| 摘要: | 由於小動物單光子放射電腦斷層掃描(Single Photon Emission Computed Tomography, SPECT)的系統架構簡單且成本低廉，十分適合應用於臨床前生醫研究。並可藉由小動物模型探討與人體相關疾病之致病機轉、進程，以及治療的藥物與方法。為開發高影像品質與高解析度之小動物針孔SPECT系統，於本研究將提出小動物針孔SPECT系統之系統校正與配置最佳化。
應用針孔SPECT於小動物造影研究中，為使針孔SPECT系統達到高空間解析度，取得高準確度的系統矩陣(H矩陣)為基本要件。於本研究，採用融合量測數據與數值模型快速建立固定式與圓軌旋轉式針孔SPECT的H矩陣。透過格點掃描與系統校正實驗所取得之實驗資料，可分析各立體像素之點響應函數(Point Response Function, PRF)與系統配置幾何參數間的關係，並建立PRF數值模型。而完整針孔SPECT的H矩陣則由PRF數值模型估算取得。本研究藉由全實驗量測與所提之H矩陣建立方法，其系統表現比較結果驗證所提之H矩陣建立方法可行性。
本研究藉由準直儀配置最佳化提出小偵測面積針孔SPECT應用於小鼠心臟造影之最佳準直儀配置。此準直儀配置最佳化流程藉數值模型評估不同配置設計之針孔SPECT的系統表現，以快速挑選最佳候選配置。隨後，透過偵測任務與傅立葉串音方法評估各最佳候選配置之系統影像品質與空間解析度，並藉由影像品質與空間解析度權衡函數決定最佳準直器配置。 此外，一系列假體重建將驗證此最佳準直器配置針孔SPECT的系統表現。
本研究亦提出簡廉閃爍晶體伽瑪相機，由NaI(Tl)閃爍晶體、64陽極光電倍增管、簡易訊號讀出設備及高效最大可能性值位置估算組成。簡易訊號讀出設備藉對稱分流電路、訊號處理電路及多通道訊號擷取系統產生16通道數位訊號。最後，本研究藉模擬與實驗評估此伽瑪相機之偵測器表現。;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. |
