The Comparative Study Of Image Reconstruction From Multi Parallel Beam Collimators

As one of the most representative devices in the current field of nuclear medicine,SPECT has been widely used for imaging human organs like brain,internal,bone and other organs.It can provide information about human organs' physiological process for clinical diagnosis or study.The activity of radiopharmaceutical taken by human must be controlled under the threshold for security reasons.The low activity will limit the photon count detected by the detector system and will result in bad image quality of the radiopharmaceutical distribution.To improve the trade-off between spatial resolution and sensitivity,a multi-parallel beam collimator design is proposed in this dissertation.A comparative study of the reconstructed image from multi-parallel beam collimator and parallel beam collimator is implemented.The image is reconstructed using the projection image from Monte Carlo simulation.The design of multi-parallel beam collimator is first given in this dissertation where the gamma ray channels are introduced in axial slices and transverse slices.The PSF formula of multi-parallel beam collimator is given,then sensitivity and RMS resolution is derived based on PSF.The relationship between view spread function and PSF of multi-parallel beam collimator is discussed in this dissertation and the response to plane source is derived based on view spread function.To verify the PSF formula,a Monte Carlo simulation of detector system detecting a point source is implemented by using GATE software.The curves of PSF from simulation and formula are plotted.To compare the trade-off between spatial resolution and sensitivity of multi-parallel beam collimator and parallel beam collimator,a series of simulations of multi-parallel beam collimator introducing gamma ray channels in transverse slices,multi-parallel beam collimator introducing gamma ray channels in axial slices and transverse slices and parallel beam collimator are implemented.The resolution-sensitivity curves are plotted based on projection image.To compare the ability of image reconstruction,Monte Carlo simulations of the 3D phantom of multi-parallel beam collimator and parallel beam collimator are implemented.The OS-EM iterative algorithm is used to reconstruct the image of phantom.A quantitative comparison of the reconstructed images from multi-parallel beam collimator and parallel beam collimator is implemented in terms of contrast,signal-to-noise ratio and normalized standard deviation.The results of comparison between multi-parallel beam collimator and parallel beam collimator can be gained as follows.The multi-parallel beam collimator introducing gamma ray channels has a better spatial resolution and sensitivity trade-off than parallel beam collimator for the reason that the channels can compensate for the decreasing sensitivity when improving collimator's resolution.In the same noise level,hot source contrast of multi-parallel beam collimator is higher than that of parallel beam collimator,especially for hot source with a small diameter.However,in the same noise level,cold source contrast of multi-parallel beam collimator is lower than that of parallel beam collimator.During the reconstruction process,the image convergence speed of multi-parallel beam collimator is slower than that of parallel beam collimator and the noise propagation speed is quicker than that of parallel beam collimator.