Thoracic imaging refers to the radiographic assessment of the chest and thoracic region. As a respiratory therapist or medical professional, this is a topic that you must be familiar with.

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What is Thoracic Imaging?

Thoracic Imaging is the radiographic process of creating a visual representation of the thorax for medical intervention. The primary types of thoracic imaging include:

  • Chest Radiograph
  • Computed Tomography (CT)
  • Ventilation–Perfusion (VQ) Scan
  • Positron Emission Tomography (PET)

Each type of thoracic imaging helps the medical professional learn more about the state of the patient’s condition.

Chest Radiograph

A chest x-ray is a radiographic imaging technique used for the assessment of the heart, lungs, and structures within the thoracic cavity.

It occurs as an x-ray passes through the chest to a film, which provides a visual representation of the structures within the thoracic cavity. The appearance of the x-ray depends on the density of the structures within the chest.

This includes air, fat, soft tissue, bone, and fluid.

Lungs that are filled with air have a black appearance on the chest x-ray, which is known as being radiolucent. Bones and fluid absorb more of the x-ray beams during the process and display more white on the chest x-ray, which is known as being radiopaque.

Computed Tomography (CT)

A CT scan is a radiographic imaging technique that generates cross-sectional images of an organ or tissue structure. It’s often performed in radiology to obtain detailed images of the body that can be used for diagnostic purposes.

In general, it’s a quick, painless, and noninvasive method to generate cross-sectional images that can be analyzed by physicians to get an idea of what’s going on with the patient.

Ventilation–Perfusion (VQ) Scan

A V/Q scan is an imaging test that uses a radiographic substance to assess the ventilation and perfusion of the lungs. By measuring the flow of air and blood within the lungs, it allows for the diagnosis of various diseases.

This scan is typically indicated to help diagnose or rule out a pulmonary embolism. It can also help physicians examine the lungs of preoperative patients.

Positron Emission Tomography (PET)

A PET scan is an imaging technique that uses radioactive substances to examine the metabolic activity of various parts of the body. Radiotracers in the body help produce gamma rays, which provide a three-dimensional visual of the target area.

In respiratory care, this type of scan is typically recommended for the diagnosis or evaluation of lung cancer.

Note: To learn more about this topic, you can read through the practice questions that are listed for you below. Also, you can consider reading the chapter inside of the Egan’s Textbook on this topic.

The Egan's book is known as the "Bible of Respiratory" and is highly recommended.

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Thoracic Imaging Practice Questions:

1. What is the definition of radiolucent?
X-rays that pass through low-density lung tissue strike the film more directly and cause an image that is darker in appearance.

2. What is the definition of radiopaque?
X-rays that pass through high-density tissue (e.g. bone) are more absorbed and cause an image that is lighter in appearance.

3. What four tissues are seen on an x-ray?
Air, fat, water, and bone

4. What are air bronchograms?
A pattern on a chest radiograph that shows air-filled bronchi surrounded by areas of consolidation

5. Does air appear radiolucent or radiopaque?

6. What is a description of the AP view?
The x-ray source is positioned in front with the film behind the patient’s back.

7. What is the best film for detecting small amounts of pleural fluid?
Lateral decubitus

8. What is the best type of imaging for the mediastinum?
CT scan

9. Does bone appear radiolucent or radiopaque?

10. Computed tomography angiography is most often used to look at what?
It is used to visualize the heart.

11. What is the conventional thickness of CT images?
3-7 mm

12. What is a costophrenic angle?
The arch where the diaphragm and chest wall meet and form a point. A blunted costophrenic angle is a sign of a pleural effusion

13. Can a CT scan identify pleural fluid?

14. Does an embolus show up on a CT scan?

15. Can an ultrasound detect pleural effusions?
Yes, even small ones.

16. Does an embolus show up on a chest radiograph?

17. Fluid build-up in the alveoli causes what appearance?
Kerley B lines

18. The heart shadow should not exceed what?
It should not exceed 50% of the thoracic diameter.

19. How does a CT scan visualize structures?
It uses cross-sections.

20. How much fluid can be detected in the lateral decubitus view?
5 mL

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21. How much fluid is required for blunting of the costophrenic angle from a pleural effusion to occur in the frontal view?
175-200 mL

22. How much fluid is required for blunting of the costophrenic angle from a pleural effusion to occur in the posterior view?
75-100 mL

23. If more than seven anterior ribs are visible above the diaphragm, this indicates what?

24. What are infiltrates?
Patchy white shadows

25. Is the diaphragm visible on a chest radiograph?

26. Kerley B lines are often seen in what type of pulmonary edema?
Cardiogenic pulmonary edema

27. What is nuclear medicine?
An imaging technique that uses radioactive material via inhalation or injection. It is used for V/Q scans and Positron Emission Tomography (PET) scans

28. Should the patient be sitting or standing for the PA view?

29. Does the PA view minimize or maximize the magnification of the heart?
It minimizes it

30. What does PET stand for?
Positron Emission Tomography

31. When is a PET scan indicated?
They are often used to localize tumors and metastases.

32. Can the pleura be seen on a conventional chest radiograph?

33. A radiograph with proper exposure should show what?
It should show intervertebral disc spaces through the shadow of the heart and blood vessels in the peripheral regions of the lungs.

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 is radiolucent?

36. What color is radiopaque?

37. What is a silhouette sign?
It can be used to describe obscuring of the margin of adjacent structures of the same density.

38. What absorbs less x-rays than soft tissue?

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, great vessels of the chest, mediastinum, and pleural diseases.

43. What do you assess first on 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 left lung and stomach gas bubble

47. What type of radiograph should you obtain for a pneumothorax?
Obtain the radiograph during exhalation with the patient sitting upright.

48. When is a radiograph in the AP view usually taken?
It is typically taken in the ICU.

49. Where is a radiograph in the PA view usually performed?
It is typically performed in the radiology department.

50. Why are ultrasounds rarely used for the lungs?
Because the lungs are air-filled

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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

53. What are infiltrates?
They are the shadows seen on an x-ray caused by the build-up 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 a CT Angiography?
It is a way to perform a CT scan of the pulmonary vessels and heart to check for a pulmonary thromboembolism. It’s 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 regarding the heart?
The heart is less magnified, and it is of better quality

58. On a standard x-ray study of the chest, what are the two most common views?
Posterior-anterior (PA) and Anterior-posterior (AP)

59. How visual is the heart in the posterior-anterior (PA) view compared to the anterior-posterior (AP) view?
The heart shadow on the AP view is larger

60. What has the greatest radiodensity?

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?
Apical lordotic projection

62. During full inspiration, the hemidiaphragms on an adult chest film should be located where?
They should be located at the level of the 10th rib.

63. When evaluating a PA film of the chest, you note that the right costophrenic angles are blunted. What does this suggest?
It suggests the presence of a pleural effusion on the right side.

64. When evaluating a PA film of the chest, you note that in the upper lobe, there is a 1 cm wide sliver along the lateral margin, descending from the apex, merging with the ribs at the 3rd rib. This narrow sliver is very black and devoid of vascular markings. What does this indicate?

65. When evaluating the position of an ET tube on an AP chest film, where should the tip of the tube rest?
It should rest at a point 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 indicate?

68. What does a flattened diaphragm indicate?
COPD or significant air-trapping

69. What does a ground glass or honeycomb pattern indicate?

70. What does radiolucent indicate?
Normal lungs

71. What do scattered patchy infiltrates indicate?

72. What does fluffy infiltrates indicate?
Pulmonary edema

73. What does plate-like or patchy infiltrates indicate?

74. What does wedge-shaped infiltrates indicate?
Pulmonary embolism

75. What does a butterfly or batwing appearance indicate?
Pulmonary edema

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76. What do air bronchograms indicate?

77. What would a normal chest x-ray show?
It 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’s too high.

79. Where should the pulmonary artery catheter appear on a radiograph?
It would appear in the right lower lung field.

80. What will Croup (laryngotracheobronchitis) look like on a lateral neck x-ray?
It will look like a steeple, picket fence, or pencil point.

81. What will epiglottitis show on a lateral neck x-ray?
It will show supraglottic narrowing with an enlarged and flattened epiglottis, and swollen aryepiglottic folds. This appearance will look like a “thumb sign.”

82. What diagnosis is likely if the chest x-ray shows consolidation?
Pneumonia or pleural effusion

83. What diagnosis is likely if the chest x-ray shows hyperlucency?
COPD or an obstructive disease

84. What does an increase in vascular markings indicate?

85. If vascular markings are absent, this would indicate what?

86. How would pulmonary edema show up on a chest x-ray?
It would show fluffy infiltrates with a butterfly/batwing pattern.

87. How would atelectasis show up on a chest x-ray?
It would show patchy or plate-like infiltrates.

88. How would ARDS show up on chest x-ray?
Ground glass appearance, honeycomb pattern, and diffuse bilateral radiopacity

89. How would a pleural effusion show up on a chest x-ray?
It would show a concave superior interface/border or basilar infiltrates with a meniscus.

90. Why do we worry about the distance from the film?
The distance is significant because the closer the patient is to the source, the greater the magnification and distortion of the objects seen on the film.

Final Thoughts

So, there you have it. That wraps up our study guide on thoracic imaging. Hopefully, use can use this material to develop a better understanding of this topic.

We have a similar guide that covers chest trauma that I think would be useful for you. Thank you so much for reading and, as always, breathe easy, my friend.

Medical Disclaimer: This content is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you read in this article. We strive for 100% accuracy, but errors may occur, and medications, protocols, and treatment methods may change over time.


The following are the sources that were used while doing research for this article:

  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020. [Link]
  • Faarc, Heuer Al PhD Mba Rrt Rpft. Wilkins’ Clinical Assessment in Respiratory Care. 8th ed., Mosby, 2017. [Link]
  • Jardins, Des Terry. Cardiopulmonary Anatomy & Physiology: Essentials of Respiratory Care. 7th ed., Cengage Learning, 2019. [Link]
  • Skinner, Sarah. “Guide to Thoracic Imaging.” PubMed, Aug. 2015,
  • Crivelli, Paola. “Role of Thoracic Imaging in the Management of Lymphangioleiomyomatosis.” PubMed, Oct. 2019,
  • Siela, Debra. “Chest Radiograph Evaluation and Interpretation.” PubMed, 7 Oct. 2020,

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