Midbrain to pons area ratio as described by Oba et al

In the method described by Oba et al the area of the midbrain and pons are calculated and the ratio midbrain : pons obtained ¹. 

The pontomesencephalic junction is defined by a line between the superior pontine notch (A) and the inferior border of the quadrigeminal plate (B). 

The pontomedullary junction is defined by a line parallel to the first line, at the level of the inferior pontine notch. 

A normal value is approximately 0.24 where as it is significantly reduced in PSP to 0.12 ¹. 

Diagram by Frank Gaillard.