Baur L A, Allen B J, Rose A, Blagojevic N, Gaskin K J
James Fairfax Institute of Paediatric Clinical Nutrition, Children's Hospital, Camperdown, New South Wales, Australia.
Phys Med Biol. 1991 Oct;36(10):1363-75. doi: 10.1088/0031-9155/36/10/005.
The design, calibration and evaluation of a facility for in vivo prompt gamma neutron capture analysis of total body nitrogen in children is described. The patient is scanned in both supine and prone positions, across a vertically collimated beam from a 1 GBq 252Cf fission source. Two NaI(T1) detectors are placed on either side of the patient, perpendicular to both the neutron beam and the scanning direction. The effective dose equivalent delivered to a child during an 840 s scan is approximately 0.14 mSv (QF = 10). Correction factors for nitrogen background (width-dependent), hydrogen background (1-4% of hydrogen gamma ray peak) and the differential attenuation of nitrogen and hydrogen gamma rays (width-dependent) can be applied to the measured nitrogen-to-hydrogen gamma ray counts ratio. By using the mass of hydrogen (based on body mass and fat mass) as an internal standard, the nitrogen mass can then be determined. Measurements with a urea-containing box phantom show that the current precision (CV) of the net nitrogen counts and of the nitrogen-to-hydrogen counts ratio is +/- 2.0% and +/- 1.5%, respectively. Using small anthropomorphic and other phantoms, estimation of the mass of nitrogen has a precision of +/- 1.4 to 5.4% and an accuracy of 97.1 to 101.5%.
本文描述了一种用于儿童体内全身氮元素的瞬发伽马中子俘获分析设备的设计、校准和评估。患者分别在仰卧位和俯卧位接受扫描，扫描时穿过来自1 GBq 252Cf裂变源的垂直准直束。两个碘化钠（铊）探测器放置在患者两侧，垂直于中子束和扫描方向。在840秒的扫描过程中，传递给儿童的有效剂量当量约为0.14毫希沃特（品质因数QF = 10）。可将氮背景（与宽度有关）、氢背景（氢伽马射线峰的1 - 4%）以及氮和氢伽马射线的微分衰减（与宽度有关）的校正因子应用于所测量的氮与氢伽马射线计数比。通过将氢的质量（基于体重和脂肪质量）用作内标，进而可以确定氮的质量。使用含尿素的盒式体模进行的测量表明，净氮计数和氮与氢计数比的当前精度（变异系数CV）分别为±2.0%和±1.5%。使用小型拟人化体模和其他体模，氮质量的估计精度为±1.4%至5.4%，准确度为97.1%至101.5%。
