Читать книгу Interventional Cardiology - Группа авторов - Страница 40

Advances in catheter‐based spectroscopy enables generation of a chemical fingerprint of atherosclerotic plaque. Near infrared spectroscopy (NIRS) is a technique that has been used for decades in the physical sciences to characterize chemical composition for substances [161]. This method could be ideal for identification of lipid‐rich and potentially vulnerable atherosclerotic plaques. The initial catheter‐based system was LipiscanTM (InfraRedx Inc., Burlington, MA, USA). Subsequently, since NIRS imaging did not provide any volumetric data of plaques, the NIRS/intravascular ultrasound (IVUS) catheter (TVC Imaging SystemTM, InfraRedx Inc., Burlington, MA, USA) was developed. NIRS generates a color map that displays the lipid content of the arterial wall as a “chemogram”. Every pixel represents the probability of lipid presence at the given location on a colour scale in which low probabilities of lipids are depicted as red, and high probabilities of lipids are shown as yellow (Figure 1.6). The “block chemogram” is a semiquantitative summary of the results for each 2 mm segment of the imaged artery. The lipid core burden index (LCBI) is the quantification of lipid present in the scanned region and is defined as the fraction of yellow pixels on the chemogram multiplied by 1000. The maximal lipid core burden index (max LCBI) per 4 mm describes the region with the highest lipid burden. ex vivo validation studies support the feasibility of NIRS imaging with reasonable sensitivity and specificity for evaluating the extent of lipidic materials [162, 163]. Signal loss behind calcium due to acoustic shadowing is an important limitation for conventional IVUS, whereas NIRS penetrates effectively through calcium and stents, not affected by lower intensity due to attenuation. Additionally, with inability of IVUS and OCT to visualize or determine actual composition of lipidic plaques due to signal drop‐out, NIRS offers a more reliable and quantitative detection of lipid core plaques than other intravascular imaging methods. On the other hand, a potential limitation of NIRS may be its inability to assess the depth of a lipid core and the measurement of lipid volume.

Figure 1.6 NIRS IVUS imaging of vulnerable plaque. Lipid rich plaque (yellow at left and right images): cross sectional image (left hand) and lon‐gitudinal pullback image with its chemogram (right hand).