[Application of harmonic analysis in quantitative heart scintigraphy (author's transl)]

Quantitative scintigraphy of the heart after equilibrium distribution of a radioactive tracer permits the measurement of time activity curves in the left ventricle during a representative heart cycle with great statistical accuracy. In the range of ventricular volumes which usually occur, the time activity curve corresponds with sufficient accuracy to the ventricular volume variation during one heart cycle. In cardiological terms, the parameters ejection fraction as well as maximum rates of ejection and filling have proved useful for evaluation of hemodynamic performance. By application of Fourier's analysis, criteria are to be attained in addition for evaluation of the volume curve as a whole. Thus the entire information contained in the volume curve is completely described in a Fourier spectrum. Because of the statistical noise, the volume curves drawn up from scintigraphic techniques require smoothing procedures, especially in determination of the differential quotients of ejection and filling rate. Smoothing by means of sliding average procedures causes a systematic deformation of the systolic dip and other similar regions of the curve, since the curve smoothened in this way does not converge towards the original curve at these points. Resynthesis after Fouier transformation seems to be an ideal method of smoothing because of its convergence in the minimum quadratic error for the type of function concerned.