Thorax (CT)

Question 1

What are the similarities and differences between CXR and CT?

Answer 1

• x-rays taken in the same way, just more of them and at all angles tf CT is CS
• transmission dependent on e-densities for both
  
  • same conventions for both
  • CT has standardized Hounsfield units (-1000 = black, air; 0 = clear, water; +1000 = white, bone and metals)
• computer dector (CT) rather than film
• CXR has better spatial resolution
• CT has better contrast resolution for soft tissue differentiation
• silhouette sign applies to both
• CT does not use mediastinal divisions or lung zones from CXR
• CT can be post-processed
  
  • change colour, plane, etc.
  • adjust brightness and contrast to look at specific range e.g. biological tissues from -200 to +200

Question 2

How is a chest CT taken?

Answer 2

• first step is conventional radiograph (digital radiograph)
  
  • pt lies on table, arms upm holds inhaled breath
• then take a single cross-sectional slice
  
  • view is from the feet up!
• *coronal reconstruction is viewed from the front of the pt
• *sagittal reconstruction (lateral) is viewed from the left of the pt