Extra shielding for improved signal-to-noise in 3D whole-body PET
Extra shielding for improved signal-to-noise in 3D whole-body PET
复制标题
额外屏蔽可改善 3D 全身 PET 的信噪比
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
M. Daube
中科院分区：
文献类型：
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作者：
R. Laforest;P. Cutler;M. Daube
在3D PET测量中，已知直接FOV外的活动会降低直接FOV内的信噪比，主要是通过增加随机重合的总体速率。在3D脑研究中，已经成功地实施了患者周围的附加屏蔽的各种配置，以限制单个视场，从而减少由断层扫描仪测量的随机性。在这项工作中，我们扩展了这一想法，用于在躯干与屏蔽配置组成的两个“蛤壳”屏蔽铅周围的患者上方和下方的轴向FOV。电极导线的厚度为6 mm，轴向长度为10或20 cm，弯曲成C形，以适合体模或患者躯干。蛤壳的上半部分靠在塑料轮上，塑料轮在安装在患者托盘边缘的两个轨道上移动，每个护罩的下半部分固定在下面。将屏蔽放置在直接视野之外，并尽可能靠近患者。噪声等效计数（NEC）曲线进行了测量，有和没有屏蔽周围的轴向长圆柱体模。然后将2D和3D患者研究的NEC率与体模导出的NEC曲线进行比较，以预测使用屏蔽可能获得的信噪比增益。在全身FDG研究的典型放射性浓度范围内，我们估计无屏蔽3D提供了约两倍的NEC优势。我们的防护罩似乎只在这个活动范围的高端提供了一个小的额外改进。
In 3D PET measurements, activity outside of the direct FOV is known to degrade signal-to-noise within the direct FOV, primarily by increasing the overall rate of random coincidences. In 3D brain studies, various configurations of additional shielding around the patient have already been successfully implemented to limit the singles field of view, and thereby reduce the randoms measured by the tomograph. In this work, we extend this idea for use in the torso with a shielding configuration consisting of two "clam-shell" shields of lead surrounding the patient both above and below the axial FOV. The lead is 6 mm thick by 10 or 20 cm in axial length, and curved into a C-shape to fit around the phantom or the patient's torso. The top half of the clam-shell rests on plastic wheels which travel on two rails mounted to the edge of the patient pallet, and the lower half of each shield is fixed beneath. The shields are placed just outside the direct field of view and as close to the patient as possible. Noise Equivalent Count (NEC) curves were measured with and without shields in place around an axially long cylindrical phantom. The NEC rates from 2D and 3D patient studies were then compared with the phantom-derived NEC curves to predict the signal-to-noise gain possible by using the shields. Over the range of activity concentrations typical of whole body FDG studies, we estimate unshielded 3D offers an NEC advantage of approximately a factor of two. Our shield appears to provide only a small additional improvement at the high end of this activity range.