Detecting whether a click occurs on a text object

I am developing an application in which I would like the user to be
able to click on a chart and have the application detect whether the
click has occurred over a specific piece of text. For example, I have
multiple lines on a chart with two y-axes, and I have the titles of
the series stacked up at the top of the chart. I would like the user
to be able to click one of the titles which would then cause the
corresponding series to switch to the other axis. Unfortunately I
still cannot figure how to retrieve the area that a piece of text
fills on the chart.

(in case it makes a difference, note that the chart can be resized at
any time, so the pixel coordinates of the text could change at any
time).

Thanks very much

Abiel