# Clinical Validation of a New Enhanced Stent Imaging Method
## 4 Discussion  
The current study qualitatively compared the inter- and intra-observer results of different image criteria of a novel ESI software (SE) to the market-available one (SB) as well as a quantitative analysis of SE. The results of the two ESI algorithms were compared as per each observer and finally SNRs for the two methods were calculated and compared to the SNR calculated from the angiographic image. ESI methods have been demonstrated to enhance contrast on fluoroscopic images, allowing better visualization of stent struts. This study demonstrated  
Figure 4: Quantitative analysis of an implanted proximal left anterior descending stent. Panel (**A**): quantitative coronary angiography analysis; Panel (**B**): StentEnhancer quantitative analysis post-implantation in two orthogonal views; Panel (**C**): StentEnhancer quantitative analysis after post-dilation. Stent expansion could be evaluated visually with clear stent struts and minimal calcifications. The pixels were transformed into millimeters using the calibration of the image. Note the presence of a second stent implanted in the ramus intermedius. Panel (**D**): Intravascular images at the minimal cross-sectional area in the stent after implantation (**left**) and after post-dilation (**right**). that SE is not inferior to SB for the criteria evaluated but a clear inter-observer variability calls for more quantitative methods. Despite this difference, both observers had a preference towards SE images to study parameters. SE can be easily integrated into procedures, independent of the X-ray angiography machine vendor, and was found in our study to provide good stent expansion assessment as well as a better stent strut visualization. The SNR of SE images was found to be superior compared to SB. We cannot provide a definite answer why this was the case, since we are unaware of the exact methods of StentBoost. However, based on the available papers, there are methodological differences. For instance, SB does not seem to perform background subtraction as can be seen in Figure 1.  
Since newer generation scaffolds tend to use thinner struts or bioresobable materials in order to reduce the risk of stent thrombosis in addition to a trend towards the use of lower X-ray power during angiographic procedures, proper stent visualization is becoming challenging [3; 20; 21; 22; 23]. The use of ESI becomes pivotal for the assessment of proper stent expansion, a major risk factor for stent thrombosis [6; 7; 8; 9; 10]. QCA remains an important, readily available, and easy-to-use tool during PCIs allowing for a more practical and standardized angiography-based approach. QCA is particularly useful for the evaluation of the minimal lumen diameter, the reference vessel diameter, the diameter stenosis percentage, the lesion length, the acute gain, and late loss [14]. Our data failed to show any correlation between the expected stent diameter and the QCA-derived one. This could be explained by the foreshortening drawback of QCA as well as the two-dimensional evaluation by QCA of a three-dimensional vessel. Our data demonstrated the feasibility of an accurate, quantitative, contrast-free assessment of stent expansion by SE. Post-dilatation remains an important step towards stent optimization. Our results are in-line with the current published literature in regard to the achieved stent diameter at a given implantation pressure being at least 10% lower than the given expected chart diameter [33; 34]. These results could be attributed to the fact that the figures provided on the compliance charts are derived from bench tests performed in water at 37 \({}^{\circ}\)C while QCA and SE are measured on stents deployed in fibrotic and calcified lesions. The diameters measured by SE remain 2-dimensional measurements of a 3-dimensional structure. A second measurement using an orthogonal view would therefore overcome this limitation. The measured mean stent diameters by SE did not differ when using the two orthogonal views indicating precise measurements between the two views.