How to avoid injecting fat into vein or artery?

This is in addition to my other question, specifically to those doctors that inject in or under muscle? 1.How do you avoid veins or arteries? Is it based in anatomical landmarks? 2. Also if blunt tip cannula used , would the amount of resistance indicate a vessel? I heard about some sort of pressure indicator device perhaps on the injecting syringe?? 3. Is this for to avoid damaging cells or prevent overfilling?? Thank you!

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