Advances in Intravascular Imaging

Table 2 summarizes some of the strengths and weaknesses of the 6 discussed techniques. Grayscale IVUS is the current workhorse in the catheterization laboratory, especially, during percutaneous interventional procedures where lumen dimensions, plaque burden, and assessment of stent implantation and procedural complications are important. Grayscale IVUS substudies are now routinely used to assess new devices and techniques. However, grayscale IVUS has 2 main weaknesses: plaque characterization and resolution. VH-IVUS was developed to improve on the limited ability of grayscale IVUS to assess plaque composition, especially detection of the lipid-rich NC (Figure 1B). However, VH-IVUS is even more limited than grayscale IVUS in thrombus identification; and the assessment of plaque composition behind calcium remains questionable. 62,95,96 Angioscopy is the most reliable tool for detecting both red cell and platelet-rich thrombus, although recent studies have suggested that OCT may also be useful in thrombus detection. The resolution of IVUS (and VH-IVUS) limits its evaluation of surface structures such as (1) the thin fibrous cap of a TCFA with its macrophage infiltration, (2) neointimal stent coverage, and (3) plaque rupture and plaque erosion; all are better assessed using other techniques (Figure 1C). Despite widespread enthusiasm, the use of VH-IVUS to detect TCFAs may be limited because the thickness of the thin fibrous cap is below the resolution of either grayscale or VH-IVUS and because thrombus appears as fibrotic or fibrofatty plaque. Similarly, the ability of OCT to detect a lipid-rich NC may need further validation. Conversely, near NIR and intravascular MRI were developed to detect lipid, and the algorithms are based on the confluent and relatively superficial lipid core; however, these 2 techniques do not provide other needed anatomic information. Although use of multiple techniques may not be practical during daily practice, these various techniques truly complement each other. Fortunately, early prototypes indicate the possibility to combine multiple modalities into 1 catheter and console.