Imaging of weak-source distributions in LSO-based small-animal PET scanners
Imaging of weak-source distributions in LSO-based small-animal PET scanners
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DOI：
10.2967/jnumed.107.040584
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发表时间：
2007-10-01
影响因子：
9.3
通讯作者：
Thompson, Christopher J.
中科院分区：
文献类型：
--
作者：
Goertzen, Andrew L.;Suk, Joon Young;Thompson, Christopher J.
由于 Lu-176 的存在，基于正硅酸镥 (LSO) 或正硅酸钇钇 (LYSO) 的 PET 扫描仪在闪烁体晶体中具有固有放射性，Lu-176 会通过 β 发射衰变，然后发生一种或多种瞬发伽马射线发射。这会导致内在的真实计数，在扫描低水平活动时可能会影响图像。在基于 LSO 的小动物 PET 扫描仪上评估了这种内在活动对低水平活动和不同能量窗口的影响。方法：测量了 100 至 750 keV 范围内的一系列低级鉴别器 (LLD) 的固有计数率和灵敏度。结合测量值和该扫描仪之前发布的数据，估算了 100 Bq 至 100 kBq 活动水平的噪声当量计数率 (NECR) 作为 LLD 的函数。使用强度分别为 55、220 和 940 Bq 以及 LLD 水平为 250、350 和 400 keV 的三个 Ge-68 源进行幻影成像。使用对比度噪声比（CNR）分析并将观察到的源活动比率与真实比率值进行比较来评估图像。结果：固有真实计数率从 250 至 750 keV 能量窗口的每秒 940 次计数 (cps) 降低至 400 至 750 keV 窗口的 < 2 cps。对于这 2 个能量窗口的外部正电子源，检测到的真实事件的灵敏度相应下降了 2 倍。 NECR 与 LLD 曲线显示出高峰值形状，最佳 LLD 约为 425 keV。当使用 250-750 keV 的能量窗口时，幻影图像结果由内在真实计数主导。通过将 LLD 提高到 400 keV，内在真实计数几乎完全被消除。对于窄能量窗口，每个源的 CNR 较高，并且在使用 350 和 400 keV LLD 水平采集的图像中可以轻松可视化 55 Bq，但在使用 250 keV LLD 时则不然。使用 400 keV 的 LLD 采集并使用二维滤波反投影重建的图像在定量上是最准确的。结论：通过将 LLD 提高到 400 keV，可以在基于 LSO 的动物 PET 系统中可视化 < 1 kBq 的源，以排除由于 LSO 中存在的内在活性而导致的大部分计数。
Lutetium oxyorthosilicate (LSO)- or lutetium-yttrium oxyorthosilicate (LYSO)-based PET scanners have intrinsic radioactivity in the scintillator crystals due to the presence of Lu-176, which decays by beta-emission followed by one or more prompt gamma-ray emissions. This leads to intrinsic true counts that can influence the image when scanning low levels of activity. An evaluation of the effects of this intrinsic activity for low levels of activity and different energy windows is performed on an LSO-based small-animal PET scanner. Methods: Intrinsic count rate and sensitivity were measured for a range of lower-level discriminators (LLDs) ranging from 100 to 750 keV. The noise equivalent count rate (NECR) as a function of LLD for activity levels from 100 Bq to 100 kBq was estimated using a combination of measurement and previously published data for this scanner. Phantom imaging was performed using three Ge-68 sources of strength 55, 220, and 940 Bq and LLD levels of 250, 350, and 400 keV. The images were assessed using a contrast-to-noise ratio (CNR) analysis and by comparing the observed ratio of source activities to the true ratio value. Results: The intrinsic true count rate is reduced from 940 counts per second (cps) for a 250- to 750-keV energy window to < 2 cps for a 400- to 750-keV window. There is a corresponding 2-fold drop in sensitivity for detected true events for external positron sources for these 2 energy windows. The NECR versus LLD curves showed a highly peaked shape, with the optimum LLD being approximately 425 keV. The phantom image results were dominated by the intrinsic true counts when an energy window of 250-750 keV was used. The intrinsic true counts were almost completely removed by raising the LLD to 400 keV. The CNR for each of the sources was higher for the narrow energy window and the 55 Bq could be easily visualized in images acquired with LLD levels of 350 and 400 keV but not when the 250-keV LLD was used. Images acquired with an LLD of 400 keV and reconstructed with 2-dimensional filtered backprojection were the most quantitatively accurate. Conclusion: It is possible to visualize sources of < 1 kBq in LSO-based animal PET systems by raising the LLD to 400 keV to exclude the majority of the counts due to the intrinsic activity present in the LSO.