A Study On SPECT Imaging With Multi-Parallel-Beam Collimators

Single-Photon Emission Computed Tomography (SPECT) is a common nuclear medical imaging techniques. It shows the physiological activities of human body by the tomography of the radiopharmaceutical distribution. In order to increase the sensitivity and reduce the acquisition time while maintain a large field of view (FOV), SPECT with multi-parallel beam (MPB) collimators are proposed in this article. The multiplexed MPB collimators is build by cutting out suits of gamma ray channels (GRCs) in the transverse direction.In order to study the characteristics of MPB, this work starts from the geometry conditions of MPB and gives the point spread function (PSF) of oblique parallel-beam (OPB) with effective hole length which caused by the introduction of GRCs. the axial and transverse PSF are written with the geometric conditions. Furthermore, the sensitivity and the traditional full width at half maximum (FWHM) spatial resolution are calculated from PSF. Because of the introduction of multiplexing, beside the FWHM resolution, root mean squared (RMS) resolution are also given to evaluated the effects of GRCs. In order to prove the mathematical results, MCNP program is used in simulation, and the record and analyze method of the particle traces is provide. The result of simulations are compared with theoretical predictions by analysis of the particle traces. We divided the transmission and the scattering form the particles which reach the detector, and analyze their influence on PSF, sensitivity and spatial resolution. After evaluate the characteristics of MPB, we mathematically model the collimators in two dimension, and calculate the system matrix with opening angle correction. In the image reconstruction, a uniformed cylinder without noise is used to evaluated the artifacts caused by the collimators in reconstruction. Then, Jaszczak phantom is use to observe the variation of the spatial resolution. In order to study the noise characteristics of the collimator system, simulation data with Poisson distribution noise is used. Uniformed cylinder phantom shows the image convergence and the noise amplification, and the multi hot lesion phantom shows the image quality in different depths. Finally, MLEM algorithm is used to prove the transmission correction of different materials in the reconstruction of MC simulation. Finally a preliminary study of the parameter optimization is studied using OSEM algorithm.MPB collimators show the many characteristics in the study. It has a high sensitivity by using the multiplexing. More photons reach to the surface of detector, which makes the sensitivity doubled. Compared to other methods in increasing the sensitive, MPB also maintains a high spatial resolution. The theoretical derivation and the MC simulation results shows that the MPB with small GRCs almost has a same spatial resolution as high sensitivity PB collimators. The MPB with a large GRCs also has a better spatial resolution than the PB collimators with a same sensitivity. The MPB collimators has higher transmission but lower scattering percentage. The MC results show that the MPB have larger transmission than PB, and we also give a transmission correction method by using an effective hole length in reconstruction. The MC results also shows that the scattering is limited (about1%). The reconstructed image of MPB do not show any additional artifacts, but it shows a smaller variation of spatial resolution than PB by analyze the hot lesions in different depth, it also has a lower noise amplification and a slower convergence but a better image quality. The reconstruction of the MC simulation shows that a better image quality appears at a high subset number and a high noise level.