Idiopathic generalized epilepsies and efficiency of advanced magnetic resonance imaging techniques in present era; perspectives in future

Epilepsy is a common disorder worldwide, with a prevalence of 4.5/1000 (0.45%) for youngsters and youths, and 1.54/1000 (0.15%) for the adult Chinese population in Hong Kong. up to 15% of epileptic patients can still leak the screening process of any structural lesion. In addition, the structural lesions detected on structural MR images may not reveal the correct degree and practical position of the abnormalities, especially with respect to malformations of cortical development. These include magnetic resonance spectroscopy (MRS) and perfusion weighted imaging (PWI). The widespread application of most of these techniques in clinical practice depends on the availability of high-performance MR imagers with the ability to accomplish fast echo-planar pulse sequences (echo-planar imaging), as well as substantial data processing capabilities. Using and PWI in study of microcirculation of tissues and vascular of lesional area on mechanisms by which selective drugs work and will provide new treatment targets for drug development. Finally, there is coupling of cerebral blood flow and metabolism, MR perfusion can act as a surrogate marker of metabolism as measured by MRS

A Digital signal processing-based predistortion technique for reduction of intermodulation distortion

Linearization of power amplifiers has been the topic of many studies, dating back to the work of H. S. Black in the 1920s. For many applications, the well-documented techniques of feedforward and feedback can be used to design low intermodulation distortion (IMD) amplifiers. However, certain applications, including the design of high-power, radio frequency amplifiers, preclude the use of these techniques. The work herein describes an alternative to presently accepted distortion reduction techniques. In-band IM distortion (multi-tone distortion located close in frequency to the desired signal) , is reduced by modifying a baseband input, upconverting this signal to the transmission frequency, then performing the amplification. This allows DSP hardware to be used, resulting in a novel IMD reduction method. The approach presented is unique in that multiple orders of nonlinearity are reduced using DSP technology, at baseband, through a commonly used method of upconversion. Existing work has addressed mostly third-order, analog solutions applied at the frequency of transmission. Theoretical work, simulations, and experimental results are used to describe the technique. Advantages and limitations are discussed, as are areas for future work

A capacitive SIW discontinuity for impedance matching

We present a shunt capacitive substrate-integrated waveguide (SIW) discontinuity for the first time. The discontinuity is parametrically characterized in terms of its reactive impedance, and an equivalent circuit model is presented and validated. $C$ -band prototypes are manufactured and measured, confirming the simulated results. The utility of the discontinuity is then demonstrated as a part of a matching network for an $S$ -band amplifier. A simple synthesis method for the matching networks is presented, which requires minimal numerical optimization. The amplifier is prototyped and measured and found to be in good agreement with simulation.The South African SKA Projecthttp://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=5503870hj2019Electrical, Electronic and Computer Engineerin

Absorption of 5G radiation in brain tissue as a function of frequency, power and time

The rapid release of 5G wireless communications networks has spurred renewed concerns regarding the interactions of higher radiofrequency (RF) radiation with living species. We examine RF exposure and absorption in ex vivo bovine brain tissue and a brain simulating gel at three frequencies: 1.9 GHz, 4 GHz and 39 GHz that are relevant to current (4G), and upcoming (5G) spectra. We introduce a highly sensitive thermal method for the assessment of radiation exposure, and derive experimentally, accurate relations between the temperature rise (ΔT), specific absorption rate (SAR) and the incident power density (F), and tabulate the coefficients, ΔT/ΔF and Δ(SAR)/ΔF , as a function of frequency, depth and time. This new method provides both ΔT and SAR applicable to the frequency range below and above 6 GHz as shown at 1.9, 4 and 39 GHz, and demonstrates the most sensitive experimental assessment of brain tissue exposure to millimeter-wave radiation to date, with a detection limit of 1 mW. We examine the beam penetration, absorption and thermal diffusion at representative 4G and 5G frequencies and show that the RF heating increases rapidly with frequency due to decreasing RF source wavelength and increasing power density with the same incident power and exposure time. We also show the temperature effects of continuous wave, rapid pulse sequences and single pulses with varying pulse duration, and we employ electromagnetic modeling to map the field distributions in the tissue. Finally, using this new methodology, we measure the thermal diffusivity of ex vivo bovine brain tissue experimentally

Gd-EOB-DTPA-enhanced MRI for evaluation of liver function: Comparison betewwn signal-intensity-based indices and T1 relaxometry

Gadolinium ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) is a paramagnetic hepatobiliary magnetic resonance (MR) contrast agent. Due to its OATP1B1/B3-dependent hepatocyte-specific uptake and paramagnetic properties increasing evidence has emerged to suggest that Gd-EOBDTPA- enhanced MRI can be potentially used for evaluation of liver function. In this paper we compare the diagnostic performance of Gd-EOB-DTPA-enhanced relaxometry-based and commonly used signal-intensity (SI)-based indices, including the hepatocellular uptake index (HUI) and SI-based indices corrected by spleen or muscle, for evaluation of liver function, determined using the Indocyanin green clearance (ICG) test. Simple linear regression model showed a significant correlation of the plasma disappearance rate of ICG (ICG-PDR) with all Gd-EOB-DTPA-enhanced MRI-based liver function indices with a significantly better correlation of relaxometry-based indices on ICG-PDR compared to SI-based indices. Among SI-based indices, HUI achieved best correlation on ICG-PDR and no significant difference of respective correlations on ICG-PDR could be shown. Assessment of liver volume and consecutive evaluation of multiple linear regression model revealed a stronger correlation of ICG-PDR with both (SI)-based and T1 relaxometry-based indices. Thus, liver function can be estimated quantitatively from Gd-EOB-DTPA-enhanced MRI-based indices. Here, indices derived from T1 relaxometry are superior to SI-based indices, and all indices benefit from taking into account respective liver volumes

Theory of the analysis of nonlinear systems

"March 3, 1958." Based on a thesis submitted to M.I.T. Dept. of Electrical Engineering, January 13, 1958.Bibliography: p. 58.Army Signal Corps Contract DA36-039-sc-78101. Dept. of the Army Task 3-99-06-108 and Project 3-99-00-100.Martin B. Brilliant

DC SQUID mikroaaltovahvistin

Alle Kelvinin Iämpötilaan jäähdytetyn DC SQUID vahvistimen kohina on parhaimmillaan kvanttirajoitteista: gigahertsin taajuuksilla sisääntulokohinalämpötila voi olla vain muutamia kymmeniä millikelvenejä. Vastaaviin kohinalämpötiloihin on mahdotonta päästä millään muulla tunnetulla vahvistin tyypillä. Tässä diplomityössä karakterisoitiin uusinta tekniikkaa edustava DC SQUID mikroaaltovahvistin, LTL 800. Laite on valmistettu Valtion teknillisessä tutkimuslaitoksessa (VTT). Toimintaperiaatteiden ymmärtämiseksi kehitimme analyyttisen mallin laitteesta, ja mittaustulokset onnistuttiin selittämään yksityiskohtaisella piirisimulaatiomallilla. Molempia malleja tullaan soveltamaan uusien SQUID vahvistimien suunnitteluun. LTL 800 SQUID vahvistimen vahvistukseksi mitattiin 22 dB taajuudella 630 MHz ja 150 MHz:n taajuuskaistalla. Vahvistus-kaista tulo, 24 GHz, on erinomainen muiden valmistajien tuloksiin verrattuna. Sisääntuloon ekvivalentiksi kohinalämpötilaksi saatiin 5,5 Kelviniä 4,2 Kelvinin mittauslämpötilassa. Mittaustulosten ja simulaatioiden perusteella vahvistimen kohinalämpötilaksi 50 mK:n mittauslämpötilassa voidaan arvioida 150 mK, joka on vain kertoimella kolme suurempi kuin kvanttiraja

Bose-Einstein condensation of K-41 and Rb-87 on an atom chip for sounding rocket missions

Im Rahmen dieser Arbeit wird die atomchipbasierte Experimentierkammer für den Einsatz in den Höhenforschungsraketenmissionen MAIUS-2 und 3 aufgebaut und mit einem bodengestützten System in Betrieb genommen. Die neue Apparatur ermöglicht innerhalb von 3.4 s die Erzeugung von Bose-Einstein-Kondensaten mit 3*10E5 Rb-87 Atomen oder 6*10E4 K-41 Atomen. Zusätzlich können quantenentartete Mischungen mit variablen Isotopenverhältnissen bereitgestellt werden. In Untersuchungen zur sympathetischen Kühlung von K-41 durch Rb-87 wird der Einfluss der Gravitation auf Thermalisierungsraten quantifiziert. Das Expansionsverhalten frei fallender Bose-Einstein-Kondensate wird für beide Isotope untersucht. Transiente Magnetfelder während des Ausschaltens der Magnetfalle zeigen dabei einen erheblichen Einfluss auf die Expansion und müssen in Simulationen berücksichtigt werden. Im Rahmen der Analyse kollektiver Anregungen reiner und gemischter Kondensate kann eine gegenseitige Dämpfung der Anregungen aufgrund der gegenseitigen Wechselwirkung aufgezeigt werden. Schließlich wird der Einfluss der Gravitation auf den Grundzustand und die Massenschwerpunktsbewegung der wechselwirkenden Ensembles durch Rotation der Apparatur in Flugzeitmessungen untersucht.This thesis presents the next generation atom chip apparatus for the sounding rocket missions MAIUS-2 and -3. With the new apparatus, Bose-Einstein condensates containing 3 · 10E5 atoms of Rb-87 or 6 · 10E4 atoms of K-41 are generated within 3.4 s in ground-based operation. In addition, quantum degenerate mixtures with variable isotope ratios can be provided. An analysis of sympathetic cooling of K-41 under the influence of gravity and prospects for thermalization rates in microgravity are given. The expansion dynamics of single species Bose-Einstein condensates released from a magnetic trap is analyzed in detail. It is shown that transient magnetic fields during trap switch-off have a considerable impact on the expansion dynamics. Further, collective excitations of single and mixed ensembles are evaluated. Due to interspecies damping, collective excitations of interacting mixtures of K-41 and Rb-87 are strongly suppressed. Finally, the influence of gravity on a trapped and strongly interacting mixture is observed via rotation of the whole apparatus.Deutsches Zentrum für Luft- und Raumfahrt/QUANTUS-IV-MAIUS/50WP1431/E