How to differentiate arterial and venous infarct in mri brain? without mr angio?

Different appearance: Venous vs arterial infarcts tend to have a different distribution on MRI but if the is a ideation of venous infarct, i would suggest an mr venogram.

Several factors: One of the factors is the distribution of the infarct. The arteries of the brain have a very well-defined territory that they supply and venous infarcts may not be isolated to one of those territories. Also, there may be direct or indirect evidence on a noncontrast ct or MRI that suggest occlusion of one of the major venous structures. Clinical history is also considered.