Thoracic Imaging: Overview and Practice Questions (2024)

Thoracic imaging plays a pivotal role in the diagnosis and management of various pulmonary and cardiovascular conditions, offering invaluable insights into the structure and pathology of the lungs, heart, and surrounding anatomical structures.

Employing an array of modalities, including X-rays, CT scans, and MRI, thoracic imaging aids clinicians in identifying abnormalities ranging from infectious diseases and malignancies to congenital defects.

As technology advances, the precision and utility of these imaging techniques continue to evolve, underscoring the necessity for an updated understanding of their applications and limitations.

What is Thoracic Imaging?

Thoracic imaging is a subspecialty of diagnostic radiology focused on the imaging and diagnosis of diseases of the chest, specifically the heart, lungs, and surrounding structures. Various imaging techniques are employed to visualize thoracic anatomy and pathology, aiding in both diagnosis and treatment planning for a wide range of conditions.

Types of Thoracic Imaging

• Chest X-ray (CXR): The most common and initial imaging modality for assessing the thoracic region. It is especially useful for detecting pneumonia, heart failure, and other lung diseases.
• Computed Tomography (CT): Offers detailed cross-sectional images and is particularly useful for identifying small or complex structures within the chest, such as nodules, tumors, and vascular anomalies.
• Ventilation–Perfusion (VQ) Scan: A nuclear medicine test primarily used to diagnose or rule out pulmonary embolism by evaluating the airflow (ventilation) and blood flow (perfusion) in the lungs.
• Magnetic Resonance Imaging (MRI): Utilized less frequently for thoracic imaging but is excellent for evaluating soft tissue structures, including the heart and major blood vessels.
• Positron Emission Tomography (PET): Often used in conjunction with CT scanning for cancer staging and evaluation of metabolic activity.
• Ultrasound: Primarily used for the assessment of pleural diseases or guiding biopsies but is limited in its ability to provide comprehensive imaging of thoracic structures.
• Angiography: Specifically used for assessing blood vessels in the lungs and heart, typically via CT or MRI.

These imaging techniques are essential tools in the diagnosis and management of a variety of conditions, such as lung cancer, pneumonia, pulmonary embolism, and heart diseases.

Thoracic imaging is often used for both initial assessment and follow-up to evaluate the effectiveness of treatment.

Chest X-ray

The most frequently utilized and accessible form of thoracic imaging, chest X-rays provide two-dimensional images of the thoracic cavity, including the heart, lungs, and bones of the chest and spine.

This modality is especially useful for initial assessments, capable of detecting a variety of conditions such as pneumonia, heart failure, and fractured ribs.

However, its limitations lie in its lower resolution compared to other imaging modalities, making it less ideal for detecting smaller or more complex structures.

Computed Tomography

Offering high-resolution, cross-sectional images of the thoracic region, computed tomography is essential for more detailed evaluations.

It is particularly adept at identifying small nodules, tumors, or vascular anomalies that may not be visible on a standard chest X-ray.

CT scans can also be performed with contrast dye to further enhance the visibility of certain structures and abnormalities, although this technique poses a risk for patients with kidney issues or allergies to iodinated contrast.

Ventilation–Perfusion Scan

This specialized nuclear medicine test is used primarily to diagnose or exclude pulmonary embolism.

By employing a dual-approach that assesses both airflow (ventilation) and blood flow (perfusion) within the lungs, the VQ scan allows for targeted identification of blockages or irregularities.

A patient inhales a radioactive gas for the ventilation component and receives an injection of a radioactive substance for the perfusion part, enabling clinicians to create detailed images that highlight problem areas in the lung.

Magnetic Resonance Imaging

Although less commonly used for thoracic applications, magnetic resonance imaging excels at visualizing soft tissue structures like the heart, major blood vessels, and even certain lung conditions.

Unlike CT scans, MRI does not involve ionizing radiation, making it a safer alternative for certain patient populations.

However, the modality is more time-consuming and may be contraindicated for patients with certain types of medical implants or claustrophobia.

Positron Emission Tomography

This advanced imaging modality is often used in conjunction with CT scans for a more comprehensive assessment of metabolic activity, particularly in cancer staging.

By injecting a small amount of radioactive material into the patient, PET scans can detect areas of high metabolic activity that may indicate malignancy.

This information is vital for both initial diagnosis and monitoring the effectiveness of treatments like chemotherapy. However, its high cost and limited availability make it less accessible compared to other imaging methods.

Ultrasound

Though not a primary tool for thoracic imaging, ultrasound is useful for evaluating pleural diseases and guiding certain procedures like biopsies or fluid drainage.

It uses sound waves to produce real-time images and is portable, making it convenient for bedside examinations.

Ultrasound is particularly advantageous in that it avoids ionizing radiation and can be safely used in various patient populations, including pregnant women.

However, it has limitations in providing comprehensive images of deeper thoracic structures.

Angiography

Primarily used to visualize the blood vessels in the thoracic region, angiography can be performed via CT or MRI modalities.

This imaging technique is especially important for diagnosing conditions like pulmonary embolism, aortic aneurysms, or vascular malformations.

Contrast agents are often administered to enhance the clarity of the images, but these can pose risks for patients with certain preexisting conditions like kidney disease.

Angiography provides crucial information for both diagnostic and interventional procedures, making it an essential tool in cardiothoracic medicine.

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?
Radiolucent

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?
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?
Yes

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

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

16. Does an embolus show up on a chest radiograph?
No

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

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?
Hyperinflation

24. What are infiltrates?
Patchy white shadows

25. Is the diaphragm visible on a chest radiograph?
Yes

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?
Standing

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?
No

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?
Black

36. What color is radiopaque?
White

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

38. What absorbs less 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, 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 the left lung and the 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

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?
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?
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?
Pneumothorax

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?
ARDS or IRDS

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

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

70. What does radiolucent indicate?
Normal lungs

71. What do scattered patchy infiltrates indicate?
ARDS

72. Fluffy infiltrates indicate what?
Pulmonary edema

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

74. Wedge-shaped infiltrates indicate what?
Pulmonary embolism

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

76. What do air bronchograms indicate?
Pneumonia

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?
CHF

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

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 a 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

Thoracic imaging is an indispensable tool in modern medicine, providing critical data for diagnosing and treating a wide spectrum of cardio-pulmonary diseases.

While current technologies like CT scans and MRIs offer high-resolution images, ongoing research aims to minimize associated risks, such as radiation exposure, and to develop more specific imaging markers for early disease detection.

As we move forward, the continuous improvement and integration of these technologies promise to significantly impact patient outcomes, making an understanding of thoracic imaging essential for any healthcare professional involved in respiratory and cardiovascular care.