Robust Arterial Spin Labeling T2 Measurements

Perfusion and bolus arrival time are often quantified physiological parameters. By additionally quantifying permeability it is hoped to better understand tissue physiology or monitor small permeability changes in cerebrovascular diseases, which are difficult to detect by traditional gadolinium contrast agents. A problem of gadolinium contrast agents is the size of the macro molecules. They cannot pass an intact or slightly damaged blood brain barrier, whereas hydrogen molecules are small enough to pass it. In arterial spin labeling (ASL) the hydrogen spins of the water molecules in inflowing blood are selectively inverted and can be used as a non-invasive endogenous contrast agent. In standard ASL modules, generally only T1 effects are considered. This is sufficient for perfusion and arrival time but not for capillary wall permeability quantification, due to the small difference of blood and tissue T1 times. In contrast to this, T2 times of blood and tissue are considerably different, which makes arterial spin labeling T2 measurements a potential method for permeability estimations if current modules are extended and optimized to include T2. Yet, accurate T2 calculations are often very time consuming, limiting the acquisition for an individual patient and the general implementation in clinical routine. In the present work, acquisition techniques and fitting routines of a multi-TI multi-TE 3D-GRASE (gradient and spin echo) sequence are presented allowing a fast and reliable T2 calculation at every inflow time, which can be used for permeability estimations. An optimized acquisition scheme and T2 calculation algorithm is found with regard to accuracy, measurement time, and signal-to-noise ratio (SNR). The concept of adaptive averaging is presented, which allows the acquisition of longer inflow times more often than shorter ones, improving SNR at long inflow times by 1.5 and more, but by simultaneously keeping the total scan time constant. The impact on T2 calculations from stimulated echoes in combination with different kinds of crusher gradients at several refocusing flip angles is evaluated in phantoms and volunteers. The fitted T2 results are compared to simulations and gold standard single spin echo T2 values. Finally, T2 values at multiple inflow times with different turbo factors (TF) are obtained. The impact of the turbo factor on the T2 calculation is simulated and verified in a volunteer study, resulting in a suggestion for an optimised imaging scheme for TF>1. For TF1 the multi-TE ASL 3D-GRASE sequence is already capable of T2 measurements at multiple inflow times, very close to T2 values obtained with the gold standard single spin echo sequence. The T2 values could be directly incorporated in a two compartment model for perfusion quantification, to further study tissue functions or disease related to permeability changes

Robust Arterial Spin Labeling T2 Measurements

Perfusion and bolus arrival time are often quantified physiological parameters. By additionally quantifying permeability it is hoped to better understand tissue physiology or monitor small permeability changes in cerebrovascular diseases, which are difficult to detect by traditional gadolinium contrast agents. A problem of gadolinium contrast agents is the size of the macro molecules. They cannot pass an intact or slightly damaged blood brain barrier, whereas hydrogen molecules are small enough to pass it. In arterial spin labeling (ASL) the hydrogen spins of the water molecules in inflowing blood are selectively inverted and can be used as a non-invasive endogenous contrast agent. In standard ASL modules, generally only T1 effects are considered. This is sufficient for perfusion and arrival time but not for capillary wall permeability quantification, due to the small difference of blood and tissue T1 times. In contrast to this, T2 times of blood and tissue are considerably different, which makes arterial spin labeling T2 measurements a potential method for permeability estimations if current modules are extended and optimized to include T2. Yet, accurate T2 calculations are often very time consuming, limiting the acquisition for an individual patient and the general implementation in clinical routine. In the present work, acquisition techniques and fitting routines of a multi-TI multi-TE 3D-GRASE (gradient and spin echo) sequence are presented allowing a fast and reliable T2 calculation at every inflow time, which can be used for permeability estimations. An optimized acquisition scheme and T2 calculation algorithm is found with regard to accuracy, measurement time, and signal-to-noise ratio (SNR). The concept of adaptive averaging is presented, which allows the acquisition of longer inflow times more often than shorter ones, improving SNR at long inflow times by 1.5 and more, but by simultaneously keeping the total scan time constant. The impact on T2 calculations from stimulated echoes in combination with different kinds of crusher gradients at several refocusing flip angles is evaluated in phantoms and volunteers. The fitted T2 results are compared to simulations and gold standard single spin echo T2 values. Finally, T2 values at multiple inflow times with different turbo factors (TF) are obtained. The impact of the turbo factor on the T2 calculation is simulated and verified in a volunteer study, resulting in a suggestion for an optimised imaging scheme for TF>1. For TF1 the multi-TE ASL 3D-GRASE sequence is already capable of T2 measurements at multiple inflow times, very close to T2 values obtained with the gold standard single spin echo sequence. The T2 values could be directly incorporated in a two compartment model for perfusion quantification, to further study tissue functions or disease related to permeability changes

A Great State Fair: The Blue Ribbon Foundation and the Revival of the Iowa State Fair

Review of: A Great State Fair: The Blue Ribbon Foundation and the Revival of the Iowa State Fair, by William B. Friedricks

Potenzial und Limitationen der direktionalen Tiefen Hirnstimulation: Ein Simulationsansatz

Direktionale Elektroden werden zum Standard bei der Tiefen Hirnstimulation. Sie ermöglichen es, das elektrische Feld nicht nur entlang der Elektrodenachse, sondern ebenfalls axial zur Elektrode zu modulieren. Bei zirkulären Elektroden ist eine Modulation des elektrischen Feldes hingegen nur entlang der Elektrodenachse möglich. Die axiale Modulation reduziert Nebenwirkungen und erweitert das therapeutische Fenster. Die Einstellmöglichkeiten werden als Kehrseite jedoch sehr komplex, sodass computergestützte Verfahren von Nöten sind, um den Mediziner bei der optimalen Einstellung zu unterstützen und für den Patienten das klinisch bestmögliche Ergebnis zu erzielen. Zudem bringt jedes System technische Limitierungen mit sich. Die vorliegende Arbeit simuliert, inwieweit eine Abweichung der Elektrode von der Zielposition durch direktionale Stimulation kompensiert werden kann, um ein definiertes Zielvolumen zu stimulieren. Zielvolumina von aktiviertem Gewebe (volume of tissue activated = VTA) wurden für verschiedene Amplituden (1 mA-5 mA) bei zirkulärer Stimulation erstellt und stellen die Zielwerte dar. Mit einer Finiten-Elemente-Methode wurden VTAs für unterschiedliche prozentuale Amplitudenverteilungen der drei Elektroden eines direktionalen Kontaktes simuliert, für 1-5 mA jeweils über 80 verschiedene Kombinationen. Die VTAs wurden dann von 0 bis 2 mm radial zur Elektroden-achse und mit Verschiebungswinkeln in Schritten von 7,5° verschoben und ihre Schnitt-menge mit dem Zielvolumen berechnet. Es zeigte sich, dass Fehlplatzierungen bis 1 mm durch direktionale Stimulation weitestgehend kompensiert werden können. Bei größeren Verschiebungen nimmt die Schnittmenge um 10-30 % zu im Vergleich zu zirkulärer Stimulation. Hierbei spielen die Amplitude und der Verschiebungswinkel eine große Rolle, diese bestimmen maßgeblich die prozentuale Verteilung der Amplitude auf die drei Elektrodenkontakte. Um die Vorteile der direktionalen Elektroden voll ausnutzen zu können, ist es daher nötig, den Verschiebungswinkel und die Größe der Abweichung genau zu kennen. Bei Verschiebungen über 1 mm ist die Kompensationsmöglichkeit limitiert, jedoch verringert sich die Menge des stimulierten Gewebes außerhalb des Zielbereiches. Hierdurch werden Nebenwirkungen reduziert, was ein großer Vorteil ist. Datensätze wie in dieser Simulation werden nötig sein, um optimierte Algorithmen für die Elektrodenprogrammierung zu entwickeln

Highway Maintenance Impacts for Water Quality, Executive Summary: Volume I

DTFH61-82-C-00085This report, Volume I in a four-volume series of reports, summarizes a research project involving impacts from highway maintenance practices on water quality. Research efforts included 1) evaluating the impact potential of routine practices, 2) developing assessment methods for specific practices, 3) identification of measures to mitigate impacts and 4) conducting field studies to better define impacts from two common practices -- herbicide application and surface treatment (seal coating)

Investigations of Impacts of Selected Highway Maintenance Practices on Water Quality: Volume II

DTFH61-82-C-00085This report, Volume II in a four-volume series of reports, describes a field research program to determine water quality impacts from two routine highway maintenance practices -- control of vegetation using herbicides and surface treatment (seal-coating) of asphaltic concrete pavements. It includes the details of monitoring site selection, precipitation and storm water runoff monitoring, performance of the above maintenance practices, and analysis of results. Two sites were monitored in the herbicide study; one was treated with 2,4-D, the other with picloram. For the surface treatment operation, an asphalt road was treated with a WS-90 asphalt emulsion followed by application of limestone gravel. Chemical analyses and bioassays conducted on runoff samples generally indicate these practices do not impact water quality

High throughput detection of Coxiella burnetii by real-time PCR with internal control system and automated DNA preparation

<p>Abstract</p> <p>Background</p> <p><it>Coxiella burnetii </it>is the causative agent of Q-fever, a widespread zoonosis. Due to its high environmental stability and infectivity it is regarded as a category B biological weapon agent. In domestic animals infection remains either asymptomatic or presents as infertility or abortion. Clinical presentation in humans can range from mild flu-like illness to acute pneumonia and hepatitis. Endocarditis represents the most common form of chronic Q-fever. In humans serology is the gold standard for diagnosis but is inadequate for early case detection. In order to serve as a diagnostic tool in an eventual biological weapon attack or in local epidemics we developed a real-time 5'nuclease based PCR assay with an internal control system. To facilitate high-throughput an automated extraction procedure was evaluated.</p> <p>Results</p> <p>To determine the minimum number of copies that are detectable at 95% chance probit analysis was used. Limit of detection in blood was 2,881 copies/ml [95%CI, 2,188–4,745 copies/ml] with a manual extraction procedure and 4,235 copies/ml [95%CI, 3,143–7,428 copies/ml] with a fully automated extraction procedure, respectively. To demonstrate clinical application a total of 72 specimens of animal origin were compared with respect to manual and automated extraction. A strong correlation between both methods was observed rendering both methods suitable. Testing of 247 follow up specimens of animal origin from a local Q-fever epidemic rendered real-time PCR more sensitive than conventional PCR.</p> <p>Conclusion</p> <p>A sensitive and thoroughly evaluated real-time PCR was established. Its high-throughput mode may show a useful approach to rapidly screen samples in local outbreaks for other organisms relevant for humans or animals. Compared to a conventional PCR assay sensitivity of real-time PCR was higher after testing samples from a local Q-fever outbreak.</p