Abnormal EKG Negative Cardiolite

I had an abnormal resting EKG so I was sent to have a Cardiolite test.  The Cardiolite result is normal but the EKG taken during the test is abnormal--exactly like the resting EKG.  My cardiologist told me I had nothing to worry about because the Cardiolite's far more sensitive and accurate than the EKG.  I think he said what's abnormal about my EKG is a "concave T segment."  I'm not sure I heard it right but it's something like that.  If this makes sense, please explain to me what it means?  Is this kind of abnomality serious?  Why do I have this abnormality in my EKG yet my stress Cardiolite test turned out normal?  Perhaps I should've asked my cardiologist out right but I didn't want to bother him with too many questions.  But after I thought it over, I do want to know the answers to these questions.  I'm female and in my late 50's.  No history of heart disease but has borderline high cholesterol (200-210) for years.