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.