本研究目的在以蒙地卡羅方法模擬雙光子斷層掃描(DuPECT)在小動物造影的表現。DuPECT是使用microPET的偵檢器以及SPECT常用的In-111核種，以期改善PET核種必須經由迴旋加速器產生的問題(成本高且核種半衰期短)，並且得到符合需求的解析度。In-111核種半衰期2.8天且99.995%會放出兩個能量分別為171keV及245keV的γ光子，利用microPET 系統的符合線路，可得每個In-111蛻變產生的兩個不同能量光子的同符事件(coincidence)，記錄其在偵檢器上的兩個位置，再利用其與多孔準直儀(multi-pinhole collimator)的兩條連線即可得一交點，因此，每記錄到一個同符事件便可得一個交點，此交點亦即核種發射的位置。在本研究中共設計5個實驗(pinhole孔徑的選擇、點射源在不同位置解析度之偵測、均勻度測試、活度定量測試以及衰減校正)以決定系統幾何及測試系統的各項特性。實驗結果顯示，使用直徑1.0 mm的點射源，在照野中心(CFOV)的解析度約為1.8 mm，靈敏度0.0295%，射源偏離CFOV越遠則變形的情況越嚴重，系統FOV為10 mm，均勻度約6.3%，由於隨機效應以及假影的影響，活度定量分析尚無法非常精確。模擬結果證明了DuPECT概念的可行性，只要能夠同時發出兩種能量不同的核種，即可使用DuPECT成像。目前的解析度與靈敏度尚未超越普遍使用的小動物核醫儀器，並且還有許多問題待改善，但現階段處於系統發展初期，未來將從多方面著手改善。

The purpose of this work is to simulate the application of dual photons computed tomography (DuPECT) in animal study. The detector of the micoPET 、multi-pinhole collimator and the isotope 111In were used in the DuPECT method. It is expected to alter the problem that the isotopes used in PET must be generated from the cyclotron (high costs and short half-life) and to obtain higher resolution. 111In disintegrates by >99.99% and then emits two γ photons with 171keV and 245keV energy. As a result of both the multi-pinhole collimator which could collimate the emitted photons and the coincidence circuit of the PET system which could obtain the coincidence, we can use the two coincidence events to each connect to the pinholes to obtain two lines which can intersect to a point but not a line of response (LOR) like microPET does. Each coincidence can use the above method to obtain one intersection which is also the position of decay. We devised 5 experiments in this paper (varies pinhole size、different position of the point source、uniformity、quantification and attenuation correction) to construct the geometry of the DuPECT system and to test the system. The results showed that the resolution in the central field-of-view is around 1.8 mm, the sensitivity is 0.0295%, the uniformity is around 6.3% and the distortion is more serious as the source farther from the CFOV. Due to the random effect and the artifact, the quantification is not precise. The simulation proved that the concept of DuPECT method is feasible if only the isotope would emits two photons with distinct energy. Both the resolution and the sensitivity are not as good as we expected. There are still many problems need to be solved, nevertheless, DuPECT is in its initial stage so that many things need to be done in the future.

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