Thoracic imaging plays a crucial role in diagnosing and managing a wide range of conditions affecting the chest, including the lungs, heart, and blood vessels.
From the basic chest x-ray to more sophisticated modalities like CT scans, MRI, and PET scans, these tools enable healthcare providers to detect, diagnose, and monitor diseases more effectively.
This article explores the most common types of thoracic imaging, highlighting their specific uses, strengths, and limitations to provide a comprehensive understanding of how they contribute to patient care.
What is Thoracic Imaging?
Thoracic imaging refers to the use of various imaging techniques to diagnose and assess diseases and conditions within the chest, including the lungs, heart, airways, and surrounding structures.
It plays a vital role in detecting abnormalities such as tumors, infections, and vascular or structural issues. Common modalities include chest X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), and ultrasound.
Thoracic imaging provides critical information that helps physicians make accurate diagnoses, monitor disease progression, and guide treatment plans. The selection of the appropriate imaging method depends on the clinical context and the type of information needed.
Types of Thoracic Imaging
Thoracic imaging encompasses a variety of techniques used to visualize the structures within the chest, including the lungs, heart, and other thoracic anatomy.
Here are the main types of thoracic imaging:
- Chest x-ray
- Computed tomography (CT)
- Ventilation–perfusion (VQ) scan
- Magnetic resonance imaging (MRI)
- Positron emission tomography (PET)
- Ultrasound
- Angiography
Watch this video and keep reading to learn more about the most common types of thoracic imaging.
Chest X-Ray
A chest x-ray is the most commonly used imaging technique for evaluating the thoracic cavity. It provides a two-dimensional image of the chest, allowing doctors to assess the lungs, heart, and bones of the chest wall.
This imaging method is quick, non-invasive, and widely accessible, making it an essential tool for detecting conditions such as pneumonia, lung cancer, heart enlargement, fractures, and other abnormalities within the chest.
Note: While it provides valuable information, a chest x-ray offers limited detail compared to more advanced imaging techniques and is often used as an initial diagnostic step.
Computed Tomography (CT)
Computed tomography (CT) scans offer a more detailed, cross-sectional view of the chest compared to standard x-rays. This imaging technique uses a combination of x-rays and computer technology to produce comprehensive images that can show the lungs, blood vessels, bones, and soft tissues in greater clarity.
CT scans are particularly valuable for detecting small nodules, tumors, blood clots, and other subtle abnormalities that may not be visible on a traditional chest x-ray. They are also commonly used to guide biopsies and assess the extent of diseases such as lung cancer or chronic pulmonary conditions.
Ventilation–Perfusion (VQ) Scan
A ventilation-perfusion (VQ) scan is a nuclear medicine test that evaluates both airflow (ventilation) and blood flow (perfusion) within the lungs. This type of imaging is particularly useful for diagnosing or ruling out pulmonary embolism (a blood clot in the lungs).
The scan involves two parts: the ventilation scan, which uses a radioactive gas or aerosol inhaled by the patient to show how well air reaches different areas of the lungs, and the perfusion scan, which involves injecting a radioactive tracer into the bloodstream to map blood flow in the lungs.
Note: The results help identify areas with mismatched ventilation and perfusion, indicating potential blockages or other issues.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) uses strong magnetic fields and radio waves to produce highly detailed images of the chest’s internal structures. Unlike x-rays and CT scans, MRI does not use ionizing radiation, making it a safer option for certain patients, such as those who require frequent imaging or are more vulnerable to radiation exposure.
MRI is particularly effective for assessing soft tissues and provides exceptional clarity for evaluating the heart, major blood vessels, and mediastinal structures. This imaging technique is often used for detailed examination of chest wall abnormalities, heart conditions, or complex lung and vascular diseases. However, due to the longer imaging time and higher cost, MRI is generally reserved for cases where more specific or detailed information is needed.
Positron Emission Tomography (PET)
Positron emission tomography (PET) is a type of nuclear imaging test that helps visualize metabolic activity and function within the tissues of the chest. This imaging technique is especially useful for detecting cancer, as cancer cells typically have a higher metabolic rate than normal tissues, making them more visible on PET scans.
During the procedure, a small amount of radioactive tracer is injected into the patient’s bloodstream, which accumulates in areas of high cellular activity. PET scans are often combined with CT scans (PET/CT) to provide both metabolic and anatomical information, which enhances the accuracy of diagnosis, staging, and treatment monitoring of conditions such as lung cancer and other thoracic malignancies.
Ultrasound
Ultrasound imaging uses high-frequency sound waves to create images of the structures within the chest. It is a non-invasive and radiation-free method that is particularly effective for evaluating soft tissues and fluid collections.
In the thoracic region, ultrasound is commonly used to guide procedures such as thoracentesis (removal of fluid from the pleural space) and to assess pleural effusions, lung consolidations, or masses near the chest wall.
Although ultrasound does not penetrate air-filled spaces effectively and is limited in its ability to image deeper lung structures, it is highly valuable for real-time imaging and bedside evaluations, especially in emergency or critical care settings.
Angiography
Angiography is an imaging technique used to visualize the blood vessels within the chest, including those in the lungs and heart. This method involves injecting a contrast dye into the bloodstream, which highlights the vascular structures on x-ray or CT imaging.
Thoracic angiography is particularly useful for diagnosing conditions such as pulmonary embolism, aneurysms, arterial blockages, and other vascular abnormalities. It can also be used to guide therapeutic procedures, such as stent placement or embolization.
While traditional angiography may be more invasive, newer methods, such as CT angiography (CTA) and MR angiography (MRA), offer non-invasive alternatives with advanced imaging capabilities, providing detailed views of the blood vessels and surrounding structures.
Thoracic Imaging Practice Questions
1. What is the definition of radiolucent?
X-rays that pass through low-density lung tissue strike the film directly, creating a darker image.
2. What is the definition of radiopaque?
X-rays that pass through high-density tissue (e.g., bone) are more absorbed, resulting in a lighter image.
3. What four types of tissue are visible on an x-ray?
Air, fat, water, and bone.
4. What are air bronchograms?
A pattern on a chest radiograph where air-filled bronchi are outlined by surrounding areas of consolidation.
5. Does air appear radiolucent or radiopaque?
Radiolucent
6. What describes the AP view on an x-ray?
The x-ray source is positioned in front of the patient, with the film placed behind their back.
7. What is the best type of film for detecting small amounts of pleural fluid?
Lateral decubitus
8. What is the preferred imaging method for evaluating the mediastinum?
CT scan
9. Does bone appear radiolucent or radiopaque?
Radiopaque
10. What is computed tomography angiography (CTA) most commonly used for?
Visualizing the heart and assessing vascular structures.
11. What is the typical thickness of CT image slices?
3-7 mm
12. What is a costophrenic angle?
The area where the diaphragm meets the chest wall, forming a sharp point. A blunted costophrenic angle indicates a pleural effusion.
13. Can a CT scan detect pleural fluid?
Yes
14. Does an embolus appear on a CT scan?
Yes
15. Can an ultrasound detect pleural effusions?
Yes, even small pleural effusions can be detected.
Access our quiz, which includes sample TMC practice questions and detailed explanations to help you master the key concepts of patient assessment.
16. Does an embolus show up on a chest radiograph?
No
17. Fluid buildup in the alveoli causes what appearance?
Kerley B lines
18. The heart shadow should not exceed what percentage of the thoracic diameter?
It should not exceed 50% of the thoracic diameter.
19. How does a CT scan visualize structures?
By using cross-sectional imaging.
20. How much fluid can be detected using the lateral decubitus view?
As little as 5 mL.
21. How much fluid is required for blunting of the costophrenic angle to appear in the frontal view due to a pleural effusion?
175-200 mL
22. How much fluid is required for blunting of the costophrenic angle in the posterior view due to a pleural effusion?
75-100 mL
23. If more than seven anterior ribs are visible above the diaphragm, what does this indicate?
Hyperinflation
24. What are infiltrates on a chest radiograph?
Patchy white shadows
25. Is the diaphragm visible on a chest radiograph?
Yes
26. Kerley B lines are commonly associated with what type of pulmonary edema?
Cardiogenic pulmonary edema
27. What is nuclear medicine?
An imaging technique using radioactive materials via inhalation or injection, often used for V/Q scans and Positron Emission Tomography (PET) scans.
28. Should the patient be sitting or standing for a PA view?
Standing
29. Does the PA view minimize or maximize heart magnification?
It minimizes heart magnification.
30. What does PET stand for?
Positron Emission Tomography
31. When is a PET scan typically indicated?
For localizing tumors and detecting metastases.
32. Can the pleura be seen on a conventional chest radiograph?
No
33. What should be visible on a properly exposed radiograph?
Intervertebral disc spaces through the heart shadow and blood vessels in the peripheral lung regions.
34. What are the radiographic signs of cardiac decompensation?
Cardiac enlargement, pleural effusion, redistribution of blood flow to the upper lobes, poor definition of central vessels, Kerley B lines, and alveolar filling.
35. What color represents radiolucency?
Black
36. What color represents radiopacity?
White
37. What is a silhouette sign?
The loss of normal borders between structures of the same radiographic density.
38. What absorbs fewer x-rays than soft tissue?
Fat
39. What allows blood vessels to be distinguished from soft tissue in a CT scan?
The injection of iodinated contrast material, which makes blood denser, radiopaque, and white in appearance.
40. What is used to assess the correct endotracheal tube position?
A bedside chest radiograph after intubation.
41. What can help diagnose a pneumothorax in a supine patient?
A decubitus or cross-table lateral radiograph.
42. What does a CT scan evaluate?
It evaluates lung nodules, masses, the great vessels of the chest, the mediastinum, and pleural diseases.
43. What do you assess first during a lung evaluation?
The size and density of the lungs.
44. Which film helps clarify lung abnormalities?
The lateral film.
45. What helps visualize the end of the endotracheal tube on a chest x-ray?
The radiopaque/opaque marker.
46. What is the first sign of a left-sided pleural effusion on an upright chest radiograph?
An increased distance between the inferior margin of the left lung and the stomach gas bubble.
47. What type of radiograph should you obtain for a pneumothorax?
A radiograph obtained during exhalation with the patient sitting upright.
48. When is a radiograph in the AP view usually taken?
Typically, in the ICU.
49. Where is a radiograph in the PA view usually performed?
In the radiology department.
50. Why are ultrasounds rarely used for the lungs?
Because the lungs are air-filled.
51. Why can pleura not be seen on a conventional chest radiograph?
They blend into the density of the chest wall, diaphragm, and mediastinum.
52. Why is there magnification of the heart shadow in the AP view?
Because the heart is closer to the x-ray source.
53. What are infiltrates?
Shadows seen on an x-ray caused by the accumulation of fluids.
54. What four tissue types are visible on an x-ray, and how do they appear?
Air (radiolucent/black), fat (dark grey), soft tissue (grey), and bone (radiopaque/white).
55. What is CT Angiography?
A CT scan of the pulmonary vessels and heart used to check for a pulmonary thromboembolism. It serves as an alternative to routine coronary angiography.
56. What is the most common chest film finding in critically ill patients?
Pulmonary edema
57. Why is the PA view preferred over the AP view for evaluating the heart?
The heart appears less magnified and provides better image quality.
58. What are the two most common views in a standard chest x-ray study?
Posterior-anterior (PA) and Anterior-posterior (AP).
59. How does the heart appear in the PA view compared to the AP view?
The heart shadow appears larger in the AP view.
60. What tissue has the greatest radiodensity?
Bone
61. A possible nodular anomaly is present in the right upper lobe on a PA film but is partially obscured by the clavicle. What view might show this anomaly better?
An apical lordotic projection.
62. During full inspiration, where should the hemidiaphragms be located on an adult chest film?
At the level of the 10th rib.
63. When evaluating a PA chest film, you notice blunted right costophrenic angles. What does this suggest?
The presence of a pleural effusion on the right side.
64. On a PA chest film, you see a 1 cm wide, dark sliver along the lateral margin descending from the apex and merging with the ribs at the 3rd rib, devoid of vascular markings. What does this indicate?
A pneumothorax
65. When evaluating the position of an ET tube on an AP chest film, where should the tip rest?
2-3 cm above the carina.
66. What are obliterated costophrenic angles an indication of?
Pleural effusion
67. What does a reticulogranular or granular pattern on a radiograph indicate?
ARDS or IRDS
68. What does a flattened diaphragm on a chest x-ray indicate?
COPD or significant air-trapping.
69. What does a ground-glass or honeycomb pattern on a chest x-ray indicate?
ARDS or IRDS
70. What does radiolucent indicate on a chest x-ray?
Normal lungs
71. What do scattered patchy infiltrates indicate?
They indicate ARDS.
72. What do fluffy infiltrates indicate?
They indicate pulmonary edema.
73. What do plate-like or patchy infiltrates indicate?
They indicate atelectasis.
74. What do wedge-shaped infiltrates indicate?
They indicate a pulmonary embolism.
75. What does a butterfly or batwing appearance indicate?
It indicates pulmonary edema.
76. What do air bronchograms indicate?
They indicate pneumonia.
77. What would a normal chest x-ray show?
A normal chest x-ray would show the trachea in the midline, bilateral radiolucency, and sharp costophrenic angles.
78. Should the tip of the ET tube be positioned above the clavicle on a chest x-ray?
No, if it is above the clavicle, it is too high.
79. Where should the pulmonary artery catheter appear on a radiograph?
It should appear in the right lower lung field.
80. What does croup (laryngotracheobronchitis) look like on a lateral neck x-ray?
It appears as a steeple, picket fence, or pencil-point sign.
81. What does epiglottitis show on a lateral neck x-ray?
It shows supraglottic narrowing with an enlarged, flattened epiglottis and swollen aryepiglottic folds, giving a “thumb sign” appearance.
82. What diagnosis is likely if a chest x-ray shows consolidation?
Pneumonia or pleural effusion.
83. What diagnosis is likely if a chest x-ray shows hyperlucency?
COPD or an obstructive disease.
84. What does an increase in vascular markings indicate?
It indicates congestive heart failure (CHF).
85. What does the absence of vascular markings indicate?
It indicates a pneumothorax.
86. How would pulmonary edema show up on a chest x-ray?
It would show as fluffy infiltrates with a butterfly/batwing pattern.
87. How would atelectasis show up on a chest x-ray?
It would appear as patchy or plate-like infiltrates.
88. How would ARDS appear on a chest x-ray?
It would have a ground-glass appearance, honeycomb pattern, and diffuse bilateral radiopacity.
89. How would a pleural effusion appear on a chest x-ray?
It would show a concave superior interface/border or basilar infiltrates with a meniscus.
90. Why is the distance from the film important?
The distance is significant because the closer the patient is to the source, the greater the magnification and distortion of the objects on the film.
91. What does a silhouette sign on a chest x-ray indicate?
It indicates the loss of normal borders between thoracic structures, often suggesting consolidation or a mass that obscures the outline of an adjacent structure, such as the heart or diaphragm.
92. What does a deep sulcus sign on a chest x-ray suggest?
It suggests a pneumothorax, especially in supine patients, as the costophrenic angle appears abnormally deep due to trapped air.
93. What might a widened mediastinum on a chest x-ray indicate?
It could indicate aortic dissection, mediastinal mass, or other conditions such as lymphadenopathy or trauma.
94. How would pleural thickening appear on a chest x-ray?
It would show as irregular or smooth opacification along the pleural surface, indicating conditions such as chronic pleuritis or mesothelioma.
95. What does hyperinflation on a chest x-ray suggest?
It suggests obstructive lung disease, such as COPD or asthma, characterized by increased lung volumes and flattened diaphragms.
96. What is the appearance of a lung abscess on a chest x-ray?
It appears as a localized area of consolidation with a central air-fluid level, indicating a collection of pus within the lung tissue.
97. How does pneumonia typically appear on a chest x-ray?
It appears as areas of increased opacity or consolidation, often with air bronchograms, indicating infection in the lung parenchyma.
98. What is the purpose of a lateral chest x-ray?
It helps assess the depth and location of lesions, visualize structures behind the heart and diaphragm, and confirm the presence of conditions such as pleural effusions.
99. What condition is suggested by a shift of the trachea or mediastinum to one side on a chest x-ray?
It suggests atelectasis, pneumothorax, or significant pleural effusion, depending on the direction of the shift.
100. What finding on a chest x-ray is indicative of interstitial lung disease?
A reticular or net-like pattern is indicative, showing thickened interstitial spaces that could be associated with conditions like pulmonary fibrosis or sarcoidosis.
Final Thoughts
Thoracic imaging has revolutionized the ability of healthcare professionals to diagnose and treat diseases within the chest. Each type of imaging, from the widely used chest x-ray to the more detailed CT, MRI, and PET scans, plays an essential role in different diagnostic scenarios.
Understanding the unique capabilities and applications of each imaging technique allows for more targeted and effective patient care.
As technology continues to evolve, thoracic imaging will only become more advanced, further improving the accuracy and efficiency of diagnosing and treating chest-related conditions.
Written by:
John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.
References
- Skinner S. Guide to thoracic imaging. Aust Fam Physician. 2015.
- Siela D. Chest radiograph evaluation and interpretation. AACN Adv Crit Care. 2008.