Advances in Intravascular Imaging

Abstract

his review updates the role of various intravascular imaging techniques (1) in the detection of vulnerable plaque and (2) during percutaneous coronary intervention (PCI), especially drug-eluting stent (DES) implantation and follow-up-including intravascular ultrasound (IVUS), virtual histology (VH-IVUS) and integrated backscatter (IB-IVUS), optical coherent tomography (OCT), near-infrared (NIR) spectroscopy, angioscopy, and MRI. IVUS, IB-IVUS, and VH-IVUSThe current intracoronary ultrasound imaging frequency range of 20 to 45 MHz provides 70 to 200 m axial resolution with Ͼ5 mm penetration. 1,2 Grayscale IVUS allows robust quantitative measurements including lumen, vessel, and plaque area; qualitative assessment of lesions preintervention; and quantitative assessment and complications of lesions postintervention; however, it has poor sensitivity for detecting lipid-rich plaque (67%). 3 High-frequency IVUS transducers can produce better resolution that should also improve plaque characterization but at the trade off of greater ultrasound reflection from blood. Blood speckle with Ͼ40 MHz ultrasound can cause confusion when identifying the lumen-tissue border, detecting in-stent neointimal tissue, etc; but it is easily solved by saline (negative contrast) injection through the guiding catheter. 4 Standard grayscale IVUS is limited, in part, because it uses only reflected ultrasound amplitude to formulate the image and requires significant postprocessing. In an effort to improve on the qualitative assessment of the reflected ultrasound signal, Kawasaki et al developed a plaque characterization algorithm called IB-IVUS using time domain information directly from the radiofrequency signal. This process has resulted in improved plaque characterization with a reported in vitro sensitivity of 90% and specificity or 92% for lipid-rich plaque. 5,6 In a similar effort to improve plaque characterization, spectral analysis (VH-IVUS) combined frequency and amplitude analysis and used an algorithm developed from known tissue types to detect fibrous plaque, fibrofatty plaque, necrotic core (NC), and dense calcium ( Figure 1AЈ, 1BЈ). Reported sensitivity and specificity of VH-IVUS are 91.7% and 96.6% for identification of the lipid-rich NC. 7-10 VH-IVUS cannot detect thrombus formation (in fact, thrombus appears as either fibrotic or fibrofatty plaque depending on the age of the thrombus) and has not been validated for assessment of stent metal or intimal hyperplasia. OCTOCT uses a light source with a wavelength centered at 1.3 m to "reflect" off the plaque and form an image analogous to the use of reflected ultrasound. Because of the short wavelength of OCT, it will reflect (and detect) very small objects including blood cells; therefore, in order for OCT to image the vessel wall, it requires a blood-free field. The original time-domain OCT technique requires continuous flushing with proximal balloon occlusion to displace the blood. Recently, faster data and image acquisition with optical frequency domain imaging (OFDI) allows r...

Acute Myocardial Infarction in Women

“…97,111 Characterization of the plaque pathology is not routinely performed because of limited availability of advanced imaging techniques, including OCT, that allow the discrimination of intact fibrous cap from ruptured fibrous cap with a much higher resolution compared with intravascular ultrasound. 112 Although stenting is known to significantly improve outcomes with plaque rupture, it has been argued that reliable characterization of plaque morphology might justify alternative approaches, including aspiration thrombectomy and catheterdirected lytic therapy without stent implantation, as the initial strategy for treatment in patients with plaque erosions. In a recent study, 31 patients presenting with STEMI who underwent thrombectomy and were found to have plaque erosions by OCT were randomized to dual antiplatelet therapy without PCI and standard angioplasty and stenting.…”

Plaque Structural Stress Estimations Improve Prediction of Future Major Adverse Cardiovascular Events After Intracoronary Imaging

“…Because plaque rupture is thought to result from superficial plaque destabilization, PSS was calculated ≤200 μm depth from the luminal contour, representing the axial resolution of VH-IVUS. 18 Variation in PSS during one cardiac cycle was also calculated, being defined as, …”

Intracoronary and Noninvasive Imaging for Prediction of Distal Embolization and Periprocedural Myocardial Infarction During Native Coronary Artery Percutaneous Intervention

“…13 IVUS provides both qualitative and quantitative information about coronary plaques, suggesting its potential to identify plaques at risk of distal embolization. Several studies have characterized IVUSdetected features of plaques associated with an increased risk of distal embolization.…”

“…24 Cited reasons for this shortcoming include reliance on video images, which limits resolution; operator-dependent parameters, such as brightness and gain; and, importantly, use of only the amplitude of the radiofrequency signal to create images. 13,24 Radiofrequency analysis of backscatter signals from a conventional IVUS catheter can be used to more reliably characterize plaque composition. 25 Virtual histology (VH) IVUS, integrated backscatter (IB) IVUS, and iMAP IVUS are 3 available radio frequency (RF) analysis technologies that have been incorporated into conventional IVUS systems.…”