Choi C W, Barker W C, Buvat I, Carrasquillo J A, Bacharach S L
Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda MD 20892-1180, USA.
Nucl Med Commun. 1997 Jan;18(1):79-86. doi: 10.1097/00006231-199701000-00016.
There is increasing clinical interest in the use of quantitative imaging for radiopharmaceuticals labelled with 111In. Dual-energy-window (DEW) scatter correction is a frequently used component of planar geometric mean quantitative imaging, but it is known that the scatter multiplier k suffers from significant dependence on the characteristics of the scatter medium. Phantom studies with a variety of source geometries were carried out to determine the clinical impact of this dependence on the quantitative accuracy of tumour imaging carried out in conjunction with attenuation correction. Spheres of various sizes (5-20 ml volumes) containing approximately 3.7 MBq (100 microCi) 111In were imaged at a variety of depths (4.8-10.5 cm) within an elliptical water-filled phantom, as well as in air. Geometric mean emission images were acquired using a 20% photopeak window at 247 keV and a 10% scatter window at 205 keV. These emission images were corrected for attenuation using measured 99Tcm transmission data that were scaled to 111In photon energies. Scatter correction was performed in two ways: (1) using the standard DEW method and (2) using a modified DEW method that takes into account benign scatter in the detector crystal. Errors in the activity estimates ranged from -4% to +3% for method 1 in water, and -5% to +3% for method 2 in water. In air, method 1 ranged from -13% to -5%, and method 2 ranged from -10% to -1%. Method 1 was found to yield an accuracy equivalent to that of method 2, except in conditions of very low patient scatter, when the modified method behaved significantly better. We conclude that in a variety of realistic geometries, variations in scatter fraction as determined by the DEW scatter correction method combined with appropriate attenuation correction need not inhibit accurate absolute quantitation of spherical 'tumours' labelled with 111In when using planar imaging.
临床上对使用定量成像技术研究用铟 - 111标记的放射性药物的兴趣日益浓厚。双能窗（DEW）散射校正是平面几何平均定量成像中常用的组成部分，但已知散射乘数k对散射介质的特性有显著依赖性。我们进行了各种源几何形状的体模研究，以确定这种依赖性对结合衰减校正进行的肿瘤成像定量准确性的临床影响。将含有约3.7 MBq（100微居里）铟 - 111的各种大小（体积为5 - 20毫升）的球体在椭圆形充水体模内以及空气中的各种深度（4.8 - 10.5厘米）进行成像。使用247 keV处的20%光电峰窗和205 keV处的10%散射窗采集几何平均发射图像。这些发射图像使用按铟 - 111光子能量缩放的实测锝 - 99m传输数据进行衰减校正。散射校正通过两种方式进行：（1）使用标准DEW方法，（2）使用考虑探测器晶体中良性散射的改进DEW方法。在水中，方法1的活度估计误差范围为 - 4%至 + 3%，方法2在水中的误差范围为 - 5%至 + 3%。在空气中，方法1的误差范围为 - 1３%至 - 5%，方法2的误差范围为 - 10%至 - 1%。发现方法1产生的准确性与方法2相当，除了在患者散射非常低的情况下，此时改进方法表现明显更好。我们得出结论，在各种实际几何形状中，当使用平面成像时，由DEW散射校正方法结合适当的衰减校正所确定的散射分数变化并不一定会妨碍对用铟 - 111标记的球形“肿瘤”进行准确的绝对定量。
