 For this reason, in approximately 15-25 of patients, additional functional testing may be required after CTA, usually in the form of stress testing 6-8. Stress testing is commonly done by exercise or pharmacologic stress with electrocardiographic monitoring and often, imaging of myocardial perfusion by nuclear scintigraphy MPI or detection of abnormal contraction by echocardiography. This requires a separate procedure, entailing time, expense and limited risk. Furthermore, in patients with previously known CAD, CTA alone is not an adequate test, because in most cases there are multiple lesions that are possible sources of ischemia. 