Intravascular optical coherence tomography: optimisation of image acquisition and quantitative assessment of stent strut apposition.

Stent expansion, apposition and symmetry were the three criteria of intravascular ultrasound (IVUS) guided optimal stent deployment in the bare metal stent era1, with at least the criterion of stent expansion maintaining its clinical relevance in the drug-eluting stent (DES) era2. Two prospective studies showed that stent malapposition immediately following DES implantation was not associated with increased adverse clinical events3,4. Thus, initial concerns that immediate stent malapposition would affect drug delivery to the vessel wall and lead to DES failure appeared to be unfounded. Coronary IVUS, however, formerly the gold standard for assessing stent strut apposition, is imprecise in the detection of stent malapposition observed in around 7% of lesions3,4, a figure which is probably grossly underestimated. This is due to the limited axial and lateral resolution of the ultrasound waves (100-150 microm) and the constant presence of artefacts around stent struts (side-lobes, shadowing). Optical coherence tomography (OCT) uses infrared light with the advantage of greater resolution (10-15 microm) and less strut induced artefacts compared with IVUS5,6. Unlike the first OCT prototypes used by Jang et al5,6, new commercial systems (LightLab Imaging Inc., Westford, MA, USA) can acquire contiguous images with a motorised pullback system as used with IVUS7. Still, OCT has some disadvantages including a more complex process of image acquisition that requires transient proximal flow occlusion with a balloon. Since there is definite learning curve to achieve optimal image quality, this article will focus on methods and techniques to attain optimal assessment of stent strut apposition, using the current OCT system.