Speaker
Description
Conventional Positron Emission Tomography (PET) relies on the detection of two back-to-back 511 keV photons originating from electron-positron annihilations. However, about 40 percent of annihilations occur via positronium formation, including ortho-positronium (o-Ps) decays into three photons. The features of positronium, including its lifetime and the ratio of 3γ to 2γ annihilations (3γ/2γ), strongly depend on the architecture of the surrounding tissue. This has led to the development of positronium imaging – an emerging PET extension that provides additional information about the imaged tissue and may improve the diagnostic process.
In contrast to the conventional PET devices, the Jagiellonian Positron Emission Tomography scanner (J-PET), based on plastic scintillators, is capable of multi-photon detection. This feature enables the registration of 3γ events, making it able to assess the properties of positronium, such as its lifetime and the 3γ/2γ decay ratio, and utilize these properties in medical imaging. The 3γ/2γ method, in contrast to positronium lifetime imaging, does not require the registration of the de-excitation photon, meaning that all commonly used PET radioisotopes are suitable for this approach. The method can be applied with standard radiopharmaceuticals, such as 18F-FDG, and with emerging isotopes like 44Sc, which we plan to utilize in J-PET.
Accurate tomographic image reconstruction requires corrections for attenuation, scatter, and random coincidences. Such methods are currently implemented in the J-PET detector for conventional 2γ imaging. However, they are not suitable for the 3γ approach. This limitation creates the need to develop correction methods dedicated to this technique.
In this work, we investigate absorption effects for both 2γ and 3γ annhilation processes using Monte Carlo (MC) simulations. Studies were performed with a custom toy MC implemented in ROOT and with the GATE simulation toolkit for a range of phantom models, including simplified geometries and the anatomically realistic XCAT phantom. The results are presented in the form of absorption maps for para- and ortho-positronium decays that can serve as a foundation for attenuation correction.
Moreover, preliminary simulations including the Total-Body J-PET detector geometry were performed to assess the role of detector effects, including detector acceptance and energy thresholds relevant for signal registration, in the feasibility of 3γ/2γ positronium imaging. The results show significantly lower detection efficiency for 3γ events compared to 2γ, due to higher attenuation of low-energy photons and limited detector acceptance. The efficiency is also strongly dependent on the energy threshold, with even small increases causing a substantial reduction in the number of detected 3γ events, while 2γ detection remains largely unaffected.
| Track | TBPET |
|---|---|
| Presentation type | Oral |