Comprehensive Radiographic Positioning and Procedures for Chest Radiography

General Radiographic Principles for Chest Imaging

Source-to-Image Distance (SID):
- A preferred SID of $72''$ ( $72\text{ inches}$ ) is utilized for chest imaging due to minimal beam divergence, particularly at the outer edges of the exposure field.
- An increased SID reduces geometric magnification of thoracic structures, directly enhancing spatial resolution.
- Increasing the SID and employing a Posteroanterior (PA) projection reduces structural magnification of the heart.
Patient Shielding Practices:
- Radiation shielding must be applied consistently as standard practice for all patients when appropriate or upon patient request.
- Acceptable shielding configurations include:
  - Freestanding mobile shields.
  - Lap shields positioned around the backside.
  - Lap shields positioned on the front side.
  - Complete wrap-around waist shields (most ideal for chest imaging).
Anatomic and Radiographic Image Marking:
- Every chest radiograph must be marked with a minimum of a Right ( $R$ ) or Left ( $L$ ) lead anatomic marker.
- PA and AP Chest Projections: The anatomic marker ( $R$ or $L$ ) must be placed in the shoulder region to prevent superimposition over pulmonary tissue.
- Left Lateral Chest Projection: The left marker (indicating the side closest to the Image Receptor [IR]) must be placed along the anterior surface of the patient, positioned superiorly in the region of the arms.
- Positional and Decubitus Markings:
  - Arrow markers may be added to indicate supine or upright patient positioning.
  - For decubitus positions, arrows indicate the "side up" or "side down" orientation.
  - Many lead markers contain three internal lead beads that shift to indicate upright versus recumbent patient orientation.
  - Decubitus chest images are best marked in the shoulder region using the anatomic marker combined with an "up arrow" or a "side up" designation to specify the elevated anatomy.
Image Display and Anatomic Orientation:
- Radiographs must be displayed facing the viewer as if viewing the patient in the anatomic position (opposite of the viewer).
- With correct left anatomical marking, the heart is displayed predominantly to the left of the thoracic midline.
- The gastric air bubble within the stomach is typically visible in the left upper quadrant (LUQ).

Ambulatory Chest Radiography Protocols

PA Projection (Ambulatory):
- Technical Considerations:
  - Peak kilovoltage range: $110\text{--}130\text{ kVp}$ .
  - Automatic Exposure Control (AEC): The two outermost AEC cells are selected when utilizing an upright Bucky.
  - SID: $72''$ ( $72\text{ inches}$ ).
- Exposure Field Size Options:
  - $14 \times 17\text{ inches}$ lengthwise for sthenic to asthenic patient body habitus.
  - $14 \times 17\text{ inches}$ crosswise.
  - $17 \times 17\text{ inches}$ .
- Patient Positioning Requirements:
  - Patient stands erect, facing the upright Bucky.
  - Shoulders are relaxed and chin is elevated.
  - Arms are wrapped around the Bucky board to roll the shoulders and scapulae anteriorly out of the lung fields.
  - Special Considerations for Female Patients: Patients with large, pendulous breasts should be instructed to lift their breasts up and laterally as they move against the upright Bucky to prevent dense tissue from obscuring the lung bases and costophrenic angles.
- Centering Location: Central ray (CR) is centered to the level of $T7/8$ along the Midsagittal Plane (MSP).
- IR Marking: Right or left lead marker placed above the corresponding shoulder.
- Breathing Instructions: Double inspiration; exposure is made and held after the second full inspiration. The radiographer must observe patient compliance during breathing instructions and while walking back to the control panel.
Left Lateral Projection (Ambulatory):
- Technical Considerations:
  - Peak kilovoltage range: $110\text{--}130\text{ kVp}$ .
  - AEC Selection: The center AEC cell is selected for the upright Bucky.
  - SID: $72''$ ( $72\text{ inches}$ ).
- Exposure Field Size Options:
  - $14 \times 17\text{ inches}$ lengthwise for all patient types.
  - $17 \times 17\text{ inches}$ .
- Patient Positioning Requirements:
  - Erect left lateral posture with feet slightly separated for stability.
  - Thorax positioned in a true lateral alignment with shoulders and hips aligned vertically.
  - Arms elevated overhead to hold the chest positioning bar; proper elevation is critical to clear soft tissue of the upper arms from the superior lung fields.
  - Chin elevated with gaze directed forward.
- Centering Location: CR centered to the level of $T7/8$ along the Midcoronal Plane (MCP), or slightly posterior to the MCP.
- IR Marking: Left lead marker placed on the anterior surface in the area of the elevated arms.
- Breathing Instructions: Double inspiration; exposure taken on held second inspiration. Patient must be monitored continuously during respiration commands.

Nonambulatory Chest Radiography Protocols

PA or AP Projections (Nonambulatory):
- Technical Considerations:
  - Peak kilovoltage range: $110\text{--}130\text{ kVp}$ .
  - AEC Selection: The two outermost AEC cells are selected for either an upright Bucky or table Bucky. Manual exposure techniques may also be considered.
  - SID Setup: $72''$ ( $72\text{ inches}$ ) when using an upright Bucky; $40''$ ( $40\text{ inches}$ ) or maximum achievable SID when utilizing a table Bucky.
- Exposure Field Size Options:
  - $14 \times 17\text{ inches}$ lengthwise for sthenic to asthenic patients.
  - $14 \times 17\text{ inches}$ crosswise for hypersthenic patients.
  - $17 \times 17\text{ inches}$ .
- Patient Positioning Options & Adaptations:
  - Erect PA (Preferred): Positioned erect facing the upright Bucky to demonstrate air-fluid levels and reduce mediastinal magnification. Shoulders relaxed, chin elevated, and arms wrapped around the board to roll scapulae forward.
  - Wheelchair Adaptations: The backrest and armrests of the wheelchair may be removed to facilitate proper chest positioning.
  - Stool Positioning: Patients unable to stand for the full examination duration may sit on a stool.
  - Stretcher Adaptations: Patients may remain on a stretcher, sitting upright with legs dangling over the edge to face the upright Bucky. If PA positioning is impossible, an alternate AP projection is performed.
  - Supine Projection: Acquired if the patient is completely unable to achieve an erect posture.
- Centering Location: CR centered to $T7/8$ along the MSP.
- IR Marking: Right or left marker placed superiorly above the shoulder.
- Breathing Instructions: Double inspiration, holding after the second full breath while observing patient compliance.
Left Lateral Projection (Nonambulatory):
- Technical Considerations:
  - Peak kilovoltage range: $110\text{--}130\text{ kVp}$ .
  - AEC Selection: Center AEC cell selected for the upright Bucky.
  - SID: $72''$ ( $72\text{ inches}$ ).
- Exposure Field Size Options:
  - $14 \times 17\text{ inches}$ lengthwise for all patients.
  - $17 \times 17\text{ inches}$ .
- Patient Positioning Options & Adaptations:
  - Standard Lateral Setup: Erect left lateral posture, true lateral thoracic alignment, hips and shoulders aligned, chin elevated, eyes facing forward.
  - Wheelchair Modifications: Remove wheelchair backrest and side armrests to eliminate radiopaque artifacts.
  - Stool Modifications: Position non-standing patients seated erect on a stool.
  - Stretcher Modifications: Elevate the head of the stretcher to bend the patient at the waist. Place a positioning bolster behind the back to displace the patient away from the stretcher backrest. Encourage the patient to reach up and grasp the chest positioning bar to elevate arm tissue away from the lung fields.
- Centering Location: CR centered to $T7/8$ along the MCP, or slightly posterior to the MCP.
- IR Marking: Left marker placed anteriorly in the area of the raised arms.
- Breathing Instructions: Double inspiration with exposure held on the second inspiration while keeping the patient under visual observation.