I just asked for help with this for you, and this was the response I got;
It's actually simple. If you are interested in art therapy, you might enter a phd program about child psychology with your special interest in art therapy. THE WAY TO GET A PHD IS TO WRITE A DISSERTATION THAT MAKES REAL, UNIQUE CONTRIBUTION TO THE FIELD OF STUDY. So the first step to figuring out what is a smart topic is to see what other grad students and authorities in the field have recently written about art therapy. IT's just like getting involved in a conversation: you have to know what everyone just said if you are going to contribute to the conversation. Hence the need for a lit review.