Antico A, Lima G, Arisi M, Ostan A, Morrica B
Allergology Department, Asola Hospital, Italy.
Ann Allergy Asthma Immunol. 2000 Aug;85(2):140-4. doi: 10.1016/S1081-1206(10)62454-4.
In dermatology and allergy there are clinical research circumstances where very small amounts of substances introduced into the skin have to be measured "in vivo." An example is the assay of reagents injected by prick test. As injected volumes are very small, it is necessary to use indicators that can be measured at very low concentrations. In in vitro studies, gamma-emitting radioisotopes have been shown suitable for use as the indicators. In in vivo studies, except for instruments devised for specific research requirements, the measurement of small sources is taken with a common gamma camera.
The purpose of the present study is to evaluate the experimental reliability of a gamma camera-based method to measure microvolumes labeled with radioisotopes and its suitable application in vivo studies.
Using a solution of 99m Tc-pertechnetate, we prepared, with precision pipettes, some sets of scalar volumes ranging from 1 micro to 200 picoliters, which correspond to activities between some micros and some hundreds of picocuries. The volumes were measured with a gamma camera both with and without a collimator. The overall reliability of the method under different experimental conditions was evaluated for sensitivity, precision, and accuracy. Last, a blind measurement was taken as a final check on the overall reliability of the method.
The volume-activity correlation appeared to be linear, with a Spearman coefficient higher than 0.99. The correlation straight lines of the measurements taken with and without a collimator proved that, in both cases, the linearity of the system did not change. The method showed a high degree of precision and accuracy. The maximum variation coefficient never exceeded 1.5% and the standard error 2%. The sampling error of the measured volumes was less than 8% in all the sets: up to 7% was due to the manual operations and to the technical characteristics of the micropipettes. The gamma camera measurement error ranged from 1% to 3%. The blind tests experimentally confirmed the overall reliability of the method.
The method we studied proved highly reliable and inexpensive. Measurement errors are almost exclusively due to sampling errors. The gamma camera is a device any nuclear medicine department is equipped with, and a solution of 99m Tc-pertechnetate is readily available.
在皮肤病学和过敏领域，存在一些临床研究情况，即需要在“体内”测量注入皮肤的极少量物质。例如，对皮内试验注射的试剂进行检测。由于注射体积非常小，有必要使用能够在极低浓度下进行测量的指示剂。在体外研究中，已证明发射γ射线的放射性同位素适合用作指示剂。在体内研究中，除了为特定研究需求设计的仪器外，小剂量源的测量使用普通γ相机进行。
本研究旨在评估基于γ相机的方法测量放射性同位素标记的微体积的实验可靠性及其在体内研究中的合适应用。
使用高锝[99mTc]酸盐溶液，我们用精密移液器制备了几组标量体积，范围从1微升至200皮升，这对应于从几微居里到几百皮居里之间的活度。使用γ相机在有准直器和没有准直器的情况下测量这些体积。在不同实验条件下评估该方法在灵敏度、精密度和准确度方面的总体可靠性。最后，进行盲法测量作为对该方法总体可靠性的最终检验。
体积 - 活度相关性呈线性，斯皮尔曼系数高于0.99。使用准直器和不使用准直器进行测量的相关直线证明，在两种情况下，系统的线性均未改变。该方法显示出高度的精密度和准确度。最大变异系数从未超过1.5%，标准误差为2%。在所有组中，测量体积的抽样误差小于8%：高达7%是由于手动操作和微量移液器的技术特性。γ相机测量误差范围为1%至3%。盲法试验通过实验证实了该方法的总体可靠性。
我们研究的方法被证明高度可靠且成本低廉。测量误差几乎完全归因于抽样误差。γ相机是任何核医学科室都配备的设备，高锝[99mTc]酸盐溶液也很容易获得。
