**2.4 Reconstruction and calculation of V/P quotient images**

Iterative OSEM is essential for SPECT reconstruction. Ventilation activity is subtracted from perfusion images. A valuable parameter in clinical SPECT is the Ventilation/Perfusion quotient, V/Pquotient (Bajc et al., 2004; Palmer et al., 2001). V/Pquotient is calculated after normalization of ventilation counts to perfusion counts. Hot spot removal is important, especially when 99mTc-DTPA is used.
