When should one consider obtaining a cardiac MRI in ischemic stroke patients?  

This is a terrific question. Cardiac MRI is increasingly utilized in the diagnostic evaluation of ischemic stroke and can uncover clinically covert cardiovascular disease. The clinical utility in ischemic stroke is most in patients with concern for LV thrombus (low EF or recent anterior ST elevation...

Cardiac MRI is extremely useful for identifying LV thrombus not appreciated on TTE (or ambiguity on the study) especially in patients with ESUS with low EF, cardiac apex aneurysm, evaluating cardiac amyloidosis (also an etiology for embolic strokes) confirming valve vegetation vs thrombus, fibroelas...