Fast Emitting Nanocomposites for High‐Resolution ToF‐PET Imaging Based on Multicomponent Scintillators

Abstract

Time‐of‐Flight Positron Emission Tomography (ToF‐PET) is a medical imaging technique, based on the detection of two back‐to‐back γ‐photons generated from radiotracers injected into the body. Its limit is the ability of employed scintillation detectors to discriminate in time the arrival of γ‐pairs, that is, the coincidence time resolution (CTR). A CTR < 50 ps will enable fast imaging with ultralow radiotracer dose. Monolithic materials do not have simultaneously the required high light output and fast emission characteristics, thus the concept of scintillating heterostructure is proposed, where the device is made of a dense scintillator coupled to a fast‐emitting light material. Here a composite polymeric scintillator loaded with hafnium oxide nanoparticles is presented. This enhanced by +300% its scintillation yield, by surpassing commercial plastic scintillators. The nanocomposite is coupled to bismuth germanate oxide (BGO) realizing a multilayer metascintillator. The energy sharing between its components is observed, which activates the nanocomposite's fast emission enabling a net CTR improvement of 25% with respect to monolithic BGO. These results demonstrate that a controlled loading with dense nanomaterials is an excellent strategy to enhance the performance of polymeric scintillators for their use in advanced radiation detection and imaging technologies.

On the Origin of the Light Yield Enhancement in Polymeric Composite Scintillators Loaded with Dense Nanoparticles

“…The POPOP emission lifetime τ = 1.32 ns is identical in all samples (Figure 1d, inset) and matches the one in diluted solution. 31 These findings demonstrate that upon direct optical excitation, the POPOP photoluminescence properties are preserved in the PS host, including its high photoluminescence quantum yield ϕ pl = 0.93. 42−44 The photoluminescence efficiency is only one of the parameters that determines the scintillation efficiency.…”

“…This value is more than twice the intrinsic POPOP emission lifetime, confirming the behavior previously observed for PS-embedded POPOP molecules upon X-ray irradiation. 31 We ascribe this behavior to a possible exciplex formation between the excited PS and POPOP molecules, 56 but further studies are still ongoing. Nevertheless, usually exciplexes are not efficient emitters, and their photoluminescence efficiency is lower with respect to the single molecule one; thus, it is realistic to assume that the system photoluminescence quantum yield ϕ pl is lower than 0.93 under high energy excitation.…”

“…On the other hand, the use of hybrid organic/inorganic compounds − or the loading of polymeric hosts with optically inert dense nanoparticles (NPs) are alternative approaches recently proposed to enhance the stopping power of liquid and polymeric conjugated scintillators. − In principle, the presence of dense NPs including high atomic number Z elements would affect indeed both the Compton and photoelectric interactions because the interaction probability with high energy photons, such as X-rays and γ-rays, quickly increases with the effective material electronic density and the effective Z value. Rather than to create luminescence centers, the role of these inorganic fillers is therefore to enhance the efficacy of the transformation of the absorbed energy into electronic excitations, which will then be transferred through nonradiative mechanisms to the final emitter. , In particular, NP-loaded composite scintillators show a composition-dependent behavior, − and trade-off conditions that maximize the ϕ LY can be found. , However, a clear explanation of the effect that correlates the presence of NPs with the scintillation performance is still under debate.…”

“…25,26 In particular, NP-loaded composite scintillators show a composition-dependent behavior, 27−29 conditions that maximize the ϕ LY can be found. 30,31 However, a clear explanation of the effect that correlates the presence of NPs with the scintillation performance is still under debate.…”

Recent Advances in Fast-Decaying Metal Halide Perovskites Scintillators

“…(BZA) 2 PbBr 4 shows a decay lifetime of 8 ns and an energy resolution of 8% (at 662 keV). Due to its fast decay time, (BZA) 2 PbBr 4 has excellent count rate ability as well as low statistical fluctuations. TOF-PET: TOF-PET is an advanced medical imaging technology which is realized by detecting two back-to-back gamma photons produced by radiotracers injected into the body . TOF-PET can significantly reduce the loss of acquisition counts, minimize the radiation dose to the patient, and improve the image quality.…”