The importance of magnification in left ventriculography

A method of measuring the magnification of ventriculograms is described. The catheter in the ventricle is X-rayed on cine film together with a radio-opaque ruler attached to the table. A second cine run is exposed after shifting the table by an amount which can be determined from the ruler. The magnification is equal to the distance that the catheter moves on the projected angiogram divided by the actual distance moved. Studies to prove the accuracy and reproducibility of the method have been undertaken. In random series of 48 patients, the linear magnification factor varied between 1.04 and 1.46. The cubic magnification as used for calculating ventricular volume ranged from 1.12 to 3.11. The error by ignoring the magnification can therefore be 211% and by taking a mean value, up to 62%.