雙光子斷層掃瞄系統可行性評估蒙地卡羅模擬研究

Feasibility Study of A Dual Photons Emission Computed Tomography (DuPECT) system - A Monte Carlo Simulation

郭翰(Kuo, Han)

指導教授 ： 莊克士

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2009年)

摘要

核子醫學上，兩個主要的分子影像儀器即為單光子斷層造影(SPECT)與正子斷層造影；SPECT與PET空間解析度表現與下列因素有關：SPECT解析度上的限制，在一般情形下主要受限於技術(例：準直儀的設計)；在PET影像，受限兩個物理因素：positron range與non-collinearity，兩者最後限制了系統解析度。
本研究目的為：以蒙地卡羅方式模擬同時結合SPECT與PET優勢的雙光子斷層掃描(DuPECT)。期許能解決PET核種由迴旋加速器製造所造成的高成本與短半衰期等問題，並獲得比SPECT系統上同核種更高的影像解析度。本實驗DuPECT方法使用縫隙(slit)、孔狀型(hole)準直儀搭配同位素Indium-111進行。
In-111核種半衰期為2.8天且衰變時99.995%會放出兩個能量分別為171 keV及245 keV的γ光子，由於縫隙式與孔狀型可以準直放射出的光子並與DuPECT上的同符線路獲得同符事件，即可以數學公式重建出空間一平面與一直線的交點，交點即為影像同位素衰變處。
模擬結果可推測若使用能同時發出雙光子的核種，DuPECT概念即可行。本方法可提供比同核種在SPECT系統下更佳的空間解析度。另能獲得即時影像(real time image)。雖仍有待克服的問題，但DuPECT在未來仍有相當的可能性。

關鍵字

In-111 ； 雙光子 ； 斷層掃描 ； 蒙地卡羅

並列摘要

In nuclear medicine, the two major molecular imaging modalities namely are single photon emission tomography (SPECT) and positron emission tomography. Spatial resolution performance in PET and SPECT is related to a number of different factors. A general observation is that improvements in SPECT resolution are effectively only limited by technology (e.g., collimator design), whereas in PET imaging, two physics-related limitations, namely positron range and photon non-collinearity, ultimately limit system resolution.
The purpose of this work is to simulate the application of dual photons computed tomography (DuPECT) which is considered to combine the benefits of SPECT and PET at the same time. It is expected to alter the problem of the high cost of isotopes used in PET. They are generated from the cyclotron and their half-life are too short to use. Also to obtain higher resolution compared to same isotopes in SPECT. The slit, hole collimators and the isotope In-111 were used in the DuPECT method.
In-111 disintegrates and emits two γ photons with 171keV and 245 keV energy by over 99.99%. The data that would be used to reconstruct images by calculating the intersection of a plane and a line is from collimating the emitted photons by slit and hole collimators and obtaining the coincidence by the coincidence circuit in DuPECT system. The intersection is also where the isotope decayed.
The simulation results show that the concept of DuPECT method is feasible if the isotope would emit two photons. The spatial resolution is also better than SPECT. Furthermore, the reconstructed image on DuPECT could be real time image. But there are still some problems. Nevertheless, DuPECT still has lots of possibilities in the future.

參考文獻

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