How to read High Resolution CT (HRCT)

Inspiratory & Expiratory phases

• Images are obtained in both inspiration and expiration.

• How do we know if the abnormal tissue is the dark or light colored tissue in an expiration film?

  • In normal expiration the lungs will contract and the alveoli will collapse - so we are basically inducing diffuse atelectasis. Atelectasis will appear bright. So in an expiratory film you will expect the lungs to have diffuse atelectasis and therefore diffusely “white” lungs. If there is “dark” lung tissue then this is the abnormal tissue that needs further investigation and is likely due to air trapping.

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