J Nucl Med. 2007; 48 (Supplement 2):426P
Instrumentation & Data Analysis: Image Generation
Image Generation Posters |
Simulation study to optimize system performance of a hybrid SPECT
Y Shao1,
T. Ma2,
P. Manchiraju1 and
R. Yao1
1 Nuclear Medicine, State University of New York at Buffalo, Buffalo, New York;
2 Tsinghua University, Beijing, China
1773
Objectives: A prototype collimator insert has been used to acquire SPECT images from a microPET scanner (hybrid SPECT), which consisted of multiple slits along the axial direction and septa perpendicular to the scanner axis to form 2D geometry for reducing the scatter events. This study is to investigate the trade-offs between different collimator geometries and the system performance at various imaging scenarios. Methods: GATE has been used to simulate the collimator design with different geometries. Imaging performance in resolution, sensitivity, and scatter fraction have been investigated. An image of hot-rods phantom with the same geometry as a commercial Ultra-Micro Hot-Rods phantom (Data Spectrum Inc.) was simulated and reconstructed with OSEM using system matrices. To accelerate the simulation, projection data from a uniform water phantom was generated first; the data were used to extract the system matrices; with the known origin of each detected interaction, only the events that originated from the "hot-rod" region was accepted for the image recon. Such process was repeated for different acquisition angles. Results: The simulated trans-axial resolutions agree with the theoretical calculations very well, with detector intrinsic resolution defined as the half of the scintillator crystal size (1.6 mm). For septa with neighboring sheets separated by half of the axial crystal size, the axial resolutions vary from 1.7 to 1.9 mm with 10 to 40 mm source-to-collimator distances, which are close to the best possible axial resolution that can be achieved (1.6 mm). The sensitivity for an 8 slit-aperture collimator with 36 mm FOV radius is 0.023%. The scatter is significantly reduced by the 2D geometry (~9% scatter fraction). The reconstructed image of hot-rods phantom shows that all rods with diameters at and above 1.0 mm are clearly separated. Conclusions: The simulation has demonstrated that well designed slit-aperture collimator can lead to high resolution, good image quality and suitable FOV size for small animal imaging. New data processing method is effective to accelerate the simulation.
