# Clinical Validation of a New Enhanced Stent Imaging Method
## 2 Materials and Methods  
### Study Design  
Between January 2016 and January 2018, patients in whom an ESI acquisition was performed after the implantation of a stent at the Centre Hospitalier Universitaire et Psychiatrique de Mons-Borinage (CHUPMB), Belgium, were retrospectively reviewed. The acquired ESI images were transferred to the SB and SE workstations (CAAS workstation software v.8.4) and reconstructed. The patients' baseline demographic and procedural characteristics were collected. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of CHUPMB and Erasme-ULB (Universite Libre de Bruxelles) (protocol code P2017/462 on 16 October 2017) who waived the requirement for written consent. Two independent blinded and experienced interventional cardiologists compared and graded the stent images obtained by each technique. The images from the same sequence (SB and SE) were blindly compared side to side (on the left side, it was either a SB or SE image and on the right side the other one). The images were graded on a scale from 0 to 2 (0 = undetectable; 1 = seen unclearly; and 2 = clearly seen) for different characteristics: (1) visualization of the proximal edge of the stent; (2) visualization of the distal edge of the stent; (3) clear visualization of the struts of the stent; and (4) the presence of underexansion and (5) calcifications. One month later, 50 sequences were randomly selected and re-analyzed a second time by one of the two observers for the intra-observer variation analysis. A subset of images was processed using a custom-designed Matlab software (version R2017a, The MathWorks, Natick, MA, USA) that computed the signal-to-noise ratio (SNR) of SB and SE images defined as the ratio of the average signal value \(\upmu_{\text{sig}}\) to the standard deviation \(\upsigma_{\text{bg}}\) of the background. As shown in Figure 1, a reference noise square of 100 by 100 pixels was manually placed in a region without interventional material (wire, previous stent, etc.) and without a bone structure such as a rib. Another rectangle was then traced around the stent, as close as possible to the struts. The same two regions were used in the SB and SE images for comparison. The standard deviation \(\upsigma_{\text{bg}}\) of the background pixel values was calculated in the square region of interest (ROI) of noise whereas the average signal value \(\upmu_{\text{sig}}\) was calculated as the average of the values of the pixels in the ROI traced around the enhanced stent. Furthermore, between January 2021 and July 2022, patients with mildly to moderately calcified de novo coronary lesions in 4 Belgian centers who were treated by stent implantation and ESI acquisition in 2 orthogonal views were prospectively included. This protocol with EudraCT code B7072020000065 was approved by the Ethics Committee Hospitalo-Facultaire Universitaire de Liege under reference 2020/87 on 13/11/2020, as well as by each local institution review board. The study was also conducted according to the guidelines of the Declaration of Helsinki and informed written consent were obtained. The patients' baseline demographic and procedural characteristics were collected. The ESI images were transferred to the SE and QCA workstations (CAAS software v.8.4) and reconstructed. Of note, one center used a Siemens X-ray system with the Clearstent ESI system, the others used a Philips system with StentBoost. SE and QCA could be measured on the DICOM files from these two manufacturers. The final QCA analysis was conducted and included maximal and minimal stent diameters as well as percent stenosis. A quantitative SE analysis of the 2 orthogonal views acquired including proximal and distal stent edge diameters as well as minimal stent diameter was conducted.