A feasibility study of PETiPIX: an ultra high resolution small animal PET scanner

Abstract

PETiPIX is an ultra high spatial resolution positron emission tomography (PET) scanner designed for imaging mice brains. Four Timepix pixellated silicon detector modules are placed in an edge-on configuration to form a scanner with a field of view (FoV) 15 mm in diameter. Each detector module consists of 256×256 pixels with dimensions of 55×55×300 µm 3 . Monte Carlo simulations using GEANT4 Application for Tomographic Emission (GATE) were performed to evaluate the feasibility of the PETiPIX design, including estimation of system sensitivity, angular dependence, spatial resolution (point source, hot and cold phantom studies) and evaluation of potential detector shield designs. Initial experimental work also established that scattered photons and recoil electrons could be detected using a single edge-on Timepix detector with a positron source. Simulation results estimate a spatial resolution of 0.26 mm full width at half maximum (FWHM) at the centre of FoV and 0.29 mm FWHM overall spatial resolution with sensitivity of 0.01%, and indicate that a 1.5 mm thick tungsten shield parallel to the detectors will absorb the majority of non-coplanar annihilation photons, significantly reducing the rates of randoms. Results from the simulated phantom studies demonstrate that PETiPIX is a promising design for studies demanding high resolution images of mice brains.

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

“…The performance of the virtual ring method is demonstrated in simulation using the PETiPIX scanner as a case study. PETiPIX is a small animal PET scanner with DoI capabilities, which offers exceptionally high spatial resolution (Li et al 2013). The trade-off for its high spatial resolution is relatively low detection sensitivity, which is a consequence of the use of direct detection of gamma photons and recoil electrons in silicon rather than traditional indirect detection via a scintillator crystal.…”

“…PETiPIX has already been extensively evaluated and characterised via Monte Carlo simulation, using the GATE Monte Carlo simulator with classical image reconstruction techniques (Li et al 2013). An overall spatial resolution of 0.29 mm FWHM was obtained using filtered backprojection, and sensitivity was estimated to be 0.01%.…”

“…To provide sufficient DoI information and increase intrinsic spatial resolution, successive generations of PET scanners have tended to reduce the size of the scintillation crystals-or, in the extreme case, may eliminate the scintillator altogether, instead using direct gamma photon detection in pixellated semiconductor detector arrays (typically fabricated from relatively thick silicon or CZT) (Domenico et al 2007, Habte et al 2007, Park et al 2007, Li et al 2013. This geometry results in a very large number of potential LoRs, especially for 3D scanners with a multi-ring geometry.…”

“…The proposed techniques are evaluated by applying them to PETiPIX, a representative ultra high resolution DoI PET system (Li et al 2013), and are shown to provide the expected very high system matrix compression ratio. The proposed methods for system matrix generation are shown to yield images exhibiting excellent image quality.…”