How to interpret chest radiographs (X-rays): a systematic approach (2024)

Chest X-rays are the most common radiological investigation requested in the NHS; this article explains how to interpret the results and identify common abnormalities. This is a Self-assessment article and comes with a self-assessment test

Introduction

From September 2022 to August 2023, more than 45 million imaging tests were reported in England on NHS patients (NHS England, 2023). Plain radiographs (or X-rays) remain the most common of all imaging tests performed within the NHS, with 21.9 million being requested through primary and secondary care (NHS England, 2023).

Chest radiographs are used to aid the diagnosis, treatment and management of a range of cardiovascular and respiratory disease processes.

There are newer and more sophisticated imaging options available, such as ultrasound, computerised tomography (CT) or magnetic resonance imaging (MRI), but chest radiographs remain the first line of investigation for most patients who present with chest injury, shortness of breath, infection localised to the chest, fluid (pleural effusions) or potential cancers within the chest (Penman et al, 2022).

Chest radiographs are also used to assess how patients are responding to treatments such as antibiotics or diuretics, as well as monitor the progression of disease such as lung cancers.

There is no doubt that the expertise of radiologists and radiographers with suitable skills and qualifications in interpretation and reporting are needed. But there are times when nurses and allied health professionals need to also interpret chest radiographs. This article will introduce and explain:

• How chest radiographs are generated;
• Patient positioning considerations;
• Best practice when requesting this investigation;
• Relevant anatomy;
• A systematic approach to assessment;
• Identifying common abnormalities with accompanying images.

However, if uncertainty remains, a radiologist or suitably qualified radiographer with skills in interpretation and reporting of chest radiographs should be consulted.

How chest radiographs are generated

How well X-rays penetrate the body is dependent on the density of the material they are passing through. The denser the material, the more X-ray energy is absorbed, and the opposite is true for less dense material.

Tissues such as bone, calcification in blood vessels, masses or infection (consolidation) will absorb more X-rays and so appear whiter (radiopaque) in colour on the chest radiograph. The chest also contains many less dense structures, such as the air-filled alveoli, bronchi, bronchus and trachea, as well as the heart, valves and blood vessels. These structures have varying degrees of density and so absorb different amounts of X-rays.

The air-filled alveoli have relatively little density and show up darker (radiolucent) on the radiograph, sometimes near black. But the trachea, heart, some blood vessels, such as the aorta and heart valves, are more dense so absorb more X-rays and, because of this, they appear in various shades of grey. The golden rule is: the denser the structure, the more radiopaque (whiter) it will be on the chest radiograph.

Patient positioning

For many of us, there are two projections (commonly called ‘views’) that we are likely to see in clinical practice: posterior anterior (PA) and anterior posterior (AP) (Fig 1).

The projection that we see on a chest radiograph is generated when the X-ray beam passes through the patient onto a film – which can now be digitally produced. It is simpler to think about this in terms of how a photographer (or you) would take a picture of someone.

In the PA view, the X-ray beam is directed from behind the patient towards the front of their chest (posterior to anterior). This is similar to taking a photo of someone who is standing with their back towards you but taking a photograph of the front of their chest (like a selfie). This projection of the radiograph offers a more desirable view than the AP view, as the diaphragm is flatter, the scapulae do not obstruct the lung fields and the heart is not magnified (Corne and Au-Yong, 2023).

In the AP view, the X-ray beam is directed from the front (anterior) of the patient towards their back (where the film or detector will be placed). This can be likened to taking a photograph of someone facing towards you with the camera pointed at their chest. In the clinical context this is often the projection we will see when a patient is unable to stand, and the X-ray is taken while the patient is on a bed or trolley.

But, in this image the scapulae often are visible within the lung field and the heart can be magnified, making interpretation more challenging than a PA view (Corne and Au-Yong, 2023).
There are other views that are speciality specific: lateral (from the side) or lordotic (that reveals the top of the lungs more clearly). Due to advances in medical imaging, many of these are no longer used as frequently.

“Sometimes it is very obvious that there is an abnormality when reviewing a chest radiograph, but it’s important to take a systematic approach to ensure that nothing is missed”

Requesting a chest radiograph

Before requesting a chest radiograph, remember to ensure that you have the right patient, the right time and right test (Thomas, 2014). There is also a clinician at the end of the request (radiologist or radiographer), so the more information you can give the better.

Always include the full clinical details, including history and clinical assessment and examination findings, as this will help the radiology department to prioritise their workload and complete urgent investigations quicker (Corne and Au-Yong, 2023).

If there is something specific that you would like to know, or have additional information that could be provided, then include it on the request. For example, if a patient’s pneumonia does not seem to be improving, even with the prescribed antibiotic, dosage and duration of treatment. This will enable to radiologist who reports on the chest radiograph to give a precise answer.

Electronic requests are often placed into a queue, where they may be reviewed and approved by a radiologist or radiographer. Once the investigation has been completed, they are normally available within minutes for review on the picture archiving and communications system (PACS).

There may be a system in the department where chest radiographs are rapidly reported, if this is not in place do ask for assistance from a more experienced colleague or the radiologist themselves. Basic interpretation can be simple, but it is best to discuss complex cases with a radiologist before treatment.

Anatomy

Knowledge of anatomy is important when starting to interpret a chest radiograph. There are several key structures that need to be identified:

• Clavicles;
• Trachea and carina;
• Anterior and posterior ribs;
• Stomach/gastric bubble;
• Left and right costophrenic angles;
• Spinous processes;
• The cardiac shadow (heart).

Fig 2 is a chest radiograph of a patient with no visible abnormalities, these important structures are labelled as well as the zones of each lung.

Before beginning interpretation

Before jumping in and starting to interpret the chest radiograph it is important that the patient’s details are checked. Chest radiographs are often now viewed digitally on a screen or mobile device, so before beginning interpretation, it is important to ensure that the patient’s first and last name, date of birth, unique identification number (NHS or hospital number) belongs to the patient you are assessing or consulting with.

Technical quality of the radiograph

Assessing the technical quality of the chest radiograph should always be completed before moving on. Initiating a treatment or management plan based on a poor-quality radiograph could have significant (and dangerous) implications for the patient.

When assessing the technical quality of a chest radiograph there are four things to consider: penetration, rotation, inspiratory effort and exposure (Corne and Au-Yong, 2023). There are many mnemonics available to help assess the technical quality of a chest radiograph. Perhaps the most common is RIPE, a mnemonic which stands for rotation, inspiration, projection and exposure.

This is a widely promoted and easy-to-use mnemonic to assess the technical quality of a radiograph and ultimately decide if a reliable treatment or management plan can then be made.

Rotation

When assessing the rotation of a chest radiograph, look for the medial ends of the clavicles and ensure that a vertebral spinous process falls between them. Each medial end of the clavicle should be equal distance from the vertebral process.

If the vertebra is not in the middle of each medial end of the clavicle, then the chest radiograph is rotated, which could make interpretation more difficult or increase the likelihood of missing a clinical sign.

Inspiration

To assess the inspiratory effort the patient has made, the ribs above the diaphragm need to be counted. The top of the right hemidiaphragm should intersect the sixth rib on the anterior side of the chest or the 10th posterior rib. If more ribs are visible, then the patient is hyperinflated – as seen in patients with chronic obstructive pulmonary disease (COPD). If there are fewer ribs visible, the patient has been unable to take a deep breath before the radiograph was taken. This could be due to pain, exhaustion due to rapid breathing, underlying disease or poor patient compliance and timing error during the capture of the radiograph (Corne and Au-Yong, 2023).

Projection

Assessment of the projection is important, as it needs to be determined if the radiograph is an AP or PA radiograph. Radiographs will usually be labelled to indicate their projection and ensure there are left and right markers on the image. As previously discussed, the heart size may differ in AP or PA radiographs, so knowing the projection is important. Finally, ensure that you can see everything you want to see – both lungs should be clearly visible, and the scapulae moved away from the lung fields.

Exposure

To assess the exposure, which is how well the X-rays have passed through the body, the vertebral bodies should be visible through the heart (known as the cardiac shadow). If they are too clearly visible then the radiograph is over penetrated and it is possible to miss low-density abnormalities (Corne and Au-Yong, 2023).

If the vertebral bodies are not visible at all then the film is under-penetrated, meaning the X-rays have not passed completely through the heart. Basically, the vertebral bodies should be faintly visible through the cardiac shadow (Hodler et al, 2019).

If, once assessing the technical quality of the radiograph, any of the above are not satisfactory, the radiology department should be contacted and the concerns outlined. It may be that the radiograph provided was the best possible with patient-limiting factors such as mobility, pain or compliance. But it may also be possible that another better-quality radiograph can be obtained if requested.

Systematic approach to interpreting chest radiographs

Sometimes, it is obvious that there is an abnormality when reviewing a chest radiograph, but it is important to take a systematic approach to ensure that nothing is missed. The ABCDE assessment is very familiar to many of us; this mnemonic can also be adopted to interpret a chest radiograph (Rodrigues et al, 2014).

Here, the airway (trachea, carina and bronchus), breathing (lung fields), circulation (heart and vessels), diaphragm and everything else (bones, soft tissues and devices) are assessed. Table 1 explains this process in greater detail.

Common abnormalities

There are a number of common abnormalities that are seen in patients with respiratory and cardiovascular disease. The next section of the article will provide information on how these may appear on a chest radiograph, as well as examples of these. For each of these, ensure that you take a systematic approach to interpretation: RIPE ABCDE.

Pulmonary oedema

This is the name given to excess fluid that collects in the alveoli or the space between blood vessels and cells (the interstitial space) of the lungs. This causes breathing difficulties and can be acute or chronic, with the most common causes being cardiac related: left ventricular failure, cardiomyopathy, hypertension or diseases of the valves in the heart (Randall et al, 2020).

Performing a chest X-ray is the most effective way of diagnosing pulmonary oedema and major changes can often be appreciated at the base of the lungs, as the fluid is affected by gravity.

Fig 3 is a chest radiograph of a patient with pulmonary oedema that is analysed using the ABCDE approach.

Consolidation

This is commonly observed on a chest radiograph. Consolidation on the chest radiograph is where a substance (such as fluid or infection) is visible in the alveoli rather than the air. Because the material is more dense, it appears more radiopaque (whiter) on the chest radiograph. Consolidation is, therefore, a term given to an increase in the density of an area of the lung, which may be due to:

• Cellular material: infection or cancer;
• Fluid: aspiration or pulmonary oedema;
• Blood: haemorrhage.

The appearance of consolidation may appear over time if the cause is chronic (fluid or cancer) or more quickly if the cause is acute (infection). Consolidation on the chest radiograph can be located to only one zone (patchy) or widespread (more than one zone) (Randall et al, 2020).

To determine if the consolidation is acute or chronic, it is important to review previous chest radiographs to see if it was present then also.

When a chest radiograph is suspicious of consolidation, the area will appear white, but the borders of this will not clearly be defined. The reason for this is that the alveoli are filled with a dense substance and so absorb more of the X-rays that pass through the patient, but the larger airways remain filled with air and so appear darker on the chest radiograph – this creates a contrast between the two known as an ‘air bronchogram’ (Corne and Au-Yong, 2023).

Fig 4 is a chest radiograph of a patient with consolidation that is analysed using the ABCDE approach, the air bronchogram is clearly visible in the hazy opacification in the middle to lower zones of the left lung.

Pneumothorax

A pneumothorax, commonly known as a collapsed lung, occurs when air becomes trapped in the plural space (Penman et al, 2022). The plural space is normally filled with a small amount of fluid which helps to both lubricate and provide resistance in the form of negative pressure that allow the lungs to expand and contract freely.

A pneumothorax can either occur spontaneously or as a result of underlying disease. The most common causes of spontaneous pneumothorax are trauma, cancer, pneumonia and placement of intravenous central lines or pacemaker insertion (Randall et al, 2020).

The most commonly known type of pneumothorax is the ‘tension pneumothorax’. This is where air enters the pleural space but becomes trapped and compresses the lung and, once the pressure is great enough, it causes the lung to collapse (Innes et al, 2018).

When considering the positioning of a patient suspected of pneumothorax for a chest radiograph, PA is the best. The pneumothorax will appear more radiolucent (black) on the chest radiograph and the lung markings will be absent (Corne and Au-Yong, 2023).

Fig 5 is a chest radiograph of a patient with a right-sided pneumothorax that is analysed using the ABCDE approach.

Pulmonary embolism

Pulmonary embolisms typically result from a deep vein thrombosis that has migrated to the lung. This presents as a patient who is short of breath, but with no desirable cause on physical examination of the lungs (Penman et al, 2022).

In many cases, the chest radiograph will often not show an abnormality and will be ‘clear’. But, in the case of a pulmonary embolism, the chest radiograph is used to eliminate any other causes of the patient’s symptoms. In a patient who is short of breath, where the respiratory examination and chest radiograph are inconclusive, there should be a high suspicion of pulmonary embolism.

The preferred method for the diagnosis of a pulmonary embolism would be a computerised tomography pulmonary angiogram (CT-PA). Here, CT is used as well as contrast dye that is injected through an intravenous line, to identify any clots (emboli) in the pulmonary vasculature (Doğan et al, 2015).

“When interpreting a chest radiograph, the practitioner must have a sound knowledge of the anatomy”

Cardiomegaly

This is a condition where the heart is enlarged, this is often due to thicker heart muscle (hypertrophy) in one or more of the chambers of the heart (Bickley, 2020). This thickening of the heart muscle is caused by conditions that cause the heart to pump harder, such as hypertension, valvular disease, coronary artery disease or anaemia (Ampanozi et al, 2018). Patients with cardiomegaly may not present with any symptoms of the disease and this can first be discovered on the chest radiograph.

To assess for cardiomegaly, the heart must be located and assessed for size. This is done assessing the transverse (side to side) internal thoracic diameter – often called the cardiothoracic ratio. When assessing this, the transverse diameter of the heart should not occupy more than 50% of the overall thoracic diameter (Rodrigues et al, 2014).

Fig 6 is a chest radiograph of a patient with cardiomegaly that is analysed using the ABCDE approach.

Cancer

Lung cancer is the leading cause of cancer-related deaths globally, responsible for the highest mortality rates among men and women (World Health Organization, 2023). Most patients with a lung cancer are symptomatic and will have haemoptysis (coughing of blood from the lungs), shortness of breath, chest pain and a chronic cough (Panunzio and Sartori, 2020).

Around 10% of patients are asymptomatic when the tumour is found incidentally and, where the symptoms described above are absent, a chest radiograph may be the first indication of a lung cancer (Panunzio and Sartori, 2020).

A chest radiograph is often the first investigation performed in patients with suspected lung cancer. Lung tumours typically present as central or peripheral radiopaque (white) masses and can be either individual or multiple (Corne and Au-Yong, 2023).

Fig 7 is a chest radiograph of a patient with lesions suspicious of lung cancer that is analysed using the ABCDE approach.

Conclusion

Chest radiographs are one of the most used investigations for many patients with respiratory or cardiovascular related symptoms. When interpreting a chest radiograph, the practitioner must have a sound knowledge of the anatomy. This knowledge must include appearance in terms of the organ’s radiographic appearance, location and colour.

When interpreting a chest radiograph, start with assessing the image quality using RIPE and then begin a systematic evaluation of the image using the ABCDE approach. Observing chest radiographs frequently will increase confidence and accuracy. But nurses must be careful to practice within their own knowledge and skills boundaries and be prepared to ask for help from senior colleagues in clinical specialties and the radiology departments.

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