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https://www.readbyqxmd.com/read/28542010/thermal-modeling-for-the-next-generation-of-radiofrequency-exposure-limits-commentary
#1
Kenneth R Foster, Marvin C Ziskin, Quirino Balzano
This commentary evaluates two sets of guidelines for human exposure to radiofrequency (RF) energy, focusing on the frequency range above the "transition" frequency at 3-10 GHz where the guidelines change their basic restrictions from specific absorption rate to incident power density, through the end of the RF band at 300 GHz. The analysis is based on a simple thermal model based on Pennes' bioheat equation (BHTE) (Pennes 1948) assuming purely surface heating; an Appendix provides more details about the model and its range of applicability...
July 2017: Health Physics
https://www.readbyqxmd.com/read/28497464/in-vivo-proton-observed-carbon-edited-poce-13-c-magnetic-resonance-spectroscopy-of-the-rat-brain-using-a-volumetric-transmitter-and-receive-only-surface-coil-on-the-proton-channel
#2
Chathura Kumaragamage, Dan Madularu, Axel P Mathieu, Henk De Feyter, M Natasha Rajah, Jamie Near
PURPOSE: In vivo carbon-13 ((13) C) MR spectroscopy (MRS) is capable of measuring energy metabolism and neuroenergetics, noninvasively in the brain. Indirect ((1) H-[(13) C]) MRS provides sensitivity benefits compared with direct (13) C methods, and normally includes a (1) H surface coil for both localization and signal reception. The aim was to develop a coil platform with homogenous B1+ and use short conventional pulses for short echo time proton observed carbon edited (POCE) MRS. METHODS: A (1) H-[(13) C] MRS coil platform was designed with a volumetric resonator for (1) H transmit, and surface coils for (1) H reception and (13) C transmission...
May 12, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28466805/aortic-stiffness-evaluated-by-echocardiography-in-female-patients-with-takayasu-s-arteritis
#3
Yong Yang, Zhen Wang, Li-Jun Yuan, Tie-Sheng Cao, Jie Liu, Rong Ren, Yun-You Duan
OBJECTIVES: The aim of this study was to evaluate the aortic stiffness (AS) in young female patients with Takayasu's arteritis (TAK) and comparable controls by measuring carotid-femoral PWV (PWVcf) using echocardiography with pulse wave Doppler. The clinical feasibility and reproducibility of this echocardiographic method were also investigated. METHODS: Twenty-five TAK female patients (mean age 28.3±6.2 years) and 25 strictly matched healthy controls were included according to rigorous inclusion and exclusion criteria...
March 2017: Clinical and Experimental Rheumatology
https://www.readbyqxmd.com/read/28464641/extent-of-lateralization-at-large-interaural-time-differences-in-simulated-electric-hearing-and-bilateral-cochlear-implant-users
#4
Regina M Baumgärtel, Hongmei Hu, Birger Kollmeier, Mathias Dietz
Normal-hearing (NH) listeners are able to localize sound sources with extraordinary accuracy through interaural cues, most importantly interaural time differences (ITDs) in the temporal fine structure. Bilateral cochlear implant (CI) users are also able to localize sound sources, yet generally at lower accuracy than NH listeners. The gap in performance can in part be attributed to current CI systems not faithfully transmitting interaural cues, especially ITDs. With the introduction of binaurally linked CI systems, the presentation of ITD cues for bilateral CI users is foreseeable...
April 2017: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/28456246/energy-compression-of-nanosecond-high-voltage-pulses-based-on-two-stage-hybrid-scheme
#5
M R Ulmaskulov, G A Mesyats, A G Sadykova, K A Sharypov, V G Shpak, S A Shunailov, M I Yalandin
Test results of high-voltage subnanosecond pulse generator with a hybrid, two-stage energy compression scheme are presented. After the first compression section with a gas discharger, a ferrite-filled gyromagnetic nonlinear transmitting line is used. The offered technical solution makes it possible to increase the voltage pulse amplitude from -185 kV to -325 kV, with a 2-ns pulse rise time minimized down to ∼180 ps. For the small output voltage amplitude of -240 kV, the shortest pulse front of ∼85 ps was obtained...
April 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28456239/high-speed-microstrip-multi-anode-multichannel-plate-detector-system
#6
Andreas Riedo, Marek Tulej, Urs Rohner, Peter Wurz
High-speed detector systems with high dynamic range and pulse width characteristics in the sub-nanosecond regime are mandatory for high resolution and highly sensitive time-of-flight mass spectrometers. Typically, for a reasonable detector area, an impedance-matched anode design is necessary to transmit the registered signal fast and distortion-free from the anode to the signal acquisition system. In this report, a high-speed microstrip multi-anode multichannel plate detector is presented and discussed. The anode consists of four separate active concentric anode segments allowing a simultaneous readout of signal with a dynamic range of about eight orders of magnitude...
April 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28454043/vacuum-scanning-capillary-photoemission-microscopy
#7
S A Aseyev, A P Cherkun, B N Mironov, V V Petrunin, S V Chekalin
We demonstrate the use of a conical capillary in a scanning probe microscopy for surface analysis. The probe can measure photoemission from a substrate by transmitting photoelectrons along the capillary as a function of probe position. The technique is demonstrated on a model substrate consisting of a gold reflecting layer on a compact disc which has been illuminated by an unfocused laser beam with a wavelength 400nm, from a femtosecond laser with a beam size of 4mm. A quartz capillary with a 2-µm aperture has been used in the experiments...
April 19, 2017: Ultramicroscopy
https://www.readbyqxmd.com/read/28444504/correction-of-parallel-transmission-using-concurrent-rf-and-gradient-field-monitoring
#8
Mustafa Çavuşoğlu, Benjamin Emanuel Dietrich, David Otto Brunner, Markus Weiger, Klaas Paul Pruessmann
OBJECTIVES: The accuracy and precision of the parallel RF excitations are highly dependent on the spatial and temporal fidelity of the magnetic fields involved in spin excitation. The consistency between the nominal and effective fields is typically limited by the imperfections of the employed hardware existing both in the gradient system and the RF chain. In this work, we experimentally presented highly improved spatially tailored parallel excitations by turning the native hardware accuracy challenge into a measurement and control problem using an advanced field camera technology to fully correct parallel RF transmission experiment...
April 25, 2017: Magma
https://www.readbyqxmd.com/read/28438666/how-to-choose-the-right-mr-sequence-for-your-research-question-at-7-t-and-above
#9
José P Marques, David G Norris
The choice of a pulse sequence at ultra-high field can be influenced by a number of considerations and constraints that are not always the same as those at lower fields. Foremost amongst these is of course the information required and the time available, but considerations of static main field- and transmit field- inhomogeneities as well as power deposition can also play an important role. In this review we first briefly examine the characteristics of high field MRI, and then describe the performance and constraints relevant to the major imaging readouts, and their implementation with parallel imaging techniques...
April 21, 2017: NeuroImage
https://www.readbyqxmd.com/read/28420761/in-situ-measurements-of-tensile-forces-in-the-tibialis-anterior-tendon-of-the-rat-in-concentric-isometric-and-resisted-co-contractions
#10
Martin Schmoll, Ewald Unger, Hazel Sutherland, Michael Haller, Manfred Bijak, Hermann Lanmüller, Jonathan C Jarvis
Tensile-force transmitted by the tibialis anterior (TA) tendon of 11 anesthetized adult male Wistar rats (body-mass: 360.6 ± 66.3 g) was measured in-situ within the intact biomechanical system of the hind-limb using a novel miniature in-line load-cell. The aim was to demonstrate the dependence of the loading-profile experienced by the muscle, on stimulation-frequency and the resistance to shortening in a group of control-animals. Data from these acute-experiments shows the type of loading achievable by means of implantable electrical stimulators activating agonists or agonist/antagonist groups of muscles during programmed resistance-training in freely moving healthy subjects...
April 2017: Physiological Reports
https://www.readbyqxmd.com/read/28418076/ultrasonic-modulation-of-tissue-optical-properties-in-ex-vivo-porcine-skin-to-improve-transmitted-transdermal-laser-intensity
#11
Paul J D Whiteside, Chenxi Qian, Nicholas Golda, Heather K Hunt
BACKGROUND AND OBJECTIVE: Applications of light-based energy devices involving optical targets within the dermis frequently experience negative side-effects resultant from surface scattering and excess optical absorption by epidermal melanin. As a broadband optical absorber, melanin decreases the efficacy of light-based treatments throughout the ultraviolet, visible, and near-infrared spectra while also generating additional heat within the surface tissue that can lead to inflammation or tissue damage...
April 18, 2017: Lasers in Surgery and Medicine
https://www.readbyqxmd.com/read/28394085/dual-echo-epi-sequence-for-integrated-distortion-correction-in-3d-time-resolved-hyperpolarized-13-c-mri
#12
Benjamin J Geraghty, Justin Y C Lau, Albert P Chen, Charles H Cunningham
PURPOSE: To provide built-in off-resonance correction in time-resolved, volumetric hyperpolarized (13) C metabolic imaging by implementing a novel dual-echo 3D echo-planar imaging (EPI) sequence and reconstruction. METHODS: A spectral-spatial pulse for single-resonance excitation followed by a dual-echo 3D EPI readout was implemented to provide 64 × 8 × 6 cm(3) coverage at 5 × 5 × 5 mm(3) nominal resolution. Multiple sources of EPI distortions were encoded using a multi-echo (1) H EPI reference scan...
April 10, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28381021/handheld-free-space-quantum-key-distribution-with-dynamic-motion-compensation
#13
Hyunchae Chun, Iris Choi, Grahame Faulkner, Larry Clarke, Bryan Barber, Glenn George, Colin Capon, Antti Niskanen, Joachim Wabnig, Dominic O'Brien, David Bitauld
Mobile devices have become an inseparable part of our everyday life. They are used to transmit an ever-increasing amount of sensitive health, financial and personal information. This exposes us to the growing scale and sophistication of cyber-attacks. Quantum Key Distribution (QKD) can provide unconditional and future-proof data security but implementing it for handheld mobile devices comes with specific challenges. To establish security, secret keys of sufficient length need to be transmitted during the time of a handheld transaction (~1s) despite device misalignment, ambient light and user's inevitable hand movements...
March 20, 2017: Optics Express
https://www.readbyqxmd.com/read/28372047/detection-of-forward-scattering-from-an-intruder-in-a-dynamic-littoral-environment
#14
Bo Lei, Yixin Yang, Kunde Yang, Yuanliang Ma
Forward scattering always occurs when an intruder moves into an underwater area between a source and a receiver. The detection of this forward-scattered signal is a challenge because a strong direct blast overwhelms the forward-scattered signal. Accordingly, an adaptive scheme for detecting the forward scattering introduced by an intruder in dynamic shallow water is proposed in this study. A short pulse was transmitted repeatedly in the water. The recorded direct blast and forward-scattered signal were assumed to be weakly correlated...
March 2017: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/28370494/tailored-spiral-in-out-spectral-spatial-water-suppression-pulses-for-magnetic-resonance-spectroscopic-imaging
#15
Jun Ma, Carrie Wismans, Zhipeng Cao, Dennis W J Klomp, Jannie P Wijnen, William A Grissom
PURPOSE: To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( B1+) inhomogeneity. METHODS: Patient-tailored spiral in-out spectral-spatial saturation pulses were designed for a three-pulse WET water suppression sequence. The pulses' identical spatial subpulses were designed using patient-specific B1+ maps and a spiral in-out excitation k-space trajectory. The subpulse train was weighted by a spectral envelope that was root-flipped to minimize peak RF demand...
March 31, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/28368803/a-delayed-excitation-data-acquisition-method-for-high-frequency-ultrasound-imaging
#16
Weibao Qiu, Jingjing Xia, Yulong Shi, Peitian Mu, Xingying Wang, Mengdi Gao, Congzhi Wang, Yang Xiao, Ge Yang, Jihong Liu, Lei Sun, Hairong Zheng
High-frequency ultrasound imaging (at >20 MHz) has gained widespread attention due to its high spatial resolution being useful for basic cardiovascular and cancer research involving small animals. The sampling rate of the analog-to-digital converter in a high-frequency ultrasound system usually needs to be higher than 120 MHz in order to satisfy the Nyquist sampling-rate requirement. However, the sampling rate is typically within the range of 40-60 MHz in a traditional ultrasound system, and so we propose a delayed-excitation method for performing high-frequency ultrasound imaging with a traditional data acquisition scheme...
March 28, 2017: IEEE Transactions on Bio-medical Engineering
https://www.readbyqxmd.com/read/28336426/sar-simulations-safety
#17
Thomas M Fiedler, Mark E Ladd, Andreas K Bitz
At ultra-high fields, the assessment of radiofrequency (RF) safety presents several new challenges compared to low-field systems. Multi-channel RF transmit coils in combination with parallel transmit techniques produce time-dependent and spatially varying power loss densities in the tissue. Further, in ultra-high-field systems, localized field effects can be more pronounced due to a transition from the quasistationary to the electromagnetic field regime. Consequently, local information on the RF field is required for reliable RF safety assessment as well as for monitoring of RF exposure during MR examinations...
March 20, 2017: NeuroImage
https://www.readbyqxmd.com/read/28269349/an-inductive-narrow-pulse-rfid-telemetry-system-for-gastric-slow-waves-monitoring
#18
Amir Javan-Khoskholgh, Zaid Abukhalaf, Ji Li, Larry S Miller, Mehdi Kiani, Aydin Farajidavar
We present a passive data telemetry system for real-time monitoring of gastric electrical activity of a living subject. The system is composed of three subsystems: an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU). Data communication between the IU and WU is based on a radio-frequency identification (RFID) link operating at 13.56 MHz. Since wireless power transmission and reverse data telemetry system share the same inductive interface, a load shift keying (LSK)-based differential pulse position (DPP) coding data communication with only 6...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/28241577/gouy-phase-shift-for-annular-beam-profiles-in-attosecond-experiments
#19
F Schlaepfer, A Ludwig, M Lucchini, L Kasmi, M Volkov, L Gallmann, U Keller
Attosecond pump-probe measurements are typically performed by combining attosecond pulses with more intense femtosecond, phase-locked infrared (IR) pulses because of the low average photon flux of attosecond light sources based on high-harmonic generation (HHG). Furthermore, the strong absorption of materials at the extreme ultraviolet (XUV) wavelengths of the attosecond pulses typically prevents the use of transmissive optics. As a result, pump and probe beams are typically recombined geometrically with a center-hole mirror that reflects the larger IR beam and transmits the smaller XUV, which leads to an annular beam profile of the IR...
February 20, 2017: Optics Express
https://www.readbyqxmd.com/read/28227591/an-inductive-narrow-pulse-rfid-telemetry-system-for-gastric-slow-waves-monitoring
#20
Amir Javan-Khoskholgh, Zaid Abukhalaf, Ji Li, Larry S Miller, Mehdi Kiani, Aydin Farajidavar, Amir Javan-Khoskholgh, Zaid Abukhalaf, Ji Li, Larry S Miller, Mehdi Kiani, Aydin Farajidavar, Larry S Miller, Amir Javan-Khoskholgh, Ji Li, Mehdi Kiani, Zaid Abukhalaf
We present a passive data telemetry system for real-time monitoring of gastric electrical activity of a living subject. The system is composed of three subsystems: an implantable unit (IU), a wearable unit (WU), and a stationary unit (SU). Data communication between the IU and WU is based on a radio-frequency identification (RFID) link operating at 13.56 MHz. Since wireless power transmission and reverse data telemetry system share the same inductive interface, a load shift keying (LSK)-based differential pulse position (DPP) coding data communication with only 6...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
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