[Evaluation of the errors in analog recording of radionuclide dilution and clearance curves]

The mathematical expression for the function of changes in the output signal of the analog medium frequency pulse meter (MFPM), supplied on the input of the dilution curve (clearance) of a radioactive indicator, is obtained. The graphs illustrating the deformation of the initial curve at different MFPM time constants and different rates of the increase and decrease in the input signal, corresponding to the real conditions occurring in the study of the regional cerebral and muscular blood flow with the use of 133Xe clearance and the study of the blood flow volume through heart and large vessels with the use of RISA-131 dilution, are plotted. The errors introduced by the MFPM to the obtained data of the basic informative parameters--a period of half-dilution, the maximum value and the area under the curve are calculated. The graphs of the errors versus the MFPM time constants are normalized by the time units relative to the maximum of the corresponding initial curves thus enabling one to use the graphs as a versatile means in the course of assessment of the dilution and clearance curves' distortions introduced by the analogous MFPM. The analysis of the results obtained is presented.