Chest Radiography: PA and Lateral Projections

Chest Radiography: PA and Lateral Projections

Chest radiography is the single most frequently ordered radiographic examination in clinical practice. Producing a diagnostic-quality chest image requires precise positioning, appropriate technical factors, and consistent attention to patient safety. Mastering the PA and lateral projections is a core competency for every limited-scope and full radiography pathway.

Patient Preparation and Safety

Before beginning, verify the patient's identity using at least two identifiers (name and date of birth). Confirm the order matches the patient. Ask about pregnancy status for all women of childbearing age; follow your facility's policy. Remove all jewelry, clothing with metal snaps, and any objects in the chest area that could create artifacts. Explain each step to the patient to reduce anxiety and improve cooperation. Shield reproductive organs when feasible without compromising the diagnostic area. Never leave a patient unattended on the radiographic table or standing at the upright Bucky.

PA Projection: Positioning and Landmarks

The posteroanterior (PA) chest is performed with the patient standing (or seated upright if unable to stand) facing the image receptor. Key steps:

• SID: 72 inches (183 cm). The increased source-to-image distance reduces magnification of the heart and minimizes patient dose.
• Image receptor placement: Top of the IR should be about 1.5 to 2 inches above the shoulders so the apices are included.
• Patient rotation: The patient hugs the IR; dorsal surface of the hands are placed on the hips with elbows rolled forward. This moves the scapulae laterally, clearing the lung fields.
• Central ray: Perpendicular to the IR, directed to the level of T7 (inferior angle of the scapula is a reliable surface landmark).
• Exposure phase: Instruct the patient to take a full, deep breath and hold it before you expose. Full inspiration depresses the diaphragm and expands the lung fields for optimal visualization.
• Collimation: Collimate to the chest wall borders; do not cut off the costophrenic angles or apices.

Evaluation criteria for the PA chest: Ten posterior ribs visible above the diaphragm on a good inspiration. No rotation — medial ends of the clavicles are equidistant from the spinous processes. Scapulae projected outside the lung fields. Sharp lung markings to the periphery. No motion blur.

Lateral Projection: Positioning and Landmarks

The left lateral is the standard because it places the heart closer to the IR, reducing cardiac magnification.

• SID: 72 inches.
• Patient position: Left side against the IR, arms raised and clasped over the head or resting on a positioning aid. Midcoronal plane centered to the IR.
• Central ray: Perpendicular to IR at the level of T7, mid-axillary line.
• Exposure phase: Same full inspiration hold as the PA.
• Collimation: Include the entire lung fields; the retrosternal and retrocardiac spaces must be visible.

Evaluation criteria for the lateral: Posterior ribs superimposed (arms and scapulae elevated out of the field). Sternum in true lateral. Open costophrenic angles. No motion.

Technical Factors

Chest radiography uses a high-kVp technique to penetrate the mediastinum while maintaining long-scale contrast that allows simultaneous visualization of both air-filled lungs and the denser cardiovascular structures. Typical ranges used in many facilities are 110–125 kVp with low mAs, though your facility's technique chart governs actual settings. Always follow your facility protocol and consult your supervising technologist when in doubt. An AEC (automatic exposure control) phototimer cell positioned behind the lung fields is standard on most fixed units.

Common Technical Errors and Corrections

| Error | Appearance | Correction |

|---|---|---|

| Rotation | Clavicle medial ends asymmetric; one lung appears smaller | Reposition patient; use positioning board |

| Poor inspiration | Fewer than 9 posterior ribs; diaphragm elevated; heart appears enlarged | Re-instruct patient; repeat exposure |

| Costophrenic angle cut-off | Bases not included | Lower IR or reposition patient |

| Motion blur | Unsharp lung markings | Shorten exposure time; re-instruct patient |

| Under-exposure | Mediastinum not penetrated; flat, gray image | Increase kVp per technique chart |

| Over-exposure | Lung detail washed out (less common with digital but still affects image quality) | Reduce mAs |

Portable (AP) Chest Technique

When patients cannot come to the radiology department, a portable AP chest is performed at the bedside. The AP projection places the anterior chest against the IR and the tube faces the patient's back. Because the heart is farther from the IR, cardiac magnification is greater than on the PA view — clinicians must account for this when interpreting heart size. Use the maximum practical SID (commonly 40–44 inches or as close to 72 inches as the environment allows). Note the exact SID on the requisition. Instruct the patient to hold inspiration; coordinate with nursing if the patient is on a ventilator. Document all technique factors in the logbook and note any patient limitations that affected positioning.

Logbook and Competency Requirements

Record every examination in your clinical logbook: patient positioning landmarks used, SID, kVp, mAs, AEC or manual technique, inspiration adequacy, and your self-evaluation of image quality. After each image review session with your supervising technologist, document specific errors identified and the corrective actions you would take. This habit prepares you directly for the image evaluation sections of the ARRT examination. Your formal chest competency checkoff requires a score of 8 out of 10 on the program's image evaluation form for both a PA and a lateral — repeat attempts are permitted until passed.