Xiao Jianbin, de Wit Tim C, Zbijewski Wojciech, Staelens Steven G, Beekman Freek J
Department of Nuclear Medicine, Image Sciences Institute, University Medical Centre Utrecht, Utrecht, The Netherlands.
J Nucl Med. 2007 Apr;48(4):637-44. doi: 10.2967/jnumed.106.037259.
(201)Tl-Chloride ((201)Tl) is a myocardial perfusion SPECT agent with excellent biochemical properties commonly used for assessing tissue viability. However, cardiac (201)Tl SPECT images are severely degraded by photons scattered in the thorax. Accurate correction for this scatter is complicated by the nonuniform density and varied sizes of thoraxes, by the additional attenuation and scatter caused by female patients' breasts, and by the energy spectrum of (201)Tl. Monte Carlo simulation is a general and accurate method well suited to modeling this scatter.
Statistical reconstruction that includes Monte Carlo modeling of scatter was compared with statistical reconstruction algorithms not corrected for scatter. In the ADS method, corrections for attenuation, detector response, and scatter (Monte Carlo-based) were implemented simultaneously via the dual-matrix ordered-subset expectation maximization algorithm with a Monte Carlo simulator as part of the forward projector. The ADS method was compared with the A method (ordered-subset expectation maximization with attenuation correction) and with the AD method (a method like the A method but with detector response modeling added). A dual-head SPECT system equipped with two (153)Gd scanning line sources was used for simultaneously acquiring transmission and emission data. Four clinically realistic phantom configurations (a large thorax and a small thorax, each with and without breasts) with a cardiac insert containing 2 cold defects were used to evaluate the proposed reconstruction algorithms. We compared the performance of the different algorithms in terms of noise properties, contrast-to-noise ratios, the contrast separability of perfusion defects, uniformity, and robustness to anatomic variations.
The ADS method provided images with clearly better visual defect contrast than did the other methods. The contrasts achieved with the ADS method were 10%-24% higher than those achieved with the AD method and 11%-37% higher than those achieved with the A method. For a typical contrast level, the ADS method exhibited noise levels around 27% lower than the AD method and 34% lower than the A method. Compared with the other 2 algorithms, the ADS reconstructions were less sensitive to anatomic variations and had better image uniformity in the homogeneously perfused myocardium. Finally, we found that the improvements that can be achieved with Monte Carlo-based scatter correction are stronger for (201)Tl than for (99m)Tc imaging.
Our results indicate that Monte Carlo-based scatter correction is suitable for (201)Tl cardiac imaging and that such correction simultaneously improves several image-quality metrics.
氯化铊（(201)Tl）是一种心肌灌注单光子发射计算机断层显像（SPECT）剂，具有优异的生化特性，常用于评估组织活力。然而，心脏(201)Tl SPECT图像会因胸部散射的光子而严重退化。由于胸部密度不均匀、大小各异，女性患者乳房引起的额外衰减和散射，以及(201)Tl的能谱，对这种散射进行准确校正变得复杂。蒙特卡罗模拟是一种通用且准确的方法，非常适合对这种散射进行建模。
将包括散射蒙特卡罗建模的统计重建与未校正散射的统计重建算法进行比较。在ADS方法中，通过双矩阵有序子集期望最大化算法，同时利用蒙特卡罗模拟器作为前向投影器的一部分，对衰减、探测器响应和散射（基于蒙特卡罗）进行校正。将ADS方法与A方法（带衰减校正的有序子集期望最大化）和AD方法（一种类似A方法但增加了探测器响应建模的方法）进行比较。使用配备两个(153)Gd扫描线源的双头SPECT系统同时采集透射和发射数据。使用四种具有临床现实意义的体模配置（一个大胸部和一个小胸部，每个都有和没有乳房），以及一个包含2个冷区的心脏插入物，来评估所提出的重建算法。我们从噪声特性、对比噪声比、灌注缺损的对比可分离性、均匀性以及对解剖变异的鲁棒性等方面比较了不同算法的性能。
ADS方法提供的图像在视觉上的缺损对比度明显优于其他方法。ADS方法实现的对比度比AD方法高10% - 24%，比A方法高11% - 37%。对于典型的对比度水平，ADS方法的噪声水平比AD方法低约27%，比A方法低34%。与其他两种算法相比，ADS重建对解剖变异的敏感性较低，并且在均匀灌注的心肌中具有更好的图像均匀性。最后，我们发现基于蒙特卡罗的散射校正对(201)Tl成像的改善比对(99m)Tc成像更强。
我们的结果表明，基于蒙特卡罗的散射校正适用于(201)Tl心脏成像，并且这种校正同时改善了多个图像质量指标。
