Photoshop :: Best Way To Create A Line Silhouette Of An Image

I have an image that has a set of curved lines in it. I want to keep just these lines from the image, and delete everything else.

Can people recommend what is the best way to accomplish this?

I know that i could use the pen tool to manually trace over these lines, and i don't need to preserve the color of the lines, so this would work. But it would be better to not have to do it manually.

I've successfully used the magic wand tool to select the area outside of these lines, and i can then invert the selection to select the area inside of these lines. This should put me about one step away from getting to where i'm trying to go, but i don't know what the final step should be.