Radioactivity measurement and data processing

Radioactivity measurement and data processing

After separating B and F, the radioactivity of the labeled antigen-antibody complex (B) can be measured, and the free labeled antigen (F) can also be determined according to the RIA experiment method and purpose. There are two types of instruments used for radioactivity measurement: crystal scintillation counters that measure radiation (marked with 125I, 131I, 37Cr as tracers) and liquid scintillation counters that measure gamma rays (marked with 3H, 32P, 14C) Because the RIA currently uses 1251 markers, the former is more commonly used and has a higher degree of automation.

The crystal scintillation counter includes three basic parts: NaI scintillation crystal, photomultiplier tube and counter. The principle of detecting Ding rays is to use Ding rays to irradiate the scintillator-NaI (T1) crystal to excite the crystal molecules. During deexcitation, the scintillator emits a certain wavelength of fluorescence, and the photomultiplier tube converts the very weak fluorescence into photoelectrons and Zoom in 107 times. The electrical signal output from the photomultiplier tube is amplified by the amplifier and screened by the single-channel splitter, and finally the obtained signal is displayed on the scaler. The radioactive signal measured by the instrument is the number of electrical pulses output by the instrument. The unit is: counts per minute (cps); if you want to calculate the radioactive decay of the nuclide, it is decay per minute (disintegration per minute, dpm) or decay per second ( disintegration persecond, dps), but need to understand the detection efficiency of the instrument (η).

After obtaining the above experimental data, it is necessary to draw a standard curve (dose-response curve) to quantify the analyte: that is, the different concentrations of the standard antigen are plotted on the abscissa, and the corresponding radioactivity count (cpm) measured at each concentration point or using the calculated parameters [ B / (B + F), B / F or B / Bo] is the ordinate; in addition, in order to make the curve easy to linearize (reduce the error of checking value), the concentration of the standard product on the abscissa is usually logarithmic (log or ln) Said. Based on the reaction parameters measured or calculated by the sample tube, the corresponding antigen concentration to be detected can be found through the standard curve. Currently, computers are generally used for data processing, automatic drawing of the standard curve and printing of sample antigen concentration.