Langenback E G, Foster W M, Bergofsky E H
Department of Medicine, SUNY at Stony Brook 11794.
J Toxicol Environ Health. 1989;27(1):139-52. doi: 10.1080/15287398909531284.
We determined the overall external counting efficiency of radiolabeled particles deposited in the sheep lung. This efficiency permits the noninvasive calculation of the number of particles and microcuries (microCi) from gamma-scintillation lung images of the live sheep. Additionally, we have calculated the attenuation of gamma radiation (120 keV) by the posterior chest wall and the gamma-scintillation camera collection efficiency of radiation emitted from the lung. Four methods were employed in our experiments: (1) by light microscopic counting of discrete carbonized polystyrene particles with a count median diameter (CMD) of 2.85 microns and tagged with cobalt-57 (57Co), we delineated a linear relationship between the number of particles and the emitted counts per minute (cpm) detected by well scintillation counting; (2) from this conversion relationship we determined the number of particles inhaled and deposited in the lungs by scintillation counting fragments of dissected lung at autopsy; (3) we defined a linear association between the number of particles or microcuries contained in the lung and the emitted radiation as cpm detected by a gamma scintillation camera in the live sheep prior to autopsy (external counting efficiency); and (4) we compared the emitted radiation from the lungs of the live sheep to that of whole excised lungs in order to calculate the attenuation coefficient (ac) of the chest wall. The mean external counting efficiency was 4.00 X 10(4) particles/cpm (5.1 X 10(-3) microCi/cpm), the camera collection efficiency was 1 cpm/10(4) disintegrations per minute (dpm), and the ac had a mean of 0.178/cm. The external counting efficiency remained relatively constant over a range of particles and microcuries, permitting a more general use of this ratio to estimate number of particles or microcuries depositing after inhalation in a large mammalian lung if a similarly collimated gamma camera system is used.
我们测定了沉积在绵羊肺内的放射性标记颗粒的整体外部计数效率。该效率使得能够根据活羊的γ闪烁肺图像对颗粒数量和微居里（μCi）进行无创计算。此外，我们还计算了后胸壁对γ辐射（120 keV）的衰减以及γ闪烁相机对肺部发射辐射的采集效率。我们的实验采用了四种方法：（1）通过光学显微镜对计数中值直径（CMD）为2.85微米且标记有钴 - 57（⁵⁷Co）的离散碳化聚苯乙烯颗粒进行计数，我们描绘了颗粒数量与通过井型闪烁计数检测到的每分钟发射计数（cpm）之间的线性关系；（2）根据这种转换关系，我们通过对尸检时解剖的肺组织碎片进行闪烁计数来确定吸入并沉积在肺内的颗粒数量；（3）我们定义了肺内所含颗粒数量或微居里与尸检前活羊体内γ闪烁相机检测到的作为cpm的发射辐射之间的线性关联（外部计数效率）；（4）我们将活羊肺部发射的辐射与整个切除肺的辐射进行比较，以计算胸壁的衰减系数（ac）。平均外部计数效率为4.00×10⁴颗粒/cpm（5.1×10⁻³μCi/cpm），相机采集效率为1 cpm/10⁴每分钟衰变次数（dpm），ac的平均值为0.178/cm。在一系列颗粒和微居里范围内，外部计数效率保持相对恒定，如果使用类似准直的γ相机系统，这使得该比率更广泛地用于估计大型哺乳动物肺吸入后沉积的颗粒数量或微居里。
