How to delete the previously drawn lines

See more:

WPF

C#3.5

I am trying to draw a line in dotted representation on a canvas using C#.
Now on Mousemove event, the dotted lines are drawn as and where the cursor is moved.But the line drawn in the previous mouse position still remains even when my mouse is moved to a new position.
My requirement is to draw a single dotted line along with the mouse cursor,
So, now question is hot to erase the previously drawn dotted lines on my mouse move?