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December 21, 2001 -- This article continues our series of white papers on radiologic patient positioning techniques. Appearing each month on AuntMinnie.com, the series explores each of the major modalities. If you'd like to comment on or contribute to this series, please e-mail . Chest x-ray lateral decubitus positioning techniques Decubitus means lying down; thus, this projection is made with the patient lying on their side and the x-ray beam horizontal (parallel) to the floor. The primary goal of performing the lateral decubitus projection is to demonstrate fluid in the pleural cavity (a pleural effusion), which is otherwise not clearly visible on a supine or upright chest radiograph. Lateral decubitus films are helpful for determining if effusion is free flowing, and are also used to determine whether there is enough fluid to sample by thoracentesis. A lateral decubitus projection can also be helpful in showing small amounts of air in the pleural cavity (a pneumothorax) as well as air fluid levels in other cases.
Ask the patient to remove all clothing from the waist up, put on a hospital gown, remove any jewelry (necklace, earrings), and, if necessary, tie hair up on top of the head. Patient position considerations
For lateral decubitus chest radiographs, place a 14 x 17-inch (35 x 43-cm) film holder or IR behind the patient, either crosswise or lengthwise depending on their build. Adjust the IR so that it extends approximately 1 ½ - 2 inches (4-5 cm) beyond their shoulders. The source to image distance (SID) should be at a minimum of 72 inches (180 cm). Central ray The central ray (CR) is set horizontal and perpendicular to the center of the cassette. Using a horizontal beam is very important; otherwise air fluid levels or a pneumothorax (the primary goal of performing this projection) can be missed. For an AP projection lateral decubitus exposure, the jugular notch is used as a landmark. The CR should be directed 3-4 inches (8-10 cm) below the jugular notch that corresponds to the center of the lung fields at the T7 level (mid-thorax). For a PA projection lateral decubitus position, the CR should be directed 7-8 inches (18-20 cm) below the vertebra prominans at the level of the inferior angle of the patient's scapula. Collimation On each side of the posterior chest, the illuminated field margins should correspond to the outer skin margins of the patient. The upper border of the illuminated field should be above the patient's shoulders. This will result in a lower collimation border of 1-2 inches (3-5 cm) below the costophrenic angle, if the central ray was correctly centered. The collimation should be adequate to allow for some margin of error in both CR placement and lung expansion during deep inspiration. Imaging technique
Oblique projections are not ordered as frequently as a few years ago, because CT is more commonly employed whenever pathology is not clearly visualized on a standard chest x-ray. However, oblique-view chest x-rays may be helpful and are requested for the following reasons:
Ask the patient to remove all clothing from the waist up, put on a hospital gown, remove any jewelry (necklace, earrings), and, if necessary, tie hair up on top of the head. Patient position Anterior (PA) oblique projections are obtained with patient upright with respective side of the chest rotated 45 degrees against the IR. The patient's arm that is closest to the cassette should be flexed, with the hand resting on the hip. The patient's opposite arm should be raised as high as possible. The patient should be looking straight ahead, with the chin raised. Posterior oblique positions are only used when the patient is too ill to be turned to a prone position. Chest position Oblique positions are named according to the chest part closest to the cassette. For anterior (PA) oblique projections the side of interest is the side furthest from the cassette.
Central ray The CR should be perpendicular to the center of the cassette at the level of T7. Film holder placement The cassette or IR should be 14 x 17 inches (35 x 43 cm) lengthwise. The SID should be at a minimum of 72 inches (180 cm). Evaluation criteria for a good oblique chest projection
AuntMinnie.com contributing writer December 21, 2001 Related Reading Mastering AP and lateral positioning for chest x-ray, November 20, 2001 Good positioning is key to PA chest x-ray exams, October 19, 2001 Copyright © 2001 AuntMinnie.com Which pathologic condition of the lungs is best demonstrated with AP chest right lateral decubitus?Chest Positioning. Which decubitus would best demonstrate right pneumothorax?A lateral decubitus projection can also be helpful in showing small amounts of air in the pleural cavity (a pneumothorax) as well as air fluid levels in other cases.
What is the general purpose for using a lateral decubitus position?The lateral decubitus position provides surgical exposure to the chest, retroperitoneum, hip, and lateral leg. Common procedures performed in this position include procedures on the lung, aorta, kidney, and hip.
Why is a left lateral projection of the chest preferable over a right lateral?A left lateral projection should be performed unless a right lateral projection is specifically requested by the physician. (The left lateral position is preferred because it permits better anatomical detail of the heart.) Make sure the patient is upright, with weight distributed evenly on both feet.
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