Click to change state on non-rectangular objects

Hi everyone

I have a picture of a pizza, when the learner click on one slice it pops out (state changes to SELECTED), when they click on it again it returns to where it was (state changes to NORMAL)

There are 5 slices each a png with a transparent background - however if say I click on the top middle slice (which is also the top item on the timeline) and then want to make the adjacent slice pop out - if I click within the 'rectangle' of the first pizza slice it puts my first slice back rather than change the state of the adjacent slice. I hope that makes sense.

Is there a way to stop the transparent parts of the image being part of the clickable area?