234 research outputs found
Clopidogrel: A Pharmacogenomic Perspective on its Use in Coronary Artery Disease
The thienopyridine antiplatelet agent clopidogrel is an effective drug for the prevention of vascular events. However, data has accumulated over time to suggest it is prone to significant interpatient variability. While there are several factors that contribute to this, one of the most important is variability in forming the active metabolite necessary for clopidogrel function. Several enzymes are involved in formation of this metabolite, and two, CYP2C19 and P-glycoprotein, appear to have alleles that both occur frequently in the population and have a clinically significant impact. Patients carrying these alleles can be identified, but it remains to be determined if this information is necessary or sufficient for risk stratification. Furthermore, if patients with high-risk alleles are identified, it is unclear how treatment should be adjusted
Evaluating a Pattern-Based Visual Support Approach for Humanitarian Landmine Clearance
Unexploded landmines have severe post-conflict humanitarian repercussions: landmines cost lives, limbs and land. For deminers engaged in humanitarian landmine clearance, metal detectors remain the primary detection tool as more sophisticated technologies fail to get adopted due to restrictive cost, low reliability, and limited robustness. Metal detectors are, however, of limited effectiveness, as modern landmines contain only minimal amounts of metal, making them difficult to distinguish from the ubiquitous but harmless metallic clutter littering post-combat areas. We seek to improve the safety and efficiency of the demining process by developing support tools that will enable deminers to make better decisions using feedback from existing metal detectors. To this end, in this paper we propose and evaluate a novel, pattern-based visual support approach inspired by the documented strategies employed by expert deminers. In our laboratory study, participants provided with a prototype of our support tool were 80% less likely to mistake a mine for harmless clutter. A follow-up study demonstrates the potential of our pattern-based approach to enable peer decision-making support during landmine clearance. Lastly, we identify several design opportunities for further improving deminers' decision making capabilities.Engineering and Applied Science
Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector
In this paper we present prospects for using the J-PET detector to search for
discrete symmetries violations in a purely leptonic system of the positronium
atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium
decays into three photons. No zero expectation values for chosen correlations
between ortho-positronium spin and momentum vectors of photons would imply the
existence of physics phenomena beyond the Standard Model. Previous measurements
resulted in violation amplitude parameters for CP and CPT symmetries consistent
with zero, with an uncertainty of about 10-3. The J-PET detector allows to
determine those values with better precision thanks to a unique time and
angular esolution combined with a high geometrical acceptance. Achieving the
aforementioned is possible due to application of polymer scintillators instead
of crystals as detectors of annihilation quanta.Comment: in Nukleonika 201
Compressive Sensing of Signals Generated in Plastic Scintillators in a Novel J-PET Instrument
The J-PET scanner, which allows for single bed imaging of the whole human
body, is currently under development at the Jagiellonian University. The dis-
cussed detector offers improvement of the Time of Flight (TOF) resolution due
to the use of fast plastic scintillators and dedicated electronics allowing for
sam- pling in the voltage domain of signals with durations of few nanoseconds.
In this paper we show that recovery of the whole signal, based on only a few
samples, is possible. In order to do that, we incorporate the training signals
into the Tikhonov regularization framework and we perform the Principal
Component Analysis decomposition, which is well known for its compaction
properties. The method yields a simple closed form analytical solution that
does not require iter- ative processing. Moreover, from the Bayes theory the
properties of regularized solution, especially its covariance matrix, may be
easily derived. This is the key to introduce and prove the formula for
calculations of the signal recovery error. In this paper we show that an
average recovery error is approximately inversely proportional to the number of
acquired samples
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
PALS investigations of free volumes thermal expansion of J-PET plastic scintillator synthesized in polystyrene matrix
The polystyrene dopped with 2,5-diphenyloxazole as a primary fluor and
2-(4-styrylphenyl)benzoxazole as a wavelength shifter, prepared as a plastic
scintillator was investigated using positronium probe in wide range of
temperatures from 123 to 423 K. Three structural transitions at 260 K, 283 K
and 370 K were found in the material. In the o-Ps intensity dependence on
temperature, the significant hysteresis is observed. Heated to 370 K, the
material exhibits the o-Ps intensity variations in time.Comment: in Nukleonika 201
Application of the Compress Sensing Theory for Improvement of the TOF Resolution in a Novel J-PET Instrument
Nowadays, in Positron Emission Tomography (PET) systems, a Time of Flight
information is used to improve the image reconstruction process. In Time of
Flight PET (TOF-PET), fast detectors are able to measure the difference in the
arrival time of the two gamma rays, with the precision enabling to shorten
significantly a range along the line-of-response (LOR) where the annihilation
occurred. In the new concept, called J-PET scanner, gamma rays are detected in
plastic scintillators. In a single strip of J-PET system, time values are
obtained by probing signals in the amplitude domain. Owing to Compress Sensing
theory, information about the shape and amplitude of the signals is recovered.
In this paper we demonstrate that based on the acquired signals parameters, a
better signal normalization may be provided in order to improve the TOF
resolution. The procedure was tested using large sample of data registered by a
dedicated detection setup enabling sampling of signals with 50 ps intervals.
Experimental setup provided irradiation of a chosen position in the plastic
scintillator strip with annihilation gamma quanta
Test of a single module of the J-PET scanner based on plastic scintillators
Time of Flight Positron Emission Tomography scanner based on plastic
scintillators is being developed at the Jagiellonian University by the J-PET
collaboration. The main challenge of the conducted research lies in the
elaboration of a method allowing application of plastic scintillators for the
detection of low energy gamma quanta. In this article we report on tests of a
single detection module built out from BC-420 plastic scintillator strip (with
dimensions of 5x19x300mm^3) read out at two ends by Hamamatsu R5320
photomultipliers. The measurements were performed using collimated beam of
annihilation quanta from the 68Ge isotope and applying the Serial Data Analyzer
(Lecroy SDA6000A) which enabled sampling of signals with 50ps intervals. The
time resolution of the prototype module was established to be better than 80ps
(sigma) for a single level discrimination. The spatial resolution of the
determination of the hit position along the strip was determined to be about
0.93cm (sigma) for the annihilation quanta. The fractional energy resolution
for the energy E deposited by the annihilation quanta via the Compton
scattering amounts to sigma(E)/E = 0.044/sqrt(E[MeV]) and corresponds to the
sigma(E)/E of 7.5% at the Compton edge.Comment: 12 pages, 6 figures; Updated with editorial corrections related to
publication in NIM
Beam profile investigation of the new collimator system for the J-PET detector
Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector
which will be used for search for discrete symmetries violations in the decays
of positronium atoms and for investigations with positronium atoms in
life-sciences and medical diagnostics. In this article we present three methods
for determination of the beam profile of collimated annihilation gamma quanta.
Precise monitoring of this profile is essential for time and energy calibration
of the J-PET detector and for the determination of the library of model signals
used in the hit-time and hit-position reconstruction. We have we have shown
that usage of two lead bricks with dimensions of 5x10x20 cm^3 enables to form a
beam of annihilation quanta with Gaussian profile characterized by 1 mm FWHM.
Determination of this characteristic is essential for designing and
construction the collimator system for the 24-module J-PET prototype.
Simulations of the beam profile for different collimator dimensions were
performed. This allowed us to choose optimal collimation system in terms of the
beam profile parameters, dimensions and weight of the collimator taking into
account the design of the 24 module J-PET detector.Comment: 14 pages, 9 figure
Processing optimization with parallel computing for the J-PET tomography scanner
The Jagiellonian-PET (J-PET) collaboration is developing a prototype TOF-PET
detector based on long polymer scintillators. This novel approach exploits the
excellent time properties of the plastic scintillators, which permit very
precise time measurements. The very fast, FPGA-based front-end electronics and
the data acquisition system, as well as, low- and high-level reconstruction
algorithms were specially developed to be used with the J-PET scanner. The
TOF-PET data processing and reconstruction are time and resource demanding
operations, especially in case of a large acceptance detector, which works in
triggerless data acquisition mode. In this article, we discuss the parallel
computing methods applied to optimize the data processing for the J-PET
detector. We begin with general concepts of parallel computing and then we
discuss several applications of those techniques in the J-PET data processing.Comment: 8 page
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