Quantification of tissue self-absorption of weak β-radiation in lyophilized whole-body sections of rats

Whole-body autoradiography has been widely used in the investigation of the distribution of radiolabeled compounds in animals. The newly introduced radioluminography offers a reliable way of quantifying the radioactivity distribution within whole-body sections. Since the radioactivity is distributed over the entire depth of the section, self-absorption of beta-radiation in tissues is supposed to relevantly affect the detection of radioactivity at the section surface. The self-absorption of radiation energy (C-14) was investigated in 28 organs/tissues of routinely produced lyophilized rat sections. Nonradioactive whole-body sections with different thickness between 20 and 120 mu m were placed between a homogeneous C-14 source and the imaging plates to detect the transmitted radioactivity, The selfabsorption was expressed in terms of percentage of transmission of the radioactivity through the sections. Transmission decreased with increasing section thickness, e.g., from 44% (20 mu m) to 28% (120 mu m) for blood. Comparison of three complete sets of data disclosed intertissue variations of up to about 30% (i.e., +/- 15%) disregarding bone. A defined bandwidth of +/- 15% around the blood transmission would cover the transmission of almost all tissues. Thus, for most organs radioactivity can be quantified by direct comparison with radioactive blood calibration samples. (C) 2000 Academic Press.