We investigated the effect of radiographic screen systems regarding image contrast. The screens used in the experiments were made of calcium tungstate and gadolinium oxysulfide phosphor. Gadolinium oxysulfide screens, having a K absorption energy lower than that of calcium tungstate, have a lower image contrast to X-rays in the 70-100 kV region. Difference in the K absorption energy of phosphors used in the screens results mainly in discrepancy of image contrast. Therefore, image contrast is affected by the subject, film and "screen" contrast.
The renal plasma flow was determined conventionally by the excretive ratio to urine using a ^<131>I-Hippuran renogram. In this report, we proposed the renal clearance, the product of the disappearance rate coefficient and the maximum counts of the bladder, for the simple quantitative value of renal plasma flow. The disapperance rate coefficient was calculated by approximating the exponential function of the initial slope from the disappearance curve of the heart. The renal clearances was compared with the renal plasma flow calculated by the conventional method. The results gave a high correlation coefficient of r=0.91. The renal clearances can be calculated easily and it offers useful renogram information.