Improvements in an in vivo neutron activation analysis (NAA) method for the measurement of fluorine in human bone
Improvements in an in vivo neutron activation analysis (NAA) method for the measurement of fluorine in human bone
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DOI：
10.1088/0967-3334/34/10/1329
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发表时间：
2013-10-01
影响因子：
3.2
通讯作者：
Prestwich, W. V.
中科院分区：
文献类型：
--
作者：
Mostafaei, F.;McNeill, F. E.;Prestwich, W. V.
我们之前发表了一种使用中子活化分析 (NAA) 体内测量骨氟化物的方法，并在对环境暴露人群的试点研究中证明了该技术的实用性。该方法涉及在麦克马斯特大学加速器实验室的辐射腔中激活手，并在由九个探测器组成的“4p”NaI(Tl)探测器阵列中采集由此产生的伽马射线信号。在本文中，我们描述了该方法的一系列改进。这是通过测量掺杂不同浓度的氟和固定量的钠、氯和钙的手模拟体模来研究的。自我们首次发表以来，对该技术的四项改进进行了测试。之前发布的使用该系统进行体模测量的检测限为 0.66 mg F/g Ca。加速器辐照和检测设施搬迁至实验室的新区域，检测系统中又增加了一台检测器。结果发现，这可将检测限降低至 0.59 mg F/g Ca，即 1.12 倍（可能是因为更好的检测屏蔽和额外的检测器）。开发了一套新的模型，在这项工作中我们表明，他们将使用锂上 2.15 MeV 质子产生的中子辐照的模型中氟化物的最低可检测限提高了 1.55 倍。我们将之前使用来自九个检测器的总信号获得的检测限与通过在反符合模式下获取光谱获得的检测限进行比较，以减少骨骼中氯的干扰信号。结果发现，氟与氯（干扰信号）的检测比率提高了 2.8 倍，并且最终的最小检测限降低了 1.2 倍。我们研究了改变伽马射线采集时间的影响。我们之前发布的数据使用了一系列 3 个 10 秒的采集，然后是 300 秒的计数。研究发现，将采集更改为一系列 6 次 5 秒采集可将检测限进一步提高 1.4 倍。我们还提供的数据表明，如果在较短的时间内将中子剂量传递到体模，即增加剂量率并缩短照射时间，则检测限可以进一步降低 1.35 倍。结果发现，通过采用所有这些变化，检测限总体提高了 3.9 倍。该技术现在的体模检测限为 0.17 mg F/g Ca，而之前的检测限为 0.66 mg F/g Ca。该系统现在可以在人类志愿者身上进行测试，看看是否可以使用这种技术将确诊为氟中毒的个体与加拿大普通人群区分开来。
We previously published a method for the in vivo measurement of bone fluoride using neutron activation analysis (NAA) and demonstrated the utility of the technique in a pilot study of environmentally exposed people. The method involved activation of the hand in an irradiation cavity at the McMaster University Accelerator Laboratory and acquisition of the resultant gamma-ray signals in a '4p' NaI(Tl) detector array of nine detectors. In this paper we describe a series of improvements to the method. This was investigated via measurement of hand simulating phantoms doped with varying levels of fluorine and fixed amounts of sodium, chlorine and calcium. Four improvements to the technique were tested since our first publication. The previously published detection limit for phantom measurements using this system was 0.66 mg F/g Ca. The accelerator irradiation and detection facilities were relocated to a new section of the laboratory and one more detector was added to the detection system. This was found to reduce the detection limit (possibly because of better detection shielding and additional detector) to 0.59 mg F/g Ca, a factor of 1.12. A new set of phantoms was developed and in this work we show that they improved the minimum detectable limit for fluoride in phantoms irradiated using neutrons produced by 2.15 MeV protons on lithium by a factor of 1.55. We compared the detection limits previously obtained using a summed signal from the nine detectors with the detection limit obtained by acquiring the spectra in anticoincidence mode for reduction of the disturbing signal from chlorine in bone. This was found to improve the ratio of the detection of fluorine to chlorine (an interfering signal) by a factor of 2.8 and the resultant minimum detection limit was found to be reduced by a factor of 1.2. We studied the effects of changing the timing of gamma-ray acquisition. Our previously published data used a series of three 10 s acquisitions followed by a 300 s count. Changing the acquisition to a series of six 5 s acquisitions was found to further improve the detection limit by a factor of 1.4. We also present data showing that if the neutron dose is delivered to the phantom in a shorter time period, i.e. the dose rate is increased and irradiation shortened then the detection limit can be reduced by a further factor of 1.35. The overall improvement in detection limit by employing all of these changes was found to be a factor of 3.9. The technique now has an in phantom detection limit of 0.17 mg F/g Ca compared to a previous detection limit of 0.66 mg F/g Ca. The system can now be tested on human volunteers to see if individuals with diagnosed fluorosis can be distinguished from the general Canadian population using this technique.