How do physicians diagnose the constrictive pericarditis verses restrictive cardiomyopathy?

See Below: The best is either an echo doppler, MRI of the heart and pericardium or a right heart catheterization. And echo doppler can show that the e to a ratio is very high, indicative of restrictive physiology. Echo or an MRI can also show the pericardium is thick, consistent with constrictive pericarditis. The right heart cath would measure the pressure inside the heart. Presentation is similar.

Difficult: Is the heart too big or is the sac too small. Can get some hints from a ct that the sac is thick, or by history and early images that help clarify any changes.