72 research outputs found
Multi-photon time-of-flight MLEM application for the positronium imaging in J-PET
We develop a positronium imaging method for the Jagiellonian PET (J-PET)
scanners based on the time-of-flight maximum likelihood expectation
maximisation (TOF MLEM). The system matrix elements are calculated on-the-fly
for the coincidences comprising two annihilation and one de-excitation photons
that originate from the ortho-positronium (o-Ps) decay. Using the Geant4
library, a Monte Carlo simulation was conducted for four cylindrical 22Na
sources of beta plus decay with diverse o-Ps mean lifetimes, placed
symmetrically inside the two JPET prototypes. The estimated time differences
between the annihilation and the positron emission were aggregated into
histograms (one per voxel), updated by the weights of the activities
reconstructed by TOF MLEM. The simulations were restricted to include only the
o-Ps decays into back-to-back photons, allowing a linear fitting model to be
employed for the estimation of the mean lifetime from each histogram built in
the log scale. To suppress the noise, the exclusion of voxels with activity
below 2-10 percent of the peak was studied. The estimated o-Ps mean lifetimes
were consistent with the simulation and distributed quasi-uniformly at high
MLEM iterations. The proposed positronium imaging technique can be further
upgraded to include various correction factors, as well as be modified
according to realistic o-Ps decay models
Towards time reversal symmetry test with o-Ps decays using the J-PET detector
One of the features of the triplet state of positronium (ortho-positronium) atoms is its relatively longer lifetime when compared to the singlet states of positronium (para-positronium) atoms. The most probable decay of ortho-positronium is into three annihilation photons. In order to test the discrete symmetry using the time-reversal symmetry odd-operator, it is important to identify ortho-positronium decay. Identification of the decay of ortho-positronium atoms by measuring the positronium annihilation lifetime with the Jagiellonian-Positron Emission Tomograph (J-PET) is presented in this article
Potential of modular J-PET for applications in the field of particle and medical physics
Modular J-PET is the new prototype of the Jagiellonian Positron Emission Tomograph. The portability feature due to its modular design makes it a unique tomograph with a larger axial field of view of 50 cm. The complete ring is composed of 24 modules that can be configured as a diagnostic chamber with a diameter of approximately 76 cm or as a detection setup consisting of several modules for experimental studies where multiple photons are generated in a single event. The J-PET collaboration explicitly studies the decays of the positronium atom (Ps), which is a bound state of electron and positron that self-annihilate into multiple photons. The modular J-PET provides a significant phase space covrage for the registration of photons originating from the decays of Ps atoms. In this paper, we discuss the properties of the modular J-PET and its potential applications in medical and particle physics
Developing a novel positronium biomarker for cardiac myxoma imaging
Purpose: Cardiac myxoma (CM), the most common cardiac tumor in adults, accounts for 50–75% of benign cardiac tumors. The diagnosis of CM is often elusive, especially in young stroke survivors and transthoracic echocardiography (TTE) is the initial technique for the differential diagnostics of CM. Less invasive cardiac computed tomography (CT) and magnetic resonance imaging (MRI) are not available for the majority of cardiac patients. Here, a robust imaging approach, ortho-Positronium (o-Ps) imaging, is presented to determine cardiac myxoma extracted from patients undergoing urgent cardiac surgery due to unexpected atrial masses. We aimed to assess if the o-Ps atom, produced copiously in intramolecular voids during the PET imaging, serves as a biomarker for CM diagnosing. Methods: Six perioperative CM and normal (adipose) tissue samples from patients, with primary diagnosis confirmed by the histopathology examination, were examined using positron annihilation lifetime spectroscopy (PALS) and micro-CT. Additionally, cell cultures and confocal microscopy techniques were used to picture cell morphology and origin. Results: We observed significant shortening in the mean o-Ps lifetime in tumor with compare to normal tissues: an average value of 1.92(02) ns and 2.72(05) ns for CM and the adipose tissue, respectively. Microscopic differences between tumor samples, confirmed in histopathology examination and micro-CT, did not influenced the major positronium imaging results. Conclusions: Our findings, combined with o-Ps lifetime analysis, revealed the novel emerging positronium imaging marker (o-PS) for cardiovascular imaging. This method opens the new perspective to facilitate the quantitative in vivo assessment of intracardiac masses on a molecular (nanoscale) level
Studies of the ortho-positronium lifetime for cancer diagnostics
Positron Annihilation Lifetime Spectroscopy (PALS) is a technique based on the analysis of the lifetime of positronium emitted from implanted or delivered positronium donors. This technique employs the lifetime and intensity dependence on the structure of analyzed material. Due to this specific features, PALS might be used in further research protocols and clinical studies for cancer diagnostic purposes. This article reports the progress in the study design, main objectives of the study, protocols of measurements and data analysis and further perspective of this study. The main goal of this work was to show the effectiveness of this method and progress in its development. For this purpose, colorectal cancer was examined
The kinetics of mutarotation in L-fucose as monitored by dielectric and infrared spectroscopy
Fourier Transform Infrared Spectroscopy and Broadband Dielectric Spectroscopy are combined to trace kinetics of mutarotation in L-fucose. After quenching molten samples down to temperatures between T=313 K and 328 K, the concentrations of two anomeric species change according to a simple exponential time dependence, as seen by an increase in absorbance of specific IR-vibrations. In contrast, the dielectric spectra reveal a slowing down of the structural (α-) relaxation process according to a stretched exponential time dependence (stretching exponent of 1.5 ± 0.2). The rates of change in the IR absorption for α- and β-fucopyranose are (at T = 313 K) nearly one decade faster than that of the intermolecular interactions as measured by the shift of the α-relaxation. This reflects the fact that the α-relaxation monitors the equilibration at a mesoscopic length scale, resulting from fluctuations in the anomeric composition
Molecular dynamics of itraconazole confined in thin supported layers
Broadband Dielectric Spectroscopy (BDS) is used to study the molecular dynamics of thin layers of
itraconazole – an active pharmaceutical ingredient with rod-like structure and whose Differential
Scanning Calorimetry (DSC) scans reveal liquid crystalline-like phase transitions. It is found that (i) the
structural relaxation process remains bulk like, within the limits of experimental accuracy, in its mean
relaxation rate, while (ii) its shape is governed by two competing events: interfacial interactions, and
crystalline ordering. Additionally, (iii) the dynamics of the d-relaxation - assigned to the flip-flop rotation
of the molecule about its short axis - deviates from bulk behaviour as the glass transition is approached
for the confined material. These observations are rationalized within the framework of molecular
dynamics as currently understood
Studies of discrete symmetries in decays of positronium atoms
A positronium - a bound state of electron and positron - is an eigenstate of parity and charge conjugation operators which decays into photons. It is a unique laboratory to study discrete symmetries whose precision is limited, in principle, by the effects due to the weak interactions expected at the level of 10−14 and photon-photon interactions expected at the level of 10−9.
The Jagiellonian Positron Emission Tomograph (J-PET) is a detector for medical imaging as well as for physics studies involving detection of electronpositron annihilation into photons. The physics case covers the areas of discrete symmetries studies and genuine multipartite entanglement. The J-PET detector has high angular and time resolution and allows for determination of spin of the positronium and the momenta and polarization vectors of annihilation quanta. In this article, we present the potential of the J-PET system for studies of discrete symmetries in decays of positronium atoms
Analysis procedure of the positronium lifetime spectra for the J-PET detector
Positron Annihilation Lifetime Spectroscopy (PALS) has shown to be a powerful
tool to study the nanostructures of porous materials. Positron Emissions
Tomography (PET) are devices allowing imaging of metabolic processes e.g. in
human bodies. A newly developed device, the J-PET (Jagiellonian PET), will
allow PALS in addition to imaging, thus combining both analyses providing new
methods for physics and medicine. In this contribution we present a computer
program that is compatible with the J-PET software. We compare its performance
with the standard program LT 9.0 by using PALS data from hexane measurements at
different temperatures. Our program is based on an iterative procedure, and our
fits prove that it performs as good as LT 9.0.Comment: 4 figures, 8 page
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