Project Details
Projekt
Digital analog-SiPMs for sub-100 ps TOF-PET applications
Subject Area
Biomedical Systems Technology
Medical Physics, Biomedical Technology
Medical Physics, Biomedical Technology
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 500540345
Functional imaging techniques, especially for the diagnosis of malignancies and neurological diseases, are an essential tool in an aging society. The most prominent is positron emission tomography (PET). Despite impressive advances in microelectronics, photodetectors and scintillation materials, PET is still awaiting a breakthrough in terms of reduced cost and increased performance. Including ultraprecise time-of-flight (TOF) information is key to increase the signal-to-noise ratio (SNR) of PET images, minimizing the radiation exposure and scan duration by an order of magnitude for a given coincidence time resolution (CTR) better than 100 ps (FWHM). State-of-the-art TOF-PET systems are far away from this benchmark, achieving CTRs of 213 ps (FWHM). Additionally, increasing the gantry size and thus the system sensitivity will not only enable early detection of pathological processes among the elderly, but also enable low-dose prenatal examinations or pediatric healthcare. However, this requires strict cost reduction of the used detector blocks.The limitations in CTR are given by the scintillator, the photodetectors and readout electronics. The speed of the scintillation is fundamentally limited by physical processes and cannot be improved, unless the process itself is revolutionized. Several proposals have been put forth, whereas the most promising is to use prompt photon emission, e.g. Cherenkov radiation in BGO crystals, which are cheap to produce, thus contributing to drastic cost cutting. However, Cherenkov detection is challenging due to its limited photon yield, which in turn requires a very high photon detection efficiency (PDE), low dark count rate (DCR) and extremely fast and innovative electronic readout schemes. Recent analog silicon photomultipliers (aSiPMs) meet the first two aspects, but lack the latter. In this project, we propose a new detector type, called DIGILOG-SiPM, that combines high PDE, low DCR and an exceptional single-photon time resolution (SPTR), so as to achieve unprecedented CTR at PET system level. To reach this goal, we will first segment state-of-the-art analog SiPMs in smaller clusters, called µSiPMs. By segmentation, the electronic readout will have negligible noise contribution with a manageable granularity at system level. Applying order-statistics theory to these measurements will enable approaching the Cramér-Rao limit for time resolution. The µSiPMs will individually fire and be aligned in time, so as to achieve an overall SPTR of 20 ps (FWHM). Multiple thresholds will be applied to each µSiPM to enable photon-density time walk correction and photon counting at µSiPM level. The electronics will be housed in the CMOS bottom-tier and the µSiPMs in the top-tier chip of a 3D-stacking configuration. The bottom tier will also house a data handling structure that is backwards compatible with conventional SiPMs and fully scalable to much larger modules.
DFG Programme
Research Grants
International Connection
Switzerland
Cooperation Partners
Privatdozent Dr. Claudio Bruschini; Professor Dr. Edoardo Charbon
