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
  • D_L – Diameter of the collapsed lung
  • D_H – Diameter of the hemithorax on the collapsed side
• Light index is given by:
  • % of pneumothorax = 100−(D_L³/D_H³×100)

Illustration:

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