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|Name = Chest radiograph
|Image = Normal posteroanterior (PA) chest radiograph (X-ray).jpg
|Caption = A normal posteroanterior (PA) chest radiograph. [[
|ICD10 =
|ICD9 = {{ICD9proc|87.3}}-{{ICD9proc|87.4}}
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In anteroposterior (AP) views, the positions of the x-ray source and detector are reversed: the x-ray beam enters through the anterior aspect and exits through the posterior aspect of the chest. AP chest x-rays are harder to read than PA x-rays and are therefore generally reserved for situations where it is difficult for the patient to get an ordinary chest x-ray, such as when the patient is bedridden. In this situation, mobile X-ray equipment is used to obtain a lying down chest x-ray (known as a "supine film"). As a result, most supine films are also AP.
Lateral views of the chest are obtained in a similar fashion as the posteroanterior views, except in the lateral view, the patient stands with both arms raised and the left side of the chest pressed against a flat surface.
===Typical views===
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In the average person, the diaphragm should be intersected by the 5th to 7th anterior ribs at the mid-clavicular line, and 9 to 10 posterior ribs should be viewable on a normal PA inspiratory film. An increase in the number of viewable ribs implies hyperinflation, as can occur, for example, with [[chronic obstructive pulmonary disease|obstructive lung disease]] or foreign body aspiration. A decrease implies hypoventilation, as can occur with [[restrictive lung disease]], [[pleural effusion]]s or [[atelectasis]]. Underexpansion can also cause [[interstitial fluid|interstitial]] markings due to parenchymal crowding, which can mimic the appearance of [[interstitial lung disease]]. Enlargement of the right descending pulmonary artery can indirectly reflect changes of [[pulmonary hypertension]], with a size greater than 16 mm abnormal in men and 15 mm in women.<ref>{{cite journal|last1=Bush|first1=A|last2=Gray|first2=H|last3=Denison|first3=DM|title=Diagnosis of pulmonary hypertension from radiographic estimates of pulmonary arterial size.|journal=Thorax|date=February 1988|volume=43|issue=2|pages=127–31|pmid=3353884|doi=10.1136/thx.43.2.127|pmc=1020754}}</ref>
Appropriate [[Penetration depth|penetration]] of the film can be assessed by faint visualization of the thoracic spines and lung markings behind the heart. The right diaphragm is usually higher than the left, with the liver being situated beneath it in the abdomen. The [[minor fissure]] can sometimes be seen on the right as a thin horizontal line at the level of the fifth or sixth rib. Splaying of the [[carina of trachea|carina]] can also suggest a tumor or process in the middle [[mediastinum]] or enlargement of the [[left atrium]], with a normal angle of approximately 60 degrees. The right paratracheal stripe is also important to assess, as it can reflect a process in the [[posterior mediastinum]], in particular the spine or paraspinal soft tissues; normally it should measure 3 mm or less. The left paratracheal stripe is more variable, and only seen in 25% of normal patients on posteroanterior views.<ref>{{cite journal|last1=Gibbs|first1=JM|last2=Chandrasekhar|first2=CA|last3=Ferguson|first3=EC|last4=Oldham|first4=SA|title=Lines and stripes: where did they go?--From conventional radiography to CT.|journal=Radiographics
Localization of lesions or inflammatory and infectious processes can be difficult to discern on chest radiograph, but can be inferenced by [[silhouette sign|silhouetting]] and the [[hilum overlay sign]] with adjacent structures. If either [[hemidiaphragm]] is blurred, for example, this suggests the lesion to be from the corresponding lower lobe. If the right heart border is blurred, than the pathology is likely in the right middle lobe, though a [[pectus excavatum|cavum]] deformity can also blur the right heard border due to indentation of the adjacent sternum. If the left heart border is blurred, this implies a process at the [[lingula (lung)|lingula]].<ref>{{cite book|last1=Gandhi|first1=Sanjay|title=Chest Radiology: Exam Revision Made Easy|date=December 7, 2013|publisher=JMD Books|pages=541 pages|edition=1st|accessdate=}}</ref>
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