SnG rookie: A4o in SB HU @ Level 9 - equal stacks

[Pov]

I rarely play SnG's or I'm sure I would have figured this out before now. Any walk-throughs of the logic behind my possible plays here would be greatly appreciated.

My situation was a low limit SnG where the Villain and I had pretty much dominated the game and now found ourselves heads up. I would say both of us had shown down strong hands and made a few plays that looked like they may have been strong bluffs. Basically, I respected Villain and I believe he probably respected me based upon what he would have seen.

Blinds are 300/600 with both of us having around 4000 in chips. We traded back and forth a little with a few flops, a few pre-flop folds and a few pre-flop raises and folds. Standard raise was to 1800 so far.

Hero is SB w/ A4o so I raise to 1800.

I can't see myself not playing this hand so the question is do I raise less or go all in with this hand in this situation?

Of course the reason I ask is my opponent went all-in after I made this raise. I quickly reasoned he probably had a medium to strong pair or a good Ace. I am solidly beaten by pretty much any hand I can see him doing this with, but I'm now getting something like 3:1 on my money and I'll be a 3:1 dog in chips if I fold having only around 3 big blinds so I can see good arguments for either calling or folding. Being in this rather unpleasant situation made me wonder if I should have raised less to make it easier to get away from this hand or raised all-in to limit the hands he may have made this play with.