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

TL;DR

This paper introduces Large-Area SiPM Pixels (LASiPs) as a cost-effective, scalable solution to improve the size, weight, and cost of full-body SPECT cameras by replacing traditional photomultiplier tubes with larger, combined SiPM arrays.

Contribution

The authors developed a novel LASiP prototype that significantly enlarges SiPM sensitive area, enabling the construction of compact, high-resolution SPECT micro-cameras and providing a framework for scaling up to full-body systems.

Findings

Achieved ~2 mm spatial resolution in prototype imaging.

Demonstrated ~11.6% energy resolution at 140 keV.

Validated system performance with Geant4 simulations.

Abstract

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.