Correct answer: d) Fractional flow reserve
Fractional flow reserve (FFR) of less than 0.8 as measured by a Doppler wire during maximal coronary hyperemia induced by intracoronary or intravenous adenosine is taken as the cut off level of functional significance of a coronary stenosis. FAME  and FAME II  trials have established the clinical utility of FFR, which is now accepted as standard of care. FFR is especially useful in those who have undergone coronary angiography without prior non invasive functional testing like a treadmill exercise ECG or myocardial perfusion imaging.
1. Tonino PA et al. Fractional flow reserve vs. angiography for guiding percutaneous coronary intervention. N Engl J Med 2009;360(3):213–224.
2. De Bruyne B et al. Fractional flow reserve-guided PCI vs. medical therapy in stable coronary disease. N Engl J Med 2012;367(11):991–1001.