NEMA NU 2-2007 performance characteristics of GE Signa integrated PET/MR for different PET isotopes

BackgroundFully integrated PET/MR systems are being used frequently in clinical research and routine. National Electrical Manufacturers Association (NEMA) characterization of these systems is generally done with F-18 which is clinically the most relevant PET isotope. However, other PET isotopes, such as Ga-68 and Y-90, are gaining clinical importance as they are of specific interest for oncological applications and for follow-up of Y-90-based radionuclide therapy. These isotopes have a complex decay scheme with a variety of prompt gammas in coincidence. Ga-68 and Y-90 have higher positron energy and, because of the larger positron range, there may be interference with the magnetic field of the MR compared to F-18. Therefore, it is relevant to determine the performance of PET/MR for these clinically relevant and commercially available isotopes.MethodsNEMA NU 2-2007 performance measurements were performed for characterizing the spatial resolution, sensitivity, image quality, and the accuracy of attenuation and scatter corrections for F-18, Ga-68, and Y-90. Scatter fraction and noise equivalent count rate (NECR) tests were performed using F-18 and Ga-68. All phantom data were acquired on the GE Signa integrated PET/MR system, installed in UZ Leuven, Belgium.Results(18)F, Ga-68, and Y-90 NEMA performance tests resulted in substantially different system characteristics. In comparison with F-18, the spatial resolution is about 1mm larger in the axial direction for Ga-68 and no significative effect was found for Y-90. The impact of this lower resolution is also visible in the recovery coefficients of the smallest spheres of Ga-68 in image quality measurements, where clearly lower values are obtained. For Y-90, the low number of counts leads to a large variability in the image quality measurements. The primary factor for the sensitivity change is the scale factor related to the positron emission fraction. There is also an impact on the peak NECR, which is lower for Ga-68 than for F-18 and appears at higher activities.ConclusionsThe system performance of GE Signa integrated PET/MR was substantially different, in terms of NEMA spatial resolution, image quality, and NECR for Ga-68 and Y-90 compared to F-18. But these differences are compensated by the PET/MR scanner technologies and reconstructions methods

Catch comparison of pulse trawls vessels and a tickler chain beam trawler

Comparative fishing trials were conducted in May 2011 (week 19) on commercial beam trawlers fishing with conventional tickler chain beam trawls (on MFV GO4), pulse wings made by HFK-Engineering of Baarn, the Netherlands (MFV TX36), and pulse trawls produced by the DELMECO-Group of Goes, the Netherlands (version used on MFV TX68). The three vessels fished side-by-side as much as possible. Landings and discards of these vessels were monitored. Special emphasis was given on cod and whiting, that were dissected to study possible spinal damage. Result for TX36 and TX68 are expressed in terms of percentages of GO4. The pulse characteristics were as follows: TX36: voltage 45 V0 to peak, pulse frequency: 45 Hz, pulse duration 380 μs; electric power on single gear: 7.0 kW; TX68: voltage 50 V0 to peak, pulse frequency: 50 Hz, pulse duration 220 μs; electric power on single gear: 8.5 kW. The fuel consumption recorded over the whole week was considerably lower for the pulse trawls, i.e. on TX36 (40%) and on TX68 (54%), than for the tickler chain beam trawls used on the GO4. The net earnings (taken as gross earnings minus fuel costs) for the TX36 were almost twice as large at 186%, and for the TX68 also considerably higher at 155%. The vessels with pulse trawls caught fewer (65-69%) target species, but also less (30-50%) immature and non-target fish ('discards'), and benthic species (48-73%) than the vessel with tickler chains on these fishing grounds and in this period. The pulse gears caught fewer (19-42%) kg per hour cod than the tickler chain beam trawls, but the catches of cod on all three vessels were very small. For plaice and dab these differences were statistically proven, for brill, turbot and cod this was not the case. There was no marked difference between both pulse trawl vessels in total landings. The TX68 caught less marketable sole, but not significantly less undersized sole than the GO4. The TX36 caught less undersized sole, but here the difference in marketable fish was not significant. Catches of brill and turbot were so small that no statistically substantiated conclusion could be drawn. Only for undersized turbot the TX36 caught less. For whiting we found a demonstrable reduction in both marketable and undersized fish in both pulse fishing vessels. The TX36 caught less whiting in number per hour. The CPUEs found from the auction data and the sampled hauls correlated reasonably well for the most abundant species, such as plaice and sole. However, for less abundant species the results did not match very well, and care should be taken to increase the sampling rate in future comparative fishing studies. Spinal fracture in cod occurred under pulse stimulation but to a limited extent in both marketable and undersized fish. There is an indication that this happens slightly more on TX68 (11%) than on TX36 (7%). Whiting hardly seems to suffer any damage

Improved quantum algorithms for the ordered search problem via semidefinite programming

One of the most basic computational problems is the task of finding a desired item in an ordered list of N items. While the best classical algorithm for this problem uses log_2 N queries to the list, a quantum computer can solve the problem using a constant factor fewer queries. However, the precise value of this constant is unknown. By characterizing a class of quantum query algorithms for ordered search in terms of a semidefinite program, we find new quantum algorithms for small instances of the ordered search problem. Extending these algorithms to arbitrarily large instances using recursion, we show that there is an exact quantum ordered search algorithm using 4 log_{605} N \approx 0.433 log_2 N queries, which improves upon the previously best known exact algorithm.Comment: 8 pages, 4 figure

Analysis of Coplanar On-Chip Interconnects on Lossy Semiconducting Substrates

In this paper, a method for analysis and modeling of coplanar transmission interconnect lines that are placed on top of silicon-silicon oxide substrates is presented. The potential function is expressed by series expansions in terms of solutions of the Laplace equation for each homogeneous region of layered structure. The expansion coefficients of different series are related to each other and to potentials applied to the conductors via boundary conditions. In the plane of conductors, boundary conditions are satisfied at Nd discrete points with Nd being equal to the number of terms in the series expansions. The resulting system of inhomogeneous linear equations is solved by matrix inversion. No iterations are required. A discussion of the calculated line admittance parameters as functions of width of conductors, thickness of the layers, and frequency is given. The interconnect capacitance and conductance per unit length results are given and compared with those obtained using full wave solutions, and good agreement have been obtained in all the cases treated

Effect of spin-orbit coupling on the excitation spectrum of Andreev billiards

We consider the effect of spin-orbit coupling on the low energy excitation spectrum of an Andreev billiard (a quantum dot weakly coupled to a superconductor), using a dynamical numerical model (the spin Andreev map). Three effects of spin-orbit coupling are obtained in our simulations: In zero magnetic field: (1) the narrowing of the distribution of the excitation gap; (2) the appearance of oscillations in the average density of states. In strong magnetic field: (3) the appearance of a peak in the average density of states at zero energy. All three effects have been predicted by random-matrix theory.Comment: 5 pages, 4 figure

Calibration of the modified Bartlett-Lewis model using global optimization techniques and alternative objective functions

The calibration of stochastic point process rainfall models, such as of the Bartlett-Lewis type, suffers from the presence of multiple local minima which local search algorithms usually fail to avoid. To meet this shortcoming, four relatively new global optimization methods are presented and tested for their ability to calibrate the Modified Bartlett-Lewis Model. The list of tested methods consists of: the Downhill Simplex Method, Simplex-Simulated Annealing, Particle Swarm Optimization and Shuffled Complex Evolution. The parameters of these algorithms are first optimized to ensure optimal performance, after which they are used for calibration of the Modified Bartlett-Lewis model. Furthermore, this paper addresses the choice of weights in the objective function. Three alternative weighing methods are compared to determine whether or not simulation results (obtained after calibration with the best optimization method) are influenced by the choice of weights

Quantum Detection with Unknown States

We address the problem of distinguishing among a finite collection of quantum states, when the states are not entirely known. For completely specified states, necessary and sufficient conditions on a quantum measurement minimizing the probability of a detection error have been derived. In this work, we assume that each of the states in our collection is a mixture of a known state and an unknown state. We investigate two criteria for optimality. The first is minimization of the worst-case probability of a detection error. For the second we assume a probability distribution on the unknown states, and minimize of the expected probability of a detection error. We find that under both criteria, the optimal detectors are equivalent to the optimal detectors of an ``effective ensemble''. In the worst-case, the effective ensemble is comprised of the known states with altered prior probabilities, and in the average case it is made up of altered states with the original prior probabilities.Comment: Refereed version. Improved numerical examples and figures. A few typos fixe

Optimal Unravellings for Feedback Control in Linear Quantum Systems

For quantum systems with linear dynamics in phase space much of classical feedback control theory applies. However, there are some questions that are sensible only for the quantum case, such as: given a fixed interaction between the system and the environment what is the optimal measurement on the environment for a particular control problem? We show that for a broad class of optimal (state-based) control problems (the stationary Linear-Quadratic-Gaussian class), this question is a semi-definite program. Moreover, the answer also applies to Markovian (current-based) feedback.Comment: 5 pages. Version published by Phys. Rev. Let

Anatomic dissociation of selective and suppressive processes in visual attention

Visual spatial attention is associated with activation in parietal regions as well as with modulation of visual activity in ventral occipital cortex. Within the parietal lobe, localisation of activity has been hampered by variation in individual anatomy. Using fMRI within regions of interest derived from individual functional maps, we examined the response of superior parietal lobule, intraparietal sulcus, and ventral occipital cortex in 11 normal adults as attention was directed to the left and right visual hemifields during bilateral visual stimulation. Activation in ventral occipital cortex was augmented contralateral to the attended hemifield (p < 0.006), while intraparietal activation was augmented ipsilaterally (p < 0.009), and superior parietal lobule showed no modulation of activity as a function of attended hemifield. These findings suggest that spatial enhancement of relevant stimuli in ventral occipital cortex is complemented by an intraparietal response associated with suppression of, or preparation of a reflexive shift of attention towards, irrelevant stimuli. The spatial attention system in superior parietal cortex, in contrast, may be driven to equal degrees by currently attended stimuli and by stimuli that are potential targets of attention