| dc.description.abstract | Since small-animal SPECT systems typically possess simple configurations and relatively lower cost, small-animal SPECT is suitable for preclinical research. Micro-SPECT along with small-animal models of human diseases is widely used to study disease mechanisms and investigate potential therapies. For developing high image quality and high resolution pinhole SPECT systems, methods of system calibrations and configuration optimizations of small-animal pinhole SPECT systems are proposed in this study.
In pinhole SPECT applied to small-animal studies, it is essential to have an accurate imaging system matrix, called H matrix, for high-spatial-resolution image reconstructions. Generally, an H matrix can be obtained by various methods, such as measurements, simulations or some combinations of both methods. In this study, combination methods of measurement and analytic models are utilized to obtain H matrices of pinhole SPECT systems, including stationary and circular-orbit rotating pinhole SPECT imagers. The method utilizes a grid-scan experiment on selected voxels and parameterizes the measured point response functions (PRFs) into 2D Gaussians. The imaging property database can be built with the measured PRFs. In addition, the geometry of pinhole SPECT systems can be described by the geometric projection models. The PRFs of missing voxels are interpolated by the relations between the Gaussian coefficients and the geometric parameters of the imaging system. A full H matrix is constructed by combining the measured and interpolated PRFs of all voxels. The feasibilities of proposed interpolation methods are validated with PRF estimations, phantom reconstructions and detection task evaluations.
An optimized configuration of multi-pinhole aperture can improve the spatial resolution and the sensitivity of pinhole SPECT simultaneously. In this study, an optimization strategy of the multi-pinhole configuration with a small detector is proposed for mouse cardiac imaging. To accelerate the optimization process, the candidates of optimal multi-pinhole configuration are decided by the preliminary evaluations with the analytic models. Subsequently, the pinhole SPECT systems equipped with the designed multi-pinhole apertures are modeled in GATE to generate the H matrices for the system performance assessments. The area under the ROC curves (AUC) of the designed systems is evaluated by detection tasks with their corresponding H matrices. In addition, the spatial resolutions are estimated by the Fourier crosstalk approach, and the sensitivities are calculated with the H matrices of designed systems, respectively. A trade-off function of AUC and resolution is introduced to find the optimal multi-pinhole configuration. Furthermore, a series of OSEM reconstruction images of synthetic phantoms are reconstructed with the H matrices of designed systems.
In this study, micro-SPECT based on a scintillation gamma camera is developed. The camera is composed of a NaI(Tl) scintillator, compact readout electronics and a maximum-likelihood position estimator (MLPE) for a 64-anode PMT. The electronic readout system consists of a symmetric charge division circuit, the signal processing circuits and a multi-channel DAQ system to output 16 channel digital signals. Moreover, the MLPE is developed with the multivariate normal model and the truncated center-of-gravity combined with local directed search method to estimate the gamma-ray event position. Simulation and experimental studies are performed to verify the feasibility of the proposed readout electronics and MLPE. | en_US |