An expiratory scan, typically referring to a CT scan performed during exhalation, is a diagnostic imaging technique used to detect air trapping in the lungs, often indicating early obstructive lung disease.
Understanding Expiratory Scans
Expiratory scans are valuable because they can reveal abnormalities that might not be apparent on standard inspiratory (inhale) CT scans or even pulmonary function tests. The key is observing how the lungs change during forced exhalation.
How It Works
During a normal exhalation, the lungs deflate evenly. However, in conditions with airway obstruction:
- Some areas of the lung may trap air.
- These areas remain inflated even after the patient has exhaled completely.
The expiratory scan images these regions of air trapping, making them visible to radiologists.
Why It's Important
- Early Detection: Expiratory scans can identify obstructive lung disease in its early stages, before significant symptoms or abnormalities on pulmonary function tests are present. The provided reference explicitly states that expiratory scans "reveal obstructive lung disease in an early stage, even when the pulmonary function test has normal findings."
- Diagnosis of Air Trapping: It is a sensitive method for detecting air trapping, a defining characteristic of airway obstruction. The reference mentions that "Expiratory scanning is sensitive for the detec- tion of air-trapping, which is a definitive sign of airway obstruction."
- Evaluating Diffuse Lung Diseases: They can be helpful in assessing the extent of air trapping in diffuse lung diseases.
Common Indications
Expiratory scans are often used when:
- There is suspicion of small airway disease.
- Pulmonary function tests are normal, but clinical suspicion for obstructive lung disease remains high.
- Evaluating patients with known lung disease for the presence and extent of air trapping.
Interpretation
Radiologists analyze the images to identify areas of the lung that do not deflate normally during exhalation. These areas appear darker on the CT scan due to the trapped air.
In summary, an expiratory scan is a sensitive imaging technique used to identify air trapping and early signs of obstructive lung disease by observing how the lungs behave during exhalation. It plays a crucial role in early diagnosis and management of various lung conditions.
