Chest X-Ray Positioning Guide: PA, Lateral, AP, Lordotic, and Decubitus Views

A chest radiograph may be the most frequently performed X-ray examination, but a diagnostic image still depends on deliberate positioning. Small errors—rotation, clipped apices, shallow inspiration, scapulae over the lungs, or an incorrect marker—can hide disease or imitate it. The radiographer must select the correct projection, adapt to the patient's condition, and recognize whether the finished image answers the clinical question.

This guide covers the routine PA and left lateral chest, the AP chest used for patients who cannot stand, and special AP lordotic, lateral decubitus, and expiration views. For bedside-specific workflow and line evaluation, also read our portable chest X-ray technique guide. For a systematic approach after acquisition, see chest X-ray interpretation basics.

Why PA Is Preferred to AP

In the PA position, the anterior chest is against the image receptor and the heart lies closer to the detector. This reduces cardiac magnification. In an AP projection, the heart is farther from the detector, so it appears larger; the clavicles also project higher and the scapulae are harder to move outside the lung fields. Consequently, an AP portable image should not be used to diagnose cardiomegaly without considering projection and patient position.

Routine PA Upright Chest

Positioning Steps

1. Confirm patient identity, indication, ability to stand safely, and pregnancy status when relevant under facility policy. Remove necklaces, clothing fasteners, bras with metal, ECG leads when clinically permissible, and other artifacts from the field.
2. Place the patient facing the upright receptor with the midsagittal plane perpendicular to its center. Distribute weight evenly on both feet.
3. Elevate the chin so it does not overlap the lung apices. Depress the shoulders.
4. Place the backs of the hands low on the hips, roll the shoulders forward, and bring the elbows forward. This rotates the scapulae laterally away from the lungs.
5. Set the top of the IR approximately 1.5–2 inches (4–5 cm) above the relaxed shoulders. Center the horizontal ray to the midsagittal plane at T7, approximately at the inferior angle of the scapula in an average adult.
6. Collimate to include both apices and costophrenic angles. Use a 72-inch (180 cm) SID when feasible; use a grid or upright Bucky according to patient thickness, equipment, and the validated department protocol.
7. Acquire the image on suspended full inspiration. A common teaching method is to ask the patient to take a deep breath, let it out, take another deep breath, and hold for exposure; follow the local breathing protocol and adapt to the patient's ability.

PA Image Evaluation Criteria

• Both lungs are included from the apices through the costophrenic angles.
• No rotation: the medial ends of the clavicles are equidistant from the thoracic spinous processes.
• Scapulae are projected outside the lung fields as much as possible.
• The chin and arms do not obscure the upper lungs.
• Adequate inspiration commonly demonstrates roughly 8–10 posterior ribs above the diaphragm at the midclavicular line on an adult PA chest, but rib count is only a guide and varies with anatomy and disease. Evaluate the whole image and document limitations rather than forcing unsafe effort.
• Thoracic vertebrae are faintly visible through the heart, and pulmonary vascular markings are visible within the lungs without motion blur.

Left Lateral Chest

The routine lateral is performed with the left side against the IR. This minimizes magnification of the heart, which is predominantly left-sided. The lateral projection localizes abnormalities seen on PA, reveals the retrosternal and retrocardiac regions, and helps assess the posterior costophrenic angles.

Positioning Steps

1. Turn the patient's left side against the upright receptor. Align the midcoronal plane perpendicular to the IR.
2. Raise both arms high above the head. Ask the patient to grasp opposite elbows or a stable support without leaning.
3. Keep the shoulders and posterior ribs superimposed. Ensure the hips do not rotate away from the detector.
4. Position the receptor high enough to include the apices—commonly about 1.5–2 inches (4–5 cm) above the shoulders—then confirm that raising the arms has not compromised inclusion of the posterior costophrenic angles.
5. Direct the horizontal CR perpendicular to the IR at T7 on the midcoronal plane. Use a 72-inch SID.
6. Expose on suspended full inspiration; the two-inspiration method may be used when it matches local protocol and the patient can cooperate.

Lateral Image Evaluation Criteria

• Apices, posterior lungs, and posterior costophrenic angles are included.
• Posterior ribs are nearly superimposed. Separation greater than about 1 cm suggests rotation.
• Arms and humeri are not superimposed over the upper lungs.
• The sternum is shown in profile, and the thoracic spine demonstrates progressively greater lucency inferiorly.
• The right hemidiaphragm can usually be followed anteriorly; the left is obscured anteriorly by the heart.

AP Upright, Semi-Erect, and Supine Chest

Use an AP chest when the patient cannot safely assume the PA position. Prefer upright or semi-erect positioning whenever the patient's condition allows: it usually improves lung expansion, permits air-fluid levels to be assessed with a horizontal beam, and avoids the gravity-dependent vascular redistribution seen on supine images.

For a supine AP chest, keep the central ray perpendicular to the receptor unless the approved protocol calls for angulation to compensate for the patient's position or receptor geometry. Unintended cephalic angulation projects the clavicles higher and can create a lordotic appearance. When imaging trauma patients, do not move the patient or remove immobilization devices without authorization. Our trauma radiography principles guide covers safe cross-table and immobilization practices.

AP Lordotic Chest for the Lung Apices

The AP lordotic projection demonstrates the lung apices without superimposition of the clavicles. It may be requested to evaluate apical pathology such as scarring, calcification, or an apical mass.

Common Lordotic Position

1. Using a stable setup, place the patient approximately 1 foot (30 cm) in front of the upright receptor, facing the tube; adjust the starting distance for the patient's height and ability.
2. Ask the patient to lean backward until the upper back and shoulders contact the IR. Keep the midsagittal plane centered, avoid rotation, and do not use this method if balance or mobility makes it unsafe.
3. Place the hands on the hips with palms out and roll the shoulders forward.
4. Direct a horizontal CR to the midsternum, approximately 3–4 inches (8–10 cm) below the jugular notch.
5. Expose on full inspiration.

If the patient cannot lean, a common alternative is to position the patient against the IR and angle the CR 15–20 degrees cephalad to the midsternum; angle and centering may be adjusted under the approved protocol for patient habitus. The clavicles should project above the apices, not through them. Excessive angulation distorts the thorax and can exclude anatomy.

Lateral Decubitus Chest

A lateral decubitus chest uses a horizontal beam to demonstrate small pleural effusions or pneumothorax and to assess whether fluid is free-flowing. The side placed down depends on the clinical question:

• Suspected pleural effusion: place the affected side down so fluid layers along the dependent lateral chest wall.
• Suspected pneumothorax: place the affected side up so pleural air rises and is easier to see.

Positioning and Timing

1. Place the patient on the requested side with the body parallel to the IR and arms raised above the head.
2. Use a radiolucent pad under the patient if needed so the entire dependent chest, including costophrenic angle, is included.
3. Allow time for pleural fluid to layer before exposure. Many teaching protocols use at least 5 minutes, but the required delay is protocol-specific and must not override urgent care or patient tolerance.
4. For the usual AP decubitus projection, center the horizontal CR near T7 at the midsagittal plane. Include both lungs and place a clearly visible marker identifying the dependent side and decubitus position.
5. Expose on full inspiration unless an expiration image is specifically requested.

Expiration Chest and Other Special Situations

An expiration chest may be ordered to evaluate diaphragmatic movement or demonstrate focal air trapping, including from an aspirated foreign body. Although pleural air can appear more conspicuous against a smaller, denser expired lung, evidence-based pneumothorax guidance recommends an inspiratory chest radiograph for initial diagnosis and does not recommend routine expiratory views because they have not shown added diagnostic benefit. Perform an expiration view for suspected pneumothorax only when specifically requested under local protocol.

Do not substitute expiration imaging for the ordered inspiratory study. Clearly label the image EXPIRATION. Modern practice may rely on CT or ultrasound for some questions, but the radiographer should still understand the projection and follow the radiologist's or department's protocol.

Exposure, Collimation, and Dose Optimization

Adult chest radiography commonly uses a relatively high-kVp, low-mAs technique to provide adequate penetration with a short exposure time that limits motion. In digital radiography, displayed contrast is also strongly affected by detector response and image processing, so the film-era statement that high kVp alone “produces long-scale contrast” is incomplete. Exact technique depends on detector, generator, grid use, patient habitus, and a locally validated exposure chart; there is no universal exposure setting.

• Use the department's anatomical programmed radiography setting or validated exposure technique chart.
• Collimate to the anatomy needed, but never crop the apices or costophrenic angles.
• Use correct AEC chambers and center accurately; poor positioning over AEC cells can cause under- or overexposure.
• Review the exposure indicator and, when available, deviation index against the exam-specific target established for that detector and facility. These values are guides—not direct patient-dose measurements—and can be affected by collimation, segmentation, prostheses, and anatomy. Display brightness alone is unreliable in digital imaging.
• Apply ALARA through accurate positioning, clear breathing instructions, and repeat prevention. Review broader principles in radiation safety for radiologic technologists.

Common Chest Positioning Errors

A Systematic Pre-Submission Check

1. Identity and markers: correct patient, date, side marker, projection, and special labels.
2. Coverage: apices through costophrenic angles, both lateral skin margins, and required anatomy.
3. Position: rotation, scapulae, chin, arm position, and upright or decubitus status.
4. Inspiration and motion: posterior rib count, diaphragm level, and sharp vascular markings.
5. Technical quality: appropriate penetration, exposure indicator, collimation, and absence of removable artifacts.
6. Clinical purpose: confirm the image answers the indication before dismissing the patient.

This checklist follows the same anatomy-position-exposure-artifact logic described in our full radiographic image critique guide. A technically imperfect image does not always require a repeat: weigh whether the anatomy and clinical question are adequately demonstrated against the additional radiation dose and patient risk.

Protocol and Evidence Note

Positioning landmarks and techniques in this guide describe common adult teaching methods, not universal orders. Patient condition, body habitus, equipment geometry, and the clinical question may require an approved variation. The evidence check used RadiologyInfo (ACR/RSNA) chest radiography guidance, the NCBI Bookshelf review of chest radiograph technical evaluation, the British Thoracic Society pneumothorax guideline, AAPM Report 116 on digital radiography exposure indicators, and the FDA medical X-ray imaging resource. Always follow the examination order, manufacturer instructions, and facility protocol.

Related Articles

• Portable Chest X-Ray Technique — bedside positioning, tubes, lines, and common ICU errors.
• Chest X-Ray Interpretation Basics — a structured method for evaluating the finished image.
• Rib X-Ray Positioning — projections and breathing techniques for upper and lower ribs.
• kVp and mAs Exposure Factors — understand receptor exposure, contrast, and the 15% rule.
• Trauma Radiography Principles — safe adaptations for patients who cannot move.