# Clinical Validation of a New Enhanced Stent Imaging Method
## 4 Discussion
However, a difference was noted for the measurements at the site of maximal stent underexpansion after post-dilation. This could be attributed to the eccentricity of lesions as well as to the visual assessment of the minimal diameter compared to adjacent ones. Despite an era where modern flat-detector technology allows excellent angiographic images, coronary stent visualization has become a challenge especially with the on-going reduction in stent strut thickness. Stents are often suboptimally visualized on plain angiography hence limiting optimal PCI outcomes. High temporal resolution is needed to qualify a moving structure. Adequate stent expansion has important short- and long-term effects after PCIs in clinical practice. It is crucial, yet challenging, to detect suboptimal stent deployment on qualitative and quantitative angiography since it is associated with an increased rate of in-stent restenosis and stent thrombosis [3; 20]. Current stent delivery systems are still suboptimal for stent expansion, requiring, in most cases, a post-dilation using a larger, higher pressure, non-compliant balloon to improve the in-lumen area. This is particularly true when increased calcifications are found [24; 35] as we demonstrated in our 157 lesions. Intracoronary imaging, including intravascular ultrasound and optical coherence tomography, remains more sensitive than angiography and QCA in determining stent under expansion as illustrated in Figure 4; their use was found to improve stent expansion results and long term outcome [6; 20; 36]. However, these techniques are limited by cost, time, and technical expertise, calling for a simpler, ready-to-use visualization method. ESI was found very useful in identifying stents under expansion, thereby improving PCI outcomes [37]. Image processing algorithm softwares based on X-ray angiography imagesoffer better stent visualization compared to angiography alone as validated by several previous studies [24; 38]. ESI also shows no risk of complications and adds little additional time or radiation to the procedure [25; 37]. Furthermore, ESI allows accurate measurements of the dimension of stents [29]. It was found useful in obese patients, long lesions, in-stent restenosis, and bifurcating lesions. Moreover, ESI was found to be superior to QCA and angiography and was highly correlated with IVUS [17; 28; 28; 30; 38]. We performed a comparison between the final diameters measured by QCA and by SE. We had 14 paired data available with no post-dilatation and 75 after final post-dilatation in the other patients. As shown in Figure 5, on average, the mean difference was \(-0.37\pm 0.42\) mm and this bias for smaller QCA diameters was significant, with the 95% confidence interval not encompassing the 0. Using IVUS as the reference, [PERSON] et al. also demonstrated that QCA underestimates MLDs in small vessels (<3.8 mm) and overestimates MLDs in vessels larger than 3.8 mm [39]. A direct head-to-head comparison of IVUS and SE might confirm a better agreement between IVUS and SE than with QCA. The wide agreement window between QCA and SE of \(\pm\) 0.84 mm reflects the differences in the two methodologies, with only manual measurements being currently possible with the SE images, while automated contour calculation and minimal and reference diameters are available with QCA. However, when there were overlap of side branches or other vessels, no QCA could be reliably measured in 3 out of the 93 cases. Without contrast, hence without any overlap, SE could always be measured. Of note, no reliable reconstruction can be calculated on very long stents and/or with long balloons when the markers are more than 30 mm apart. Several ESI softwares are currently available on the market but each one can only be used on the specific vendor's angiographic system. The StentEnhancer software computes enhanced fluoroscopy images using the balloon markers as references, delivering an easily integrated, high-quality image independent of the angiography instrument vendor.