Fig. 20.

Fourier decomposition used in a 4-year-old girl with common variable immunodeficiency. a Radial k space-trajectory spin echo (PROPELLER), Fourier decomposition ventilation (b) and (c) perfusion generated maps. Note in (a) darker area in the left lower lobe (black arrow), which consists of an area of trapped air. In the correspondent (b) ventilation map that area appears not ventilated (thin arrow). The same area in the perfusion map (c) shows reduced perfusion (thick arrow), according to the physiological reflex of hypoxic vasoconstriction