J-PET (Jagiellonian-PET TOMOGRAPHY)


Jagiellonian PET is the first Positron Emission Tomography scanner build from plastic scintillators.

The plastic scintillators, in contrast to inorganic ones, are relatively cheap and easy to shape. This will allow for preparation of the cost-effective device enabling a symultaneous metabolic imaging of the whole human body.

The primary aim of the group is to develop a technology for:

  • the cost effective whole-body PET,
  • the MR and CT compatible PET insert and
  • a modular and transportable PET with the field of view adjustable to the patient size.
Have a look the dream solution.

A first full scale J-PET prototype is shown in the photo below. It is used also for studies of the discrete symmetries in the decays of positronium atoms and multi-partite entanglement of photons originating from the decay of positronium.

The Jagiellonian PET collaboration lead by P. Moskal is an interdisciplinary and international group including physicists, chemists, electronic engineers, computer scientists, quantum information physicists as well as bio and medical physicists from the Jagiellonian University, National Centre for Nuclear Research, Maria Curie-Skłodowska University, University of Vienna, National Laboratory in Frascati and from the company Nowoczesna Elektronika.

Plastic scintillators are superior to the crystal ones in terms of their time resolution. The novelty of the J-PET detector lies also in the fact that the information about the place of gamma quanta interaction is extracted solely from the time, rather than the energy deposition measurement.

In each of the 196 modules of the J-PET detector there are two photomultipliers mounted at the both ends of a scintillator. Signals are sampled at four voltage levels at the leading and trailing edges with the newly developed, dedicated digital multi-threshold electronics. The place of a gamma quantum interaction in the scintillator (Δl) is determined from the times measured at both ends of the same strip. For the determination of the position of the annihilation point along a line-of-response (Δx) a time-of-flight (TOF) method is used basing on the times registered in a pair of opposite strips. Furthermore, timing of signals is used for suppression of scatterings via the the time-over-threshold (TOT) method.

In order to compensate for the lower gamma quanta registration efficiency in the organic scintillators more detection layers can be used. This together with a large light attenuation length in the plastic scintillators allowed for construction of a tomogrph with a large axial field-of-view, competitive in terms of spatial resolution and cheaper than commercially available scanners.

Furthermore, the J-PET constitues a high acceptance multi-purpose detecor optimized for the detection of photons from the positron-electron annihilation and can be used in the broad interdisciplinary investigations including, among others:

  • medical imaging,
  • studies of discrete symmetries in the decays of positronium atoms,
  • quantum entanglement of high energy photons originating from the decay of ortho-positronium,
  • research in the field of life- and material-sciences.

The first full scale prototype of the J-PET detector. The J-PET detector is made of three cylindrical layers of EJ-230 plastic scintillator strips (black) with dimension of 7 × 19 × 500 mm3 and Hamamatsu R9800 vacuum tube photomultipliers (grey). The signals from photomultipliers are probed in the voltage domain at four thresholds with a timing accuracy of 30 ps and the data acquisition is working in the trigger-less mode. The prototype was built with the support from the Polish National Center for Development and Research through grant INNOTECH-K1/IN1/64/159174/NCBR/12.

In the typical detectors with vacuum tube photomultipliers, only few first registered photons contribute to the leading edge of the electrical signal. Therefore, the time resolution may be improved by making a readout allowing to record timestamps from larger number of scintillation photons arriving at the scintillator edge. This can be achieved by the preparation of a a read-out system in the form of an array with several SiPM photomultipliers. In such a case, a set of all registered scintillation photons is divided into several subgroups and the time of the registration of the first photon in each subgroup is recorded.

The upper diagram shows a single detection element of the first J-PET detector consisting of the scintillator strip read out on two sides by vacuum tube photomultipliers. The lower part shows a diagram of an exemplary multi-SiPM readout allowing for determination of timestamps of 20 detected photons (10 on each side).

A single module of the new detection layer of the J-PET tomograph will constitute an independent detection unit which sends information about timing of the signals via optical links to the data acquisition boards. It will consist of 13 plastic scintillator strips each read out at the ends by the matrices of silicone photomultipliers (SiPM). The SiMPs will be connected directly to the newly designed voltage suppliers as well as front-end and digitizing electronics shown symbolically in green. A single module with a weight of only about 2 kg can be easily handled, and can be connected and disconnected, thus giving a possibility of constructing the tomographic chamber with an adjustable diameter. A new detection layer of the J-PET will be built from 24 modules. It is designed to be inserted into the J-PET prototype.

Due to the application of the matrix of the silicon photomultipliers, the new layer of the J-PET is characterized by even better timing resolution than the first prototype.

Medical diagnostics and PET imaging

Furthermore, the ability of the J-PET detector to reconstruct the decays of orthopositronium (o-Ps) atoms into three photons was proved. The method is based on trilateration (GPS-like method) and allows for a simultaneous reconstruction of both location and time of the decay. Altough gamma quanta interact in the plastic scintillators predominantly via the Compton effect, making a direct measurement of their energy impossible, it was shown that the J-PET scanner will enable studies of the o-Ps→3γ decays with angular and energy resolution equal to σ(θ) ≈ 0.4o and σ(E) ≈ 4.1 keV, respectively.

Left: A diagram of the J-PET detector with gamma quantum hit positions marked in black and the o-Ps decay plane indicated in gray. Right: Diagram of the decay reconstruction reduced to a two-dimensional problem in the decay plane. Each of hit coordinates constitutes the center of a circle describing possible photon origin point, where radius of the circle depends on the recording time and the unknown o-Ps decay time.


More information can be found in:

Development of J-PET range monitoring for hadron therapy

The main advantage of the proton therapy over the conventional radiotherapy (which uses X-ray or electrons) is the possibility to precisely deposit the radiation dose only in the tumor region. This is a consequence of the characteristic energy loss distribution of ionizing radiation when the proton beam moves through matter. The maximum of energy deposition is localized immediately before the maximum movement range (the Bragg peak).

Altought the range of the proton beam in a homogenous medium of know properties can be precisely calculated, the expected range in the patient's body is determined only with limited precision. Therefore, in order to cover the entire volume of tumor a margin of healthy tissues surrounding it are also exposed to radiation.

The availability of beam range monitoring would allow for more precise therapy planning and for a more complete usage of proton therapy benefits.

The result of proton beam interactions with the atoms in the patient's tissues is the emission of the secondary particles, mainly: neutrons, photons (promt-gamma) and charged particles. Additionally, due to the nuclear interaction isotopes which decay via the β+ decay are created. Emited positrons annihilate with the electrons from the patients body and two back to back gamma quanta with a minimum energy of 511 keV are emitted. These gamma quanta can escape from the patient's body and be registered. The aim of the project developed in colaboration with the Institute of Nuclear Physics of the Polish Academy of Sciences is to test the usefulness of the J-PET technology for the monitoring of the proton beam range.

Bio-medical studies

Positron Annihilation Lifetime Spectroscopy (PALS) is widely used to correlate the mean o-Ps lifetime value with cavity size in which annihilation takes place. PALS makes it possible to study many properties of materials such as the presence of defects, thermal expansion, temperature of phase transitions in polymers, processes of gas, or steams sorption in pores. Unfortunately it was applied in a very limited number of cases concerning living biological material. The PALS method combined with J-PET system will enable the determination of early and advanced stages of carcinogenesis by observing changes in biomechanical parameters between healthy and tumor cells.

The o-Ps lifetime as a function of the water vapor sorption time. The measurements were conducted in four stages: (1) in vacuum, (2) in dried air, (3) with the presence of water vapor, and (4) with drop of water placed in the chamber containing yeast.

Environmental scanning electron microscopy (ESEM) images of lyophilized yeasts (upper) and dried under normal conditions after addition of water (bottom).

More information can be found in:

Pilot studies with cultured cell lines

Chosen normal (melanocytes) and cancer (melanoma) cell lines were cultured with standard procedures. For the PALS measurement cells were suspended in different freezing mediums, centrifugate and then lyophilised (freeze–dried). The composition of mediums were chosen from standard kryo - preservation reagents (DMSO) and some used in lyophilization process like PROH and trehalose. Viability studies performed before and after freeze-drying, showed best results for cells lyophilised in medium with DMSO and PROH/trehalose.

Ortho-positronium lifetime and intensities for cultured cell lines normal – melanocytes (red square), cancer – melanoma WM115 (blue circle), melanoma WM266 (yellow triangle) freeze–dried in different mediums, in order to determine which one will preserve cells the best without changing their structure. The optimal medium was choose to be 1.5 M PROH + 0.5 M Trehalose (based on viability and NMR studies before and after freeze-drying). For this medium significant differences beetwen o-Ps lifetime and intensity can be observed. Cells preserved with DMSO, even though they showed good viability, proved to not be applicable in PALS, since DMSO as a reagent gives strong signal itself.
Optical microscope image of melanoma cells in culture (left). Freeze–dried cells prepared for measurement in a holder – melanocytes (middle), melanoma (right).
Exemplary photos of a cardiac myxoma tumor (left) and normal adipose tissue (right).
Ortho-positronium lifetime and intensities for (left) cardiac myxoma tumors fixed in formaldehyde/non-fixed and adipose tissue measured on the PALS spectrometer. Results show significance differences between normal and tumor tissue. (right) Non-fixed cardiac myxoma tumor and adipose tissue measured on J-PET and then on PALS. Results for the sample measured on both detectors are consistent with each other, which proves J-PET can be used for morphometric imaging.
Holder with a sample during the measurement on a standard PALS spectrometer (left) and in J-PET detector (right).

Testing fundamental principles of physics

Tests of discrete symmetries with the J-PET tomograph are supported by the National Science Centre through the grant no. 2016/21/B/ST2/01222.

Positronium is the lightest purely leptonic object decaying into photons. As an atom bound by a central potential, it is a parity eigenstate and as an atom built out of an electron and an antielectron it is an eigenstate of the charge conjugation operator. Positronium in the ground substates with orbital angular momentum L = 0 is formed in a singlet state of the anti-parallel spins orientation (para-positronium, p-Ps), or in a triplet state of parallel spin orientation (ortho-positronium, o-Ps). Due to the symmetry of charge conjugation p-Ps undergoes annihilation with emission of an even number of photons (most often: two), while o-Ps undergoes annihilation with emission of an odd number of photons (most often: three).

The J-PET detector enables to perform tests of discrete symmetries in the leptonic sector via the determination of the expectation values of the discrete-symmetriesodd operators, which may be constructed from the spin of o-Ps and the momenta and polarization vectors of photons originating from its annihilation.

With respect to the previous experiments performed with crystal based detectors, J-PET provides superior time resolution, higher granularity, lower pile-up and an opportunity of determining photon’s polarization. These features allow us to expect improvement by more than an order of magnitude in tests of discrete symmetries in decays of positronium atoms.

Schematic representation of a possible oPs spin direction determination with the J-PET detector. A β+ source is located in the center of a vacuum-filled cylinder covered by aerogel (green band) in which o-Ps formation and decays take place. Red lines denote lines of flight of the three photons used to reconstruct the decay vertex which, in turn, allows us to estimate the positron momentum direction and spin direction of the ortho-positronium. Yellow arrow indicates 1.27 MeV gamma quantum from the Na decay.

More information can be found in:

Material science

Together with development of the detector new scintillating materials of properties desired for digital PET are designed, synthesised and investigated with the aim of developing plastic scintillators with better light output and timing properties than those comercialy available. The novelty of the concept of the J-PET scintillator lies in application of the 2-(4-styrylphenyl)benzoxazole as a wavelength shifter. The substance has not been used as scintillator dopant before. A dopant shifts the scintillation spectrum towards longer wavelengths making it more suitable for applications in long scintillator strips and light detection with digital silicon photomultipliers.

Left and middle: The polymerization of the scintillating mixture in conducted in the furnace. It leads to a scintillating material in the form of a strip. The furnace chamber enables a uniform temperature distribution in the whole volume. Precise temperature control (1°C) and programming the whole temperature cycle are possible as well. Right: The photograph of the J-PET scintillator in UV light. The scintillating material is optically homogeneous and does not contain any defects.

More information can be found in:


List of articles

Concept First tests of the single and double module prototypes Preliminary estimation of the scatter-fraction and accidental coincidences and discussion on event selection method Estimation of NEMA characteristics with J-PET Estimation of CRT and comparison of FIGURE-OF-MERIT for the whole-body imaging A test of additional WLS layer to improve axial spatial resolution 3-photon imaging with J-PET and concept of the morphometric imaging with positronium atoms Front end electronics is based solely on FPGA More advanced methods for the hit-position reconstruction Proposal for the studies of discrete symmetries in decays of positronium atoms Studies of Quantum entanglement with J-PET

Members

Prof. dr hab. Tomasz Kozik

Recent publications

  1. Feasibility study of the positronium imaging with the J-PET tomograph
  2. Witnessing Entanglement In Compton Scattering Processes Via Mutually Unbiased Bases
  3. QED AND FUNDAMENTAL SYMMETRIES IN POSITRONIUM DECAYS?

Recent theses

  1. Double-strip prototype of polymer time-of-flight positron emission tomograph based on multi-level analog electronics
  2. Synthesis and characterization of polystyrene scintillators and their application in positron emission tomography
  3. Investigations of fundamental symmetries with the electron-positron systems
  4. Hit-time and hit-position reconstruction of gamma quanta in the J-PET tomography system based on a library of model signals

Recent reports

  1. The study of changes of the shape of the light pulses in strips of polymer scintillators
  2. Raporty z badań prowadzonych w roku 2012 w ramach przedsięwzięcia Paskowy Pozytonowy Tomgraf Emisyjny