Exposure Stability of Quantitative Fluorine-18 Measurements On The Biograph Vision Quadra PET/CT System

Background: Our aim was to determine sets of reconstruction parameters for the Biograph Vision Quadra (Siemens Healthineers) PET/CT system that result in quantitative images compliant with the European Association of Nuclear Medicine Research Ltd. (EARL) criteria. Using the Biograph Vision 600 (Siemens Healthineers) PET/CT technology but extending the axial field of view to 106 cm, gives the Vision Quadra currently an around fivefold higher sensitivity over the Vision 600 with otherwise comparable spatial resolution. Therefore, we also investigated how the number of incident positron decays - i.e. exposure - affects EARL compliance. This will allow estimating a minimal acquisition time or a minimal applied dose in clinical scans while retaining data comparability. Methods: We measured activity recovery curves on a NEMA IEC body phantom filled with an aqueous 18 F solution and a sphere to background ratio of 10 to 1 according to the latest EARL guidelines. Reconstructing 3570 images with varying OSEM PSF iterations, post-reconstruction Gaussian filter full width at half maximum (FWHM), and varying exposure from 0.2 MDecays/ml (= 10 sec frame duration) to 59.2 MDecays/ml (= 1 h frame duration), allowed us to determine sets of parameters to achieve compliance with the current EARL 1 and EARL 2 standards. Recovery coefficients (RCs) were calculated for the metrics RC max , RC mean , and RC peak , and the respective recovery curves were analysed for monotonicity. Results: Using 6 iterations, 5 subsets and 7.8 mm Gauss filtering resulted in best EARL 1 compliance and recovery curve monotonicity in all analysed frames. Most robust EARL2 compliance and monotonicity was achieved with 4 iterations, 5 subsets, and 4.6 mm Gauss FWHM in frames with durations between 10 min and 30 sec. RC peak only impeded EARL2 compliance in the 10 sec frame. Conclusions: While EARL1 compliance proved to be robust over all exposure ranges, EARL2 compliance required exposures between 0.6 MDecays/ml to 11.5 MDecays/ml. The Biograph Vision Quadra’s high sensitivity makes frames as short as 10 sec feasible for comparable quantitative images. Lowering EARL2 RC max limits closer to unity would possibly even permit 10 sec EARL2 compliant frames.

Random Beamforming in Mobile mmWave Systems: Performance Evaluation and Parameters Optimization

Random Beamforming (RBF) is considered one of the most promising beamforming techniques especially for Massive MIMO mmWave systems. It has been proven to achieve optimal sumrate capacity for downlink MIMO systems for many applications. In this paper, the RBF is implemented in a mmWave MIMO systems with mobile users and the effect of this mobility is studied. Beside that, some parameters of the system have been optimized for different realistic scenarios. The mathematical derivation of the system model and the simulation using some practical values have been conducted. The resulted degradation in system throughput as a consequence of beamforming outage that results from users mobility is calculated. Many factors that affect the system throughput were considered in the derivation. The second part of the paper is going a further step in optimizing the network parameters for different operation scenarios. These parameters include the frame duration and beam width. Taking in consideration that the outage probability is a Convex optimization problem, the optimal values of these parameters were derived. for the walking and running users cases.

Radiation forces constrain the FRB mechanism

ABSTRACT We provide constraints on fast radio burst (FRB) models by careful considerations of radiation forces associated with these powerful transients. We find that the induced Compton scatterings of the coherent radiation by electrons/positrons accelerate particles to very large Lorentz factors (LFs) in and around the source of this radiation. This severely restricts those models for FRBs that invoke relativistic shocks and maser-type instabilities at distances less than about 1013 cm of the neutron star. Radiation travelling upstream, in these models, forces particles to move away from the shock with an LF larger than the LF of the shock front. This suspends the photon generation process after it has been operating for less than ∼0.1 ms (observer frame duration). We show that masers operating in shocks at distances larger than 1013 cm cannot simultaneously account for the burst duration of 1 ms or more and the observed ∼GHz frequencies of FRBs without requiring an excessive energy budget (>1046 erg); the energy is not calculated by imposing any efficiency consideration, or other details, for the maser mechanism, but is entirely the result of ensuring that particle acceleration by induced Compton forces upstream of the shock front does not choke off the maser process. For the source to operate more or less continuously for a few ms, it should be embedded in a strong magnetic field – cyclotron frequency ≫ wave frequency – so that radiation forces do not disperse the plasma and shut off the engine.

Impact of Frame Duration and Modulation Coding Schemes With WiMAX Bandwidth Asymmetry in Transmission Control Protocol Variants

WiMAX stands for Worldwide Interoperability for Microwave Access which is based on IEEE 802.16 specification and is considered as de facto standard for the broadband wireless data transfer over the internet. The different values of various WiMAX parameters for different TCP variants may affect the performance of the network. This article compares the performance of different TCP variants with bandwidth asymmetry, frame duration, and modulation coding schemes, along with the operating parameter namely number of wireless nodes. During the simulation study the performance was evaluated only for one-way data transfer. The finding suggests that the TCP New Reno performed better than other variants included in the simulation study for the comparison. The performance was measured on the basis of throughput, goodput and packets dropped.

Activation Process of ONU in EPON/GPON/XG-PON/NG-PON2 Networks

This article presents a numerical implementation of the activation process for gigabit and 10 gigabit next generation and Ethernet passive optical networks. The specifications are completely different because GPON, XG-PON and NG-PON2 were developed by the International Telecommunication Union, whereas Ethernet PON was developed by the Institute of Electrical and Electronics Engineers. The speed of an activation process is the most important in a blackout scenario because end optical units have a timer after expiration transmission parameters are discarded. Proper implementation of an activation process is crucial for eliminating inadvisable delay. An OLT chassis is dedicated to several GPON (or other standard) cards. Each card has up to eight or 16 GPON ports. Furthermore, one GPON port can operate with up to 64/128 ONUs. Our results indicate a shorter duration activation process (due to a shorter frame duration) in Ethernet-based PON, but the maximum split ratio is only 1:32 instead of up to 1:64/128 for gigabit PON and newer standards. An optimization improves the reduction time for the GPON activation process with current PLOAM messages and with no changes in the transmission convergence layer. We reduced the activation time from 215 ms to 145 ms for 64 ONUs.

Interference Aware Optimisation of Throughput in Cognitive Radio System

<p>In the cognitive radio (CR) system where spectrum sensing and data transmissions are performed simultaneously, the proper selection of frame duration (τ) is of utmost importance. Small τ leads to an increased false alarm probability while large value of it delays implementation of sensing decision of the current frame to the next. The former case decreases the achievable throughput of the CR user while latter one may disturb the licensed user communication. Under the constraints of maintaining a target detection probability of dP, this paper attempts to design a frame duration τ where achieved throughput of the CR system is maximised. To do so, an analysis of achievable throughput with τ was performed which reveals that, initially, with the increase in τ, the achievable throughput increases sharply, but after its certain value, the increments are negligible and achievable throughput appears to maintain a constant value. The performed analysis shows that, it is not possible to perfectly optimize τ, however, a close optimisation can still be performed which can maximise the achievable throughput. From the realistic point of view, the CR system is further modelled under uncertain noise conditions. The achieved simulation results well justify the presented analysis.</p><p><strong>Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 312-318, DOI: http://dx.doi.org/10.14429/dsj.65.8739</strong></p>