Chapter 20 Review of Thoracic Imaging

1. Chapter 20Review of Thoracic Imaging

2. Learning Objectives List the four tissue densities seen on the chest radiograph. Define the terms radiolucent and radiopaque. Describe how to evaluate the technical quality of a chest radiograph. State the differences between the PA chest film and the AP chest film.

3. Learning Objectives (cont.) List the anatomic structures seen on the chest radiograph. List the steps used to interpret thoracic imaging studies. Identify the value of the computed tomography (CT) scan, high-resolution CT scan, and CT angiography. Describe the common radiographic abnormalities seen in the pleura, lung parenchyma, and mediastinum.

4. Review of Thoracic Imaging: Introduction Chest imaging is important part of diagnosing patients with lung disease RT needs to be able to recognize significant radiographic abnormalities in certain situations Plain chest radiograph is very popular, inexpensive, & reliable in most cases

5. Review of Thoracic Imaging: Overview • Chest radiograph is created by passing x-ray beam through chest • X-ray beam strikes film after passing through chest; x-rays passing through lung turn film black, while x-rays absorbed by more dense tissue (e.g., bone) leave film white • Resulting chest radiograph represent various shades of gray shadows

6. Review of Thoracic Imaging: Overview (cont.) • 4 different tissue densities are visible on normal chest radiograph • Air, fat, water, & bone • Air (lung) absorbs x-rays least & results in dark shadow (radiolucent) • Bone (ribs) absorb most x-ray energy & result in white shadow (radiopaque) • Fat & water shadows are different degrees of gray

7. Tissues that absorbs the least amount of energy and appear black in an x-ray film are called: Translucent Radiolucent Transparent Radiopaque

8. Review of Thoracic Imaging: Overview (cont.) • Digital technology has replaced traditional photographic film • Currently, most X-rays are recorded & display in digital format • Digital films have advantages: • Can be manipulated to enhance interpretation • Can be stored & retrieved quickly from any location/time • Can be copied, shared & transported quickly • Image quality does not deteriorate over time

9. Review of Thoracic Imaging

10. All of the following are clinical indications for a chest x-ray except: After an orotracheal intubation Suddenonset of dyspnea Duringcardiopulmonaryresuscitation Sudden drop in oxygenation

11. Approach to Reading Chest Film Disciplined approach is needed First, make sure name on film matches patient being evaluated Second, evaluate technical quality of film (proper patient position, x-ray penetration, etc.) Third, systematically evaluate all anatomical structures seen on film following prescribed series of steps

12. CXR Reading Technique • Is film properly label? • Correct patient • Date & time of film • Right & left side identification • Is entire chest imaged on film? • Was patient properly positioned? • Were penetration & exposure settings correct? (Quality of image) • Overpenetration leaves lung shadows too dark • Underpenetration causes lung shadows too white

13. PA Chest Film PA chest film is created in radiology department, usually with patient standing X-ray beam passes from posterior to anterior (PA) with film placed against patient’s chest Usually results in high-quality film with minimal magnification of heart shadow

14. AP Chest Film • Taken with portable x-ray machine in ICU • X-ray source is in front of patient & film is behind patient • AP films are often more difficult to read because quality is not as good as PA film • Heart shadow is more magnified with AP film since heart is closer to x-ray source & farther from film • Rotation of patient is more likely

15. Which of the following problems is most common during a portable AP chest x-ray? Patient is not centered on the film Improper side labeling Cardiac shadow is reduced Obscured pulmonary vessels

16. Film Penetration • Improper penetration may conceal structures & important details • Proper penetration shows intervertebral disc spaces through shadow of heart • Under-exposed or under-penetrated films show an increase in chest whiteness (white-out xray) • Over-exposed or over-penetrated films leave lung parenchyma black without vascular markings

17. Chest Anatomy on Film

18. Normal Chest Films

19. Lateral View

20. Assessment of Structures Chest Wall & Mediastinum Lung Evaluation Size, density & symmetry Lung edges in frontal & lateral films Vascular markings Presence of free air or fluid Consolidations & infiltrates • Symmetry of chest • Rib fractures • Bone changes • Heart size • Presence of free air or fluid

21. In the PA projection the diameter of the heart should not exceed __________ of the chest. three quarters one third half of the diameter one quarter

22. Advanced Chest Imaging Computed tomography (CT) is very helpful in certain situations CT visualizes structures cross-sectionally with great detail up to ~2 mm structures inside lung CT scanning creates images looking like “slices” of patient’s chest (5 to 7 mm thick) Conventional CT scanning is used to evaluate lung nodules & masses, great vessels, mediastinum, & pleural disease

23. Advanced Chest Imaging (cont.) • High-resolution CT (HRCT) scanning examines 1-mm slices of lung, producing greater lung detail • High-resolution CT scanning is ideal for evaluating diffuse parenchymal lung diseases: • Interstitial lung disease • Emphysema • Bronchiectasis

24. CT Angiograms

25. Magnetic Resonance Imaging • Uses radio waves from realigning Hydrogen nuclei to generate MRI image (no x-rays are used) • Most often used to image mediastinum, hilar regions, & large vessels in lung • MRI has limitations in chest medicine • Cannot be used in patients with pacemaker • Metal objects (i.e., gas cylinders or regular ICU ventilators) cannot be used near MRI machine

26. Ultrasound • Images created by passing high-frequency sound waves into body & detecting sound waves that bounce back (echo) from tissues of body • Ultrasonic evaluation of lung itself is rare • Uses very portable equipment • Commonly used to guide placement of central & arterial catheters, & to detect & quantify pleural effusions • Very common in ICU

27. Ultrasound (cont.)

28. An ICU patient is suspected of having a pulmonary emboli. Which of the following radiological tests would you recommend to assess his situation? Chest x-ray Positron Emission Tomography Magnetic Resonance Imaging HRCT Angiography

29. Hydrothorax Also called pleural effusion Blunted costophrenic angle on chest x-ray indicates pleural effusion is present About 200 ml of pleural fluid will blunt costophrenic angle Best chest x-ray view for detecting small pleural effusion is lateral decubitus Pus in pleural space = empyema

30. Pleural Effusion

31. Empyema

32. Pneumothorax Refers to collection of air in pleural space May occur spontaneously, with trauma, or with invasive procedure May occur with mechanical ventilation; called barotrauma in such cases Pneumothorax causes lung margin to pull away from chest wall in affected region Presence of air can be better visualized by comparing inspiratory vs expiratory CXR

33. Blunted or rounded costophrenic angles in an AP or PA chest x-ray may suggest the presence of: Patient is not centered on the film Improper side labeling Cardiac shadow is reduced Basilar atelectasis

34. Pneumothorax (cont.)

35. Tension Pneumothorax • Represents serious medical emergency • Occurs when air within pleural space is under pressure • Air accumulates in pleural space on inspiration but cannot exit on exhalation • Chest film will show shift of mediastinum away from pneumothorax • Requires immediate decompression with chest tube or needle aspiration of trapped air • Can lead to cardiac tamponade & hemodynamic collapse

36. Tension Pneumothorax (cont.)

37. Pulmonary Infiltrates • Seen on chest radiograph when alveoli fill with watery fluid (edema), pus, blood, or fat-rich material • Seen as white shadows in lung • Air-filled airways surrounded by infiltrates will cause “air bronchograms” • Air bronchograms are hallmark of infiltrates that fill alveoli (air space disease)

38. Air Bronchograms

39. Right Middle Lobe Pneumonia

40. Pulmonary Edema Pulmonary edema due to left heart failure is common finding on chest radiograph Left heart failure causes enlargement of pulmonary blood vessels in apex of lung (cephalization) Kerley B-lines are often seen with pulmonary edema due to left heart failure Chest radiograph often shows enlarged heart & pleural effusion with CHF

41. Pulmonary Edema (cont.)

42. Interstitial Disease • Chest radiograph usually shows diffuse, bilateral infiltrates • Infiltrates may look like scattered ill-defined nodules • Many different types of ILDs; 2 most common: • Idiopathic pulmonary fibrosis • Sarcoidosis • Because most patients with ILD have similar findings, it does not usually establish specific diagnosis

43. Interstitial Lung Disease

44. Atelectasis • Common finding on chest radiograph, especially in postoperative patient • When localized to subsegmental portion of lung - called “plate atelectasis” • Lobar atelectasis occurs when major bronchus is obstructed by mucus plug, tumor, or foreign body • Signs of volume loss = elevation of hemidiaphragm & shift of hilum towards affected side

45. Plate atelectasis (cont.)

46. Hyperinflation • Commonly seen with emphysema • If more than 7 anterior ribs above diaphragm, hyperinflation is present • Other signs of hyperinflation include: • Flattening of hemidiaphragms • Large retrosternal airspace • Narrowed mediastinum • Increased AP diameter • Emphysema causes loss of visible blood vessels in lung

47. Emphysema

48. Which of the following chest x-ray findings is consistent with a tension pneumothorax Tracheal deviation towards the affected side Elevated hemidiaphram in the opposite side Presence of a meniscus in the affected side Absence of lung markings in the affected side

49. Solitary Pulmonary Nodule (SPN) • Defined as parenchymal opacity smaller than 3 cm in diameter surrounded by aerated lung • Chest CT scanning offers better method for studying nodule • Nodules having central calcification are round & have smooth edge are most likely benign • Positron Emission Tomography (PET) scanning is often very useful in evaluating SPN

50. SPN(cont.)