Reporting using custom fields

It's one of my first non-straight-forward attempts to use BIRT. I think I am missing something in my understanding.
I added custom fields (enumeration) to my work items (specifically - defects).
I want to create a report that counts the number of defects with each value.
When creating a DataSet using BIRT I do not see these custom fields.
Where are they and how can I use them?
Thank you,
Shahar
I added custom fields (enumeration) to my work items (specifically - defects).
I want to create a report that counts the number of defects with each value.
When creating a DataSet using BIRT I do not see these custom fields.
Where are they and how can I use them?
Thank you,
Shahar