bounding polygon of a sprite from pixi to p2

I am importing a sprite into PIXI using

var texture= PIXI.Texture.fromImage("img.png");
var sprite = new PIXI.Sprite(texture);
// I set the position
stage.addChild(sprite);

I want to detect collisions on this sprite and since PIXI has no collision detection support. I am using p2.js and this needs a polygon bounding box for collision detection

How can I get the polygon from pixi and pass it to p2 and detect a collision?

Any sample or some pointers will be very helpful.