ceboruco is a 2280 m high stratovolcano located in Nayarit State, Mexico. Despite its last eruption which occurred in 1870, it is the most active volcano in the area, showing volcanicearthquake activity together with ongoing vapor emissions. The magnetotelluric survey was carried out in November 2016. It was part of a geothermal project (CeMIEGeo-P24) and focused on the determination of the electrical conductivity distribution in the subsurface of the volcano.
The Magnetotelluric Apparent Resistivity Tensor, as introduced by Brown (2016), can be decomposed into an amplitude and a phase tensor. The fundamental physics behind those new tensors were presented in Hering et al. (2019), using canonical models in 1-D (isotropic and anisotropic) and 2-D resistivity environments. Here, the tensors are introduced for a high-quality data set, where their interpretational benefits become very obvious. Additionally, results from an isotropic 3-D inversion are presented and compared to an alternative 3-D anisotropic forward model.
In November 2016, magnetotelluric (MT) data were collected at the Ceboruco Volcano in cooperation with the Centro de Sismología y Volcanología de Occidente (SisVoc, Universidad de Guadalajara, Mexico). The Ceboruco is a 2280 m high stratovolcano, located in Nayarit State, Mexico. It is placed in the central part of the Tepic-Zacoalco Rift (TZR), which constitutes the north-western end of the Trans-Mexican Volcanic Belt. Together with Chapala and Colima (in the Jalisco Block), they form the triple rift system developed as a consequence of the ongoing subduction of the Rivera and Cocos oceanic plates beneath the North American continental crust. Although its last eruption occurred in 1870, it is the most active volcano in the area, showing volcanic-earthquake activity together with ongoing vapor emissions. The survey was part of a geothermal project (CeMIEGeo-P24) and focused on the determination of electrical conductivity properties to characterize the deep structure and the geothermal potential of the Volcano. Frequency dependent magnetotelluric response functions were calculated from 25 broadband MT stations, which covered an area of 10 x 10 km2 including its crater, calderas and foreland. The results were interpreted using anisotropic 3-D forward modelling and isotropic 3-D inversion approaches, considering strong topographical effects. The final resistivity model implies a highly conductive layer, reaching from near-surface to approximately 2 km depth, which might be related to a hydrothermal system. Here, mineralized fluids and clay minerals can cause high conductivities around 1 S/m. For longer periods, the principal axes of the MT response tensors (phase tensor, apparent resistivity tensor) are in good agreement with the strike direction of the underlying rift system. However, they are not rendered by the isotropic inversion. Thus the data suggest an anisotropic electrical conductivity at greater depth with its principal axis determined by the response tensors.
The complex magnetotelluric (MT) apparent resistivity tensor can be decomposed into two real tensors, the apparent resistivity and the resistivity phase tensors, which represent relationships between the observed electric field at a point on the Earth's surface and an associated apparent current density. We explain the differences between these tensors and conventional estimates of apparent resistivity and phase for simple resistivity environments and demonstrate, using canonical models in 1‐D and 2‐D environments, that both tensors are more sensitive to vertical and horizontal resistivity gradients than their conventional counterparts. The properties of the new tensors are explained using electromagnetic induction theory and the effects of associated charges at resistivity boundaries. We introduce a new way to plot tensor ellipses, which brings significant improvements to the interpretation of MT data, using appropriate visualization software. The apparent resistivity tensor gives information about the magnitude and direction of apparent resistivity subsurface structures and has a strong response to vertical resistivity contrasts. The resistivity phase tensor is highly sensitive to vertical boundaries and the associated fields in the TM mode. It is also free from static distortions under the same conditions implied for the conventional phase tensor. These findings have prompted a study in the potential of the new tensors for 3‐D inversions. The results from a 3‐D inversion of a canonical oblique conductor straddling two quarter spaces show distinct improvements in resolving the boundaries of the conductor and open a promising field for future studies.
Background: Antidepressant medication is commonly used to treat depression. However, many patients do not respond to the first medication prescribed and improvements in symptoms are generally only detectable by clinicians 4–6 weeks after the medication has been initiated. As a result, there is often a long delay between the decision to initiate an antidepressant medication and the identification of an effective treatment regimen.
Previous work has demonstrated that antidepressant medications alter subtle measures of affective cognition in depressed patients, such as the appraisal of facial expression. Furthermore, these cognitive effects of antidepressants are apparent early in the course of treatment and can also predict later clinical response. This trial will assess whether an electronic test of affective cognition and symptoms (the Predicting Response to Depression Treatment Test; PReDicT Test) can be used to guide antidepressant treatment in depressed patients and, therefore, hasten treatment response compared to a control group of patients treated as usual.
Methods/design: The study is a randomised, two-arm, multi-centre, open-label, clinical investigation of a medical device, the PReDicT Test. It will be conducted in five European countries (UK, France, Spain, Germany and the Netherlands) in depressed patients who are commencing antidepressant medication. Patients will be randomised to treatment guided by the PReDicT Test (PReDicT arm) or to Treatment as Usual (TaU arm). Patients in the TaU arm will be treated as per current standard guidelines in their particular country. Patients in the PReDicT arm will complete the PReDicT Test after 1 (and if necessary, 2) weeks of treatment. If the test indicates non-response to the treatment, physicians will be advised to immediately alter the patient’s antidepressant therapy by dose escalation or switching to another compound. The primary outcome of the study is the proportion of patients showing a clinical response (defined as 50% or greater decrease in baseline scores of depression measured using the Quick Inventory of Depressive Symptoms – Self-Rated questionnaire) at week 8. Health economic and acceptability data will also be collected and analysed.
Discussion: This trial will test the clinical efficacy, cost-effectiveness and acceptability of using the novel PReDicT Test to guide antidepressant treatment selection in depressed patients.
Trial registration: ClinicalTrials.gov, ID: NCT02790970. Registered on 30 March 2016.