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provided by Elsevier - Publisher Connector Journal of the American College of Cardiology Vol. 47, No. 8 Suppl C © 2006 by the American College of Cardiology Foundation ISSN 0735-1097/06/$32.00 Published by Elsevier Inc. doi:10.1016/j.jacc.2005.11.047 Imaging Vulnerable Plaque by Ultrasound Anthony N. DeMaria, MD, MACC,* Jagat Narula, MD, PHD, FACC,† Ehtisham Mahmud, MD, FACC,* Sotirios Tsimikas, MD, FACC* San Diego and Irvine, California

Diagnostic techniques to identify vulnerable plaques are rapidly evolving. (IVUS) has the ability to detect and localize plaque as well as quantitate plaque burden. Recent IVUS studies have suggested that patients presenting with acute coronary syndromes have an approximate 25% incidence of additional ruptured plaques in other than the culprit lesion. The ability of IVUS to detect vulnerable plaques before rupture is currently being evaluated by novel techniques. Initially, IVUS was shown to be able to characterize plaque broadly as calcified or fibrofatty but was limited in its ability to more precisely detect lipid-rich plaques, necrotic cores, and . Recent advances in new applications of IVUS, such as integrated backscatter, wavelet analysis, and virtual histology, have focused on evaluating and mathematically transforming the radiofrequency signal from ultrasound waves into a color-coded representation of plaque characteristics such as lipid, fibrous tissue, calcification, and necrotic core. In addition, targeted contrast agents, applicable to both intravascular and transthoracic studies, are being evaluated in experimental models and aim to highlight specific plaque components, such as endothelial adhesion molecules and other plaque components that might be useful in targeting vulnerable plaques. These advances pave the way for future clinical trials in assessing the ability of such techniques to diagnose vulnerable plaques and to assess the effects of both pharmacologic and mechanical therapies on plaque characteristics. (J Am Coll Cardiol 2006;47:C32–9) © 2006 by the American College of Cardiology Foundation

Attempts to identify vulnerable plaques have focused on occupy the entire perimeter of a vessel or be eccentric and imaging techniques, including cardiac ultrasound. These occupy only a portion of the vessel wall. Atherosclerotic efforts have primarily employed intravascular ultrasound lesions often result in an expansion of the overall vessel to (IVUS), although recently contrast echocardiographic ap- accommodate plaque without encroaching upon the lumen, proaches have been pursued. Intravascular ultrasound was a process termed positive remodeling (8). In addition, made possible by the miniaturization of ultrasound trans- ruptures or ulcerations of lesions can be detected, typically in ducers so that they could be placed at the tip of very small culprit vessels responsible for acute coronary syndromes diameter catheters. With an IVUS catheter positioned in a (ACS) (9). Thus, an IVUS examination can detect and coronary , an ultrasound beam is directed perpendic- localize plaque, characterize it as hypoechoic, fibrous, or ular to the course of the vessel and steered either electron- calcified, and determine whether it is ulcerated or manifests ically or mechanically throughout its 360° circumference. positive expansile remodeling. As compared with angiogra- Thereby, an image of cross-sectional arterial anatomy is phy, which evaluates only by its indirect obtained (1). Intravascular ultrasound’s cross-sectional im- effect upon the lumen, IVUS has the obvious advantage of ages in normal arteries depict a sharp, bright endothelial/ looking directly at plaque contained within the vessel wall. lumen border, a clear sonolucent media, and an echo dense adventitia (2). PREVALENCE OF UNSTABLE PLAQUES Plaque formation results in a thickening of the intimal- Angiographic and angioscopic studies. Data regarding medial segments and an overall thickening of the vessel wall. the prevalence of unstable plaques in patients undergoing Plaque morphology by ultrasound is often characterized by cardiac catheterization have been provided by , the intensity of the signals as soft (gray) echoes, very high angioscopy, and IVUS. These studies have corroborated intensity (bright) reflectors that create distal shadowing, and earlier pathologic studies (10). In a landmark angiographic echoes of intermediate intensity, features that correspond to study, Goldstein et al. (11) showed that approximately 60% tissue, calcification, and fibrosis (3). In addition, echolucent of patients presenting with acute myocardial or signal free zones have been found to represent lipid (AMI) have single complex plaques, whereas approximately accumulations (4–7). Plaques might be circumferential and 40% of patients have multiple complex coronary plaques that portend a worse 1-year prognosis. The finding of From the *Division of Cardiology, University of California San Diego, San Diego, multiple plaques with vulnerable characteristics is consistent California; and the †Division of Cardiology, University of California-Irvine School of Medicine, Irvine, California. Over the years, Dr. DeMaria has been on the scientific with angioscopic data showing that approximately 90% of advisory boards, a consultant/speaker, and/or received research grants from virtually culprit, but not disrupted, lesions are yellow and are asso- all echocardiography companies and pharmaceutical companies that distribute con- ciated histologically with vulnerable characteristics (12). In trast agents. Dr. William A. Zoghbi acted as guest editor. Manuscript received June 16, 2005; revised manuscript received November 2, 2005, addition, the prevalence of yellow plaques in non-culprit accepted November 8, 2005. lesions per coronary artery was 3.2, suggesting a pan- JACC Vol. 47, No. 8 Suppl C DeMaria et al. C33 April 18, 2006:C32–9 Imaging the Vulnerable Plaque by Ultrasound

response to medical therapy without significant change in Abbreviations and Acronyms plaque dimensions, as also previously documented in patho- 3D-IB-IVUS ϭ three-dimensional intravascular ultrasound logical studies showing multiple layers of plaque rupture and with integrated back scatter healing within the same area (22). ϭ ACS acute coronary syndromes Recent studies have also shown that the pattern of ICAM ϭ intracellular adhesion molecules IVUS ϭ intravascular ultrasound calcification is different in patients with ACS versus those PS ϭ phosphatidylserine with stable angina (23–25). Patients with ACS and ruptured RF ϭ radiofrequency plaques manifest a larger number of small, discrete calcium deposits, often present as spotty superficial and/or deep calcium deposits. Patients with ACS tended to have less coronary process. Interestingly, follow-up angioscopic stud- overall calcification than patients with stable angina pectoris ies do suggest that complete plaque healing, manifested by but also more positive remodeling. neointimal coverage of the disrupted plaque and resolution of thrombus, occurs only in a minority of lesions at IVUS PLAQUE CHARACTERIZATION 13-month follow-up (13). It has recently been shown that lipid-lowering therapy with atorvastatin reduced the yellow The initial attempts to identify vulnerable plaque by IVUS score of such lesions, compared with a control group, which involved defining the image characteristics of culprit lesions had increased yellow score (14). that had lead to ACS (9). A number of lesion characteristics IVUS studies. Recently, several IVUS studies have ad- were described in the majority of patients in this setting vanced these concepts by interrogating all three major (Table 1). Although these characteristics were observed epicardial vessels and quantitating the frequency of plaque with variable frequency, it was generally found that these rupture in patients presenting with ACS. In a small study plaques were hypoechoic, eccentric, positively remodeled, of 24 patients (72 arteries) with troponin-positive ACS, and relatively free of calcification. Volumetric analysis of Rioufol et al. (15) showed a mean prevalence of two IVUS images accurately quantitate volume and ruptured plaques (range 0 to 6) per patient; 37.5% of are useful in assessing changes in plaque regression and progression in trials of lipid lowering agents (26). Three- patients had plaque rupture at the presumed culprit lesion, dimensional (3D) reconstruction allows morphological as- and 79% of patients also had ruptured plaques in non- sessment of lesions but is not as useful in detecting clinically culprit arteries. In addition, 12.5% of patients had plaque relevant plaque characteristics such as lipid content. rupture in all three coronary arteries, and 69% of arteries Obviously, plaque vulnerability can only be assessed with had at least one plaque rupture. Hong et al. (16) showed in certainty by serial observations that demonstrate the transi- 235 patients that plaque rupture of the infarct-related vessel tion of a lesion from stability to instability. To date, only occurred in 66% of AMI patients and in 27% of stable one study has made such serial observations. Yamagishi angina patients. In addition, multiple plaque ruptures oc- et al. (27) examined 114 coronary sites in 106 patients by curred in 20% of AMI and 6% of stable angina patients. IVUS during a follow-up period of nearly 22 months. The Tanaka et al. (17) performed a similar study in patients with coronary sites at which an event occurred that had been ACS and showed that 47% of culprit lesions had plaque previously examined were characterized by large, eccentric rupture and that 24% of patients had plaque ruptures in lesions. The vast majority of these plaques contained more than one coronary artery. These data are consistent echolucent zones that were usually shallow but occasionally with other IVUS studies showing that culprit plaques have deep in the vessel wall. Subsequent studies have also verified more vulnerable characteristics, such as more plaque burden, that positive (outward) remodeling is typically found in positive remodeling, and thrombus, than non-culprit culprit lesions. Thus, the IVUS characteristics of a vulner- plaques in patients with ACS (18,19). The overall preva- able plaque that have emerged include eccentric lesions with lence of multiple ruptured coronary plaques in these studies echolucent zones in areas of positive expansile remodeling. as a whole is approximately 25% (20); however, it is possible Although, the IVUS descriptors of vulnerable plaque that that this is an underestimate, because IVUS is limited in have been proposed seem reasonable, a number of consid- adequately imaging plaque erosion and overlying thrombus, erations prevent them from being accepted as definitive. which might obscure ruptured plaques and the fact that Table 1. some plaque ruptures might have occurred at bifurcations IVUS Characteristics Associated With Culprit Lesions and branch vessels that were not imaged in these studies. 1) Echolucent core Differences in the prevalence of plaque rupture in these 2) Eccentricity 3) Positive remodeling studies also likely reflect differences in the patient popula- 4) Ulceration tion, selection bias in IVUS imaging, and the retrospective 5) Thrombosis nature of some studies. Subsequently, Rioufol et al. (21) also 6) Calcification showed that approximately 50% of these plaques heal in IVUS ϭ intravascular ultrasound. C34 DeMaria et al. JACC Vol. 47, No. 8 Suppl C Imaging the Vulnerable Plaque by Ultrasound April 18, 2006:C32–9

Figure 1. (A) Three-dimensional (3D) color-coded maps of the coronary arterial plaques constructed by 3D intravascular ultrasound with integrated back scatter. (B) 3D color-coded maps of each characteristic. The number of voxels of each tissue characteristic was automatically calculated. Reprinted with permission from Kawasaki et al. (29).

Nearly all of the studies upon which the descriptors are regarding morphology before that episode. Secondly, the based have been retrospective. Knowing plaque morphology characteristics reported for vulnerable plaque by IVUS have after an acute event cannot provide certain information differed from study to study. Thirdly, non-culprit plaques in

Figure 2. Color-coded maps of the coronary arterial plaques constructed by three-dimensional (3D) intravascular ultrasound with integrated back scatter imaging at baseline and after statin therapy. (A) At baseline. The plaque consists of a large lipid core (blue) that is covered with a fibrous cap (green). (B) After statin therapies. The lipid core (blue) decreased and the fibrous area (green) increased. (C) Cut out image of 3D color-coded map at baseline. There was a small lipid core (blue) in the center of the plaque. (D) Cut-out image of 3D color-coded map after statin therapy. Note the reduction in the lipid core. Red ϭ high signal lesion; yellow ϭ mixed lesion. Reprinted with permission from Kawasaki et al. (29). JACC Vol. 47, No. 8 Suppl C DeMaria et al. C35 April 18, 2006:C32–9 Imaging the Vulnerable Plaque by Ultrasound stable patients have often been found to show the same teristics. For example, Kawasaki et al. (29) recently de- characteristics associated with vulnerable plaque. For exam- scribed the usefulness of 3D-IB-IVUS in detecting lipid- ple, a study by Schoenhagen et al. (28) found that culprit rich plaques and monitoring their response to lipid lowering lesions from patients with ACS were identical in “vulnerable therapy. They evaluated the tissue characteristics of a IVUS characteristics” to lesions observed in patients with coronary arterial segment 18-mm-long and then random- stable angina, thereby casting uncertainty on the ability of ized patients to atorvastatin, pravastatin, or placebo for 6 IVUS to identify plaques susceptible to rupture, fissure, or months. The 6-month 3-IB-IVUS images showed a signif- erosion. Fourthly, the resolution of IVUS (150 to 300 ␮m) icant reduction in lipid volume and a similar increase in is too low to detect thin fibrous caps (50 to 75 ␮m), which fibrous and mixed lesion volume in response to both statins have been identified as one of the features of vulnerable but not to placebo (Figs. 1 and 2). These changes were plaques. detected despite no significant changes in lumen area, vessel These limitations notwithstanding, several novel ap- area, plaque area, and diameter , further defining the proaches have recently been developed to more precisely ability of this technique to identify early changes in plaque define plaque characteristics. characteristics before geometric plaque regression and sug- 3D IVUS with integrated back scatter. Three-dimensional gesting a role for defining plaque stabilization. IVUS with integrated back scatter (3D-IB-IVUS) allows Wavelet analysis. Wavelet analysis of RF IVUS signals is color coding and integration of sequential 1-mm segments a novel mathematical model for assessing focal differences obtained by motorized pullback to provide more optimal within arterial walls. Color coding of the wavelet correlation plaque characterization. Radiofrequency (RF) signals digi- coefficient derived from the RF signal allows detection of tized at 2 GHz can be obtained with a conventional 40 changes in the geometrical profile of time-series signals to MHz IVUS catheter. Subsequent IB signals of the RF derive an image of plaque components (Figs. 3 and 4). With signal can be calculated and color coded, providing a wavelet analysis, Murashige et al. (30) showed that lipid- quantitative visual readout. This system uses a conventional rich plaques, derived from necropsy specimens and subse- IVUS instrument, a digital analog converter, and computer quently confirmed as such by histology, could be detected software to identify, and quantitate, various plaque charac- with a sensitivity of 83% and specificity of 83% in an in vitro

Figure 3. Representative examples of in vitro Wavelet analysis of radiofrequency (RF) intravascular ultrasound (IVUS) signals from a lipid-laden plaque (A) and from a fibrous plaque without a lipid core (B). The upper panel shows RF signals, the middle panel, the results of Wavelet analysis, and the lower panel, histologic specimen of the corresponding arterial cross-section with Masson’s trichrome. In the time-scale domain color-coded mapping of Wavelet analysis, an apparently different pattern of pink area from an RF signal vector of a lipid-laden plaque is observed between scale 20 and scale 30, compared with the fibrous plaque. F ϭ fibrous area; L ϭ lipid core. Reprinted with permission from Murashige et al. (30). C36 DeMaria et al. JACC Vol. 47, No. 8 Suppl C Imaging the Vulnerable Plaque by Ultrasound April 18, 2006:C32–9

Figure 4. Representative examples of in vivo Wavelet analysis of radiofrequency (RF) intravascular ultrasound (IVUS) signals from a lipid-laden plaque (A) and from a fibrous plaque without a lipid core (B). The left panel shows conventional IVUS images, the middle panel, the results of Wavelet analysis, the right panel, histologic cross section of the corresponding directional coronary atherectomy specimen with Hematoxylin-Eosin and Azan stains. A similar pattern of color mapping was observed from the RF signal vector of a lipid-laden plaque as seen in the in vitro study. Reprinted with permission from Murashige et al. (30). system. Furthermore, IVUS imaging of the coronary arteries IVUS AND TRANSTHORACIC performed in 13 patients showed similar results with con- ULTRASOUND WITH TARGETED CONTRAST AGENTS firmation of the presence of lipid-rich components by Recent years have seen the development of new micro- histology after obtaining tissue by directional atherectomy. bubble ultrasound contrast agents and enhanced recording Virtual histology. “Virtual histology” applies spectral anal- instrumentation that enable the opacification and visualiza- ysis of the IVUS backscatter RF signal to characterize tion not only of the cardiac chambers but also blood vessels plaque components on the basis of tissue characteristics such and myocardium (33). Thus, myocardial contrast echocar- as density, compressibility, concentration of various compo- diography can provide visualization of myocardial perfusion nents, and size. With quantitative spectral parameters and after the intravenous injection of a variety of ultrasonic advanced mathematical techniques to classify plaque com- contrast agents; however, the microbubble agents have a position, this approach has been validated with histological finite lifespan before dissolving and might be destroyed by techniques on ex vivo coronary specimens in classifying the ultrasound energy applied in the process of imaging. In lesions as calcified, fibrofatty, calcified-necrotic core, and addition, the generalized myocardial and vascular opacifica- lipid-rich areas (31,32). This methodology allows real-time, tion produced by contrast echocardiography might mask 3D plaque cross-sectional and longitudinal views of the uptake of microbubbles by plaque. Therefore, there are a entire vessel and allows one to visualize the complete length number of challenges to identifying vulnerable plaque by of the artery and assess individual plaque components. contrast echocardiography. Although this technique seems promising and is currently at Imaging methods to detect vulnerable plaque have often the forefront of this approach, its clinical usefulness awaits been based on targeted imaging with the use of a signal- ongoing clinical trials. generating compound that, when attached to the target of These refinements of IVUS suggest that identification of interest, is detectable by the imaging technique. For ultra- plaque characteristics, including lipid-rich components, sound, the “beacon” that can be detected is the signal from might be clinically feasible in the near future and might microbubble contrast agents. Assuming that the target is allow identification of vulnerable plaques and new avenues specific for plaque (vulnerable or otherwise), it is not of diagnosis and therapy. necessary to image the vessel to establish the presence of the JACC Vol. 47, No. 8 Suppl C DeMaria et al. C37 April 18, 2006:C32–9 Imaging the Vulnerable Plaque by Ultrasound target. Thus far, contrast echo has been confined primarily Although most microbubble ultrasonic contrast agents to the identification of white blood cells and endothelial cell rapidly transit the bed, it was an early observation surface markers such as adhesion molecules; however, the that some microbubble agents became transiently attached principles will be the same for identifying specific markers of to vessels, particularly venules (35). Subsequent studies vulnerable plaque when they are defined. related this prolonged residence within the microcirculation In light of the aforementioned issues, the strategy that to a negative surface charge of the bubble (usually due to a has emerged to achieve targeted diagnostic imaging by con- lipid shell) with subsequent phagocytosis by white blood trast echocardiography has been to have the microbubbles or cells gathered along the surface of the . To date acoustically reflective liposomes ingested by or attached to the the ingestion of microbubbles by leukocytes has been found to specific target to be visualized (33,34). Attachment has been be sufficiently avid to enable identification of inflammation achieved either by virtue of the inherent properties of the such as that encountered after ischemia/reperfusion or trans- microbubble shell or by attaching specific ligands such as plant rejection in the experimental setting (36,37). monoclonal antibodies. In experimental models, these micro- The detection of white blood cells associated with plaque bubbles are then injected, and after a suitable time is allowed inflammation as a marker of vulnerable plaque would present a for either ingestion or attachment, conventional echocar- serious challenge; however, an alternate approach consists of diographic recordings are obtained. In this fashion the bulk using microbubble contrast to identify leukocyte adhesion of the contrast injected has disappeared, and the only molecules such as selectins or integrins, which might be residua are the microbubbles ingested by or attached to the upregulated in vulnerable plaque. Initial in vitro studies, target. employing either microbubble contrast agents or lipid emul-

Figure 5. The top panel shows the dissected intact aorta (left) and the opened aorta (right) showing yellow plaques. In the middle panel, (A) shows baseline ultrasound image of the aortic plaque (arrow), (B) shows microbubbles in the aortic lumen soon after intravenous injection, and (C) shows microbubble enhancement of the aortic plaque about 25 min after injection. The lumen is free of circulating microbubbles, and high mechanical index ultrasound imaging was done after 25 min. Note the brighter appearance of the plaque. The lower panel shows another example in which the figure on the left is the baseline image of a plaque and the figure on the right is color-coded, baseline-subtracted, videointensity image of the microbubble-enhanced atheroma. C38 DeMaria et al. JACC Vol. 47, No. 8 Suppl C Imaging the Vulnerable Plaque by Ultrasound April 18, 2006:C32–9 sions to which antibodies to intracellular adhesion mole- CONCLUSIONS cules (ICAM) had been incorporated, documented the At the moment, intravascular and transthoracic ultrasonic ability of these agents to attach to and be visualized on techniques for the detection of vulnerable plaque must be endothelium in which these molecules had been upregulated considered as either not established or experimental. Recent (38). Subsequently, targeted identification of leukocytes ad- advances, however, suggest that plaque characterization herent to the endothelium of venules was accomplished by with a variety of techniques might be feasible. Ultimately, microbubbles to which phosphatidylcholine was incorpo- clinical trials will determine whether ultrasound approaches rated into the lipid shell. Microbubbles, to which ligands to might identify vulnerable plaques or result in new algo- ICAM1 have been incorporated, have also been used to rithms in patient care. visualize transplant rejection in the experimental setting (39). Thus, exploiting both shell characteristics and incor- Reprint requests and correspondence: Dr. Anthony N. porated ligands to specific targets, microbubbles have been DeMaria, Cardiology Division, UCSD Medical Center, 200 found to be capable of identifying white blood cells as well West Arbor Drive, San Diego, California 92103-8411. E-mail: as adhesion molecules (34,40). Imaging of additional in- [email protected]. flammatory targets, such as phosphatidylserine (PS) recep- tors, which are ubiquitously expressed by , are REFERENCES being explored with echogenic liposomes enriched in PS phospholipids (Fig. 5). The imaging was performed with 1. Mintz GS, Nissen SE, Anderson WD, et al. American College of Cardiology clinical expert consensus document on standards for the premise that these bubbles will be preferentially at- acquisition, measurement and reporting of intravascular ultrasound tracted by the lesions that harbor abundant macrophages (or studies (IVUS) 13: a report of the American College of Cardiology vulnerable plaque). With this hypothesis, experimental task force on clinical expert consensus documents developed in collaboration with the European Society of Cardiology endorsed by atherosclerotic lesions were developed in rabbits by bal- the society of cardiac angiography and interventions. J Am Coll loon de-endothelialization of the infradiaphragmatic Cardiol 2001;37:1478–92. aorta, followed by 1% , 6% peanut oil diet for 2. Nishimura RA, Edwards WD, Warnes CA, et al. Intravascular ultrasound imaging: in vitro validation and pathologic correlation. 4 months. Such animals develop American Heart Asso- J Am Coll Cardiol 1990;16:145–54. ciation type II (20%), III (30%), and IV (50%) lesions. 3. Kimura BJ, Bhargava V, DeMaria AN. Value and limitations of Intravenous administration of PS-rich microbubbles filled intravascular ultrasound imaging in characterizing coronary atheroscle- rotic plaque. Am Heart J 1995;130:386–96. with perfluorocarbon were injected, and images were re- 4. Gronholdt ML. Ultrasound and as predictors of lipid- corded showing enhancement of the aortic plaque. The rich, rupture-prone plaques in the carotid artery. Arterioscler Thromb potential for additional endothelial cell surface markers to Vasc Biol 1999;19:2–13. 5. Prati F, Arbustini E, Labellarte A, et al. Correlation between high be used as targets for contrast echo detection of atheroscle- frequency intravascular ultrasound and histomorphology in human rosis is obvious. coronary arteries. Heart 2001;85:567–70. A number of challenges exist to the detection of vulnerable 6. Wickline SA. Plaque characterization: surrogate markers or the real thing? J Am Coll Cardiol 2004;43:1185–7. plaque by targeted echocardiographic contrast imaging. To 7. Honda O, Sugiyama S, Kugiyama K, et al. Echolucent carotid plaques begin with, it must be possible to achieve a minimum concen- predict future coronary events in patients with . tration of microbubbles at the target site. Secondly, the number J Am Coll Cardiol 2004;43:1177–84. 8. Glagov S, Weisenberg E, Zarins CK, Stankunavicius R, Kolettis GJ. of microbubbles and the ultrasonic signal transmitted must be Compensatory enlargement of human atherosclerotic coronary arter- capable of generating a sufficiently strong signal from the ies. N Engl J Med 1987;316:1371–5. tethered/ingested microbubbles. Finally, one must be able to 9. Maehara A, Mintz GS, Bui AB, et al. Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultra- distinguish the resident microbubbles from both circulating sound. J Am Coll Cardiol 2002;40:904–10. microbubbles and from ultrasonic signals generated by the 10. Davies MJ, Thomas A. Thrombosis and acute coronary-artery lesions blood-intimal border. Thus, targets must be chosen that are in sudden cardiac ischemic death. N Engl J Med 1984;310:1137–40. 11. Goldstein JA, Demetriou D, Grines CL, Pica M, Shoukfeh M, present in sufficient quantity and that can attract an ade- O’Neill WW. Multiple complex coronary plaques in patients with quate number of microbubbles per target to be detected by acute . N Engl J Med 2000;343:915–22. external ultrasonic imaging. Given these constraints, it is 12. Asakura M, Ueda Y, Yamaguchi O, et al. Extensive development of vulnerable plaques as a pan-coronary process in patients with myocar- likely that targeted imaging by contrast echocardiography dial infarction: an angioscopic study. J Am Coll Cardiol 2001;37: might find that detecting vulnerable plaque in the carotid 1284–8. arteries or in the coronary arteries in conjunction with IVUS 13. Takano M, Inami S, Ishibashi F, et al. Angioscopic follow-up study of coronary ruptured plaques in nonculprit lesions. J Am Coll Cardiol imaging will be its initial clinical application. Contrast 2005;45:652–8. echocardiography offers the opportunity to detect vulnerable 14. Takano M, Mizuno K, Yokoyama S, et al. Changes in coronary plaque plaque by noninvasive imaging but presents significant color and morphology by lipid-lowering therapy with atorvastatin: serial evaluation by coronary angioscopy. J Am Coll Cardiol 2003;42: challenges to the recording of microbubbles tethered to 680–6. specific sites. Nevertheless, the safety, repeatability of re- 15. Rioufol G, Finet G, Ginon I, et al. Multiple atherosclerotic plaque cording, portability, and cost of ultrasound provide a sub- rupture in acute coronary syndrome: a three-vessel intravascular ultrasound study. Circulation 2002;106:804–8. stantial incentive to develop approaches using this modality 16. Hong MK, Mintz GS, Lee CW, et al. Comparison of coronary plaque for the identification of vulnerable plaque. rupture between stable angina and acute myocardial infarction: a JACC Vol. 47, No. 8 Suppl C DeMaria et al. C39 April 18, 2006:C32–9 Imaging the Vulnerable Plaque by Ultrasound

three-vessel intravascular ultrasound study in 235 patients. Circulation patients with unstable and stable presentation. Arterioscler Thromb 2004;110:928–33. Vasc Biol 2003;23:1895–900. 17. Tanaka A, Shimada K, Sano T, et al. Multiple plaque rupture and 29. Kawasaki M, Sano K, Okubo M, et al. Volumetric quantitative C-reactive protein in acute myocardial infarction. J Am Coll Cardiol analysis of tissue characteristics of coronary plaques after statin therapy 2005;45:1594–9. using three-dimensional integrated backscatter intravascular ultra- 18. Fujii K, Kobayashi Y, Mintz GS, et al. Intravascular ultrasound sound. J Am Coll Cardiol 2005;45:1946–53. assessment of ulcerated ruptured plaques: a comparison of culprit and 30. Murashige A, Hiro T, Fujii T, et al. Detection of lipid-laden nonculprit lesions of patients with acute coronary syndromes and atherosclerotic plaque by wavelet analysis of radiofrequency intravas- lesions in patients without acute coronary syndromes. Circulation cular ultrasound signals: in vitro validation and preliminary in vivo 2003;108:2473–8. application. J Am Coll Cardiol 2005;45:1954–60. 19. Kotani Ji, Mintz GS, Castagna MT, et al. Intravascular ultrasound 31. Nair A, Kuban BD, Obuchowski N, Vince DG. Assessing spectral analysis of infarct-related and non-infarct-related arteries in patients algorithms to predict atherosclerotic plaque composition with normal- who presented with an acute myocardial infarction. Circulation 2003; ized and raw intravascular ultrasound data. Ultrasound Med Biol 107:2889–93. 2001;27:1319–31. 20. Libby P. Act local, act global: inflammation and the multiplicity of 32. Nair A, Kuban BD, Tuzcu EM, Schoenhagen P, Nissen SE, Vince “vulnerable” coronary plaques. J Am Coll Cardiol 2005;45:1600–2. DG. Coronary plaque classification with intravascular ultrasound 21. Rioufol G, Gilard M, Finet G, Ginon I, Boschat J, Andre-Fouet X. radiofrequency data analysis. Circulation 2002;106:2200–6. Evolution of spontaneous atherosclerotic plaque rupture with medical 33. Lindner JR, Song J, Xu F, et al. Noninvasive ultrasound imaging of therapy. Long-term follow-up with intravascular ultrasound. Circula- inflammation using microbubbles targeted to activated leukocytes. tion 2004;110:2875–80. Circulation 2000;102:2745–50. 22. Burke AP, Kolodgie FD, Farb A, et al. Healed plaque ruptures and 34. Hamilton AJ, Huang SL, Warnick D, et al. Intravascular ultrasound sudden coronary death: evidence that subclinical rupture has a role in molecular imaging of atheroma components in vivo. J Am Coll Cardiol plaque progression. Circulation 2001;103:934–40. 2004;43:453–60. 23. Beckman JA, Ganz J, Creager MA, Ganz P, Kinlay S. Relationship of clinical presentation and calcification of culprit coronary artery steno- 35. Yasu T, Schmid-Schonbein GW, Cotter B, DeMaria AN. Flow ses. Arterioscler Thromb Vasc Biol 2001;21:1618–22. dynamics of QW7437, a new dodecafluoropentane ultrasound contrast 24. Ehara S, Kobayashi Y, Yoshiyama M, et al. Spotty calcification typifies agent, in the microcirculation: microvascular mechanisms for persis- the culprit plaque in patients with acute myocardial infarction: an tent tissue echo enhancement. J Am Coll Cardiol 1999;34:578–86. intravascular ultrasound study. Circulation 2004;110:3424–9. 36. Christiansen JP, Leong-Poi H, Klibanov AL, Kaul S, Lindner JR. 25. Fujii K, Carlier S, Mintz GS, et al. Intravascular ultrasound study of Noninvasive imaging of myocardial reperfusion injury using leukocyte- patterns of calcium in ruptured coronary plaques. Am J Cardiol targeted contrast echocardiography. Circulation 2002;105:1764–7. 2005;96:352–7. 37. Weller GE, Lu E, Csikari MM, et al. Ultrasound imaging of acute 26. Nissen SE, Tuzcu EM, Schoenhagen P, et al. Effect of intensive cardiac transplant rejection with microbubbles targeted to intercellular compared with moderate lipid-lowering therapy on progression of adhesion molecule-1. Circulation 2003;108:218–24. coronary atherosclerosis: a randomized controlled trial. JAMA 2004; 38. Villanueva FS, Jankowski RJ, Klibanov S, et al. Microbubbles targeted 291:1071–80. to intercellular adhesion molecule-1 bind to activated coronary artery 27. Yamagishi M, Terashima M, Awano K, et al. Morphology of endothelial cells. Circulation 1998;98:1–5. vulnerable coronary plaque: insights from follow-up of patients exam- 39. Weller GE, Lu E, Csikari MM, et al. Ultrasound imaging of acute ined by intravascular ultrasound before an acute coronary syndrome. cardiac transplant rejection with microbubbles targeted to intercellular J Am Coll Cardiol 2000;35:106–11. adhesion molecule-1. Circulation 2003;108:218–24. 28. Schoenhagen P, Stone GW, Nissen SE, et al. Coronary plaque 40. Kaul S, Lindner JR. Visualizing coronary atherosclerosis in vivo: morphology and frequency of ulceration distant from culprit lesions in thinking big, imaging small. J Am Coll Cardiol 2004;43:461–3.