. Roentgen interpretation; a manual for students and practitioners . tion andforced expiration. ^ / \ Fig. 98.—Mitral disease. The patient is then rotated to the left so that his right chest isin contact with the screen, and the posterior mediastinal space withthe arch of the aorta are studied. By changing the position of thepatient slightly, the size of the shadow of the aorta will be seen togrow larger or smaller. The smallest possible shadow which can beobtained represents the true diameter of the aorta plus the amountof magnification due to its distance from the screen. A tracing
. Roentgen interpretation; a manual for students and practitioners . tion andforced expiration. ^ / \ Fig. 98.—Mitral disease. The patient is then rotated to the left so that his right chest isin contact with the screen, and the posterior mediastinal space withthe arch of the aorta are studied. By changing the position of thepatient slightly, the size of the shadow of the aorta will be seen togrow larger or smaller. The smallest possible shadow which can beobtained represents the true diameter of the aorta plus the amountof magnification due to its distance from the screen. A tracing is made of the aorta in this position for comparison 120 THE CHEST with the tracing made in the anteroposterior view. From the twotracings an estimate can be made of the amount of overlapping ofthe ascending and descending aorta. The glass with its tracing isremoved and the pulsation of the various chambers of the heartis studied and compared. If there is anything in the findingswhich suggests a pericardial effusion, the patient is examined in theprone Fig. 99.—The water-bottle shape of the heart shadow seen in pericardialeffusion with the patient upright. After the fluoroscopic observations are completed, a mark is placedon the patients chest opposite the center of the heart shadow toserve as a point upon which to focus the tube for the plate which istaken with the patient standing. The focal spot of the tube shouldbe at a distance of at least six feet from the plate. Special care must be taken so to place the patient that the centralrays from the tube pass through the chest at right angles to its THE HEART AND GREAT VESSELS 121 transverse diameter. At this distance a small amount of displace-ment of the tube to the right or the left from the median line doesnot appreciably distort the heart shadow, but a slight rotation ofthe patient does produce definite distortion. In stout patients it is better to have the plate in contact with thechest wall and the patient
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