Kojima Akihiro, Matsumoto Masanori, Tomiguchi Seiji, Katsuda Noboru, Yamashita Yasuyuki, Motomura Nobutoku
Institute of Resources Development and Analysis, Kumamoto University, Japan.
Ann Nucl Med. 2004 Feb;18(1):45-50. doi: 10.1007/BF02985613.
We investigated scatter correction in transmission computed tomography (TCT) imaging by the combination of an uncollimated transmission source and a parallel-hole collimator. We employed the triple energy window (TEW) as the scatter correction and found that the conventional TEW method, which is accurate in emission computed tomography (ECT) imaging, needs some modification in TCT imaging based on our phantom studies. In this study a Tc-99m uncollimated line array source (area: 55 cm x 40 cm) was attached to one camera head of a dual-head gamma camera as a transmission source, and TCT data were acquired with a low-energy, general purpose (LEGP), parallel-hole collimator equipped on the other camera head. The energy spectra for 140 keV-photons transmitted through various attenuating material thicknesses were measured and analyzed for scatter fraction. The results of the energy spectra showed that the photons transmitted had an energy distribution that constructs a scatter peak within the 140 keV-photopeak energy window. In TCT imaging with a cylindrical water phantom, the conventional TEW method with triangle estimates (subtraction factor, K = 0.5) was not sufficient for accurate scatter correction (micro = 0.131 cm(-1) for water), whereas the modified TEW method with K = 1.0 gave the accurate attenuation coefficient of 0.153 cm(-1) for water. For the TCT imaging with the combination of the uncollimated Tc-99m line array source and parallel hole collimator, the modified TEW method with K = 1.0 gives the accurate TCT data for quantitative SPECT imaging in comparison with the conventional TEW method with K = 0.5.
我们通过将非准直透射源和平行孔准直器相结合，研究了透射计算机断层扫描（TCT）成像中的散射校正。我们采用三能量窗（TEW）进行散射校正，并且基于体模研究发现，在发射计算机断层扫描（ECT）成像中准确的传统TEW方法，在TCT成像中需要进行一些改进。在本研究中，将一个Tc-99m非准直线阵源（面积：55 cm×40 cm）连接到双头γ相机的一个探头作为透射源，并使用安装在另一个探头上的低能通用（LEGP）平行孔准直器采集TCT数据。测量并分析了透过各种衰减材料厚度的140 keV光子的能谱，以获取散射分数。能谱结果表明，透射的光子具有在140 keV光峰能量窗内形成散射峰的能量分布。在使用圆柱形水体模的TCT成像中，采用三角形估计的传统TEW方法（减法因子，K = 0.5）不足以进行准确的散射校正（水的μ = 0.131 cm⁻¹），而K = 1.0的改进TEW方法给出了水的准确衰减系数0.153 cm⁻¹。对于非准直Tc-99m线阵源和平行孔准直器相结合的TCT成像，与K = 0.5的传统TEW方法相比，K = 1.0的改进TEW方法为定量SPECT成像提供了准确的TCT数据。
