Regional renal function measured by videodensitometry.

The videodensitometric method was applied for the determination of regional renal blood flow and filtration fraction using 2 contrast agents, where Thorotrast represented an intravascular indicator and Angiografin will be distributed in the intravascular and interstitial space and, in addition being freely filtrable in the glomeruli. The contrast density was continuously monitored from the light intensity on a TV-screen, where the region to be analyzed could be outlined by a light pen. The passage time of Angiografin analyzed from the videodensitometric curve was compared to that of 125I-labelled Angiografin as analyzed in the venous effluent. The two methods yielded almost identical values. Knowing the volume of distribution of the agents, the regional blood flow could be calculated and was found to be the same for the two contrast agents used. The curves for Thorotrast showed a rapid passage with a rapid declination towards the base-line. For Angiografin the curves ended in an almost horizontal plateau reflecting the fraction of the Angiografin filtered and remaining into the tubular system. The height of the plateau was then used for the determination of the filtration fraction. The figure obtained was compared to that obtained by conventional clearance techniques, and was found to yield similar values. It is concluded that the videodensitometric method allows for evaluation of the functional characteristics of the kidney in addition to the anatomical information given by the conventional angiography performed in parallel to the videodensitometric measurements.