The Advantages of Direct Magnification Technic in the Newborn Chest

Abstract

The roentgenographic examination of the newborn chest is difficult because of the small size of the structures and lesions to be evaluated. The premature infant further intensifies this difficulty. The problem does not limit itself to the question of seeing information that is there, for at times this may be partially remedied by a magnifying glass or other means of indirect magnification. The problem includes the inability to resolve structures that are usually seen in older children and adults, as well as the poor definition of densities which even when indirectly magnified remain ill-defined and uninterpretable. Leinbach (1) in a study of the diameter of pulmonary artery branches in normal chest films of children had great difficulty with those under one year of age, for arterial visualization was too poor for measurement. The problem of distinguishing between vascular and parenchymal abnormalities in the newborn has also been a chronic one. An example of this has been the difficulty in differentiating total anomalous venous return from the aspiration syndrome (2) or other parenchymal processes (3). The difficulties in interpreting the regular newborn chest film are amplified even further by the severity and acuteness of the medical problems associated with the infant who does not breathe normally. Because of these limitations of the regular chest film, direct magnification radiography of the newborn chest has been studied in over 150 cases. Method The direct magnification films are obtained with a Siemens fine-focus tube, powered by a 3-phase generator. The effective focal spot of 0.26 mm is achieved by the use of an 11· target angle rather than the usual 17·. This tube, with a high-speed anode (6,000 rpm), has a capacity of 8 kw as compared with the 2 kw rating of a standard 3-mm focus tube. The tube is located within a special room in the Newborn Special Care Unit (Fig. 1). When necessary, the infant's time out of special environmental equipment can be limited to a few minutes. In addition to a magnification film, a regular-size chest film is obtained at the same time for comparison, using the same fine-focal spot. If the usual larger focal spot tube were employed for the comparison film, a larger penumbra and less clarity would be expected. Therefore, the magnification film in every case is compared to a regular film of exceptional quality. When the patient's size permits, both the regular and the magnification radiographs are obtained on the same 14 × 17-in. film. The cassette is placed on the Plexiglas table (Fig. 1) and directly under the supine infant for the regular film, and then placed on the floor under the table with an appropriate adjustment of the tube height to obtain a direct linear magnification of approximately 2.5×. Technics used for the comparison film and the direct magnification film are presented in Table I.