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Thoracic imaging, or what is often called as chest X-ray (CXR) is a radiographic projection of the thorax intended to diagnose the conditions affecting the thorax, its contents and the nearby structures. CXR uses ionized radiation in the form of X-ray. In order to form a radiograph, the dosage of radiation for adults is around 0.06 mSv.

CXR is used to diagnose numerous conditions involving thoracic wall, thoracic vertebrae, and the structures within the thoracic cavity, including the lung, heart and great vessels. Pneumonia and congestive heart failure are often diagnosed by CXR. CXR is often used for the screenings of pulmonary diseases related to industrial works such as mining where the workers are exposed to dust.

In general, the functions of CXR are:
- to observe congenital abnormalities (the heart, vascular)
- to observe the presence of trauma (pneumothorax, hemothorax)
- to observe the presence of infection (generally tuberculosis/TB)
- to check the heart' s condition
- to check the lung' s condition

In some conditions, CXR is suitable for screening, but not for diagnosing. At times when, based on the CXR, abnormalities are suspected, additional thoracic imaging test can be performed to obtain a surer diagnosis or evidences supporting the CXR diagnosis.

Different images of the thorax can be obtained by altering the body' s relative orientation and the direction of X-ray. The most common images are posteroanterior (PA), anteroposterior (AP) and lateral.

1. Posteroanterior (PA)

In PA, X-ray source is positioned so as to it comes in from the posterior (back) part of the thorax and comes out from the anterior (front) part where it will be detected. To get this image, an individual stands facing a flat surface that functions as X-ray detector. Radiation source is placed behind the patient at a standard distance, and the X-ray is then transmitted to the patient.

2. Anteroposterior (AP)

In AP, the position of X-ray and detector is the opposite of PA. AP chest X-ray is harder to interpret than PA, and therefore it is used in a situation where it is difficult to get a normal chest X-ray due to the patient' s inability to get up from the bed. In such situation, mobile X-ray is used to get a lying down CXR ("supine film"). As a result, most supine films are also AP.

3. Lateral

Lateral image can be obtained using similar methods employed in PA, but in lateral the patient stands with both arms raised and the left side of the thorax being pressed against a flat surface.

Abnormalities usually spotted through CXR are:

1. Nodule (a distinct spot on the lung)

It is usually caused by benign/malignant neoplasm, granuloma (tuberculosis), infection (pneumoniae), vascular infarction, varix, Wegener' s granulomatosis and rheumatoid arthritis. The growth speed, classification, shape and location of a nodule can assist in the diagnosis. The nodule can be many.

2. Cavity

Cavity is a walled hollow structure within the lung. It is usually caused by cancer, pulmonary embolism, Staphylococcus aureus infection, tuberculosis, Klebsiella pneumoniae, anaerobic bacteria and fungi, and Wegener' s granulomatosis.

3. Pleural abnormality

Pleural fluid is a fluid existing between the lung and the thoracic wall. Pleural effusion can occur on cancer, sarcoid, connective tissue disease and lymphangioleiomyomatosis.

Though CXR is a cheap and relatively safe method, there are several severe thoracic conditions that may give a normal CXR result, such as the result of a patient with acute myocardial infarction.