Chest

Published on 03/05/2015 by admin

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Last modified 03/05/2015

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Chest

Chest—Positioning Considerations and Radiation Protection ^*

Restricting the primary beam coverage is a very effective way to reduce patient exposure in chest radiography. This requires accurate and correct location of the central ray (CR).

Correct CR Location

Correct CR location to the midchest (T7) allows for accurate collimation and protection of the upper radiosensitive region of the neck area. It also prevents exposure to the dense abdominal area below the diaphragm, which produces scatter and secondary radiation to the radiosensitive reproductive organs.

Fig. 1-1 Correct CR location.

T7 for the PA chest can be located posteriorly in reference to C7, the vertebra prominens. Level of T7 is 7-8 inches (18-20 cm) below the vertebra prominens.

The CR for the AP chest is 3-4 inches (8-11cm) below the jugular notch and angled 3°–5° caudad.

Shielding

Shielding of radiosensitive organs and tissues should be used for all procedures unless it obscures key anatomy. Shielding is not a substitute for close collimation.

Backscatter Protection

Shields placed between the patient and the wall Bucky and wall can also be used to keep scatter and secondary radiation from these structures from reaching the patient’s gonadal regions.

Digital Imaging Considerations ^*

The following technical factors will reduce dose to the patient and improve image quality:

Collimation:

Close collimation reduces dose to the patient and scatter radiation reaching the image receptor.

Accurate Centering:

Most digital systems recommend that the anatomy be centered to the receptor.

kV Range:

Digital systems allow the use of higher kV as compared to analog (film-based) systems, which will reduce patient dose.

Exposure Indicator:

Check the exposure indicator to verify that the optimal exposure factors were used to produce the least amount of radiation to the patient.

Grids:

Grids generally are not used with analog (film-screen) imaging for body parts measuring 10 cm or less. However, with certain digital systems, the grid may or may not be able to be removed from the receptor. In those cases it is departmental protocol that determines if a grid is left in place or removed.

PA Chest ^*

• 35 × 43 cm L.W. or C.W. (14 × 17″)

Fig. 1-2 PA chest (CR ≈20 cm [8″] below vertebra prominens) (average female, 18 cm [7″]).

Position

• Erect, chin raised, hands on hips with palms out, roll shoulders forward

• Center CR to T7 region. Top of IR will be approximately 2″ (5 cm) above shoulders on average patient.

• Center thorax bilaterally to IR borders with equal margins on both sides; ensure there is no rotation of thorax.

Central Ray:

CR ⊥, to T7, or 7-8″ (18-20 cm) below vertebra prominens (is also near level of inferior angle of scapula)

SID:

72-120″ (183 to 307 cm)

Collimation:

Upper border to vertebra prominens; sides to lateral skin borders

Respiration:

Expose at end of 2nd deep inspiration.

Lateral Chest ^*

• 35 × 43 cm L.W. (14 × 17″)

Fig. 1-3 Left lateral chest.

Position

• Erect, left side against IR (unless right lateral is indicated)

• Arms raised, crossed above head, chin up

• True lateral, no rotation or tilt. Midsagittal plane parallel to IR (Don’t push hips in against the IR holder.)

• Thorax centered to CR, and to IR anteriorly and posteriorly

Central Ray:

CR ⊥, to midthorax at level of T7. Generally IR and CR should be lowered ≈1″ (2.5 cm) from PA on average patient.

SID:

72-120″ (183-307 cm)

Collimation:

Upper border to level of vertebra prominens, sides to anterior and posterior skin margins

Respiration:

Expose at end of 2nd full inspiration.

Lateral, Wheelchair or Stretcher ^*

• 35 × 43 cm L.W. (14 × 17″)

Fig. 1-4 Left lateral on stretcher.

Position

• Erect, on stretcher or in wheelchair

• Arms raised, crossed above head, or hold on to support bar

• Center thorax to CR, and to IR anteriorly and posteriorly

• No rotation or tilt, midsagittal plane parallel to IR, keep chin up

Central Ray:

CR ⊥, to midthorax at level of T7

SID:

72-120″ (183-307 cm)

Collimation:

Upper border to level of vertebra prominens, sides to anterior and posterior skin margins

Respiration:

Expose at end of 2nd full inspiration.

PA (AP) Chest

Evaluation Criteria

Anatomy Demonstrated:

• Both lungs from apices to costophrenic angles

• 9-10 ribs demonstrated above the diaphragm

Position:

• Chin sufficiently elevated

• No rotation, SC joints and lateral rib margins equal distance from spine

Exposure:

• No motion, sharp outlines of diaphragm and lung markings visible

• Exposure sufficient to visualize faint outlines of midthoracic and upper thoracic vertebrae through heart and mediastinal structures

Fig. 1-5 PA chest.

Lateral Chest

Evaluation Criteria

Anatomy Demonstrated:

• From apices to costophrenic angles, from sternum to posterior ribs

Position:

• Chin and arms elevated to prevent superimposing apices

• No rotation, R and L posterior ribs superimposed except side away from IR projected slightly (1-2 cm) posteriorly because of divergent rays

Exposure:

• No motion, sharp outlines of diaphragm and lung markings

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