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To the Editor: Dr. Brito takes exception to your editorial comment because "the technique of taking a radiograph has nothing to do with the way it is examined." While his statement is generally true, there is an important exception: stereoscopic roentgenography.
A set of stereoscopic roentgenograms is made by taking two films while the patient holds still and with the two films in as nearly the same position as is practical. Between the exposures, the x-ray tube is shifted a distance proportional to the interpupillary distance.
To minimize geometric distortion of the heart, frontal chest roentgenograms are usually made in the PA (posteroanterior) projection, which is the radiologist's shorthand notation that the beam of x-rays passes through the patient from spine to sternum before it reaches the film. While a set of stereoscopic PA chest roentgenograms may be viewed in many ways, a few of which give an illusions of
DORST JP. WHICH END IS UP?-Reply. Am J Dis Child. 1965;110(5):573–574. doi:10.1001/archpedi.1965.02090030597021