Developing medical imaging systems in nuclear medicine using GATE (Geant4 Application for Tomographic Emission)

Full text: One of the aims of nuclear medical imaging research is to optimize the design of imaging systems and to improve the quality and quantitative accuracy of the reconstructed images. In medical imaging systems, Monte Carlo modeling is used to solve the transport equation describing the interaction of photons with non-uniformly attenuating human body structures and complex detector geometries, present in nuclear medicine imaging systems. Among existing Monte Carlo simulation software, Geant4 (Geometry and Tracking 4) has been widely used to simulate applications in many fields, such as particle, nuclear and medical physics. It provides well validated physics models, geometry modeling tools and efficient visualization utilities. The GATE (Geant4 Application for Tomographic Emission) system is a modular, versatile, scripted simulation tool kit, developed in C++ by the Geant4 collaboration (Agostinelli et al, 2003). They decided to foster long-term support and maintenance by sharing code development among many research groups forming the OpenGATE collaboration (Jan et al, 2004). GATE was developed to simulate emission tomography, as SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography) systems, but has been extended to computed tomography (CT) systems. The usability of GATE is greatly improved by a scripting mechanism by which users can design and control simulations, from geometry, detection and source modeling, using macros. One of the most innovative features of GATE is the handling of time dependent phenomena, which includes detector motion, patient motion, radioactive decay, dead time, time of flight, and tracer kinetics. Interfaces to voxelized phantoms and image reconstruction packages are also available. A number of human and small animal PET, SPECT and hybrid commercial systems have been modeled using GATE. The latest version allows its use for dose calculations in internal dosimetry and modeling of radiation therapy experiments (Jan et al, 2011). Finally, GATE has been extended to simulate the scintillation photons through the crystal to the light sensor and the conversion of these photons into electronic signals. These optical simulations may help to better understand the performance of existing systems and assist in research on novel detectors. In this paper, we present an overview of GATE framework and its functionalities. Some examples of the application of GATE in the development of new imaging systems and its validation against real data obtained with PET and SPECT commercial systems will be provided. (author)