Abstract
Scintillation detector development is an active field of research, especially for its application to the medical imaging field and in particular to the positron emission tomography (PET). Effective sensitivity and signal-to-noise ratio in PET are greatly enhanced when improving detector timing capabilities: the availability to provide time-of-flight (TOF) information. However, physical barriers related to the characteristics of available organic and inorganic scintillators create a tradeoff between photon kinetics and gamma detection efficiency. We introduce the novel concept of metascintillators, composite topologies comprising of multiple scintillating and light-guiding materials functioning in synergy, that break this compromise. We provide an overview of published, ongoing and upcoming developments within this framework. Unconventional topologies, such as the multiple slabs approach comprising of a high-Z host and a fast emitter; materials such as CdSe/CdS nanoplatelets; and treatments related to nanostructured metamaterials and photonic interactions, are reviewed and complemented with new, unpublished advances in simulations and analysis. Future perspectives are further presented, encompassing developments in signal analysis and system integration. Within this concept, an improved generation of detectors and PET scanners with unprecedented time resolution is researched, paving the way toward the 10-ps TOF PET challenge for the advancement of PET and improvement of public health.
Highlights
The gamma detector block in a positron emission tomography (PET) scanner is based on the physical process of scintillation. This is the characteristic property of particular materials able of capturing an incoming high energy gamma-ray and release part of its energy in a shower of lower energy optical photons. These scintillation photons are detected by photosensors such as silicon photomultipliers (SiPMs), capable of producing a measurable electric signal
Concerning scintillators, we could define as meta-scintillators the composite topologies of scintillating and light-guiding materials, arranged to produce a synergistic effect at some step of the scintillation process, from gamma absorption to light detection, combining the favorable physical characteristics of their constituting components
Due to the high refractive index of crystal scintillators in their emission spectrum, total internal reflection (TIR) is the main optical propagation mechanism. This means that the probability of reaching the extraction side of the scintillator, where a photosensor is placed, in an angle that allows direct extraction is small and a significant percentage of photons, up to 90% in the case of Bismuth Germanium Oxide (BGO) are reflected back
Summary
In positron emission tomography (PET) and related applications, one can denote an increasing demand for PET examinations [1], curtailed only by the techno-economical, engineering and physical limitations of the process. This spatial TOF resolution approaches the physical limit of positron range [7] and is similar to the standard voxel dimensions of existing scanners This might allow for virtually reconstruction-less acquisitions and a quantum leap in detector effective sensitivity [8], leading to an important reduction of radiotracer dose and examination duration. With such coincidence timing and corresponding sensitivity improvement, PET technology gains an unprecedented advantage in the nascent fields of molecular imaging and theranostics [9]
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