陳怡君

The single photon emission microscope (SPEM) is an instrument which is developed in order to acquire high spatial resolution single photon emission computer tomography (SPECT) projection images which are necessary for tomographic reconstruction. The SPEM system consists of a thallium-doped cesium iodide [CsI(Tl)] columnar scintillator, a 7-pinhole collimator, a demagnifying tube (DM Tube) and an electron-multiplying charge-coupling device (EMCCD). For any imaging system, it is crucial to have an accurate imaging system matrix, called H matrix, in order to obtain high spatial resolution image reconstructions. In order to generate the H matrix, geometric calibration and the established imaging model are used. In order to get the geometry of the 7-pinhole SPEM system, a three-point phantom filled with 99mTc pertechnetate liquid solution is rotated in order to acquire 64 projections. The geometry of the camera, including the pinhole positions, the parameters of the axis of rotation and the linear and rotary shifts are estimated by getting the centroids of the projections. The grid-scan experiment is used to parameterize the measured point response functions (PRFs) into 2D Gaussians. These PRFs is used to create the imaging model which consists of flux and width models. By having the geometric parameters and the established imaging model, the complete H matrix can be built. In this paper, a helical reconstruction algorithm is developed in order to lessen axial blurring brought by circular-orbit reconstructions and thus, improve sampling and increase resolution. The helical orbit is accomplished through the combination of circular motion and linear motion of the imaged object along the axis of rotation (AOR). The projection images of the three-point phantom and resolution phantom are reconstructed with the H matrix of the designed system. The image reconstruction software tool is based on the maximum likelihood algorithm and its ordered-subset version. Correction of the designed H matrix is being explored in order to produce better reconstruction images.