Chest X-ray : Radiography

Thursday, March 5, 2015

X-ray of the Chest : Plain Film

   Chest xray is the most common examination on radiology department. It uses a very small amount of radiation to produce an image of inside the chest, including heart and adjoining structure in the chest. Posteroanterior (PA), anteroposterior (AP) and lateral are the common projection and routinely done. 

    Posteroanterior (PA) projection in an upright position is preferred, because it prevents congestion of blood in the pulmonary vessels, air fluid levels can be demonstrates and naturally depress the diaphragm and puts the heart closer to Image receptor for less magnification. Preliminary radiograph, Scouts film or pre-initial film of the chest is also done before undergoing for a major procedure for clearance purposes. A different views and special projection and methods on chest may require to rule out possible pathology and for accurate radiographic studies.

Basic Projection of the Chest:

Special Projection and Methods of the Chest:

Chest X-ray Technical Factors

The exposure factors and accessories needed when performing the chest x-ray or examining the thoracic viscera depend on the radiographic characteristic of the patient’s pathologic condition. A high penetration (kVp) of xray is usually use demonstrate all thoracic anatomy on the radiograph. If a non-grided cassette is used the kVp or penetration is lowered otherwise if the selected kVp is too low, the contrast is increased resulting in a few shades of gray, radiograph may appear penetrated but the mediastinum of the chest appears underexposed. On the other hand if the kVp is too high, contrast is decreased, which can result in low detailed film and finer lung marking is not acquired. However, Adequate selection of kVp penetrates the mediastinum area and demonstrates a distinct shadow of the thoracic spine. Whenever possible, a 72 inches (183 cm) source-to-image (SID) is used, to minimize magnification of the heart and to obtain a greater recorded detail of delicate lung structures. In conventional radiography of the chest a 120 inches (305 cm) SID is commonly used. For the opaque areas within the lung fields a grid technique is recommended, this will also demonstrate a thickened pleural membranes of the lungs structures.
chest xray
Radiograph with Pleural Effusion comparison on same Patient

Normal Chest Radiograph

For a PA Projection of the chest the thoracic viscera shows the air-filled trachea, the lungs, the diaphragmatic domes, the heart and aortic knob this can be seen if it is enlarged laterally, the thyroid and thymus gland is seen. If the exposure is successfully made at the end of the exposure, the vasclar markings are much more clearer. On oblique angle, the bronchial tree is shown, and a filled esophagus is well demonstrated if barium sulfate suspension is used for a special studies.
A clear demonstration on a normal chest radiograph of the following:
  • Lung fields from the apex to costrophrenic angles are included on radiograph.
  • No rotation of the sternal ends of the clavicles, and equal is distance from the verterbral spine.
  • The Trachea should be in the middle of the neck.
  • Scapula are winged out from the lung fields.
  • At least 10 posterior ribs are visible on the radiograph.
  • Sharp outlines of the heart and diaphragm.
  • Distinct shadow of the ribs and superior thoracic vertebrae is visible through the heart shadow.
  • Lung markings like the hilum are evident to the periphery of the lungs.
  • A variation of  chest radiograph during inspiration and expiration. Notice of higher diaphragm level on expiration and at least one fewer rib is seen in the lung field.
  • Womens with large pendulous breast are checked for adequate radiation penetration specially on  the  inferior lobes of both lungs.

Radiation Protection on Chest X-ray

A very effective way to reduce the patient exposure to radiation when taking chest radiograph is to restrict the primary beam coverage by accurately and correctly collimating the central ray (CR). Radiation protection of patient from unnecessary radiation is the professional responsibility of the radiologic technicians. Gonads area can be protected by restricting the primary beam which is the use of proper collimation. In addition, the use of abdominal and gonadal shielding is appropriate, ensuring that the anatomy of interest will not be obscured on the radiograph.

Breathing Instruction for Chest X-ray

On a normal chest x-ray, take radiograph on a 2nd full inspiration because more air is inhaled during the second inspiration rather the first breath. A deep inspiration causes the diaphagm to move downward, resulting in elongation of the heart. If the heart is the interest anatomy exposure should be made at the end of normal inspiration to eliminate distorted image of the heart. On a normal breathing (inspiration), the costal muscle pulls the anterior ribs up and widens laterally, the shoulder will rise, and the thorax expands from front to back and side to side. This changes in the height and dimension of the thorax must be considered when positioning the patient.

PA and Lateral View of the Lung lobes and Fissures

PA and lateral projections is required to study the the lobes and outlines of the lungs, specially when the Horizontal fissures are to be study. Unlike on oblique fissure only lateral view is only needed. Unfortunately, outlines of the lungs are is tricky to image because central ray and fissures must be parallel to each other. An understanding on the positions of this fissure help us to image correctly.
On a lateral view the lung lobes are not overlapped while in PA view this fissures are overlapping. The middle lobe of the right lung and the lingula of the left upper lobe are in the level of the heart on either side anteriorly. The middle lobe of the right lung is larger and extending to a level higher than the middle lobe and lingula, these structures are posterior to the heart. Generally, in PA view the extended portion of the upper lobe, the middle lobe is adjacent below, and fully over lapped on the upper portion of lower lobe.
chest xray

Lung Positions:

Image A: Lateral view of the Left lung.The linguala of the upper lobe is against the heart.
Image B: Right lung lateral view. The middle lobe is at the level of the heart and the lower lobe is posteriorly extended.
Image C: Left lung anterior view.
Image D: Right lung anterior view.

PA and AP Chest Radiograph Comparison

The two images are taken in different position but the radiograph on both image are the same with the anatomy in the anatomic position. As the golden rule of viewing radiograph, the patient left side is on your right, as though the patient were facing the reader as presented by the image.
chest xray
PA and AP Chest Radiograph

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