Analysis of radiohippuran renogram by subtraction of extrarenal radioactivity.
A method is presented for the simple, non-computerized analysis of the radiohippuran renogram by subtraction of the extrarenal radioactivity as monitored simultaneously by a detector centered over the manubrium sterni. This method requires the application of a calibration factor, relating the level of radioactivity recorded by the sternal detector to that over each kidney area at the end point of the phase of initial rise on each side separately. The results in 15 normal individuals showed a narrow range of values, indicating a high degree of resolution. Verification of the basis of this method of analysis was obtained by accounting for all of the counting rate as extrarenal sources in the tracings of nephrectomized subjects. A further advantage is that the tracing recorded by the sternal detector may be used to calculate renal blood flow.