モンテカルロ計算を用いたSPECT用コリメータの設計

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  • Collimator analysis using a Monte Carlo method in single photon emission CT

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Abstract

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SPECT画像における空間解像度の低下やコントラストに影響を及ぼす要因の一つに収集データに混入する散乱線の問題がある。本研究では、SPECT装置のコリメータ部分における散乱線の定量的な評価をモンテカルロシミュレーションによって行なった。対象としたコリメータは平行多孔型のモデルを用い、隔壁（セプタ）の厚さ、孔の大きさ、核種等を変えた幾つかのモデルについてシミュレーションを行なった。

In Single Photon Emission CT (SPECT), compton scattering and penetration in collimator septa have an effect on spatial resolution and contrast of reconstructed images. In order to reconstruct accurate SPECT images, it is important to analize the behavior of these photons. To the task, Monte Carlo simulation is an effective method in estimating scattered and penetrated photons quantitatively. The purpose of the study is to estimate the distribution of incident photons to the detector surface equipped with a parallel-hole collimator accurately. In the collimator model the hole shape was supposed to be square and the distance between the collimator and the point source was 10cm. We examined four kinds of parallel-hole collimators. Collimator types are low energy general purpose (hole size:2.5mm/septa thickness:0.25mm), low energy high resolution (3.0mm/0.3mm), general purpose for 300keV (3.0mm/1.0mm), and medium energy general purpose (3.0mm/2.0mm). The results showed that when the energy of a point source was low, few photons were scattered and penetrated in the collimator septa. In case of a high-energy source, many photons were scattered and penetrated at the collimator septa.

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