Investigation pseudo 3D imaging method for small field of view (SFOV) using a SFOV gamma camera

We have investigated a limited angle gamma imaging system that enables pseudo 3D reconstruction of small objects such as thyroid, prostate and etc. In this particular study, we are interested preliminary results using small phantom imaging that provides 3D imaging information by typical planar imaging configuration. To achieve the goal, we developed a system equipped with a multi-pinhole collimator and the corresponding reconstruction method that provides transverse slices of the small field of view (SFOV). Our group has been developing a high resolution SFOV gamma camera system. Simulation studies have been conducted using a geant4 application for tomographic emission (GATE) simulation tool. We make three sphere phantoms which lay through the center of FOV with different depths. An eight-pinhole collimator with 2mm diameter aperture was configured for the simulation. For image reconstruction, system matrix for a maximum likelihood expectation maximization (MLEM) was developed based on the geometry of the collimator. The projector and back-projector were separately implemented based on the ray-driven and voxel-driven methods respectively. Simulations have been conducted with respect to 60, 90, 120 degree angle spans and 3, 6, 9 degree angle pitches. Preliminary results showed that the system distinguished the three sphere phantoms (2.5 cm depth). In addition, Contrast enhancement of phantom regions was observed as number of iteration increased. In the future, we will continue to investigate the optimum pinhole configurations pinhole size, angle span, and angle pitch, etc.