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 $sim50$-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$times$6~mm$^2$. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6$times$6~mm$^2$ SiPM. We built a proof-of-concept micro-camera consisting of a 40$times$40$times$8~mm$^3$ NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of $15times15$~mm$^2$, where we were able to reconstruct images of a $^{99m}$Tc capillary with an intrinsic spatial resolution of $sim2$~mm and an energy resolution of $sim11.6$% 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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