**6.4 Interstitial pneumonitis**

156 Pulmonary Embolism

Fig. 18. Cardiac failure (volume overload). Note vascular redistribution to the super-anterior

Fig. 19. Pneumonia (triangulation in coronal, sagittal and tranverse slices). Note the large

trans-segmental defect. Absent ventilation with some partial residual perfusion.

regions while normal gradient is preserved in ventilation.

Some recent work suggests that usual interstitial pneumonitis (UIP) can give rise to a rather specific pattern of sub pleural mismatch of crescent shape (Suga, Kawakami et al. 2009). The posterior surfaces of the lungs have to be excluded from the analysis however because in a supine position, this phenomenon is frequently observed because of gravity dependent atelectasis.
