Radioisotope renogramに関する臨床的研究 第2編: Computer simulation法によるRadioisotope renogramの定量的解析についての研究

Abstract

[I] Quantitative Analysis of Radioisotope Renograms Since the introduction of radioisotope renogram in 1956 by Taplin et al. its usefulness as a kidney function test has been evident. Many methods of analysis, both qualitative and quantitative, have been presented. In the earlier studies, the RI renogram was interpreted on a purely qualitative basis，e.g. visual comparison of the tracings. For clinical purposes this method is still widely used. But differences in qualitative interpretations and high incidence of falsely positive or negative results have led to more objective semi-quantitative or quantitative interpretations The semi-quantitative methods compare the amplitudes of the curve at different times. Several investigators calculated ratios derived from measurements of amplitudes at selected parts of the curves. Another method utilizes value calculated from time axis of the renogram curve. Some of the most frequently used parameters are time to maximum count, time to 75 % or 50 % of the maximum count on the descending slope. More sophisticated mathematical analysis have been reported. One of the most thorough studies is that presented by Pircher et al., who measured 28 parameters derived from normal renograms. Hirakawa et al. suggest a quantitative interpretation by “Renogram index". The most advanced mathematical analysis, mostly based on the compartmental analysis, have been reported. Most of these studies are possible only when computers areavailable. Though these new methods of analysis are closest to a true RI renogram interpretation, their highly specialized content makes them available only to a few persons. However, the great potential value of aveliable precise method of studying unilateral renal function by RI renogram warrants a more intensive investigation of the possibility for an internationally accepted mode on quantitative analysis. [II ] Quantitative Analysis of Radioisotope Renogram by Analog Simulation Method By analog simulation method, 131I-Hippuran renogram and 131I-sodium iothalamate renogram with concomitant 25 minutes excretion rate are analyzed in terms of 1) total RPF and total GFR, 2) their right to left ratio, 3)“Mean Transit Time" as a sum of time delay and time constant. Over 5, 000 cases of analysis， this method has been fully evaluated as clinically useful renal function test. "Mean Transit Time" is an important parameter resulted from analog simulation and it indicates characteristically the delay in excretion of RI in patients with renal artery stenosis, hydronephrosis，polycystic kidney and nephrotic syndrome. Though the clinical usefulness of the quantitative interpretation of RI renogram by analog simulation method has been established，it does not follow that this method has no problems for argument. Some problems concerning this simulation method and parameters derived from it were discussed. In conclusion, in the quantitative analysis of RI renograms by the analog simulation method in terms of RPF and GFR， the correct urinary excretion rate of given RI and adequate diuretic state of patients are necessary conditions. [III] Quantitative Analysis 01 Radioisotope Renogram by Digital Simulation Method Using a mini-computer and “BASIC" program language, quantitative interpretation of RI renogram by digital simulation method was tried. The principles of this method are the same as that of analog simulation method. RI renogram counts are registered in the computer with paper tape perforation. Then, using RPF or GFR tracking programs, these counts are computed for calculating RPF or GFR and other parameters. Finally these computed parameters and RI renogram curve are automatically typed by the teletypewriter attached to the computer. Adopting this digital simulation method, the time for analysis is shorter than that of analog simulation and the simulation is carried out nearly automatically.