[Simplified method of obtaining the correction factor for calculating ventricular volumes].

For the accurate measurement of ventricular volume it is required the obtainment of a correction factor for the magnification caused by the non-parallel X-rays and the "pincushion" distortion, which causes more magnification in the periphery than in the center of the fluoroscopic field. The Kasser and Kennedy method is based in the attainment of the relation between the actual and projected dimensions of a micrometrically calibrated grid filmed at the distance measured between the intensifier tube and the mid-thoracic line during the ventriculography. This technique is very accurate but expensive and troublesome. With the simpler catheter method it is obtained the relation between the projected and actual linear dimensions of the ventriculographic catheter inmediately before ventriculography. This study was aimed to compare the accuracy of the catheter method and two other proposed methods, in which the relation between the projected and actual dimensions were obtained by filming one central coin or five arranged through the fluoroscopic field at the distance measured between the tube and the patients during the ventriculography. These four correction factors were obtained in 15 patients undergoing a diagnostic cardiac catheterization. The catheter method showed a poor correlation with the grid method (r = 0.34), while both coin methods showed a high correlation with the grid method (r = 0.93 and 0.92, respectively). It is concluded that the catheter method is inaccurate and therefore is unwise to use it for the estimation of ventricular volumes. Because the peripheric distortion is clinically unimportant, the central coin methods is proposed as a simplified method for obtaining the magnification correction factor.(ABSTRACT TRUNCATED AT 250 WORDS)