Detect mouse click in irregular area

I want to capture a mouse click on a PictureBox and perform one action if it is in area A but a different action if it is in area B. Unfortunately the shape is not a rectangle or circle. It will be more or less a semi-circle. I don't want to actually draw this semi-circle, just be able to tell whether or not the click is in the given area using some kind of coordinate system.

I know how to capture a mouse click in general, just need help with the specific area part.

Well, now that I think about it, this is really pretty similar to an old-school image map hyperlink in HTML!

Any ideas?

Thanks!

Rectangle and RectangleF have bool IntersectsWith() methods.

Region has several bool IsVisible() overloads, one of which is bool IsVisible( Point ).

Even GraphicsPath can be used because one of Region's constructors takes a GraphicsPath argument.

System.Drawing.Region.IsVisible()

Edit: There may even be better ways of doing hit testing, but I don't know 'em. Yet.

Any idea how this works in WPF?