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

📅 July 21, 2026 · Updated September 17, 2026📖 14 min read🏷️ Positioning Guide

Chest radiography is one of the most frequently performed examinations in medical imaging, but producing a diagnostic chest X-ray requires more than simply placing the patient in front of a detector.

Small positioning errors can significantly alter the appearance of the chest. Rotation may distort the mediastinum, shallow inspiration can exaggerate the apparent size of the heart, and incorrect centering may exclude the lung apices or costophrenic angles.

This guide covers the major chest projections radiography students and technologists should understand:

Important: The techniques described here are common adult teaching methods. Always follow the imaging order, equipment instructions, patient condition, and your facility's approved positioning protocol.

Why Is a PA Chest Preferred Over an AP Chest?

For an ambulatory patient, the routine frontal chest projection is usually performed PA.

In the PA position, the anterior chest is placed against the image receptor. Because the heart lies relatively close to the detector, cardiac magnification is reduced.

With an AP chest, the heart is farther from the detector and therefore appears more magnified.

This difference is particularly important when evaluating cardiac size.

PA chest advantages

A PA chest generally provides:

When is an AP chest used?

An AP projection is commonly performed when the patient cannot safely stand or assume the PA position because of:

Remember:

An enlarged-appearing heart on an AP portable chest should not automatically be interpreted as true cardiomegaly.

Projection and patient positioning must be considered.

Routine PA Upright Chest

Patient Position

  1. Confirm the patient's identity and examination request.
  2. Remove removable artifacts from the chest when clinically appropriate, including necklaces, metal fasteners, and other objects that could obscure anatomy.
  3. Position the patient facing the upright image receptor.
  4. Align the midsagittal plane perpendicular to the center of the receptor.
  5. Ask the patient to elevate the chin so that it does not overlap the lung apices.
  6. Depress the shoulders.
  7. Place the backs of the hands on the hips and rotate the shoulders forward.

This helps move the scapulae laterally away from the lungs.

Central Ray and SID

Use approximately:

SID: 180 cm / 72 inches

when permitted by the equipment and department protocol.

Center approximately at:

T7

The inferior angle of the scapula is commonly used as an approximate surface landmark in an average adult.

The detector should be positioned high enough to include the lung apices while still including the costophrenic angles.

Breathing

The exposure is normally made on suspended full inspiration.

A commonly taught instruction is:

Take a deep breath in, breathe out, take another deep breath in, and hold it.

This two-inspiration method may help achieve full lung expansion, but breathing instructions should be adapted to the patient and local protocol.

PA Chest Image Evaluation

A diagnostic PA chest should demonstrate:

Complete lung coverage

The image should include:

Minimal rotation

The medial ends of the clavicles should appear approximately equidistant from the thoracic spinous processes.

Unequal distances suggest rotation.

Scapulae outside the lungs

The scapular borders should be moved laterally away from most of the lung fields whenever patient mobility permits.

Adequate inspiration

A commonly used teaching guideline is approximately:

8–10 posterior ribs visible above the diaphragm

on a well-inspired adult PA chest.

However, this is a guideline rather than an absolute rule.

Body habitus, age, disease, respiratory ability, and clinical condition can alter the appearance of inspiration.

Evaluate the entire image rather than relying on rib count alone.

Appropriate technical quality

You should be able to evaluate:

without significant motion blur.

Rotation Check

A quick way to evaluate rotation is to compare the medial clavicles with the thoracic spinous processes.

Equal clavicle-to-spine distances = minimal rotation

Unequal distances = probable rotation

Anatomical asymmetry can occasionally affect this appearance, so rotation should be assessed together with the rest of the image.

Left Lateral Chest

The routine lateral chest is normally performed with the:

Left side against the detector.

Why?

Because the heart is predominantly left-sided. Keeping the left side closer to the detector reduces magnification of the cardiac silhouette compared with a right lateral projection.

The lateral image also helps evaluate structures that may be difficult to separate on the PA image, including:

Left Lateral Positioning

  1. Position the patient's left side against the upright detector.
  2. Align the midcoronal plane perpendicular to the receptor.
  3. Raise both arms above the head.
  4. The patient may grasp opposite elbows or an appropriate support.
  5. Avoid allowing the patient to lean or rotate.
  6. Make sure the posterior costophrenic angles remain included after the arms are raised.

Central Ray

Center near:

T7 at the midcoronal plane

with the beam perpendicular to the receptor.

SID

Use approximately:

180 cm / 72 inches

when permitted by local protocol.

Breathing

Expose on suspended full inspiration.

Lateral Chest Image Evaluation

Look for:

Minor separation of posterior ribs may occur, but marked separation usually indicates rotation.

AP Upright, Semi-Erect, and Supine Chest

An AP chest is commonly used when the patient cannot safely assume the standard PA position.

Whenever clinically possible, an upright or semi-erect AP chest is usually preferable to a completely supine image because it allows:

AP Upright or Semi-Erect

Position the patient's back against the detector.

Keep:

Roll the shoulders forward when the patient is able.

Center near T7 and use a horizontal beam.

A long SID should be used when practical to help limit magnification.

AP Supine Chest

For a supine patient:

The beam is normally perpendicular to the image receptor unless a specific approved protocol calls for an alternative angle.

Important limitations of the supine chest

A supine AP chest may demonstrate:

Because pleural fluid can spread posteriorly rather than forming the classic upright meniscus, a small effusion may be difficult to recognize on a supine radiograph.

A classic prospective study reported approximately 67% sensitivity for pleural effusion on supine chest radiography. This number should be understood as the result of that individual study—not as a universal sensitivity for every supine chest examination.

Therefore:

A normal supine chest radiograph does not completely exclude pleural effusion.

AP Lordotic Chest

The AP lordotic projection is designed primarily to demonstrate the:

Lung apices free of clavicular superimposition.

It may be requested when evaluating suspected apical abnormalities such as:

Lordotic Positioning

A commonly taught lordotic technique is:

  1. Position the patient in front of the upright detector.
  2. Ask the patient to move slightly forward from the receptor.
  3. Keeping the body straight, have the patient lean backward until the shoulders and upper back contact the detector.
  4. Keep the midsagittal plane centered.
  5. Avoid rotation.
  6. Place the hands on the hips and roll the shoulders forward when possible.
  7. Direct a horizontal central ray toward the midsternal region.
  8. Expose on suspended full inspiration.

The exact distance the patient stands from the detector depends on height, mobility, and body habitus.

Do not attempt this position if the patient cannot safely maintain balance.

Alternative Lordotic Technique

When the patient cannot lean backward, an alternative technique can be performed with the patient upright against the detector and the central ray angled approximately:

15–20° cephalad

toward the midsternal region.

The exact angle may require modification according to patient anatomy and approved department protocol.

Lordotic Image Evaluation

A properly positioned AP lordotic image should demonstrate:

Some apparent distortion of the ribs and thoracic structures is expected because of the lordotic projection.

Under-angulation

If the clavicles remain superimposed over the lung apices, the lordotic effect may be insufficient.

Excessive lordosis or angulation

Excessive angulation can produce exaggerated thoracic distortion and may compromise inclusion of required anatomy.

The objective is not simply to make the clavicles as high as possible.

The goal is to demonstrate the apices clearly while maintaining useful diagnostic anatomy.

Lateral Decubitus Chest

A lateral decubitus chest uses a:

Horizontal X-ray beam

while the patient lies on one side.

This projection may be used to investigate:

Fluid Down, Air Up

This is one of the most useful chest-positioning memory aids.

Suspected pleural effusion

Place the:

Affected side DOWN.

Free pleural fluid moves toward the dependent side and can layer along the lateral chest wall.

Suspected pneumothorax

Place the:

Affected side UP.

Pleural air rises toward the nondependent lateral chest.

Remember:

Fluid down. Air up.

Decubitus Positioning

  1. Position the patient on the requested side.
  2. Keep the body aligned with the receptor.
  3. Raise the arms above the head when possible.
  4. Use a radiolucent support if necessary to include the dependent costophrenic angle.
  5. Use a horizontal central ray.
  6. For a typical AP decubitus chest, center approximately near T7.
  7. Include both lungs.
  8. Clearly identify the dependent side with an appropriate marker.
  9. Expose on suspended full inspiration unless another breathing instruction has specifically been requested.

How Long Should the Patient Remain in the Decubitus Position?

Many traditional radiographic teaching protocols recommend allowing approximately:

5 minutes

for pleural fluid to redistribute before exposure.

However, this is protocol-specific rather than a universal requirement.

Patient stability, urgency, tolerance, and departmental practice take priority.

Approximate Pleural-Effusion Detectability

Radiographic detection of pleural fluid depends strongly on patient position.

Approximate values reported in the literature include:

Projection Approximate finding
Lateral decubitus Very small free-flowing effusions may become visible; approximately 10–25 mL has been reported under suitable conditions
Upright lateral A meniscus may become visible at roughly 50 mL
Upright PA Blunting of the costophrenic angle commonly becomes apparent at roughly 200 mL
Larger effusion Around 500 mL may obscure part of the hemidiaphragm on an upright frontal image
Supine AP Fluid may distribute posteriorly and can be considerably more difficult to recognize

Do not memorize these as absolute cutoffs

These are approximate study-derived observations, not fixed diagnostic thresholds.

Visibility depends on:

Modern ultrasound is generally more sensitive than chest radiography for identifying small pleural effusions and is frequently used clinically when small-volume fluid must be detected or characterized.

However, lateral decubitus positioning remains important for radiographers to understand because it demonstrates the effect of gravity on free pleural fluid and may still be requested according to the clinical question and local protocol.

Expiration Chest

An expiration chest may be requested for specific indications such as:

Historically, expiration images were frequently taught for pneumothorax because reducing lung volume can make pleural air appear more conspicuous.

However, routine expiration radiographs have not demonstrated enough additional diagnostic benefit to be recommended as a standard pneumothorax view.

For most initial chest radiography:

An inspiratory image remains the standard examination.

Perform an expiration image when it is specifically requested or required by local protocol.

Clearly label the image:

EXPIRATION

Exposure and Dose Optimization

Adult chest radiography generally uses a relatively:

High-kVp / low-mAs technique

to provide adequate thoracic penetration while maintaining a short exposure time.

A short exposure time helps reduce respiratory and cardiac motion.

Exact technique varies according to:

There is no single universal chest exposure technique.

Exposure Index and Deviation Index

Digital imaging systems can automatically adjust displayed image brightness.

Therefore:

A radiograph can appear appropriately bright even after excessive detector exposure.

Displayed brightness alone should not be used to judge exposure.

Review the system's:

against the facility's established targets.

Remember:

EI and DI are indicators of detector exposure and exposure consistency; they are not direct measurements of patient radiation dose.

Values may also be influenced by:

Use the facility's validated exposure chart and detector-specific target values.

Collimation

Collimate to the required anatomy while ensuring that you do not exclude:

Good collimation helps:

Common Chest Positioning Errors

Error Appearance Correction
Rotation Unequal clavicle-to-spine distances and distorted thoracic anatomy Re-center the midsagittal plane and equalize shoulder position
Shallow inspiration Elevated diaphragm, crowded pulmonary vessels, enlarged-appearing heart Practice breathing before exposure and expose on full inspiration when possible
Scapulae over lungs Scapular borders obscure lung fields Roll shoulders forward and place hands appropriately
Chin over apices Mandible overlaps upper lungs Raise the chin without causing the patient to lean backward
Clipped apices Upper lung anatomy missing Position receptor sufficiently above the shoulders
Clipped costophrenic angles Lower lung or pleural disease may be excluded Verify receptor height, centering, and field coverage
Motion Blurred ribs and vascular markings Use clear breathing instructions and a short exposure time
AP projection mistaken for PA Cardiac magnification may be misinterpreted Use correct projection markers and document portable/semi-erect status
Lordotic under-angulation Clavicles remain over apices Increase lordotic positioning/cephalad angle according to protocol
Excessive lordotic angulation Excessive thoracic distortion Reduce the angle or degree of lean

Recommended study references

If you are building a radiography library, these standard references are useful companions to this article. Always follow your program's required book list first.

Disclosure: As an Amazon Associate, Radiography 101 earns from qualifying purchases. Product links do not influence our clinical or educational guidance.

Pre-Submission Chest X-Ray Checklist

Before dismissing the patient, ask:

1. Is the correct patient identified?

Confirm:

2. Is all required anatomy included?

Check:

3. Is the patient rotated?

Compare the medial clavicles with the spinous processes.

4. Are the scapulae and chin clear?

Ensure removable positioning problems are not obscuring anatomy.

5. Is inspiration adequate for this patient?

Use diaphragm position, lung expansion, and posterior rib count together.

6. Is there motion?

Look carefully at ribs and pulmonary vascular markings.

7. Is exposure appropriate?

Evaluate:

8. Does the image answer the clinical question?

A radiograph does not need to be cosmetically perfect to be diagnostically useful.

Before repeating an image, consider whether the clinical question has already been answered and whether the benefit of repeating the exposure outweighs the additional radiation and patient burden.

Quick Positioning Memory Guide

PA chest
Heart close to detector → less cardiac magnification.

Left lateral chest
Left side against detector → minimizes heart magnification.

AP chest
Used when PA positioning is not possible.

AP lordotic
Clavicles above apices → demonstrates upper lungs.

Pleural effusion decubitus
Fluid DOWN.

Pneumothorax decubitus
Air UP.

Decubitus imaging
Horizontal beam.

Evidence and Protocol Note

This guide describes commonly taught adult chest-radiography positioning methods. Positioning techniques and exposure parameters should never override a patient's clinical condition or an approved facility protocol.

The revised clinical statements in this article are consistent with established radiographic positioning principles and current evidence concerning chest radiograph technical evaluation, pleural-effusion imaging, pneumothorax radiography, and digital radiography exposure indicators.

Particular caution should be used when teaching numerical thresholds. Values such as pleural-fluid detectability represent observations from individual studies and should be treated as approximate guides—not universal diagnostic cutoffs.

Similarly, exposure index and deviation index help radiographers monitor detector exposure consistency but should not be interpreted as direct measurements of patient radiation dose.

Always follow the examination order, manufacturer recommendations, departmental exposure charts, and local positioning protocols.

References and Further Reading

Related Articles

📝 ARRT-Style Practice Questions

Test Your Knowledge

Select an answer to reveal feedback and an explanation. These are independent study questions, not official ARRT content.

1. Why is a PA chest preferred over an AP chest in an ambulatory patient?
Answer: B. In the PA position, the heart is closer to the detector. Reduced object-to-image distance combined with the long chest SID reduces cardiac magnification.
2. Which instruction is commonly used to obtain full inspiration for a routine PA chest?
Answer: C. The two-inspiration technique is commonly taught for routine chest radiography. The exact instruction should be adapted to patient condition and departmental protocol.
3. A patient has a suspected free-flowing right pleural effusion. Which position best demonstrates the fluid?
Answer: A. For suspected pleural fluid, position the affected side down so free fluid layers along the dependent lateral chest wall. A horizontal beam demonstrates the layering.
4. On a nonrotated PA chest, the medial ends of the clavicles should be:
Answer: C. Approximately equal distances between the medial clavicles and spinous processes indicate minimal thoracic rotation.
5. Which projection is specifically intended to demonstrate the lung apices without clavicular superimposition?
Answer: D. The AP lordotic projection moves the clavicles superiorly so that the pulmonary apices can be evaluated more clearly.
6. Which finding best indicates a properly positioned AP lordotic chest?
Answer: B. A successful AP lordotic image demonstrates the lung apices free of clavicular superimposition. The clavicles should appear relatively horizontal and project superior to the apices.
7. Why is a horizontal beam essential for a lateral decubitus chest?
Answer: C. The diagnostic value of a decubitus image depends on gravity. Fluid moves dependently while pleural air rises. A horizontal beam demonstrates this distribution without superimposing it in the same way as a vertical-beam image.
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Radiography 101 Clinical Team

Educational content for radiologic technology students and professionals. Always follow the imaging order, equipment instructions, and your facility's approved positioning and exposure protocols.