本研究中，使用取樣完整性係數(SCC, Sampling Completeness Coefficient)評估單光子放射電腦斷層掃瞄系統(SPECT)在單針孔及多針孔下，針對偵測器所作之圓形軌跡及螺旋軌跡掃描，其影像擷取及三維影像重建的適切性，藉以優化掃描軌跡來提高實驗數據之準確性。更進一步，可以評估實驗所需要之影像品質，在預備實驗的階段先作影像預測評估，減低錯誤率，提高整體實驗規劃之效率。 我們所使用之取樣完整性係數原理來自於圖伊條件(Tuy’s Condition)，起源於電腦斷層掃描系統(CT)，藉由系統架構之相似性以及偵測器位置的改變，修改應用至單光子放射電腦斷層掃描系統。再於本實驗室提出之單針孔及四針孔SPECT系統架構下，以本研究開發之繞行軌跡，由49×49mm2偵測器感測，發展小鼠全身造影的取樣完整性係數評估。 儀器控制方面，藉由LabVIEW使用含三軸線性平移台以及旋轉平台的定位控制系統，執行偵測器平均響應函數(MDRF, Mean Detector Response Function)實驗，並撰寫小鼠影像擷取實驗的儀控程式，使其兼具人性化及自動化設定。 ;In this study, a sampling completeness evaluation model for pinhole SPECT is proposed based on the Tuy’s condition in cone-beam CT: every plane intersected with the object space should also intersect the sampling orbit at least once. Since the sampling geometries are similar in cone-beam CT and pinhole SPECT, the focal point of cone-beam CT is substituted with the pinhole center of pinhole SPECT in the sampling completeness evaluation.The pitch limitation for helical trajectories in cone-beam CT is also modified to incorporate the magnification in pinhole SPECT imaging. The Sampling Completeness Coefficient (SCC) values are calculated by the proposed model for single- and multi-pinhole Micro-SPECT systems to evaluate the performance of circular, single-helix and double-helix trajectories. According to the reconstructions of 7-disk Defrise phantom with the circular-orbit 4-pinhole SPECT systems, the axial distortion exists in the regions where SCCs are less than 0.9. Therefore, the sufficient sampling threshold is set at SCC greater than or equal to 0.9. For mouse whole-body imaging in a cylindrical Field of View (FOV) enclosed by a 40×40×100 mm3 cuboid with a 4-pinhole SPECT system, two helical scanning modes, the single helix and double helix, are compared with their SCC maps. The results show that the helical 4-pinhole SPECT system with double helix has 96.9% voxels satisfying the SCC threshold. A 1/2 extended pitch at both ends of the FOV further increases the sufficient sampling volume to 99.7%. In the instrument control part, all the data acquisition routines are programmed in the LabVIEW environment to attain automation and user-friendly interfaces. A positioning system with three orthogonal linear stages and one rotary stage is utilized in the experiments for the Mean Detector Response Function (MDRF), the system matrix, and mouse whole-body imaging.
