1,931 research outputs found
Diagnostic performance of the specific uptake size index for semi-quantitative analysis of I-123-FP-CIT SPECT: harmonized multi-center research setting versus typical clinical single-camera setting
Introduction: The specific uptake size index (SUSI) of striatal FP-CIT uptake is independent of spatial resolution in the SPECT image, in contrast to the specific binding ratio (SBR). This suggests that the SUSI is particularly appropriate for multi-site/multi-camera settings in which camera-specific effects increase inter-subject variability of spatial resolution. However, the SUSI is sensitive to inter-subject variability of striatum size. Furthermore, it might be
more sensitive to errors of the estimate of non-displaceable FP-CIT binding. This study compared SUSI and SBR in the multi-site/multi-camera (MULTI) setting of a prospective multi-center study and in a mono-site/mono-camera (MONO) setting representative of clinical routine.
Methods: The MULTI setting included patients with Parkinson’s disease (PD, n = 438) and healthy controls (n = 207) from the Parkinson Progression Marker Initiative. The MONO setting included 122 patients from routine clinical patient care in whom FP-CIT SPECT had been performed with the same double-head SPECT system according to the same acquisition and reconstruction protocol. Patients were categorized as “neurodegenerative” (n = 84) or “non-neurodegenerative” (n = 38) based on follow-up data. FP-CIT SPECTs were stereotactically normalized to MNI space. SUSI and SBR were computed for caudate, putamen, and whole striatum using unilateral ROIs predefined in MNI space. SUSI analysis was repeated in native patient space in the MONO setting. The area (AUC) under the ROC
curve for identification of PD/“neurodegenerative” cases was used as performance measure.
Results: In both settings, the highest AUC was achieved by the putamen (minimum over both hemispheres), independent of the semi-quantitative method (SUSI or SBR). The putaminal SUSI provided slightly better performance with ROI analysis in MNI space compared to patient space (AUC = 0.969 vs. 0.961, p = 0.129). The SUSI (computed in MNI space) performed slightly better than the SBR in the MULTI setting (AUC = 0.993 vs. 0.991, p = 0.
207) and slightly worse in the MONO setting (AUC = 0.969 vs. AUC = 0.976, p = 0.259). There was a trend toward larger AUC difference between SUSI and SBR in the MULTI setting compared to the MONO setting (p = 0.073). Variability of voxel intensity in the reference region was larger in misclassified cases compared to correctly classified cases for both SUSI and SBR (MULTI setting: p = 0.007 and p = 0.012, respectively).
Conclusions: The SUSI is particularly useful in MULTI settings. SPECT images should be stereotactically normalized prior to SUSI analysis. The putaminal SUSI provides better diagnostic performance than the SUSI of the whole striatum. Errors of the estimate of non-displaceable count density in the reference region can cause misclassification by both SUSI and SBR, particularly in borderline cases. These cases might be identified by visual checking FP-CIT uptake in the reference region for particularly high variability
Исследование и разработка резонансного преобразователя давления с улучшенными метрологическими характеристиками для информационно-измерительных систем ракетно-космической техники
Numerical Study of the Features of Ti-Nb Alloy Crystallization during Selective Laser Sintering
The demand for implants with individual shape requires the development of new methods and approaches to their production. The obvious advantages of additive technologies and selective laser sintering are the capabilities to form both the external shape of the product and its internal structure. Recently appeared and attractive from the perspective of biomechanical compatibility are beta alloys of titanium-niobium that have similar mechanical properties to those of cortical bone. This paper studies the processes occurring at different stages of laser sintering using computer simulation on atomic scale. The effect of cooling rate on the resulting crystal structure of Ti-Nb alloy was analysed. Also, the dependence of tensile strength of sintered particles on heating time and cooling rate was studied. It was shown that the main parameter, which determines the adhesive properties of sintered particles, is the contact area obtained during sintering process. The simulation results can both help defining the technological parameters of the process to provide the desired mechanical properties of the resulting products and serve as a necessary basis for calculations on large scale levels in order to study the behaviour of actually used implants
Evaluation of the cerebrovascular reactivity in patients with Moyamoya Angiopathy by use of breath-hold fMRI: investigation of voxel-wise hemodynamic delay correction in comparison to [O]water PET
PURPOSE: Patients with Moyamoya Angiopathy (MMA) require hemodynamic assessment to evaluate the risk of stroke. Hemodynamic evaluation by use of breath-hold-triggered fMRI (bh-fMRI) was proposed as a readily available alternative to the diagnostic standard [O]water PET. Recent studies suggest voxel-wise hemodynamic delay correction in hypercapnia-triggered fMRI. The aim of this study was to evaluate the effect of delay correction of bh-fMRI in patients with MMA and to compare the results with [O]water PET.
METHODS: bh-fMRI data sets of 22 patients with MMA were evaluated without and with voxel-wise delay correction within different shift ranges and compared to the corresponding [O]water PET data sets. The effects were evaluated combined and in subgroups of data sets with most severely impaired CVR (apparent steal phenomenon), data sets with territorial time delay, and data sets with neither steal phenomenon nor delay between vascular territories.
RESULTS: The study revealed a high mean cross-correlation (r = 0.79, p < 0.001) between bh-fMRI and [O]water PET. The correlation was strongly dependent on the choice of the shift range. Overall, no shift range revealed a significantly improved correlation between bh-fMRI and [O]water PET compared to the correlation without delay correction. Delay correction within shift ranges with positive high high cutoff revealed a lower agreement between bh-fMRI and PET overall and in all subgroups.
CONCLUSION: Voxel-wise delay correction, in particular with shift ranges with high cutoff, should be used critically as it can lead to false-negative results in regions with impaired CVR and a lower correlation to the diagnostic standard [O]water PET
Motivations and Needs of Older People for Work and Active Lifestyle
The article presents the results of a poll of older people on the example of a particular region (The Tomsk Region) to identify the need for an active lifestyle and penchant for productive work. The system ofhypotheses under article issues is tested. The aim of the work is to analyze problems of older people which affect their labor activity.The empirical base for the study was the results of the survey (sample frame 400 pers.). The respondents were older people living in urban and rural areas of the Tomsk Region. To test the generated hypothesesstatistical methods (analysis of variance, correlation analysis, etc.) are used. There are three main problems the elderly related to their needs and inclinations to work. It was determined that the formationof a stable demand of older people in productive work and active lifestyle will help to solve a number of problems of socio-psychological and economic nature at the present stage of social development inRussia and abroad
The quiescent light curve and evolutionary state of GRO J1655-40
We present ellipsoidal light-curve fits to the quiescent B, V, R and I light
curves of GRO J1655-40 (Nova Scorpii 1994). The fits are based on a simple
model consisting of a Roche-lobe filling secondary and an accretion disc around
the black-hole primary. Unlike previous studies, no assumptions are made about
the interstellar extinction or the distance to the source; instead these are
determined self-consistently from the observed light curves. In order to obtain
tighter limits on the model parameters, we used the distance determination from
the kinematics of the radio jet as an additional constraint. We obtain a value
for the extinction that is lower than was assumed previously; this leads to
lower masses for both the black hole and the secondary star of 5.4 +/- 0.3 Msun
and 1.45 +/- 0.35 Msun, respectively. The errors in the determination of the
model parameters are dominated by systematic errors, in particular due to
uncertainties in the modeling of the disk structure and uncertainties in the
atmosphere model for the chemically anomalous secondary in the system. A lower
mass of the secondary naturally explains the transient nature of the system if
it is either in a late case A or early case B mass-transfer phase.Comment: 12 pages, 4 figures, submitted to MNRA
Evaluation of intensity modulated radiation therapy dose painting for localized prostate cancer using 68 Ga-HBED-CC PSMA-PET/CT: A planning study based on histopathology reference
AbstractPurposeTo demonstrate the feasibility and to evaluate the tumour control probability (TCP) and normal tissue complication probability (NTCP) of IMRT dose painting using 68Ga-HBED-CC PSMA PET/CT for target delineation in prostate cancer (PCa).Methods and materials10 patients had PSMA PET/CT scans prior to prostatectomy. GTV-PET was generated on the basis of an intraprostatic SUVmax of 30%. Two IMRT plans were generated for each patient: Plan77 which consisted of whole-prostate IMRT to 77Gy, and Plan95 which consisted of whole-prostate IMRT to 77Gy and a simultaneous integrated boost to the GTV-PET up to 95Gy (35 fractions). The feasibility of these plans was judged by their ability to adhere to the FLAME trial protocol. TCP-histo/-PET were calculated on co-registered histology (GTV-histo) and GTV-PET, respectively. NTCPs for rectum and bladder were calculated.ResultsAll plans reached prescription doses whilst adhering to dose constraints. In Plan77 and Plan95 mean doses in GTV-histo were 75.8±0.3Gy and 96.9±1Gy, respectively. Average TCP-histo values for Plan77 and Plan95 were 70% (range: 15–97%), and 96% (range: 78–100%, p77 and Plan95 were 55% (range: 27–82%), and 100% (range: 99–100%, p95 (p=0.25). There were no significant differences in rectal (p=0.563) and bladder (p=0.3) NTCPs.ConclusionsIMRT dose painting using PSMA PET/CT was technically feasible and resulted in significantly higher TCPs without higher NTCPs
The structure of the nuclear stellar cluster of the Milky Way
We present high-resolution seeing limited and AO NIR imaging observations of
the stellar cluster within about one parsec of Sgr A*, the massive black hole
at the centre of the Milky Way. Stellar number counts and the diffuse
background light density were extracted from these observations in order to
examine the structure of the nuclear stellar cluster.Our findings are as
follows: (a) A broken-power law provides an excellent fit to the overall
structure of the GC nuclear cluster. The power-law slope of the cusp is
, the break radius is or
pc, and the cluster density decreases with a power-law index of
outside of . (b) Using the best velocity
dispersion measurements from the literature, we derive higher mass estimates
for the central parsec than assumed until now. The inferred density of the
cluster at the break radius is . This high density agrees well with the small extent and flat slope
of the cusp. Possibly, the mass of the stars makes up only about 50% of the
total cluster mass. (c) Possible indications of mass segregation in the cusp
are found (d) The cluster appears not entirely homogeneous. Several density
clumps are detected that are concentrated at projected distances of and
from Sgr A*.(e) There appears to exist an under-density of horizontal
branch/red clump stars near , or an over-density of stars of similar
brightness at and . (f) The extinction map in combination with
cometary-like features in an L'-band image may provide support for the
assumption of an outflow from Sgr A*.Comment: accepted for publication by A&A; please contact first author for
higher quality figure
Hopping Transport in the Presence of Site Energy Disorder: Temperature and Concentration Scaling of Conductivity Spectra
Recent measurements on ion conducting glasses have revealed that conductivity
spectra for various temperatures and ionic concentrations can be superimposed
onto a common master curve by an appropriate rescaling of the conductivity and
frequency. In order to understand the origin of the observed scaling behavior,
we investigate by Monte Carlo simulations the diffusion of particles in a
lattice with site energy disorder for a wide range of both temperatures and
concentrations. While the model can account for the changes in ionic activation
energies upon changing the concentration, it in general yields conductivity
spectra that exhibit no scaling behavior. However, for typical concentrations
and sufficiently low temperatures, a fairly good data collapse is obtained
analogous to that found in experiment.Comment: 6 pages, 4 figure
Semantic Labelling and Learning for Parity Game Solving in LTL Synthesis
We propose "semantic labelling" as a novel ingredient for solving games in
the context of LTL synthesis. It exploits recent advances in the automata-based
approach, yielding more information for each state of the generated parity game
than the game graph can capture. We utilize this extra information to improve
standard approaches as follows. (i) Compared to strategy improvement (SI) with
random initial strategy, a more informed initialization often yields a winning
strategy directly without any computation. (ii) This initialization makes SI
also yield smaller solutions. (iii) While Q-learning on the game graph turns
out not too efficient, Q-learning with the semantic information becomes
competitive to SI. Since already the simplest heuristics achieve significant
improvements the experimental results demonstrate the utility of semantic
labelling. This extra information opens the door to more advanced learning
approaches both for initialization and improvement of strategies
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