針孔單光子發射斷層掃描成像系統已被廣泛應用於小動物實驗中。在此基礎之上，使用多針孔準直儀可以增加成像系統的靈敏度而螺旋形偵收軌道則可以進一步增加視野或成像系統照野大小。傳統的針孔單光子發射斷層掃描所使用的系統模型為射束追蹤法，包含了單射束射束追蹤與多射束射束追蹤演算法。然而，在所有的射束追蹤法的演算法皆沒有辦法處裡針孔之有限孔徑與單光子發射斷層掃描的深度效應問題。在此研究中，我們提出一個全新的系統模型計算方式來模擬光子的發射與偵收模式，稱為體素基準模型。體素基準模型是透過幾何計算而得，此模型同時包含了有針孔限孔徑與單光子發射斷層掃描之深度效應的資訊。此外，射束追蹤法會造成的資料遺失現象也不會在體素基準模型中發生。結果顯示，使用體素基準模型在多針孔系統中，能重建出較高品質的影像，並且可以判斷體素基準模型亦適用於螺旋形軌道偵收系統。多針孔螺旋形偵收系統乃是一個高空間解析度與大照野的成像系統，而體素基準模型除了適用於這個成像系統外，更可以進一步提高影像品質，進而可以大幅提高針孔單光子發射斷層掃描有更高的臨床實驗與研究的可用性。

Pinhole SPECT imaging systems are widely used in small animal studies. The multi-pinhole system improves the low sensitivity while the helical trajectory system improves the field of view (FOV) size. Conventional system model for the pinhole system is based on ray-tracing (RT) algorithm including single-ray ray-tracing (SRRT) and multi-ray ray-tracing (MRRT).However, the RT series algorithm could not solve the finite aperture effect
and depth effect in a pinhole SPECT system. Moreover, both SRRT andMRRT algorithm may cause missing information because of characteristic
geometry of pinhole collimator. Here, we proposed a new system model
called voxel-driven (VD) model to describe the emission and detection of photons. The VD model are calculated based on geometry and this model accounts for both depth effect and finite aperture for pinhole SPECT imaging system. The missing-information phenomenon caused by RT algorithm won’t happen in this model. The results show that using VD model can improve the reconstructed images’ quality and this model are also suitable to be applied in helical trajectory pinhole SPECT system. Multi-pinhole and helical trajectory pinhole SPECT is a high resolution and larger FOV imaging system, and VD model is not only suitable for this imaging system but also able to further improve the image quality.

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