[An approximation for improving the accuracy of compartmental analysis after intravenous 133Xe].

Perfusion of transplanted kidneys is studied in our clinic by intravenous injection of 133Xe with subsequent graphic compartmental analysis of time-activity curves. Where there is poor perfusion of the renal cortex, it is not possible to obtain a half-value time for the first compartment--which is the significant measure for specific blood flow -- since few points are available for the tail end of the curve. A correction is described which produces an approximation to a bolus, based on the time-activity curve of the expired air. If this is applied to the proximal part of the time-activity curve, with respect to background activity, compartmental analysis can be performed with a higher degree of accuracy in the calculation of renal perfusion.