Basics of Reading Chest X-ray: Complete Guide | CXR for Beginners

You are probably here because you questioned yourself- “How to Read Chest Xray?”. Chest Xray is one of the most common modalities of modern medicine used to interpret differential diagnosis in clinical practice. However, it can be challenging for beginners to understand and properly read the chest X-Ray without proper training and guidance.

By the end of this article, you will grab the basic concepts of reading chest xray, including the anatomy of Xray and differentiating between normal vs abnormal.

In this article, we will provide you with step-by-step instructions for interpreting, tips for identifying structures and abnormalities, and the typical findings which you should not miss.

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How to Read an Xray?

The systematic approach to presenting an Xray involves 6 steps. These are:

1. Read TYPE and PROJECTION in Xray
2. Read the Patient’s Name
3. Read the Date when the X-ray was taken
4. Ensure film quality is adequate
5. Start ABCDE assessment
6. Read a concise summary at the end

Examples

1. Type and Projection in Xray

Type- PA view, Projection- Chest. Therefore, this is a PA Chest Xray.

2. Patient’s Name

This is a PA Chest Xray of John.

3. Date

This is a PA Chest Xray of John which was taken on 29th January 2023.

4. Adequate Film Quality of Xray

This is a PA Chest Xray of John which was taken on 29th January 2023. The film is not rotated and there is adequate inspiration.

5. ABCDE assessment

This is a PA Chest Xray of John which was taken on 29th January 2023. The film is not rotated and there is adequate inspiration.

A: The trachea is central.
B: The lungs are uniformly expanded and the lung fields are clear.
C: The heart size is normal. There is no mediastinal shift. The mediastinal contours and hila appear normal.
D: There is no fracture or bony abnormality.
E: There is no evidence of air under the diaphragm, surgical emphysema, or any foreign body.

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How to Interpret a Normal Chest Xray

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Film Quality

Before considering the potential anomalies on a chest radiograph, you must first evaluate the technical quality of the film to verify the picture is adequate. There are two things to look out for.

1. Rotation
2. Adequate inspiration: Adequate inspiration is necessary because excessively shallow inspiration can cause the heart to seem artificially enlarged, producing the impression of cardiomegaly. Furthermore, if the lungs are not appropriately inflated, the arteries at the lung bases may seem more prominent, giving the misleading impression of consolidation or collapse.

Some physicians may additionally want that you remark on whether the film's exposure is acceptable. This is no longer essential, as photos that are over- or under-exposed are terminated very immediately by the radiographer and retaken.

You may also use the mouse to adjust the contrast and brightness of a computer X-ray viewer to compensate for poor exposure.

1. Rotation

Examine the spinous processes of the upper thoracic vertebrae. If the patient is not rotated, they should lie halfway between the medial ends of the clavicle.

When the patient is rotated, the spinous processes of the upper thoracic vertebrae deviate to the left or right rather than lying midway between the medial ends of the clavicles.

Left Rotation: The patient is rotated to the left, with the medial ends of the clavicles deviated to the left of the spinous processes of the upper thoracic vertebrae.

Right Rotation: The patient is rotated to the right, with the medial ends of the clavicles deviated to the right of the spinous processes of the upper thoracic vertebrae.

This rule of ration applies to both PA and AP views. A normal Xray should not be rotated.

It is critical to examine rotation since a rotated film might make the heart and mediastinum appear bigger or smaller than they are.

Normal vs Rotated Film

You can easily make out when a film is rotated and hence not adequate.

2. Adequate Inspiration

If the hemidiaphragm is at or below the level of the sixth anterior rib, the inspiration is acceptable. If eight or nine posterior ribs are seen in the lung fields, this also suggests appropriate inspiration.

Adequate vs Inadequate Inspiration Films

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Understanding Chest Xray

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Chest Xray Views

There are primarily two views that are often performed. These are AP and PA views.

• AP or Anteroposterior view- The view is from front to back.
• PA or Posteroanterior view- The view is from back to front

A PA (posterior-anterior) erect chest X-ray is the standard view. Unless otherwise specified, all chest X-rays are taken PA erect. Unless it says AP or supine, you should always presume a chest radiograph is PA erect.

The patient is standing with their anterior chest against an X-ray film. The X-ray tube is preferably situated 6 feet behind the patient so that the X-rays travel posterior-anterior.

To guarantee proper inspiration, the patient takes a deep breath and holds it during the X-ray.

On the other hand, when a patient is unable to stand, an AP (anterior-posterior)/supine CXR is done (e.g. Intensive Care Unit or A&E Resuscitation). The X-ray tube is situated in front of the patient, and the X-rays are directed anteriorly and posteriorly.

When compared to PA films, the main drawback of AP/supine films is that the mediastinum and heart size seem wider on an AP/supine film due to venous distension and magnification.

As a result, you SHOULD NOT make any comments on the cardiac or mediastinal size on an AP/supine film.

Why is a PA view preferred?

PA view is preferred because of two reasons:

1. Accurate cardiac size measurement owing to low magnification.
2. The scapulae can be moved out of the way by rotating them.

Why is the Erect view preferred?

An erect view is best because of the following reasons:

1. Gas ascends: This makes pneumothorax and free air beneath the diaphragm easier to identify.
2. Fluids descend: Pleural effusion is more easily recognized because fluid flows downhill.
3. Blood vessels and lungs in physiological form (if done supine, the mediastinal veins and upper lobe vessels may be more swollen than normal, leading to misinterpretation).

Other Views

1. Lateral CXR

Lateral CXR is utilized to provide additional views of the lungs and heart, as well as further information on the anatomical position of lesions. It is hardly used nowadays because CT provides better information.

2. Expiratory PA Erect CXR

Expiratory PA erect CXR is used seldom to aid in the detection of a suspected pneumothorax or bronchial blockage with air trapping.

Difference between PA vs AP view Chest Xray

Features	PA view	AP view
Position of clavicle	Oblique	Horizontal
Scapula	Away from the lung field	Over the lung field
Spirolamina angle	Inverted ‘V’	Not significant

PA is the most common X-Ray done whereas AP is usually done when the patient cannot stand and an XRay machine is brought to him on the bed and a view is taken from anterior to posterior.

The point to add is that there is apparent Cardiomegaly in the AP view compared to the PA view because there is a slight magnification of the heart since the heart is away from the view capturing film.

Cardiomegaly on Chest Xray

• A/B x 100 = cardio ratio
• In the PA view, Cardiomegaly when the ratio is more than 50%
• In AP view, Cardiomegaly when the ratio is more than 60%

Erect vs Supine Position

There is a fundal view in an erect position because all the air in the stomach comes into the fundus when the patient is standing.

Inspiratory vs Expiratory

If the anterior end of the 6th or 7th rib reaches the mid-clavicular line of the diaphragm, it is Inspiratory Xray.

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Counting Ribs on Chest Xray

Two points can just help you quickly count ribs from top to bottom:

• The front opaque appearing side of the ribs is actually its posterior side.
• Ribs are counted from the anterior sides.

Before we proceed, let us see what structures lie in a normal Chest Xray:

The Chest Xray is usually divided into three zones:

• Upto 2nd rib- First zone
• 2nd to 4th rib- Second zone
• 4th to 6th rib- Third zone

Now let’s proceed to start studying the Xray.

Lucency and Opacity in Chest Xray

Lucency

Anything that appears dark or black on a chest xray is said to be lucent.

• This is because of less density.
• The black color appears because of AIR.

Opacity

Anything that appears light or white on a chest xray is said to be Opaque.

• This is because of high density.
• White color appears because of Bones and soft tissues.

Therefore, we can conclude the following easily:-

Increase in lucency:

• Increase in air
• Decrease in soft tissues or absence of bone

Increase in Opacity:

• Increase in soft tissue or abnormal bone
• Decrease in air

The basic approach when seeing a chest xray always sequentially as:-

1. Define whether the xray is normal or abnormal
2. If the xray is abnormal, where is this abnormality
3. Extent of abnormality
4. What is the final diagnosis

Before we proceed to pathological approaches to Chest X-Rays, let’s see what layers the xrays hit when they enter the body. Note this strengthens further basics:

Muscle> Ribs> Pleura> Lung

Talking about when Hyperlucency (increase in blackness) or Hyperopacity (increase in whiteness) occurs:

Unilateral Lung Hyperopacity

1. Consolidation- Replacement of air by something abnormal
2. Atelectasis- Collapse of the lung resulting in loss of air

Also seen in Plethora, i.e, an increase in vascularity.

The differential diagnosis of three important causes of unilateral (one side) opaque thorax are:-

1. Atelectasis- the collapse of the lung

• Displacement of interlobar fissure: because the lobes of the lung collapse, the fissures in between the lobes move up or down because of the hyperinflation of the normal lobe against the collapsed lobe. This is the most reliable direct sign of Collapse.
• Mediastinal shift: The structures on the mediastinum shift to the side of collapsed lung
• Crowding of ribs
• Elevation of hemidiaphragm
• Sharp-defined margins of opacity

2. Consolidation- replacement of air

• No mediastinal shift
• Ill-defined margins of opacity
• Air bronchogram sign: visualization of air in bronchus surrounded by alveolar opacity

Positive Airbronchogram sign is seen in:

• All except interstitial (viral) pneumonia
• Pulmonary edema (water replaces air)
• ARDS (Acute respiratory distress syndrome)
• Goodpasture syndrome (blood)
• HMD (Hyaline membrane disease)
• Pulmonary alveolar proteinosis (macrophages congested in alveoli making crazy paving pattern)

Air bronchogram sign is NOT seen in:

• Lung abscess
• All except bronchoalveolar carcinoma

3. Pleural effusion-accumulation of fluid

Normally, there is no air in pleura. But effusion in pleura can occur.

• Mediastinal shift: which is on the opposite side, i.e, structures shift to the opposite side of pleural effusion.

Note: Pleural effusion and Haemothorax cannot be differentiated because soft tissue cannot be differentiated on Chest Xray.

Unilateral Lung Hyperlucency

• Rotation: apparent increase in the air gap
• Scoliosis
• Mastectomy
• Poland syndrome (absent pectoralis major muscle)
• Airway obstruction
• Large pulmonary embolus
• Pneumothorax

A small mnemonic to quickly grab the names:

POEMS

• P- Poland syndrome/Pneumothorax
• O- Oligemia/Obstruction (like Pulmonary embolism)
• E- Emphysema
• M- Mastectomy/Mucous plug
• S- Swyer’s James syndrome

ABCDEF Approach to Reading Chest X-Ray

Before Analyzing

Before Analyzing Chest Xray, ABCDEF approach for preliminary check can be used as:

A: AP or PA view

B: Body Position

C: Confirm the Name of the patient on film

D: Date of Xray

E: Exposure adequate?

F: Films for comparison

Analysis of Chest XRay

Again, an ABCDEFGHI approach can be used to recall the steps of the Analysis of Chest Xray. It can be related as:

A: Airways- Initially check tracheal deviation, and then check for hilar adenopathy or enlargement

B: Bones / Breast Shadows- Check for fracture of ribs, scapula, or clavicle)

C: Cardiac Silhouette- Cardiac Enlargement/ Costophrenic Angles- Check for sharp angles, if blunt could be pleural effusion

D: Diaphragm- Check for free air, which could mean perforation peritonitis/ Digestive tract

E: Extra-thoracic tissues / Edges- Apices for fibrosis, pneumothorax, pleural thickening, or plaques)

F: Fields- Check for alveolar filling in lung fields / Failure- Alveolar air space disease with prominent vascularity with or without pleural effusions

G: Gastric Bubble- Visible at the left upper abdomen

H: Hilum- Check for lymph node enlargement

I: Insertion / Artefacts: Check for any external object appearing in the xray film

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What is an X-Ray?

X-rays are a form of ionizing radiation. They are part of the electromagnetic spectrum and have enough energy to trigger ionization. They have higher energy than ultraviolet (UV) waves but less energy than gamma rays.

What is Radiation in Chest Xray?

The transmission of energy in the form of particles or waves is referred to as radiation.

On the other hand, Ionising radiation is radiation with enough energy to produce ionization, which is the process by which radiation takes an electron from an atom’s outer shell.

Thus, ionizing radiation can trigger chemical alterations in physiologically essential substances (e.g. DNA).

The application of Ionising radiation includes the following:

• Plain film X-rays
• Contrast investigations
• Computed tomography (CT)
• Nuclear medicine
• PET Scan (Positron Emission Tomography)

How are Xrays Produced?

In simple words, hitting a high-energy electron beam on a tungsten target results in the production of Xrays. If the electron has enough energy, it can knock out another electron from the tungsten atom’s inner shell.

As a result, electrons from higher energy levels fill the vacancy, causing X-rays to be produced. Because the X-ray manufacturing process is inefficient (0.1%), the bulk of the energy in the electron beam is wasted as heat.

This is why better cooling solutions for X-ray tubes are necessary. The generated X-rays pass through the body and onto a detecting device, which creates an image.

Structures can only be visible if there is enough contrast between them and the surrounding tissues (contrast is the difference in absorption between one tissue and another).

Production of Image on Xray Film

The picture on the X-ray film that results is a two-dimensional (2D) depiction of a three-dimensional (3D) structure.

The X-ray beam is absorbed in proportion to the cube of the atomic number of the various tissues through which it travels when traveling through a patient. According to tradition, the more radiation that hits a detector, the darker the picture.

As a result, the less “dense” a substance is, the more X-rays pass through and the darker the film. In contrast, the more ‘dense’ a substance is, the more X-rays it absorbs and the film appears whiter. Those with a low density seem darker than materials with a high density.

How are Xray Processed and Stored?

Radiographs are produced onto X-ray film in some hospitals, but most now employ a computer-based digital film storage system to store X-ray pictures, removing the need for film.

PACS is the abbreviation for this system (Picture Archiving and Communication System). Doctors and other healthcare professionals may examine the pictures (radiographs) on a computer screen, making it simple to edit the image (for example, increasing the contrast, zooming in/out, and so on).

The benefits include increased accessibility, cost savings, and no more lost films. The downsides are the initial expense and the possibility of a system failure, which might be disastrous.

What are the considerations for Radiation Hazards?

Radiation dangers develop as a result of radiation damage to cells. Actively dividing cells (such as bone marrow, lymph glands, and gonads) are especially vulnerable. Cell death, mitotic inhibition, and chromosome/genetic damage resulting in mutations are all examples of the damage.

The kind and extent of cell damage from these Xrays vary depending on the following factors:

• Radiation dosage and dose rate
• Amount of tissue exposed
• Type of radiation (alpha particles, X-rays, neutrons, etc).

IRMER 2000

The Ionising Radiation (Medical Exposure) Regulations 2000, enacted in 2000, establish the fundamental procedures for radiation safety for patients. They refer to three key individuals involved in the patient’s protection.

1. The Referrer (a doctor or other accredited health professional seeking the exposure, such as an emergency nurse practitioner):
   • must give appropriate and relevant clinical information to allow the practitioner to justify the exposure.
2. The Practitioner (often a radiologist who justifies the radiation):
   • On a case-by-case basis, decides on the necessary imaging and justifies any radiation exposure. The potential advantages must outweigh the risks to the patient (for example, a CT head scan on a one-year-old adds a 1/500 lifetime risk of cancer and raises the likelihood of cataract development). As a result, the benefits of this scan must outweigh the hazards to the kid).
3. The Operator (often a radiographer who handles the practical aspects):
   • checks that the preceding two processes have been done correctly
   • maintains as little legitimate exposure as possible by:
     • reducing the number of X-ray films obtained
     • directing the X-ray beam to the desired location
     • Using ultrasonic or magnetic resonance imaging (MRI) instead of mobile X-rays wherever practical.

Xrays in Pregnancy

There is often a debate on whether X-rays are safe during pregnancy or not. Ideally, one should always avoid exposure to radiation in pregnant women. Further points worth noting include:

• Reduce radiation exposure to the abdomen and pelvis.
• Ask each woman of reproductive age if she is pregnant, and avoid exposing pregnant women to radiation. The most essential time is between 3 and 4 months gestation when fetal organogenesis is taking place and the fetus is radiosensitive. If feasible, X-rays of the abdomen and pelvis should be performed when fetal sensitivity is low (i.e. post – 24 weeks gestation, or ideally until the baby is born).
• At any moment throughout pregnancy, exposure to distant parts (chest, cranium, and limbs) with limited fetal exposure is permissible.