A very important part in the cardiovascular examination of a patient is accurately to determine the size of the heart. In particular, and justifiably, much reliance is placed on x-ray measurement of heart size, provided certain sources of error are recognized and taken into account. The commonest cause of error has been that of distortion of the heart shadow by magnification when the x-ray tube is too close to the heart; this error has been much reduced and largely discounted by obtaining films with the tube from 6 to 7 feet (2 meters) behind the chest, with the front of the chest pressed against the film. This error is thus almost universally avoided, except that it is not yet everywhere appreciated that even the teleroentgenographic ("6 or 7 foot" film) heart shadow is considerably larger than the accurate heart shadow projection or orthodiagram; a statement should always be made as
McGINN S, WHITE PD. EPIPERICARDIAL FAT: ITS NONRECOGNITION A COMMON CAUSE OF ERROR IN X-RAY MEASUREMENT OF HEART SIZE. JAMA. 1936;107(3):200–201. doi:10.1001/jama.1936.02770290028007
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