Monte Carlo simulated model of a preclinical PET insert and experimental validation based on NEMA performance measurements

Abstract

Positron Emission Tomography combined with Magnetic Resonance (PET/MR) is a medical imaging method, used to investigate the distribution of a previously administered radioactive tracer in humans or animals. Among others, it can be used for diagnosis of cancer and neurological disorders. Before newly developed methods or tracers can be used in clinical routines, extensive research is necessary. This can be done using preclinical scanners, specifically designed for imaging small animals such as mice or rats, or using Monte Carlo simulations to reproduce the imaging process. However, Monte Carlo (MC) models for available scanners need to be established and compared to the real systems. In this work, a preclinical PET/MR system, the model ”Si 198”, manufactured by the ”Bruker BioSpin GmbH”, available at the Medical University of Vienna, was experimentally characterized following standardized performance measurements. Subsequently, the system was modeled in the MC simulation environment GATE. Then, the performance of the MC model was compared to its real counterpart. Specifically, the performance of the system was determined following the standardized measurement protocol ”NEMA NU4-2008”. In this process, the scanner was assessed regarding its sensitivity to radioactivity, its count rate behavior, its spatial resolution and the resulting image quality. For sensitivity measurements, a Na point source was stepped through the field of view along the scanner axis and the count rate was brought in relation to source-activity. To evaluate the count rate behavior, two F line sources in polyethylene cylinders with different dimensions were measured and the acquired counts were classified in scattered, random and true counts. The measurements for spatial resolution evaluation were performed with the same point source as sensitivity measurements, whereas for spatial resolution, the source was stepped transaxially through the field of view. The image quality was assessed using a complex cylinder system made from PMMA, which was filled with