minimal lumen area of 6 mm2 suggests a physiologically significant lesion for which patients may benefit from revas- cularization. A minimal lumen area 7.5 mm2 suggests that revascularization may be safely deferred.490 A minimal lumen requires further physiological assessment, such as measurement of FFR.487,500 For non left main stenoses, minimal lumen diameter 2.0 mm and min- imal lumen area 4.0 mm2 correlate with low event rates.489 However, in smaller-diameter arteries (minimal lumen area ), measurement of FFR may more accurately reflect a significant stenosis.488 Studies correlating IVUS measures with ischemia have not specified the size of coronary arteries for which such correlations are IVUS assessment after stent thrombosis may serve to identify stent underexpansion or malapposition.499 IVUS is superior to angiography in the early detection of the diffuse, immune-mediated, cardiac allograft vasculopathy; recom- mendations about the use of IVUS for this purpose were published in 2010 by the International Society of Heart and Lung Transplantation.492 Whereas IVUS has been an impor- tant research tool in interventional cardiology, most clinical studies of IVUS have not been able to demonstrate that its routine use results in a reduction of MACE or restenosis rates.498,501,502 IVUS has been inappropriately used in clinical practice to justify implanting stents in mildly diseased seg- ments that may require no intervention.503 5.4.3. Optical Coherence Tomography Compared with IVUS, optical coherence tomography has greater resolution (10 to 20 micronmeter axially) but more limited depth of imaging (1 to 1.5 mm).504,505 Unlike IVUS, optical coherence tomography requires that the artery be perfused with saline solution or crystalloid during image acquisition and therefore does not permit imaging of ostial lesions. 