The performance of a light sharing and recirculation mechanism that allows the extraction of depth of interaction (DOI) are investigated in this paper, with a particular focus on timing. In parallel, ...a method to optimize the coincidence time resolution (CTR) of PET detectors by use of the DOI information is proposed and tested. For these purposes, a dedicated 64-channels readout setup has been developed with intrinsic timing resolution of 16 ps FWHM. Several PET modules have been produced, based on LYSO:Ce scintillators and commercial silicon photomultiplier (SiPM) arrays, with mm2 individual SiPM size. The results show the possibility to achieve a timing resolution of 157 ps FWHM, combined with the already demonstrated spatial resolution of 1.5 mm FWHM, DOI resolution of 3 mm FWHM, and energy resolution of 9% FWHM at 511 keV, with 15 mm long crystals of section mm2 and mm2. At the same time, the extraction of the DOI coordinate has been demonstrated not to deteriorate the timing performance of the PET module.
A new method for obtaining depth of interaction (DOI) information in PET detectors is presented in this study, based on sharing and redirection of scintillation light among multiple detectors, ...together with attenuation of light over the length of the crystals. The aim is to obtain continuous DOI encoding with single side readout, and at the same time without the need for one-to-one coupling between scintillators and detectors, allowing the development of a PET scanner with good spatial, energy and timing resolutions while keeping the complexity of the system low. A prototype module has been produced and characterized to test the proposed method, coupling a LYSO scintillator matrix to a commercial SiPMs array. Excellent crystal separation is obtained for all the scintillators in the array, light loss due to depolishing is found to be negligible, energy resolution is shown to be on average 12.7% FWHM. The mean DOI resolution achieved is 4.1 mm FWHM on a 15 mm long crystal and preliminary coincidence time resolution was estimated in 353 ps FWHM.
Gas hydrates are a major component in the organic carbon cycle. Their stability is controlled by temperature, pressure, water chemistry, and gas composition. The bottom‐simulating reflector (BSR) is ...the primary seismic indicator of the base of hydrate stability in continental margins. Here we use seismic, well log, and core data from the convergent margin offshore NW Borneo to demonstrate that the BSR does not always represent the base of hydrate stability and can instead approximate the boundary between structure I hydrates above and structure II hydrates below. At this location, gas hydrate saturation below the BSR is higher than above and a process of chemical fractionation of the migrating free gas is responsible for the structure I‐II transition. This research shows that in geological settings dominated by thermogenic gas migration, the hydrate stability zone may extend much deeper than suggested by the BSR.
Key Points
Structure II gas hydrates form below a bottom‐simulating reflector due to thermogenic gas migration and coexist with free gas
A chemical fractionation process provokes a transition at the bottom‐simulating reflector from structure II to structure I hydrates
Gas hydrate systems sourced by thermogenic fluids can be characterized by more hydrates below than above bottom‐simulating reflectors
RATIONALE:At the onset of ST-elevation acute myocardial infarction (STEMI), patients can present with very high circulating interleukin-6 (IL-6) levels or very low-IL-6 levels.
OBJECTIVE:We compared ...these 2 groups of patients to understand whether it is possible to define specific STEMI phenotypes associated with outcome based on the cytokine response.
METHODS AND RESULTS:We compared 109 patients with STEMI in the top IL-6 level (median, 15.6 pg/mL; IL-6 STEMI) with 96 in the bottom IL-6 level (median, 1.7 pg/mL; IL-6 STEMI) and 103 matched controls extracted from the multiethnic First Acute Myocardial Infarction study. We found minimal clinical differences between IL-6 STEMI and IL-6 STEMI. We assessed the inflammatory profiles of the 2 STEMI groups and the controls by measuring 18 cytokines in blood samples. We exploited clustering analysis algorithms to infer the functional modules of interacting cytokines. IL-6 STEMI patients were characterized by the activation of 2 modules of interacting signals comprising IL-10, IL-8, macrophage inflammatory protein-1α, and C-reactive protein, and monocyte chemoattractant protein-1, macrophage inflammatory protein-1β, and monokine induced by interferon-γ. IL-10 was increased both in IL-6 STEMI and IL-6 STEMI patients compared with controls. IL-6IL-10 STEMI patients had an increased risk of systolic dysfunction at discharge and an increased risk of death at 6 months in comparison with IL-6IL-10 STEMI patients. We combined IL-10 and monokine induced by interferon-γ (derived from the 2 identified cytokine modules) with IL-6 in a formula yielding a risk index that outperformed any single cytokine in the prediction of systolic dysfunction and death.
CONCLUSIONS:We have identified a characteristic circulating inflammatory cytokine pattern in STEMI patients, which is not related to the extent of myocardial damage. The simultaneous elevation of IL-6 and IL-10 levels distinguishes STEMI patients with worse clinical outcomes from other STEMI patients. These observations could have potential implications for risk-oriented patient stratification and immune-modulating therapies.
Metasurfaces and, in particular, metalenses have attracted large interest and enabled various applications in the near-infrared and THz regions of the spectrum. However, the metalens design in the ...visible range stays quite challenging due to the smaller nanostructuring scale and the limited choice of lossless CMOS-compatible materials. We develop a simple yet efficient design of a polarization-independent, broadband metalens suitable for many CMOS-compatible fabrication techniques and materials and implement it for the visible spectral range using niobium pentoxide (Nb2O5). The produced metalens demonstrates high transmittance and focusing ability as well as a large depth of focus, which makes it a promising solution for a new generation of silicon photomultiplier photodetectors with reduced fill factor impact on the performance and reduced electron–hole generation regions, which altogether potentially leads to improved photodetection efficiency and other characteristics.
We propose a new statistical method, called generalized mixed‐effects random forest (GMERF), that extends the use of random forest to the analysis of hierarchical data, for any type of response ...variable in the exponential family. The method maintains the flexibility and the ability of modeling complex patterns within the data, typical of tree‐based ensemble methods, and it can handle both continuous and discrete covariates. At the same time, GMERF takes into account the nested structure of hierarchical data, modeling the dependence structure that exists at the highest level of the hierarchy and allowing statistical inference on this structure. In the case study, we apply GMERF to Higher Education data to analyze the university student dropout phenomenon. We predict engineering student dropout probability by means of student‐level information and considering the degree program students are enrolled in as grouping factor.
The digital silicon photomultiplier (SiPM) has been commercialised by Philips as an innovative technology compared to analog silicon photomultiplier devices. The Philips digital SiPM, has a pair of ...time to digital converters (TDCs) connected to 12800 single photon avalanche diodes (SPADs). Detailed measurements were performed to understand the low photon time response of the Philips digital SiPM. The single photon time resolution (SPTR) of every single SPAD in a pixel consisting of 3200 SPADs was measured and an average value of 85 ps full width at half maximum (FWHM) was observed. Each SPAD sends the signal to the TDC with different signal propagation time, resulting in a so called trigger network skew. This distribution of the trigger network skew for a pixel (3200 SPADs) has been measured and a variation of 50 ps FWHM was extracted. The SPTR of the whole pixel is the combination of SPAD jitter, trigger network skew, and the SPAD non-uniformity. The SPTR of a complete pixel was 103 ps FWHM at 3.3 V above breakdown voltage. Further, the effect of the crosstalk at a low photon level has been studied, with the two photon time resolution degrading if the events are a combination of detected (true) photons and crosstalk events. Finally, the time response to multiple photons was investigated.
Silicon photomultipliers (SiPMs) and scintillators are often arranged in the shape of arrays in Positron Emission Tomography (PET) systems. Digital SiPMs provide signal readout in single photon ...avalanche diode (SPAD) level. From the photon count rate measurement of each SPAD cell of digital SiPM, we found that the output scintillating photons distribute in an area larger than the scintillator physical coupling area. Taking advantage of the possibility to enable/disable individual cells of the digital SiPM, a group of Lutetium-yttrium oxyorthosilicate (LYSO) crystals with different dimensions coupled to a digital SiPM was used to study the influence of using different SiPM active area on the number of photons detected, energy resolution and coincidence time resolution (CTR). For the same crystal coupled to the digital SiPM, the larger the active area of digital SiPM, the higher the number of photons detected. The larger active area of the digital SiPM also results in a better energy resolution after saturation correction. The best energy resolution full width half maximum (FWHM) obtained for the 2 x 2 x 5 mm super(3), 2 x 2 x 10 mm super(3), 2 x 2 x 15 mm super(3), 2 x 2 x 20 mm super(3) LYSO crystals was 10.7%, 11.6%, 12.1%, 12.5%, respectively. For crystals with different cross sections coupled to the digital SiPM, we found that the larger the cross section of coupling area, the more photons were detected and thus a better energy resolution was obtained. The CTR of crystals fully wrapped with Teflon or without wrapping was measured by positioning two identical crystals facing each other. A larger area of digital SiPM improves the CTR and the CTR reaches the plateau when the active area is larger than 2.2 x 2.2 mm super(2) with both two configurations of wrapping. The best CTR value for the 2 x 2 x 5 mm super(3), 2 x 2 x 10 mm super(3), 2 x 2 x 15 mm super(3), 2 x 2 x 20 mm super(3) LYSO crystals was 128.9 ps, 148.4 ps, 171.6 ps, 177.9 ps, respectively. The measurements performed lead us to conclude that optimising the coupling between crystal and SiPM to extract more scintillating photons can improve the energy resolution and CTR.
Partially observed functional data are frequently encountered in applications and are the object of an increasing interest by the literature. We here address the problem of measuring the centrality ...of a datum in a partially observed functional sample. We propose an integrated functional depth for partially observed functional data, dealing with the very challenging case where partial observability can occur systematically on any observation of the functional dataset. In particular, differently from many techniques for partially observed functional data, we do not request that some functional datum is fully observed, nor we require that a common domain exist, where all of the functional data are recorded. Because of this, our proposal can also be used in those frequent situations where reconstructions methods and other techniques for partially observed functional data are inapplicable. By means of simulation studies, we demonstrate the very good performances of the proposed depth on finite samples. Our proposal enables the use of benchmark methods based on depths, originally introduced for fully observed data, in the case of partially observed functional data. This includes the functional boxplot, the outliergram and the depth versus depth classifiers. We illustrate our proposal on two case studies, the first concerning a problem of outlier detection in German electricity supply functions, the second regarding a classification problem with data obtained from medical imaging.
Supplementary materials
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