Dilmanian F A, Lidofsky L J, Stamatelatos I, Kamen Y, Yasumura S, Vartsky D, Pierson R N, Weber D A, Moore R I, Ma R
Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Phys Med Biol. 1998 Feb;43(2):339-49. doi: 10.1088/0031-9155/43/2/009.
The prompt-gamma neutron activation facility at Brookhaven National Laboratory was upgraded to improve both the precision and accuracy of its in vivo determinations of total body nitrogen. The upgrade, guided by Monte Carlo simulations, involved elongating and modifying the source collimator and its shielding, repositioning the system's two NaI(Tl) detectors, and improving the neutron and gamma shielding of these detectors. The new source collimator has a graphite reflector around the 238PuBe neutron source to enhance the low-energy region of the neutron spectrum incident on the patient. The gamma detectors have been relocated from positions close to the upward-emerging collimated neutron beam to positions close to and at the sides of the patient. These modifications substantially reduced spurious counts resulting from the capture of small-angle scattered neutrons in the NaI detectors. The pile-up background under the 10.8 MeV 14N(n, gamma)15N spectral peak has been reduced so that the nitrogen peak-to-background ratio has been increased by a factor of 2.8. The resulting reduction in the coefficient of variation of the total body nitrogen measurements from 3% to 2.2% has improved the statistical significance of the results possible for any given number of patient measurements. The new system also has a more uniform composite sensitivity.
布鲁克海文国家实验室的瞬发伽马中子活化装置进行了升级，以提高其体内全身氮含量测定的精度和准确性。此次升级在蒙特卡罗模拟的指导下进行，包括延长和改造源准直器及其屏蔽装置、重新定位系统的两个碘化钠（铊）探测器，以及改善这些探测器的中子和伽马屏蔽。新的源准直器在238钚铍中子源周围有一个石墨反射器，以增强入射到患者身上的中子谱的低能区。伽马探测器已从靠近向上出射的准直中子束的位置重新定位到靠近患者且在患者两侧的位置。这些改进大幅减少了碘化钠探测器中因捕获小角度散射中子而产生的杂散计数。10.8兆电子伏14氮（n，伽马）15氮谱峰下的堆积本底已降低，使得氮峰与本底之比提高了2.8倍。全身氮测量的变异系数由此从3%降至2.2%，提高了在任何给定患者测量次数下结果的统计显著性。新系统还具有更均匀的复合灵敏度。
