A New Method for Determination of Left-to-Right Cardiac Shunts

Abstract

Left-to-right cardiac shunt quantitation can be determined from first pass radionuclide angiography. The traditional technique fits a gamma variate to the lung time-activity curve (TAC) and a second gamma variate to the recirculation portion of the curve. Problems may arise, however, with the fitting of the gamma variate to the subtracted recirculation curve. We have investigated a new technique in which the recirculation fitting is no longer required. The new method fits a gamma variate to the first-pass portion of the lung TAC. This gamma variate is used to generate a curve which simulates the expected shape of a normal lung TAC in response to systemic recirculation. The simulated data is then subtracted from the observed lung TAC. A correlation coefficient of r = 0.87 was obtained when these two methods were compared. We now prefer the new method since it overcomes the problem of fitting the subtracted recirculation position of the curve.