Light index of pneumothorax

  • Light index is used to calculate the size of pneumothorax from a posteroanterior view chest X-ray
  • To calculate light index, 2 measurements are required
    • DL – Diameter of the collapsed lung
    • DH – Diameter of the hemithorax on the collapsed side
  • Light index is given by:
    • % of pneumothorax = 100−(DL3/DH3×100)

Illustration:

  • Assume that DL = 6cm and DH = 10cm
  • Then percentage of pneumothorax = 100 – 216/1000*100  =  100-21.6  =  78.4%

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