Performance simulation of a compact PET insert for simultaneous PET/MR breast imaging

Abstract

We studied performance metrics of a small PET ring designed to be integrated with a breast MRI coil. Its performance was characterized using a Monte Carlo simulation of a system with the best possible design features we believe are technically available, with respect to system geometry, spatial resolution, shielding, and lesion detectability. The results indicate that the proposed system is able to achieve about 6.2% photon detection sensitivity at the center of field-of-view (FOV) (crystal design: 2.2×2.2×20mm3, height: 3.4cm). The peak noise equivalent count rate (NECR) is found to be 7886cps with a time resolution of 250ps (time window: 500ps). With the presence of lead shielding, the NECR increases by a factor of 1.7 for high activity concentrations within the breast (>0.9μCi/mL), while no noticeable benefit is observed in the range of activities currently being used in the clinical setting. In addition, the system is able to achieve spatial resolution of ~1.6mm (2.2×2.2×20mm3 crystal) and ~0.77mm (1×1×20mm3 crystal) at the center of FOV, respectively. The incorporation of 10mm DOI resolution can help mitigate parallax error towards the edge of FOV. For both 2.2mm and 1mm crystal designs, the spatial resolution is around 3.2–3.5mm at 5cm away from the center. Finally, time-of-flight (TOF) helps in improving image quality, reduces the required number of iteration numbers and the scan time. The TOF effect was studied with 3 different time resolution settings (1ns, 500ps and 250ps). With a TOF of 500ps time resolution, we expect 3mm diameter spheres where 5:1 activity concentration ratio will be detectable within 5min achieving contrast to noise ratio (CNR) above 4.