1. Chapter 20 Review 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
Answer: B

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. After an orotracheal intubation Sudden onset of dyspnea
All of the following are clinical indications for a chest x-ray except:
After an orotracheal intubation
Sudden onset of dyspnea
During cardiopulmonary resuscitation
Sudden drop in oxygenation
Answer: C

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. Patient is not centered on the film Improper side labeling
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
Answer: A

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
Fig 20-1

18. Normal Chest Films
Fig 20-2

19. Lateral View

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

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
Answer: C

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. Positron Emission Tomography Magnetic Resonance Imaging
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
Answer: D

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
Fig 20-10

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. Patient is not centered on the film Improper side labeling
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
Answer:

34. Pneumothorax (cont.)
Fig 20-11

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
Fig 20-14

39. Right Middle Lobe Pneumonia
Fig 20-15

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.)
Fig 20-16

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
Fig 20-19

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
Fig 20-24

48. Tracheal deviation towards the affected side
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
Answer: D

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.)
Fig 20-26

51. Catheters, Lines, & Tubes
Chest radiograph is obtained after placement of endotracheal tube, CVP line, or pulmonary artery catheter
Film helps confirm tube or catheter is in correct position
Tip of endotracheal tube should be 5 to 7 cm above carina with patient’s head in neutral position

52. Endotracheal Tube Placement
Fig 20-32

53. Catheters, Lines, & Tubes (cont.)
Tracheostomy tubes should extend half distance from stoma to carina
Tip of CVP catheter should be in superior vena cava
Pulmonary artery catheters can be seen in Pulmonary artery about 90% of time
Chest tubes should be within pleural space following contour of chest wall or diaphragm
Intra-aortic balloon pump tip should be located just below origin of Subclavian artery