Influence of image filtering on fully automatic measurement of left ventricular ejection fraction

Pre-filtering of gated blood pool studies, before fully automatic measurement of left ventricular ejection fraction, should be able to improve the results in terms of success and accuracy, compared to unfiltered series of pictures. We have evaluated 12 filters refering to four different principles (Metz, Wiener, Butterworth and band-pass) and correlated the results with those obtained without filtering, as well as with a reference achieved by an experienced observer, using a manual technique of regions of interest drawing. Most filters (10 out of 12) provided 100% success and correlations with coefficients higher than 0.9, and finally we propose to use in clinical practice the Butterworth filter, with 0.2 cycles per pixel cut-off frequency and 10th order, mainly due to its independence of the characteristics of the imaging system (no involvement of the modulation transfer function) rather than to its excellent results, although not significantly different from others.