How to build filter for counting unique issue with same sumary field

[sc]

Dear all,

From our customer service Desk, each service when used by user create a corresponding issue type which has the name of the service populated inside the summary field of the issue.

For all issue from the Service Desk I need to build a dashboard wich the return the number of issue for each unique summary.

I have try to use the Statistic gadget in order to analyse by summary field, but that field is not available in the selection.

How can I generate that dashbord to count record by unique summary field ?

regards