19 research outputs found
Towards improving the sensitivity of the CPT symmetry in positronium decays with the modular J-PET detector
The Jagiellonian Positron Emission Tomograph (J-PET) is the first plastic scintillator-based tomographic device used to test discrete symmetries in the charged leptonic sector. One of such tests is for the CPT symmetry, under the combined transformation of charge, parity, and time reversal in the decays of positronium atoms. J-PET performed its first measurement for the CPT symmetry test by searching for non-vanishing CPT-violating angular correlations between the spin and orientation of the decay plane of ortho-positronium (o-Ps) atoms, which is the triplet state of positronium. The sensitivity of testing CPT symmetry with the J-PET detector reaches the precision level of 10. Here, we will discuss the prospects of improving the sensitivity of this test beyond the level of 10 by enhancing the photon registration efficiency using a new layer of densely packed plastic scintillators and a spherical annihilation chamber as a positronium production medium
Modular J-PET with improved o-Ps detection efficiency for CPT tests
J-PET is a photon detector built of plastic scintillators, which already has been commissioned for CPT studies in the decays of positronium. In the first experiment, J-PET has achieved a sensitivity to CPT violation at a level of 10−4, and now it aims to reach a level of 10−5. This will be done by enhancing the three-photon registration efficiency for ortho-positronium decays using a new layer of densely packed plastic scintillators termed Modular J-PET. We present the simulation studies performed for different experimental detection setups to be used for the next CPT test with the Modular J-PET detector
CPT symmetry test in positronium annihilations with the J-PET detector
Discrete symmetry under combined transformation of charge, parity and time reversal (CPT) can be tested in the decays of positronium atom, the lightest bound system built of charged leptons. Jagiellonian Positron Emission Tomograph (J-PET) device constructed from plastic scintillators, detects the photons originating from electron positron annihilation. This feature enables J-PET to study CPT symmetry in the three photon annihilations of the triplet state of positronium. Signs of violation of the CPT symmetry can be sought as a non-vanishing expectation value of an angular correlation operator that is odd under CPT transformation. A technique to estimate the spin of ortho-positronium and momenta of annihilation photons for single recorded ortho-positronium annihilation events allows J-PET to measure the expectation value of a CPT symmetry odd angular correlation operator. J-PET measures a broad range of kinematical configurations of ortho-positronium annihilation to three photons and is the first experiment to determine the full range of the CPT-odd angular correlation
Simulating NEMA characteristics of the modular total-body J-PET scanner -- an economic total-body PET from plastic scintillators
The purpose of the presented research is estimation of the performance
characteristics of the economic Total-Body Jagiellonian-PET system (TB-J-PET)
constructed from plastic scintillators. The characteristics are estimated
according to the NEMA NU-2-2018 standards utilizing the GATE package. The
simulated detector consists of 24 modules, each built out of 32 plastic
scintillator strips (each with cross section of 6 mm times 30 mm and length of
140 cm or 200 cm) arranged in two layers in regular 24-sided polygon
circumscribing a circle with the diameter of 78.6 cm. For the TB-J-PET with an
axial field-of-view (AFOV) of 200 cm, a spatial resolutions of 3.7 mm
(transversal) and 4.9 mm (axial) are achieved. The NECR peak of 630 kcps is
expected at 30 kBq/cc activity concentration and the sensitivity at the center
amounts to 38 cps/kBq. The SF is estimated to 36.2 %. The values of SF and
spatial resolution are comparable to those obtained for the state-of-the-art
clinical PET scanners and the first total-body tomographs: uExplorer and
PennPET. With respect to the standard PET systems with AFOV in the range from
16 cm to 26 cm, the TB-J-PET is characterized by an increase in NECR
approximately by factor of 4 and by the increase of the whole-body sensitivity
by factor of 12.6 to 38. The TOF resolution for the TB-J-PET is expected to be
at the level of CRT=240 ps (FWHM). For the TB-J-PET with an axial field-of-view
(AFOV) of 140 cm, an image quality of the reconstructed images of a NEMA IEC
phantom was presented with a contrast recovery coefficient (CRC) and a
background variability parameters. The increase of the whole-body sensitivity
and NECR estimated for the TB-J-PET with respect to current commercial PET
systems makes the TB-J-PET a promising cost-effective solution for the broad
clinical applications of total-body PET scanners.Comment: 31 pages, 11 figures, 6 tables, submitted to Physics in Medicine and
Biology 202
Optimisation of the event-based TOF filtered back-projection for online imaging in total-body J-PET
We perform a parametric study of the newly developed time-of-flight (TOF)
image reconstruction algorithm, proposed for the real-time imaging in
total-body Jagiellonian PET (J-PET) scanners. The asymmetric 3D filtering
kernel is applied at each most likely position of electron-positron
annihilation, estimated from the emissions of back-to-back -photons.
The optimisation of its parameters is studied using Monte Carlo simulations of
a 1-mm spherical source, NEMA IEC and XCAT phantoms inside the ideal J-PET
scanner. The combination of high-pass filters which included the TOF filtered
back-projection (FBP), resulted in spatial resolution, 1.5 higher in
the axial direction than for the conventional 3D FBP. For realistic -minute
scans of NEMA IEC and XCAT, which require a trade-off between the noise and
spatial resolution, the need for Gaussian TOF kernel components, coupled with
median post-filtering, is demonstrated. The best sets of 3D filter parameters
were obtained by the Nelder-Mead minimisation of the mean squared error between
the resulting and reference images. The approach allows training the
reconstruction algorithm for custom scans, using the IEC phantom, when the
temporal resolution is below 50 ps. The image quality parameters, estimated for
the best outcomes, were systematically better than for the non-TOF FBP
Positronium imaging with the novel multiphoton PET scanner
In vivo assessment of cancer and precise location of altered tissues at
initial stages of molecular disorders are important diagnostic challenges.
Positronium is copiously formed in the free molecular spaces in the patient's
body during positron emission tomography (PET). The positronium properties vary
according to the size of inter- and intramolecular voids and the concentration
of molecules in them such as, e.g., molecular oxygen, O2; therefore,
positronium imaging may provide information about disease progression during
the initial stages of molecular alterations. Current PET systems do not allow
acquisition of positronium images. This study presents a new method that
enables positronium imaging by simultaneous registration of annihilation
photons and deexcitation photons from pharmaceuticals labeled with
radionuclides. The first positronium imaging of a phantom built from cardiac
myxoma and adipose tissue is demonstrated. It is anticipated that positronium
imaging will substantially enhance the specificity of PET diagnostics.Comment: 10 pages, 5 figure
From tests of discrete symmetries to medical imaging with J-PET detector
We present results on CPT symmetry tests in decays of positronium performed with the precision at the level of 10, and positronium images determined with the prototype of the J-PET tomograph. The first full-scale prototype apparatus consists of 192 plastic scintillator strips readout from both ends with vacuum tube photomultipliers. Signals produced by photomultipliers are probed in the amplitude domain and are digitized by FPGA-based readout boards in triggerless mode. In this contribution we report on the first two- and three-photon positronium images and tests of CPT symmetry in positronium decays
Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography
Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies in predictions for the electron–positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10−4, with an over threefold improvement on the previous measurement
ProTheRaMon : a GATE simulation framework for proton therapy range monitoring using PET imaging
Objective. This paper reports on the implementation and shows examples of the use of the ProTheRaMon framework for simulating the delivery of proton therapy treatment plans and range monitoring using positron emission tomography (PET). ProTheRaMon offers complete processing of proton therapy treatment plans, patient CT geometries, and intra-treatment PET imaging, taking into account therapy and imaging coordinate systems and activity decay during the PET imaging protocol specific to a given proton therapy facility. We present the ProTheRaMon framework and illustrate its potential use case and data processing steps for a patient treated at the Cyclotron Centre Bronowice (CCB) proton therapy center in Krakow, Poland. Approach. The ProTheRaMon framework is based on GATE Monte Carlo software, the CASToR reconstruction package and in-house developed Python and bash scripts. The framework consists of five separated simulation and data processing steps, that can be further optimized according to the user’s needs and specific settings of a given proton therapy facility and PET scanner design. Main results. ProTheRaMon is presented using example data from a patient treated at CCB and the J-PET scanner to demonstrate the application of the framework for proton therapy range monitoring. The output of each simulation and data processing stage is described and visualized. Significance. We demonstrate that the ProTheRaMon simulation platform is a high-performance tool, capable of running on a computational cluster and suitable for multi-parameter studies, with databases consisting of large number of patients, as well as different PET scanner geometries and settings for range monitoring in a clinical environment. Due to its modular structure, the ProTheRaMon framework can be adjusted for different proton therapy centers and/or different PET detector geometries. It is available to the community via github (Borys et al 2022)
Transformation of PET raw data into images for event classification using convolutional neural networks
In positron emission tomography (PET) studies, convolutional neural networks (CNNs) may be applied directly to the reconstructed distribution of radioactive tracers injected into the patient's body, as a pattern recognition tool. Nonetheless, unprocessed PET coincidence data exist in tabular format. This paper develops the transformation of tabular data into
-dimensional matrices, as a preparation stage for classification based on CNNs. This method explicitly introduces a nonlinear transformation at the feature engineering stage and then uses principal component analysis to create the images. We apply the proposed methodology to the classification of simulated PET coincidence events originating from NEMA IEC and anthropomorphic XCAT phantom. Comparative studies of neural network architectures, including multilayer perceptron and convolutional networks, were conducted. The developed method increased the initial number of features from 6 to 209 and gave the best precision results (79.8) for all tested neural network architectures; it also showed the smallest decrease when changing the test data to another phantom