  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
$15\times15$~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.
