Comparative studies of the sensitivities of sparse and full geometries of Total-Body PET scanners built from crystals and plastic scintillators

Abstract

Background: Alongside the benefits of Total-Body imaging modalities, such as higher sensitivity, single-bed position, low dose imaging, etc., their final construction cost prevents worldwide utilization. The main aim of this study is to present a simulation-based comparison of the sensitivities of existing and currently developed tomographs to introduce a cost-efficient solution for constructing a Total-Body PET scanner based on plastic scintillators.

Methods: For the case of this study, eight tomographs based on the uEXPLORER configuration with different scintillator materials (BGO, LYSO), axial field-of-view (97.4 cm and 194.8 cm), and detector configurations (full and sparse) were simulated. In addition, 8 J-PET scanners with different configurations, such as various axial field-of-view (200 cm and 250 cm), different cross sections of plastic scintillator, and multiple numbers of plastic scintillator layers (2, 3, and 4), based on J-PET technology have been simulated by GATE software. Furthermore, Siemens' Biograph Vision has been simulated to compare the results with standard PET scans. Two types of simulations have been performed. The first one with a centrally located source with a diameter of 1 mm and a length of 250 cm, and the second one with the same source inside a water-filled cylindrical phantom with a diameter of 20 cm and a length of 183 cm.

Results: With regards to sensitivity, among all the proposed scanners, the ones constructed with BGO crystals give the best performance ([Formula: see text] 350 cps/kBq at the center). The utilization of sparse geometry or LYSO crystals significantly lowers the achievable sensitivity of such systems. The J-PET design gives a similar sensitivity to the sparse LYSO crystal-based detectors while having full detector coverage over the body. Moreover, it provides uniform sensitivity over the body with additional gain on its sides and provides the possibility for high-quality brain imaging.

Conclusion: Taking into account not only the sensitivity but also the price of Total-Body PET tomographs, which till now was one of the main obstacles in their widespread clinical availability, the J-PET tomography system based on plastic scintillators could be a cost-efficient alternative for Total-Body PET scanners.

Keywords: GATE simulation; J-PET; Sensitivity; Total-Body PET; uEXPLORER.

Conflict of interest statement

The authors declare that they have no competing interests.

© 2023. Springer Nature Switzerland AG.

Figures

Fig. 1

A.I, Visualization of uEXPLORER TB PET scanner consisting of 8 detection units (rings). Each unit is made up of 24 detection blocks (B.I). The blocks in uEXPLORER are composed of arrays (C.I). The arrays are the smallest detection units of uEXPLORER and hold 6 × 7 scintillation crystals (blue) together and couple them to the SiPM matrix (black). A.II shows the sparse geometry based on uEXPLORER, including 29 detection units (rings). In contrast, arrays are distributed in smaller detection blocks (B.II). A.III TB J-PET consists of 4 layers of EJ-230 plastic scintillator strips (gray), which have been located parallel to the axial axes of the scanner (B.III). The modules in TB J-PET have been equipped with wavelength-shifting plastics (WLS, green)

Fig. 2

Illustration of scintillators arrangements, the principle of detection and reconstruction of annihilation positions. (Left) Representation of J-PET plastic scintillator-based technology where the axially arranged scintillator (blue) is readout by two photomultipliers of both ends (gray). (Right) Representation of crystal-based technology with the radially arranged scintillators (blue), where each one is read out with corresponding photomultipliers (gray). The fractional energy resolution for the energy deposited by the annihilation photon in a single plastic scintillator strip has been measured σ(E)/E≈0.044/E(MeV), based on the previous investigation in J-PET collaboration [25]

Fig. 3

Schematic visualization of uEXPLORER (I) (blue) [8, 10, 13]) and sparse geometry (transparent yellow) with 194.8 cm of AFOV and dual layers. TB J-PET (II) with axially arranged plastic scintillators (gray) coupled with SiPMs (black) at each end and arrays of WLS (green) between each layer. The oblique LORs (with large values of θ) have a negative contribution in the spatial resolutions due to the parallax error. To avoid it, uEXPLORER uses a ring-based cut that accepts the coincidences within a maximum of 5 rings. As shown in figure (II), TB J-PET uses continuous plastic scintillators (gray), θAA denotes the acceptance angle applied for it to cut oblique LORs. θMax demonstrate the largest angle of detectable oblique coincidences

Fig. 4

a Sensitivity [cps/kBq] profiles of all the TB PET geometries with a 2.5 m line source located in their central axial axis. b Sensitivity [cps/kBq] profiles of all the TB PET geometries with a 2.5 m line source located in their central axial axis with 57∘ degree of acceptance angle for J-PET based scanners and five ring difference cut for uEXPLORER tomographs

Fig. 5

a Sensitivity [cps/kBq] profiles of the TB PET scanners with a 2.5 m line source inside a 183 cm water-filled cylindrical phantom with a diameter of 20 cm. b Sensitivity [cps/kBq] profiles of the TB PET scanners with a 2.5 m line source inside a 183 cm water-filled cylindrical phantom with a diameter of 20 cm, with 57∘ of acceptance angle for J-PET-based scanners and five ring difference cut for uEXPLORER tomographs

Fig. 6

Sensitivity [cps/kBq] profile of the TB PET scanners with a 2.5 m line source inside a 183 cm long water-filled cylindrical phantom with a diameter of 20 cm and acceptance cut. The schematic visualization of a male patient is added to represent the position of a 183 cm height person in the sensitivity profile of the tomographs with 57∘ of acceptance angle for J-PET-based scanners and five ring difference cut for uEXPLORER tomographs

Fig. 7

Representation of the total sensitivity of the scanner as a function of the sum of the required photomultiplier covered area. The TB PET systems based on the J-PET technology are marked with black circles. Four additional ring-based TB J-PET geometries are marked with blue circles. The crystal-based geometries are marked in the plot with black triangles. Each ring of the J-PET is constructed as a separate tomograph with 50 cm length scintillators. Two existing systems (Biograph Vision and uEXPLORER from LYSO crystals) were colored red