4.4 Article

Large-Area SiPM Pixels (LASiPs): A cost-effective solution towards compact large SPECT cameras

Journal

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.ejmp.2021.01.066

Keywords

SPECT; Silicon photomultiplier (SiPM); Gamma camera; Large-area SiPM

Funding

  1. Regione Toscana - POR CREO FESR 2014-2020
  2. Tuscany Government, POR FSE 2014-2020 [INFN-RT2 172800]

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This article introduces the potential advantages of using Large-Area SiPM Pixels (LASiPs) instead of PMTs in full-body SPECT cameras, and provides a larger sensitive area LASiP prototype. Performance of the LASiP was evaluated through experiments and the validity of Geant4 simulations, providing guidance for optimizing the implementation of LASiPs in large SPECT cameras.
Single Photon Emission Computed Tomography (SPECT) scanners based on photomultiplier tubes (PMTs) are still largely employed in the clinical environment. A standard camera for full-body SPECT employs - 50-100 PMTs of 4?8 cm diameter and is shielded by a thick layer of lead, becoming a heavy and bulky system that can weight a few hundred kilograms. The volume, weight and cost of a camera can be significantly reduced if the PMTs are replaced by silicon photomultipliers (SiPMs). The main obstacle to use SiPMs in full-body SPECT is the limited size of their sensitive area. A few thousand channels would be needed to fill a camera if using the largest commercially-available SiPMs of 6 x 6 mm2. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6 x 6 mm2 SiPM. We built a proof-of-concept micro-camera consisting of a 40 x 40 x 8 mm3 NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of 15 x 15 mm2, where we were able to reconstruct images of a 99mTc capillary with an intrinsic spatial resolution of - 2 mm and an energy resolution of - 11.6% at 140 keV. We used these measurements to validate Geant4 simulations of the system. This can be extended to simulate a larger camera with more and larger pixels, which could be used to optimize the implementation of LASiPs in large SPECT cameras. We provide some guidelines towards this implementation.

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