False positive on Thallium Stress Test

What is the incidence of a getting a false positive on a thallium stress test?  
This happened to my 31 year old nephew.  A subsequent cardiac catherization showed no blockages in any arteries.  
His 32 year old brother will soon be scheduled for a cardiac catherization because he, too, had a positive thallium stress test.  N.B.: They had different cardiologists, in different states.  Should t 32 year old re-take the thallium stress or move on to the Cardiac Catherization or what?
The reason for this testing:  Their 38 year old brother had a sudden cardiac death 3 weeks ago, an autopsy showed 3 highly occluded arteries.  
Both of these young men had had heart scans at the Ohio Heart Ultrafast CT Scanning facility in Columbus, OH, prior to the thallium stress testing, ...and,both showed the presence of Calcium in the mid-left anterior descending artery, other arteries being negative.  Their plaque buildup exceeded the 75th percentile for their age/gender.
Please comment on the efficacy of the Ultrafast CT Scan.

[CCF CARDIO MD - DLB]

Dear Lydia

The false positive rate is quite high in 30 year old men, as their likelihood of coronary artery disease is so small. However, given their brother's history, I would have gotten a Thallium and proceeded with a catheterization if the Thallium was positive. I am not a believer in the CT scanning - I think it is mostly marketing hype (but patients love it).

I hope this has been useful. I wish you the best of luck.