1,721,344 research outputs found
Mobiili mittauslaitteisto ja signaalinkeruun ohjausmenetelmä keskiarvoistettuihin EEG-herätevastemittauksiin
No full textEvent-related potentials (ERPs) are a result of the activity elicited in the brain during the performance of a cognitive task. They can be studied by using an EEG, and are used to investigate the brain functions related to the processing of sensory data, and memory. The technique is flexible, and affordable, and has various potential diagnostic applications. The clinical feasibility, however, is limited due to the low measurement reliability. In addition, performance of the tests could be enhanced if the recording devices were more robust.
The current study presents two ways of improving the performance of ERP measurements. The first deals with the improvement of the efficiency of the recording procedure and the second, with the optimization of the recording system design for clinical use. In addition, the discussion on improving the measurement reliability is contributed to by conducting a study with mismatch negativity (MMN) to determine the relationship between the measurement error and the test-retest reliability.
To improve the recording procedure, an acquisition control method is suggested which helps optimize the amount of data recorded in terms of its concurrent quality. It allows optimization of the recording time and control of the measurement error, which reduces subject discomfort and improves measurement repeatability. In the MMN study conducted, the effect varied, depending on the parameterization, and whether the deviant responses were studied separately or as a profile. It was, however, generally significant, and repeatability was estimated to keep improving until the error level went below 10% of the peak amplitude.
Second, a mobile ERP recording system design with an integrated audio stimulation unit is presented. It is easy to apply, and capable of performing online data analysis. It is also tolerant of external interference because of its compact size, close proximity to the measured target, and the average grounding arrangement it uses. This kind of design allows fluent performance of the measurements in applications where the target activity is well-defined, which is important in an attempt to allow clinical use to be made of them. Together with the application of the algorithm developed, it provides easy access to ERPs and makes the investigations efficient, and less inconvenient.EEG-herätevasteilla (ERP:lla) tarkoitetaan sähköisiä signaaleja, joita syntyy kognitiivisen aivotoiminnan seurauksena. Niitä voidaan tarkastella aivosähkökäyrän avulla ja hyödyntää tutkittaessa aistiherätteiden synnyttämää aivotoimintaa sekä muistia. Menetelmä on joustava, edullinen ja kliinisten sovellusten kannalta monikäyttöinen. Käytettävyys on kuitenkin rajallista mittausten heikon luotettavuuden takia. Lisäksi tehokkuutta voitaisiin parantaa kehittämällä robustimpia mittalaiteratkaisuja.
Tässä työssä esitetään kaksi tapaa mittausten kehittämiseksi. Toinen näistä liittyy mittausprosessin ja toinen mittausjärjestelmien parantamiseen. Lisäksi tutkimuksessa otetaan kantaa keskusteluun mittausten luotettavuudesta tutkimalla mittausvirheen vaikutusta poikkeavuusnegatiivisuusvasteen (MMN) toistettavuuteen.
Mittausprosessin tehostamiseksi esitellään laadunhallintamenetelmä, joka auttaa optimoimaan mitatun aineiston määrää, sen laadun perusteella. Menetelmän avulla voidaan optimoida mittauksen kestoa ja hallita mittausvirheen suuruutta, mikä vähentää mittausten epämukavuutta sekä parantaa tulosten toistettavuutta. MMN-kokeissa vaikutus riippui vasteen parametrisoinnista sekä siitä, että tulkittiinko vasteita erillisinä vai toisiinsa suhteutettuina. Se oli kuitenkin yleisesti merkitsevä ja toistettavuuden arvioitiin parantuvan ainakin kunnes virhe laskisi alle 10%:iin vasteen huippuamplitudista.
Mittausjärjestelyjä ajatellen esitellään mobiili mittalaitetoteutus, jossa herätelähde on rakennettu osaksi mittausyksikköä. Toteutus on helppokäyttöinen ja kykenee suorittamaan aineistoanalyysiä mittauksen aikana. Lisäksi se sietää hyvin ulkoisia häiriöitä pienen kokonsa, mitatun kohteen läheisyyden, sekä käytetyn keskiarvomaajärjestelyn ansiosta. Kliinistä käyttöä ajatellen on tärkeää, että mittaukset kyetään suorittamaan mahdollisimman sujuvasti. Esitetynkaltainen laitteisto soveltuu erityisesti tunnettujen vasteiden mittaamiseen. Yhdessä laadunhallintamenetelmän kanssa, sellaisen arvioidaan helpottavan herätevasteiden tutkimista sekä vähentävän mittausten epämukavuutta
EEG and BOLD-contrast fMRI in brain : Cerebrovascular reactivity, suppression of neuronal activity, global and local brain injury
Get PDFAbstractThe purpose of the present study was to gain more insight into the blood oxygen level-dependent (BOLD)-contrast functional MRI (fMRI) in the brain and its connection to EEG, both in global and local scales of their temporal and spatial relations.BOLD signal changes were studied during hyperventilation (HV) induced EEG reactivity of intermittent rhythmic delta activity (IRDA). The BOLD signal in gray matter decreased 30% more in subjects with IRDA (N = 4) than in controls (N = 4), during the first two minutes of HV. This difference disappeared during IRDA in EEG. BOLD signal changes may provide additional information about dynamic hemodynamic changes relative to HV induced EEG reactivity.BOLD signal changes were investigated during sudden deepening of thiopental anesthesia into EEG burst-suppression level in pigs (N = 5). Positive (6–8%) or negative (-3– -8%) group average BOLD signal changes correlated to the thiopental bolus injection were seen. Positive and negative responses covered 1.6% and 2.3% of the brain voxels, respectively. BOLD signal changes in brain are associated with sudden deepening of thiopental anesthesia into EEG burst-suppression level, but they are spatially inconsistent and scarce.Somatosensory BOLD response was studied in brain before and after globally induced methotrexate (MTX) exposition in pigs (N = 4). After the MTX exposure, reduced (from 2–4% to 0–1%) or negative (-2% to -3%) BOLD responses were detected. Somatosensory BOLD-contrast response shows a slight difference in brain before and after globally induced MTX exposition.An experimental epilepsy model for development of simultaneous EEG and BOLD-contrast fMRI in the localization of epilepsy was developed and tested. Dynamic penicillin induced local epilepsy was applied in deep isoflurane anesthesia in pigs (N = 6). Relatively high (10–20%) and localized BOLD signal increase was found. The dynamic penicillin induced focal epilepsy model in deep isoflurane anesthesia with simultaneous EEG and BOLD-contrast fMRI is feasible for the development of these methods for localization of epileptic focus or foci.In conclusion, with careful experimental design and analysis, BOLD-contrast fMRI with EEG provides a potential tool for monitoring and localising functional changes in the brain.Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Auditorium 7 of Oulu University Hospital, on September 10th, 2004, at 12 noon.Abstract
The purpose of the present study was to gain more insight into the blood oxygen level-dependent (BOLD)-contrast functional MRI (fMRI) in the brain and its connection to EEG, both in global and local scales of their temporal and spatial relations.
BOLD signal changes were studied during hyperventilation (HV) induced EEG reactivity of intermittent rhythmic delta activity (IRDA). The BOLD signal in gray matter decreased 30% more in subjects with IRDA (N = 4) than in controls (N = 4), during the first two minutes of HV. This difference disappeared during IRDA in EEG. BOLD signal changes may provide additional information about dynamic hemodynamic changes relative to HV induced EEG reactivity.
BOLD signal changes were investigated during sudden deepening of thiopental anesthesia into EEG burst-suppression level in pigs (N = 5). Positive (6–8%) or negative (-3– -8%) group average BOLD signal changes correlated to the thiopental bolus injection were seen. Positive and negative responses covered 1.6% and 2.3% of the brain voxels, respectively. BOLD signal changes in brain are associated with sudden deepening of thiopental anesthesia into EEG burst-suppression level, but they are spatially inconsistent and scarce.
Somatosensory BOLD response was studied in brain before and after globally induced methotrexate (MTX) exposition in pigs (N = 4). After the MTX exposure, reduced (from 2–4% to 0–1%) or negative (-2% to -3%) BOLD responses were detected. Somatosensory BOLD-contrast response shows a slight difference in brain before and after globally induced MTX exposition.
An experimental epilepsy model for development of simultaneous EEG and BOLD-contrast fMRI in the localization of epilepsy was developed and tested. Dynamic penicillin induced local epilepsy was applied in deep isoflurane anesthesia in pigs (N = 6). Relatively high (10–20%) and localized BOLD signal increase was found. The dynamic penicillin induced focal epilepsy model in deep isoflurane anesthesia with simultaneous EEG and BOLD-contrast fMRI is feasible for the development of these methods for localization of epileptic focus or foci.
In conclusion, with careful experimental design and analysis, BOLD-contrast fMRI with EEG provides a potential tool for monitoring and localising functional changes in the brain
Implementation of 0.23 T magnetic resonance scanner to perioperative imaging in neurosurgery
Get PDFAbstractThe purpose of the present study was to implement a unique low-field open magnetic resonance scanner for perioperative imaging in neurosurgery.A paradigm was created for joint intraoperative/interventional MRI, including premises, surgical practice and an operational model. The feasibility of the paradigm was tested in clinical work. The joint use of the facilities between the Departments of Neurosurgery and Diagnostic Radiology was found to enhance the economic rationale and provide for perioperative imaging. It was also found to be organizationally viable in the long run.Intraoperative MRI was implemented and studied in connection with neuronavigation and other intraoperative instruments, tools and imaging modalities. The unique shut down possibility of the magnet enabled staged operating-imaging practice, use of non-MRI-compatible instruments and devices, multimodal imaging with navigation, and avoidance of safety risks associated with operating in magnetic fringe fields.Two dynamic contrast enhanced MR imaging sequences, which used undersampled projection reconstruction, were implemented in the low-field scanner. The applicability of these imaging sequences to follow contrast enhancement of meningiomas was studied in laboratory experiments and in two patient cases. The laboratory experiments showed a nearly linear response in signal intensity to the concentration of gadopentetate dimeglumine in purified water up to 1.25 mM. The patient cases showed results consistent with an earlier study performed at high-field strength.The potential of low-field MRI study including dynamic contrast enhanced imaging to predict surgical and histopathologic characteristics of meningiomas was studied in a series of 21 patients. Dynamic contrast enhanced imaging could be used to evaluate microvessel densities of meningiomas. Surgical bleeding, blood loss during operation, progesterone receptor expression and collagen content were statistically best correlated to the relative intensity of meningioma on FLAIR images. Tissue hardness correlated best with relative intensity on T2-weighted images.Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in Auditorium 1 of Oulu University Hospital, on December 9th, 2005, at 12 noonAbstract
The purpose of the present study was to implement a unique low-field open magnetic resonance scanner for perioperative imaging in neurosurgery.
A paradigm was created for joint intraoperative/interventional MRI, including premises, surgical practice and an operational model. The feasibility of the paradigm was tested in clinical work. The joint use of the facilities between the Departments of Neurosurgery and Diagnostic Radiology was found to enhance the economic rationale and provide for perioperative imaging. It was also found to be organizationally viable in the long run.
Intraoperative MRI was implemented and studied in connection with neuronavigation and other intraoperative instruments, tools and imaging modalities. The unique shut down possibility of the magnet enabled staged operating-imaging practice, use of non-MRI-compatible instruments and devices, multimodal imaging with navigation, and avoidance of safety risks associated with operating in magnetic fringe fields.
Two dynamic contrast enhanced MR imaging sequences, which used undersampled projection reconstruction, were implemented in the low-field scanner. The applicability of these imaging sequences to follow contrast enhancement of meningiomas was studied in laboratory experiments and in two patient cases. The laboratory experiments showed a nearly linear response in signal intensity to the concentration of gadopentetate dimeglumine in purified water up to 1.25 mM. The patient cases showed results consistent with an earlier study performed at high-field strength.
The potential of low-field MRI study including dynamic contrast enhanced imaging to predict surgical and histopathologic characteristics of meningiomas was studied in a series of 21 patients. Dynamic contrast enhanced imaging could be used to evaluate microvessel densities of meningiomas. Surgical bleeding, blood loss during operation, progesterone receptor expression and collagen content were statistically best correlated to the relative intensity of meningioma on FLAIR images. Tissue hardness correlated best with relative intensity on T2-weighted images
Studies on via coupling on multilayer printed circuit boards
Get PDFAbstractDesign and manufacturing techniques of printed circuit boards (PCB’s) have advanced from early one or two-layer structures to the multilayer boards where ten or more layers are no longer uncommon. These give additional routing space, potential decrease in device size and various design possibilities like solid ground and power planes. Unfortunately multilayer boards are vulnerable to high coupling between signal vias especially due to PCB resonances.In this study via crosscoupling is investigated on multilayer PCB’s. Special attention is given to the coupling due to resonances and vertically aligned blind vias. Problem is approached from the electromagnetic compatibility (EMC) point of view andhigh accuracy of measurements or models is not the objective. Instead ways to increase isolation are considered important. EMC is considered to include internal functionality of the device.Analytical methods are used to calculate resonant frequencies, fields and quality factors for simple rectangular structures. The PCB cavity is reduced to two-dimensions for numerical calculation of same quantities. Aplac finite-difference time-domain simulator is used to model coupling due to PCB resonances. Isolation between vertically aligned blind vias is estimated analytically. A quasi-static numerical model is used to study a coaxial via structure. Multilayer test boards are constructed for measurement purposes. Simplified resonator structures on two-layer boards are used to test different methods to increase isolation.Measurements show that high coupling between vias may occur due to PCB resonances. This leads to the situation, where previously used isolation methods between vias are not necessarily effective enough. Several means to reduce effects of PCB resonances are described in this study. Measured and modelled results agree well from an EMC point of view. Coupling due to vertically aligned blind vias is also shown to be high. A simple capacitance model may be used to approximate this up to frequencies where the dynamic wave nature of the board starts to be important. From a PCB designer’s point of view these results mean that when the board size is not small compared to the wavelength, there is a possibility of resonances and reduction methods have to be taken into account. Also placement of the vias have to be carefully selected especially if blind or buried vias are used.Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Oulunsali (Auditorium L5), Linnanmaa, on April 23rd, 1999, at 12 noon.Abstract
Design and manufacturing techniques of printed circuit boards (PCB’s) have advanced from early one or two-layer structures to the multilayer boards where ten or more layers are no longer uncommon. These give additional routing space, potential decrease in device size and various design possibilities like solid ground and power planes. Unfortunately multilayer boards are vulnerable to high coupling between signal vias especially due to PCB resonances.
In this study via crosscoupling is investigated on multilayer PCB’s. Special attention is given to the coupling due to resonances and vertically aligned blind vias. Problem is approached from the electromagnetic compatibility (EMC) point of view andhigh accuracy of measurements or models is not the objective. Instead ways to increase isolation are considered important. EMC is considered to include internal functionality of the device.
Analytical methods are used to calculate resonant frequencies, fields and quality factors for simple rectangular structures. The PCB cavity is reduced to two-dimensions for numerical calculation of same quantities. Aplac finite-difference time-domain simulator is used to model coupling due to PCB resonances. Isolation between vertically aligned blind vias is estimated analytically. A quasi-static numerical model is used to study a coaxial via structure. Multilayer test boards are constructed for measurement purposes. Simplified resonator structures on two-layer boards are used to test different methods to increase isolation.
Measurements show that high coupling between vias may occur due to PCB resonances. This leads to the situation, where previously used isolation methods between vias are not necessarily effective enough. Several means to reduce effects of PCB resonances are described in this study. Measured and modelled results agree well from an EMC point of view. Coupling due to vertically aligned blind vias is also shown to be high. A simple capacitance model may be used to approximate this up to frequencies where the dynamic wave nature of the board starts to be important. From a PCB designer’s point of view these results mean that when the board size is not small compared to the wavelength, there is a possibility of resonances and reduction methods have to be taken into account. Also placement of the vias have to be carefully selected especially if blind or buried vias are used
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
MR-guided interventions at 0.23T : Facilities, user interface, guiding technology and musculoskeletal applications
Get PDFAbstractMagnetic resonance imaging (MRI) has excellent soft tissue contrast, which can be enhanced by different contrast agents, multiplanar imaging capability and high temporal and spatial resolution. Even blood vessels can be easily visualised, and MRI parameters are sensitive to temperature. Therefore, MRI has the greatest potential for guiding and monitoring interventional and surgical procedures.The aim of this study was to design and evaluate new solutions for MR-guided procedures and surgery, to develop the technique and to assess the feasibility of MR-guided nerve root infiltration, bone biopsy and sacroiliac (SI) joint arthrography.The possibilities for versatile use of MR scanners were studied with a setup where an MR scanner with a 0,23 T open magnet was installed in a full-scale operating room (OR) to allow diagnostic MRI examinations, research, radiological interventions and neurosurgical operations to be performed in the same facility. All of the 144 MR-guided radiological interventions and neurosurgical operations performed in Oulu University Hospital between February 1999 and September 2000 were included in the study. The studied setup was a functionally feasible solution for combined neurosurgical and radiological use.To further improve MR-guided interventions, a new user interface was developed and preliminary tested with simulated clinical experiments. The new user interface seemed to be easily adobted by radiologists for interventional procedures.MR-guided nerve root infiltrations were studied by using MRI guidance on 34 consequent patients referred for first sacral root infiltration. Needle placement into the first sacral nerve root sheath was successful in 34 of the 35 (97%) cases, and the average duration of the procedure was 32 minutes.Bone biopsies were performed using a bone biopsy set designed in our institution to be connected to an optical tracking system. The feasibility of this new guiding system was evaluated with biopsies from five different anatomical areas. The bone biopsy system was successfully applied to all patients and provided a safe and accurate guidance method for all phases of the procedure.Twenty patients with low back pain suspected to arise from the SI joint underwent MR-guided SI joint arthrography. The procedure was successfully performed in all cases. The needle guiding with optical tracking inside the soft tissues proved to be accurate enough for successful procedures.In conclusion, versatile use of MR scanners for diagnostic imaging, radiological procedures and neurosurgery is feasible if planned properly. The prototype of a new user interface for MR-guided procedures allows radiologist to fully control the MR-scanner during the procedure. MRI is a suitable and accurate guidance method for musculoskeletal interventions.Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Auditorium 7 of the University Hospital of Oulu, on April 26th, 2002, at 12 noon.Abstract
Magnetic resonance imaging (MRI) has excellent soft tissue contrast, which can be enhanced by different contrast agents, multiplanar imaging capability and high temporal and spatial resolution. Even blood vessels can be easily visualised, and MRI parameters are sensitive to temperature. Therefore, MRI has the greatest potential for guiding and monitoring interventional and surgical procedures.
The aim of this study was to design and evaluate new solutions for MR-guided procedures and surgery, to develop the technique and to assess the feasibility of MR-guided nerve root infiltration, bone biopsy and sacroiliac (SI) joint arthrography.
The possibilities for versatile use of MR scanners were studied with a setup where an MR scanner with a 0,23 T open magnet was installed in a full-scale operating room (OR) to allow diagnostic MRI examinations, research, radiological interventions and neurosurgical operations to be performed in the same facility. All of the 144 MR-guided radiological interventions and neurosurgical operations performed in Oulu University Hospital between February 1999 and September 2000 were included in the study. The studied setup was a functionally feasible solution for combined neurosurgical and radiological use.
To further improve MR-guided interventions, a new user interface was developed and preliminary tested with simulated clinical experiments. The new user interface seemed to be easily adobted by radiologists for interventional procedures.
MR-guided nerve root infiltrations were studied by using MRI guidance on 34 consequent patients referred for first sacral root infiltration. Needle placement into the first sacral nerve root sheath was successful in 34 of the 35 (97%) cases, and the average duration of the procedure was 32 minutes.
Bone biopsies were performed using a bone biopsy set designed in our institution to be connected to an optical tracking system. The feasibility of this new guiding system was evaluated with biopsies from five different anatomical areas. The bone biopsy system was successfully applied to all patients and provided a safe and accurate guidance method for all phases of the procedure.
Twenty patients with low back pain suspected to arise from the SI joint underwent MR-guided SI joint arthrography. The procedure was successfully performed in all cases. The needle guiding with optical tracking inside the soft tissues proved to be accurate enough for successful procedures.
In conclusion, versatile use of MR scanners for diagnostic imaging, radiological procedures and neurosurgery is feasible if planned properly. The prototype of a new user interface for MR-guided procedures allows radiologist to fully control the MR-scanner during the procedure. MRI is a suitable and accurate guidance method for musculoskeletal interventions
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