Our own experience suggests that the positive predictive value of this technique nears that of SPECT scans. In our pilot study with 45 patients with PD or APS who underwent SPECT and TCS we found a positive prediction value of 95%. This would predict that, if TCE is compatible with PD, a SPECT does not provide additional information; so in theory one might reduce the amount of SPECT's in almost 50% of cases.