Читать книгу Interventional Cardiology - Группа авторов - Страница 249

Initially, intracoronary NIRS was developed as an independent imaging modality, but a major drawback was the inability to provide spatial orientation to match the lipid content alongside the plaque distribution. However, current co‐registered NIRS‐IVUS catheters (TVC Imaging System, InfraReDx Inc, Burlington, MA, USA) provide data regarding both the vessel structure and the plaque composition.

After completion of an automatic pullback, data are processed displaying a two‐dimensional map of the vessel, revealing the probability of the presence of a lipid core plaque (LCP), with the pullback position in millimeters on the x‐axis and the circumferential position on the y‐axis. This display is known as the “chemogram.” For each pixel of 0.1 mm and 1°, length and angle respectively, the lipid core probability is calculated from the spectral data collected and semi‐quantitatively coded on a color scale from 0 for red and to 1 for yellow. Whenever a pixel lacks sufficient data, for instance the guidewire is shadowing, the pixel appears black.

The block chemogram, also created from the NIRS images, combines the results for each 2‐mm section of the artery to create a “virtual block” that summarizes and reflects the probability of LCP intervals. The numeric value of each block produced is the 90th percentile of all pixel values obtained in the corresponding 2‐mm section of the artery in the chemogram. Here, the red coloration indicates a low probability of an LCP, whereas yellow coloration determines a higher probability of an LCP, alongside the intensity of the color reflecting the amount of cholesterol present. In isolation, the block chemogram specifically adapts a four‐color scale method of analysis (red (p < 0.57), orange (0.57 ≤ p < 0.84), tan (0.84 ≤ p < 0.98) and yellow (p ≥ 0.98)) that reflects the probability of the existence of an LCP in each 2‐mm block of pullback which aids the overall visual interpretation. Spectral data are paired with corresponding IVUS frames, overall displayed as a ring around the IVUS image. The lipid core burden index (LCBI) measures the portion of pixels that exceed an LCP probability of 0.6, in all viable pixels within the scanned region, multiplied by 1000. This is a quantitative measure of the intensity of yellow pixels present on the chemogram. The LCBI values vary from 0 to 1000 and the maximum value of LCBI for any of the 4‐mm segments along the analyzed segment is defined as the maxLCBI_4mm.