Tissue characterization of coronary plaques: comparison of integrated backscatter intravascular ultrasound with virtual histology intravascular ultrasound

Innovations in Intracoronary Imaging: Present Clinical Practices and Future Outlooks

Engaging intracoronary imaging (IC) techniques such as intravascular ultrasound or optical coherence tomography enables the precise description of vessel architecture. These imaging modalities have well-established roles in providing guidance and optimizing percutaneous coronary intervention (PCI) outcomes. Furthermore, IC is increasingly recognized for its diagnostic capabilities, as it has the unique capacity to reveal vessel wall characteristics that may not be apparent through angiography alone. This manuscript thoroughly reviews the contemporary landscape of IC in clinical practice. Focused on current methodologies, the review explores the utility and advancements in IC techniques. Emphasizing their role in clarifying coronary pathophysiology, guiding PCI, and optimizing patient outcomes, the manuscript critically evaluates the strengths and limitations of each modality. Additionally, the integration of IC into routine clinical workflows and its impact on decision-making processes are discussed. By synthesizing the latest evidence, this review provides valuable insights for clinicians, researchers, and healthcare professionals involved in the dynamic field of interventional cardiology.

Relationship between tissue characteristics and mechanical properties of coronary plaques: a comparison between integrated backscatter intravascular ultrasound (IVUS) and speckle-tracking IVUS

High-risk coronary plaques have certain morphological characteristics. Thus, comprehensive assessment is needed for the risk stratification of plaques in patients with coronary artery disease. Integrated backscatter intravascular ultrasound (IB-IVUS) has been used successfully used to evaluate the tissue characteristics of coronary plaques; however, the mechanical properties of plaques have been rarely assessed. Therefore, we developed Speckle-tracking IVUS (ST-IVUS) to evaluate the mechanical properties of coronary plaque. This study aimed to evaluate the relation between the tissue characteristics of coronary plaques using IB-IVUS and their mechanical properties using ST-IVUS. We evaluated 95 non-targeted plaques in 95 patients undergoing elective percutaneous coronary intervention to the left anterior descending artery. We set regions of interest (ROIs) in the cross-sectional images of coronary plaques where we divided 120 degree plaques into four quadrants (every 30 degrees), with the center at the area of maximum atheroma thickness. We measured relative calcification area (%CA, relative fibrous area (%FI) and relative lipid pool area (%LP) in a total of 380 ROIs. In ST-IVUS analysis, we measured strain in the circumferential direction of the lumen area (LA strain: %), the external elastic membrane area strain (EEM strain: %), and strain in the radial direction (radial strain: %). On global cross-sectional area IB-IVUS analysis, the %CA was 1.2 ± 1.2%; the %FI was 49.0 ± 15.9%, and the %LP was 49.7 ± 16.5%. In ST-IVUS analysis, the LA strain was 0.67 ± 0.43%; the EEM strain was 0.49 ± 0.33%, and the radial strain was 2.02 ± 1.66%. On regional analysis, the %LP was not associated with the LA strain (r = - 0.002 p = 0.97), the EEM strain (r = - 0.05 p = 0.35), or with the radial strain (r = - 0.04 p = 0.45). These trends were seen between the %FI and the LA strain (r = 0.02 p = 0.74), the %FI and the EEM strain (r = 0.05 p = 0.35), and the %FI and the radial strain (r = 0.04 p = 0.50). A significant correlation was only observed between the %CA and the LA strain (r = - 0.15 p = 0.0038). Our findings indicate that the associations between mechanical properties and tissue characteristics lacked statistical significance, more often than not, and that it is necessary to evaluate the mechanical properties as well as plaque characteristics for risk stratification of coronary plaques.

Development of 60 MHz integrated backscatter intravascular ultrasound and tissue characterization of attenuated signal coronary plaques that cause myocardial injury after percutaneous coronary intervention

The purpose of the present study was to develop a 60 MHz integrated backscatter intravascular ultrasound (IB-IVUS) and to evaluate its usefulness for the detection of lipid area with backward attenuation of ultrasound signal (AT) that for the prediction of post-procedural myocardial injury (PMI) after percutaneous coronary intervention (PCI). In a pathological study, images were acquired from 221 cross-sections of 18 coronary arteries from 13 cadavers obtained at autopsy. In the clinical training study, we compared non-targeted plaques in 38 patients by a previous IB-IVUS system (38 MHz) and a new IB-IVUS system (60 MHz). In the clinical testing study, we included 70 consecutive patients who underwent PCI. Serum troponin-I was measured just before and 24 h after PCI to evaluate PMI. As the % microcalcification + % cholesterol cleft area increased, the attenuation of IB values increased (r = 0.56, p < 0.001). The slopes of regression lines of the area of each tissue component between 38 and 60 MHz IB-IVUS were excellent. The lipid pool area with AT tended to be more useful than that of the conventional lipid pool area for the prediction of PMI (p = 0.11). We developed a 60 MHz IB-IVUS imaging system for tissue characterization of coronary plaques. Cutoff value of purple color was the most reliable value for the prediction of PMI.

A 100-V Withstanding Analog-Front-End for High-Resolution Intravascular Ultrasound Imaging

Intravascular Ultrasound ultrasonic imaging (IVUS) can microscopically image blood vessels and reveal tissue layers from within the blood vessel lumen. It has high tissue penetration ability for lesion classification and can image through blood. Compared to optical techniques, however, IVUS has lower resolution arising from low acoustic bandwidths which cannot resolve sharp edges. The presented 100-V withstanding Analog-Front-End (AFE) was developed to enable a high resolution, low cost IVUS system using a high-bandwidth focused polymer transducer with 40-MHz center frequency. The fabricated AFE interfaced with the transducer with minimal insertion loss, could withstand and duplex 100-V high voltage pulses and echo signal, and had a total signal chain gain of 9.8 dB. The AFE achieved a signal-to-noise ratio (SNR) of 20.1 dB including the insertion loss of the high-impedance transducer. AFE SNR was limited by input impedance required for high-voltage pulse clamping circuitry, but was sufficient for IVUS echo reception.Clinical Relevance- This work has the potential to enable much higher resolution, and potentially cheaper, IVUS imaging in blood vessels by integrating low-cost acoustic transducers with interface amplifiers directly on the catheter.

Integrated backscatter-intravascular ultrasound and modification of plaque during excimer laser coronary angioplasty

This study aims to test the hypothesis that the effect of excimer laser coronary angioplasty (ELCA) not only vaporizes thrombi and their underlying coronary plaque, it also changes their quality. We performed a series of cross-sectional analyses in 52 lesions in 51 patients before and after ELCA with integrated backscatter-intravascular ultrasound (IB-IVUS). The constituent parts of the plaque can be assessed by IB-IVUS (i.e., calcified, fibrous, lipid) according to integrated backscatter values. Minimum lumen diameter, lumen volume and vessel volume expanded after ELCA, while plaque volume did not significantly decrease. There was also a decrease of ‘lipid’ component (35.4–30.3%, P < 0.001) and an increase of IB-IVUS-derived ‘fibrous’ part (34.5–38.3%, P < 0.001). These results may help in understanding plaque change after ELCA. Excimer laser coronary angioplasty seems to contribute to the modification of coronary plaque composition in addition to debulking it.

Effects of Fatty Acid Therapy in Addition to Strong Statin on Coronary Plaques in Acute Coronary Syndrome: An Optical Coherence Tomography Study

BACKGROUND

Vascular healing response associated with adjunctive n‐3 polyunsaturated fatty acid therapy therapy in patients receiving strong statin therapy remains unclear. The aim of this study was to evaluate the effect of polyunsaturated fatty acid therapy with eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in addition to strong statin therapy on coronary atherosclerotic plaques using optical coherence tomography.

METHODS AND RESULTS

This prospective multicenter randomized controlled trial included 130 patients with acute coronary syndrome treated with strong statins. They were assigned to either statin only (control group, n=42), statin+high‐dose EPA (1800 mg/day) (EPA group, n=40), statin+EPA (930 mg/day)+DHA (750 mg/day) (EPA+DHA group, n=48). Optical coherence tomography was performed at baseline and at the 8‐month follow‐up. The target for optical coherence tomography analysis was a nonculprit lesion with a lipid plaque. Between baseline and the 8‐month follow‐up, fibrous cap thickness (FCT) significantly increased in all 3 groups. There were no significant differences in the percent change for minimum FCT between the EPA or EPA+DHA group and the control group. In patients with FCT <120 µm (median value), the percent change for minimum FCT was significantly higher in the EPA or EPA+DHA group compared with the control group.

CONCLUSIONS

EPA or EPA+DHA therapy in addition to strong statin therapy did not significantly increase FCT in nonculprit plaques compared with strong statin therapy alone, but significantly increased FCT in patients with thinner FCT.

Registration

URL: https://www.umin.ac.jp/ctr/; Unique identifier: UMIN 000012825.

Reliable in vivo intravascular imaging plaque characterization: A challenge unmet

Intravascular imaging has enabled in vivo assessment of coronary artery pathology and detection of plaque characteristics that are associated with increased vulnerability. Prospective invasive imaging studies of coronary atherosclerosis have demonstrated that invasive imaging modalities can detect lesions that are likely to progress and cause cardiovascular events and provided unique insights about atherosclerotic evolution. However, despite the undoubted value of the existing imaging techniques in clinical and research arenas, all the available modalities have significant limitations in assessing plaque characteristics when compared with histology. Hybrid/multimodality intravascular imaging appears able to overcome some of the limitations of standalone imaging; however, there are only few histology studies that examined their performance in evaluating plaque pathobiology. In this article, we review the evidence about the efficacy of standalone and multi-modality/hybrid intravascular imaging in assessing plaque morphology against histology, highlight the advantages and limitations of the existing imaging techniques and discuss the future potential of emerging imaging modalities in the study of atherosclerosis.

Impact of neointimal tissue characterization and heterogeneity of bare-metal stents and drug-eluting stents on the time course after stent implantation evaluated by integrated backscatter intravascular ultrasound

Pathological studies have suggested the different process of in-stent restenosis (ISR) of bare-metal stents (BMS) and drug-eluting stents (DES). Here, we evaluated the components of neointimal tissue using integrated backscatter intravascular ultrasound (IB-IVUS) and focused on the time course after stent implantation and tissue signal distribution. We evaluated 125 lesions of 125 patients who underwent target lesion revascularization for ISR (BMS: n = 73, DES: n = 52). Volume analysis of a 4-mm length centered on a minimum lumen area in every 1-mm cross-sectional area was performed. For IB-IVUS analysis, color-coded maps were constructed from the default setting based on the integrated backscatter (IB) values (middle-IB value, green: fibrous and low-IB value, blue: lipid pool). For the neointimal tissue volume, we evaluated the ratios of the green (%G) and blue (%B) areas. Tissue signal distribution (TD) was also obtained from the default setting based on IB values in each pixel of IB-IVUS imaging. We compared values of neointimal tissues measured by IB-IVUS between the DES and BMS and time course. The observed period was longer after BMS implantation than after DES implantation (BMS: 2545 days, DES: 1233 days, p < 0.001). Overall, %G and %B were similar between the BMS and DES groups (%G: 55% and 51%, respectively, p = 0.10; %B: 36% and 38%, respectively, p = 0.51); however, TD was significantly higher in the DES group than in the BMS group (1091 vs. 1367, p < 0.001). TD in the DES group remained high during the follow-up periods. However, TD in the BMS group was low in the early phase and significantly increased over time (r = 0.56, p < 0.001). When analyzing the ISR within 2 years after stent implantation, the BMS was distinguished with a sensitivity of 66% and a specificity of 90% (cut-off value: TD = 1135, area under the curve 0.83, 95% confidence interval 0.74-0.92). TD could differentiate neointimal tissue after BMS implantation in the early phase. TD can be a useful index in the observation of neoatherosclerosis.

Morphological Features and Plaque Composition in Culprit Atheromatous Plaques of Patients with Acute Coronary Syndromes

Background: The independent role of each plaque feature in relation to plaque vulnerability is still the subject of ongoing research. This study aimed to compare the morphologic characteristics of vulnerable atheromatous coronary plaques with the ones of stable, non-vulnerable plaques, and in plaques with different locations in the coronary tree, in order to identify the most relevant imaging-based biomarkers associated with coronary plaque vulnerability.

Material and methods: This was a prospective observational, non-randomized study that included 50 patients with unstable angina who underwent computed tomography angiography for assessment of the entire coronary artery tree followed by complex morphologic analysis of all lesions, divided into two groups: group 1 – 25 patients with vulnerable plaque (VP) and group 2 – 25 age- and gender-matched patients with non-vulnerable plaque (NVP).

Results: Lesions with a stenosis degree >70% were significantly longer than those with a stenosis degree <70% (8.27 ± 2.74 mm vs. 5.56 ± 4.11 mm, p = 0.04). VP presented significantly higher values of plaque thickness (p = 0.0005), plaque burden (p = 0.0004), and higher total plaque volume (p = 0.0005) than NVP. The remodeling index was not significantly different between the groups (p = 0.6), but the eccentricity index was (0.24 ± 0.14 compared to 0.14 ± 0.17, p = 0.023). Linear regression analysis revealed a significant correlation between plaque burden and plaque components in VP (r = 0.76, p <0.0001 for necrotic core; r = 0.62, p = 0.0008 for fibro-fatty tissue; and r = 0.5, p = 0.01 for fibrotic tissue volume). Culprit plaques located in the right coronary artery presented significantly larger plaque burden volumes (91.17 ± 4.88 mm3 vs. 83.35 ± 8.47 mm3, p = 0.04), larger volumes of necrotic core (82.03 ± 47.85 mm3 vs. 45.84 ± 43.72 mm3, p = 0.02) and fibrofatty tissue (53.23 ± 31.92 mm3 vs. 23.76 ± 20.90 mm3, p = 0.02) than the ones situated in the left coronary artery.

Conclusions: VPs from the culprit lesions exhibit a different phenotype than non-vulnerable ones, and vulnerability features are present in a significantly larger extent in VPs from the right coronary artery as compared to those from the left coronary artery.

Impact of Water- and Lipid-Soluble Statins on Nonculprit Lesions in Patients with Acute Coronary Syndrome

Statins can be differentiated into two types, based on their solubility, which have potentially differing effects on the coronary artery wall. However, suspected differences in statins' effects on plaque composition have not been systemically investigated.Sixty-seven patients with acute coronary syndrome (ACS) were randomly assigned to either atorvastatin (10 mg/day) or rosuvastatin (2.5 mg/day). Intravascular ultrasound (IVUS) and integrated backscatter (IB)-IVUS, an established tool to quantify each plaque's components, were performed immediately after emergent percutaneous coronary intervention (PCI). Follow-up IVUS was performed between 6 and 12 months after PCI. Serial changes in serum lipid profiles and plaque composition volumes were compared between the two groups.Thirty-five patients were eligible for serial IB-IVUS analyses. The mean low-density lipoprotein-cholesterol level significantly decreased in the atorvastatin and rosuvastatin groups (P < 0.001); plaque volumes were also significantly reduced from 82.0 ± 46.2 to 74.9 ± 41.3 mm³ (P = 0.01) and from 74.7 ± 35.3 to 67.7 ± 27.0 mm³ (P = 0.02), respectively. IB-IVUS revealed a significant reduction in fibrous volume from 33.8 ± 20.0 to 27.5 ± 14.9 mm³ (P < 0.01) and from 29.6 ± 13.6 to 24.8 ± 7.6 mm³ (P < 0.05), respectively; however, significant changes were not noted in the volume of the lipid pool for the atorvastatin group and the rosuvastatin group, respectively.Water- and lipid-soluble statins may be similarly effective in reducing coronary plaques in patients with ACS as judged qualitatively and quantitatively. Further study is needed to determine whether differences between water- and lipid-soluble statins affect plaque components.

Advances in Intravascular Imaging: New Insights into the Vulnerable Plaque from Imaging Studies

The term “vulnerable plaque” denotes the plaque characteristics that are susceptible to coronary thrombosis. Previous post-mortem studies proposed 3 major mechanisms of coronary thrombosis: plaque rupture, plaque erosion, and calcified nodules. Of those, characteristics of rupture-prone plaque have been extensively studied. Pathology studies have identified the features of rupture-prone plaque including thin fibrous cap, large necrotic core, expansive vessel remodeling, inflammation, and neovascularization. Intravascular imaging modalities have emerged as adjunctive tools of angiography to identify vulnerable plaques. Multiple devices have been introduced to catheterization laboratories to date, including intravascular ultrasound (IVUS), virtual-histology IVUS, optical coherence tomography (OCT), coronary angioscopy, and near-infrared spectroscopy. With the use of these modalities, our understanding of vulnerable plaque has rapidly grown over the past several decades. One of the goals of intravascular imaging is to better predict and prevent future coronary events, for which prospective observational data is still lacking. OCT delineates microstructures of plaques, whereas IVUS visualizes macroscopic vascular structures. Specifically, plaque erosion, which has been underestimated in clinical practice, is gaining an interest due to the potential of OCT to make an in vivo diagnosis. Another potential future avenue for intravascular imaging is its use to guide treatment. Feasibility of tailored therapy for acute coronary syndromes (ACS) guided by OCT is under investigation. If it is proven to be effective, it may potentially lead to major shift in the management of millions of patients with ACS every year.

Catheter-Mounted CMOS Front-Ends for Broadband Intravascular Ultrasonic Imaging

Intravascular ultrasonic (IVUS) imaging catheters currently use ceramic piezoelectric transducers to form radial images of blood vessel walls. Further improvements in image quality may be enabled through Capacitive and Piezoelectric Micromachined Ultrasonic Transducers (CMUTs and PMUTs). Polymer PMUTs offer many benefits in imaging quality, however, the low acoustic sensitivity and high electrical impedance of polymer PMUTs prevents unbuffered use with 50-Ω IVUS cables. Here, we present the design and optimization of an integrated CMOS front-end specifically designed to be integrated on a 0.8-mm imaging catheter. A series-duplexer topology with active limiter was selected for simplicity of integration, and compatibility with conventional high-voltage IVUS pulser-receiver systems. Noise optimization of the front-end revealed that an impedance-matching optimum exists, which balances the system parasitic capacitances relative to the transducer complex impedance. Optimized design equations compared favorably to simulation results in predicting front-end bandwidth and transducer-referred SNR. Large-signal transient simulation showed that the front-end can withstand 100-V pulses while recovering in 240 ns for echo reception. The integrated front-end occupied 0.74 × 1.8 mm die area (including large solder-bump bond pads), with an estimated transducer-referred noise floor of 6.5 n V R M S / H z over a 100-MHz imaging bandwidth.

A randomized controlled trial of eicosapentaenoic acid in patients with coronary heart disease on statins

BACKGROUND

There is a residual risk of coronary heart disease (CHD) despite intensive statin therapy for secondary prevention. The aim of this study was to investigate whether coronary plaque regression and stabilization are reinforced by the addition of eicosapentaenoic acid (EPA) to high-dose pitavastatin (PTV).

METHODS

We enrolled 193 CHD patients who underwent percutaneous coronary intervention (PCI) in six hospitals. Patients were randomly allocated to the PTV group (PTV 4mg/day, n=96) or PTV/EPA group (PTV 4mg/day and EPA 1800mg/day, n=97), and prospectively followed for 6-8 months. Coronary plaque volume and composition in nonstenting lesions were analyzed by integrated backscatter intravascular ultrasound (IB-IVUS).

RESULTS

The PTV/EPA group showed a greater reduction in total atheroma volume compared to PTV group. IB-IVUS analyses revealed that lipid volume was significantly decreased during follow-up period in only PTV/EPA group. The efficacy of additional EPA therapy on lipid volume reduction was significantly higher in stable angina pectoris (SAP) patients compared to acute coronary syndrome patients. EPA/AA ratio was significantly improved in PTV/EPA group compared to PTV group. There was no significant difference in the incidence of major adverse cardiovascular events and side effects.

CONCLUSIONS

Combination EPA/PTV therapy significantly reduced coronary plaque volume compared to PTV therapy alone. Plaque stabilization was also reinforced by EPA/PTV therapy in particular SAP patients. The addition of EPA is a promising option to reduce residual CHD risk under intensive statin therapy.

The Role of Virtual Histology Intravascular Ultrasound in the Identification of Coronary Artery Plaque Vulnerability in Acute Coronary Syndromes

Markers of coronary plaque vulnerability, such as a high lipid burden, increased inflammatory activity, and a thin fibrous cap, have been identified in histological studies. In vivo, grayscale intravascular ultrasound (IVUS) provides more in-depth information on coronary artery plaque burden than conventional angiography but is unable to accurately distinguish between noncalcific tissue types within the plaque. An analysis of IVUS radiofrequency backscatter based on spectral pattern recognition, such as virtual histology IVUS, allows detailed scrutiny of plaque composition and classification of coronary lesions. This review discusses the virtual histology IVUS technology and its accuracy in identifying vulnerable plaque features, focusing on its use in predicting patient outcomes after acute coronary syndrome, and its limitations in clinical practice.

Impact of Serum Uric Acid Levels on Coronary Plaque Stability Evaluated Using Integrated Backscatter Intravascular Ultrasound in Patients with Coronary Artery Disease

AIM

Because the prevalence of hyperuricemia is lower in females than in males, the association between hyperuricemia and cardiovascular disease has been frequently reported in females. Increased serum uric acid levels are associated with the presence of cardiovascular risk factors such as hypertension, renal dysfunction, insulin resistance, and metabolic syndrome. However, it is controversial whether hyperuricemia is an independent risk factor for coronary artery disease in both the genders. The purpose of this study was to investigate the relationship between serum uric acid levels and coronary plaque components assessed using integrated backscatter intravascular ultrasound (IB-IVUS) in males and females.

METHODS

In total, 385 patients (298 males and 87 females) who underwent percutaneous coronary intervention using IB-IVUS were divided into three groups in each gender according to their serum uric acid levels. We characterized tissue from coronary plaques in culprit lesions.

RESULTS

Serum uric acid levels significantly correlated with percent lipid volume (r=0.37) and inversely correlated with percent fibrous volume (r=－0.35). Multivariate analysis showed that the uric acid level was independently associated with lipid-rich plaques (odds ratio 2.43, 95%, confidence interval 1.75-3.47). The prevalence of lipid-rich plaques increased with increasing uric acid levels in both genders.

CONCLUSION

Increased serum uric acid levels were associated with larger lipid content plaques in both genders.

Integrated intravascular ultrasound and optical coherence tomography technology: a promising tool to identify vulnerable plaques [INVITED PAPER]

Heart attack is mainly caused by the rupture of a vulnerable plaque. IVUS-OCT is a novel medical imaging modality that provides opportunities for accurate assessment of vulnerable plaques in vivo in patients. IVUS provides deep penetration to image the whole necrotic core while OCT enables accurate measurement of the fibrous cap of a plaque owing to its high resolution. In this paper, the authors describe the fundamentals, the technical designs and the applications of IVUS-OCT technology. Results from cadaver specimens are summarized, which indicated the complementary nature of OCT and IVUS for assessment of vulnerable plaques, plaque composition, and stent-tissue interactions. Furthermore, previously reported in vivo animal experiments are reviewed to assess the clinical adaptability of IVUS-OCT. Future directions for this technology are also discussed in this review.

Ultrafast optical-ultrasonic system and miniaturized catheter for imaging and characterizing atherosclerotic plaques in vivo

Atherosclerotic coronary artery disease (CAD) is the number one cause of death worldwide. The majority of CAD-induced deaths are due to the rupture of vulnerable plaques. Accurate assessment of plaques is crucial to optimize treatment and prevent death in patients with CAD. Current diagnostic techniques are often limited by either spatial resolution or penetration depth. Several studies have proved that the combined use of optical and ultrasonic imaging techniques increase diagnostic accuracy of vulnerable plaques. Here, we introduce an ultrafast optical-ultrasonic dual-modality imaging system and flexible miniaturized catheter, which enables the translation of this technology into clinical practice. This system can perform simultaneous optical coherence tomography (OCT)-intravascular ultrasound (IVUS) imaging at 72 frames per second safely in vivo, i.e., visualizing a 72 mm-long artery in 4 seconds. Results obtained in atherosclerotic rabbits in vivo and human coronary artery segments show that this ultrafast technique can rapidly provide volumetric mapping of plaques and clearly identify vulnerable plaques. By providing ultrafast imaging of arteries with high resolution and deep penetration depth simultaneously, this hybrid IVUS-OCT technology opens new and safe opportunities to evaluate in real-time the risk posed by plaques, detect vulnerable plaques, and optimize treatment decisions.

Noninvasive Tissue Characterization of Lung Tumors Using Integrated Backscatter Intravascular Ultrasound: An Ex Vivo Comparative Study With Pathological Diagnosis

BACKGROUND

Endobronchial ultrasonography (EBUS) facilitates a lung cancer diagnosis. However, qualitative tissue characterization of lung tumors is difficult using EBUS. Integrated backscatter (IBS) is an ultrasound technique that calculates the power of the ultrasound signal to characterize tissue components in coronary arteries. We hypothesized that qualitative diagnosis of lung tumors is possible using the IBS technique. The aim of the present study was to elucidate whether the IBS technique can be used in lung tissue diagnoses.

METHODS

Thirty-five consecutive patients who underwent surgery for lung cancer were prospectively enrolled. Surgical specimens of the lung and the tumor tissue were obtained, and the IBS values were measured within 48 h after surgery. Histologic images of lung and tumor tissues were compared with IBS values, and the relative interstitial area according to results of Masson's trichrome staining were determined by using an imaging processor.

RESULTS

The IBS values in tumor tissue were significantly lower than those in normal lung tissue (-50.9 ± 2.6 dB and -47.6 ± 2.6 dB, respectively; P < .001). The IBS values of adenocarcinomas associated with a good 5-year survival rate were higher than those of non-adenocarcinomas (-48.1 ± 1.6 dB and -52.6 ± 1.4 dB; P < .001). There were significant correlations between the IBS values and the relative interstitial area or micro air area in tumor (r = 0.53 and r = 0.67; P < .01). After combining normal lung tissue and adenocarcinomas with a good prognosis, the sensitivity and specificity for establishing the presence of lung tumors were 84% and 85%.

CONCLUSIONS

Qualitative diagnosis of lung tumors was possible, with a sensitivity of 84% and a specificity of 85%, using the ultrasound IBS technique.

Association of Estimated Glomerular Filtration Rate and Proteinuria With Lipid-Rich Plaque in Coronary Artery Disease

BACKGROUND

Estimated glomerular filtration rate (eGFR) and proteinuria are both important determinants of the risk of cardiovascular disease and mortality. The aim of the present study was to investigate the independent and combined effects of eGFR and proteinuria on tissue characterization of the coronary plaques of culprit lesions.

METHODS AND RESULTS

Conventional intravascular ultrasound and 3-D integrated backscatter intravascular ultrasound (IB-IVUS) were performed in 555 patients undergoing elective percutaneous coronary intervention. They were divided into 2 groups according to the absence or presence of proteinuria (dipstick result ≥1+). Patients with proteinuria had coronary plaque with significantly greater percentage lipid volume compared with those without (43.6±14.8% vs. 48.6±16.1%, P=0.005). Combined analysis was done using eGFR and absence or presence of proteinuria. Subjects with eGFR 45-59 ml/min/1.73 m2 and proteinuria were significantly more likely to have higher percent lipid volume compared with those with eGFR >60 ml/min/1.73 m2 without proteinuria. After multivariate adjustment for confounders, the presence of proteinuria proved to be an independent predictor for lipid-rich plaque (OR, 1.85; 95% CI: 1.12-3.06, P=0.016).

CONCLUSIONS

The addition of proteinuria to eGFR level may be of value in the risk stratification of patients with coronary artery disease.

Influence of plaque characteristics on fractional flow reserve for coronary lesions with intermediate to obstructive stenosis: insights from integrated-backscatter intravascular ultrasound analysis

The aim of this study was to determine the correlation between the fractional flow reserve (FFR) values and volumetric intravascular ultrasound (IVUS) parameters derived from classic gray-scale IVUS and integrated backscatter (IB)-IVUS, taking into account known confounding factors. Patients with unstable angina pectoris with the frequent development of vulnerable plaques often showed the discrepancy between the FFR value and the quantitative coronary angiography findings. Our target population was 107 consecutive subjects with 114 isolated lesions who were scheduled for elective coronary angiography. The FFR was calculated as the mean distal coronary pressure divided by the mean aortic pressure during maximal hyperemia. Various volumetric parameters such as lipid plaque volume (LPV) and percentage of LPV (%LPV) were measured using IB-IVUS. Simple and multivariate linear regression analysis was employed to evaluate the correlation between FFR values and various classic gray-scale IVUS and IB-IVUS parameters. The Akaike information criterion (AIC) was used to compare the goodness of fit in an each model. Both the %LPV (r = -0.24; p = 0.01) and LPV (r = -0.40; p < 0.01) were significantly correlated with the FFR value. Only the LPV (AIC = -147.0; p = 0.006) and %LPV (AIC = -152.9; p = 0.005) proved to be independent predictors for the FFR value even after the adjustment of known confounding factors. The volumetric assessment by IB-IVUS could provide better information in terms of the relationship between plaque morphology and the FFR values as compared to the classic IVUS 2-dimensional gray-scale analysis.

Currently available methodologies for the processing of intravascular ultrasound and optical coherence tomography images

Optical coherence tomography and intravascular ultrasound are the most widely used methodologies in clinical practice as they provide high resolution cross-sectional images that allow comprehensive visualization of the lumen and plaque morphology. Several methods have been developed in recent years to process the output of these imaging modalities, which allow fast, reliable and reproducible detection of the luminal borders and characterization of plaque composition. These methods have proven useful in the study of the atherosclerotic process as they have facilitated analysis of a vast amount of data. This review presents currently available intravascular ultrasound and optical coherence tomography processing methodologies for segmenting and characterizing the plaque area, highlighting their advantages and disadvantages, and discusses the future trends in intravascular imaging.

An integrated backscatter ultrasound technique for the detection of coronary and carotid atherosclerotic lesions

The instability of carotid and coronary plaques has been reported to be associated with acute coronary syndrome, strokes and other cerebrovascular events. Therefore, recognition of the tissue characteristics of carotid and coronary plaques is important to understand and prevent coronary and cerebral artery disease. Recently, an ultrasound integrated backscatter (IB) technique has been developed. The ultrasound IB power ratio is a function of the difference in acoustic characteristic impedance between the medium and target tissue, and the acoustic characteristic impedance is determined by the density of tissue multiplied by the speed of sound. This concept allows for tissue characterization of carotid and coronary plaques for risk stratification of patients with coronary and cerebral artery disease. Two- and three-dimensional IB color-coded maps for the evaluation of tissue components consist of four major components: fibrous, dense fibrosis, lipid pool and calcification. Although several ultrasound techniques using special mathematical algorithms have been reported, a growing body of literature has shown the reliability and usefulness of the IB technique for the tissue characterization of carotid and coronary plaques. This review summarizes concepts, experimental procedures, image reliability and the application of the IB technique. Furthermore, the IB technique is compared with other techniques.

A combination of plaque components analyzed by integrated backscatter intravascular ultrasound and serum pregnancy-associated plasma protein a levels predict the no-reflow phenomenon during percutaneous coronary intervention

AIMS

Previous studies reported that integrated backscatter intravascular ultrasound (IB-IVUS) provides high diagnostic accuracy for tissue characterization of coronary plaques and that pregnancy-associated plasma protein A (PAPP-A) could be a marker of adverse cardiac outcome in patients with cardiovascular disease. We examined whether IB-IVUS and PAPP-A levels could predict the incidence of no-reflow during percutaneous coronary intervention (PCI) METHODS AND RESULTS: About 176 consecutive patients (138 men, mean age 68 ± 11 years) who underwent PCI with IB-IVUS were prospectively enrolled. Combined no-reflow, including transient filter no-reflow by using distal protection devices, was observed in 31 patients. The percentages of coronary lipid volume (%LV) analyzed by IB-IVUS and serum PAPP-A were significantly higher in patients with combined no-reflow than normal-reflow. To predict no-reflow, a receiver operating characteristic (ROC) analysis determined cut-off values of %LV as 62% and serum PAPP-A as 7.71 ng/mL. The multivariate logistic regression analysis showed that %LV (hazard ratio 4.5, 95% confidence interval 1.6-13.4, P < 0.01) and PAPP-A (hazard ratio 4.32, 95% confidence interval 1.5-12.7, P < 0.01) were independent predictors of combined no-reflow

CONCLUSIONS

%LV analyzed by IB-IVUS and serum PAPP-A levels were closely associated with the coronary no-reflow phenomenon. © 2014 Wiley Periodicals, Inc.

Decision Fusion of Multiple Classifiers for Coronary Plaque Characterization from IVUS Images

Vascular tissue characterization is of great importance concerning the possibility of an Acute Cardiac Syndrome (ACS). Gray-scale intravascular ultrasound (IVUS) is a powerful tomographic modality providing a thorough visualization of coronary arteries. Among the existing methods, virtual histology (VH) is the most popular and clinically available technique for plaque component analysis, it suffers however from a poor longitudinal resolution. In order to surmount this demerit, a new image-based methodology for plaque assessment is suggested here that differentiates tissue components into four classes: calcium, necrotic core, fibrous and fibro-lipid. A rich set of five textural feature families are extracted from IVUS images, computed at different scales. The main contribution of this paper is that tissue classification is accomplished using the principles of multiple classifiers combination approach. At the first stage, an ensemble of base SVM classifiers is constructed from each feature family, separately. The fuzzy outputs of the individual classifiers are then aggregated to provide the final fused results. We investigate four efficient decision fusion schemes of the literature and the SVM fuser. Extensive experimentation is carried out to highlight the merits of the suggested schemes against single SVM classifiers that use reduced feature subsets obtained after feature selection or the entire feature space. The analysis demonstrates that the decision fusion techniques offer improved classification accuracies, compared to single SVM classifiers and existing methods in IVUS imaging. In addition, the method provides accurate assessments of plaque composition in IVUS images.

Expectations and limitations of contemporary intravascular imaging: lessons learned from pathology

Acute coronary syndrome is the leading cause of death worldwide and plaque rupture is the most common underlying mechanism of coronary thrombosis. During the last 2 decades the understanding of atherosclerotic plaque progression advanced dramatically and pathology studies provided fundamental insights of underlying plaque morphology, which paved the way for invasive imaging modalities, which bring a new area of atherosclerotic plaque characterization in vivo. The development of intravascular ultrasound (IVUS) allowed the field to evaluate the principles of vascular anatomy, which is often underestimated by coronary angiography. Furthermore, IVUS image technologies were developed to obtain improved characterization of plaque composition. However, since spatial resolution of IVUS is insufficient to distinguish details of plaque morphology, a broad adoption of this technology in clinical practice was missing. Optical coherence tomography is a light-based imaging modality with higher spatial resolution compared to IVUS, which enables the assessment of vascular anatomy with great detail.

Combination therapy of eicosapentaenoic acid and pitavastatin for coronary plaque regression evaluated by integrated backscatter intravascular ultrasonography (CHERRY study)-rationale and design

BACKGROUND AND PURPOSE

Many clinical trials have shown that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) can significantly reduce coronary artery disease in both primary and secondary prevention. A recent study showed that aggressive lipid-lowering therapy with strong statins could achieve coronary artery plaque regression, as evaluated with gray-scale intravascular ultrasound (IVUS). However, it is unknown whether coronary plaque regression and stabilization are reinforced when eicosapentaenoic acid (EPA) is used with a strong statin.

METHODS AND SUBJECTS

We aim to assess patients with stable angina or acute coronary syndrome who had undergone successful percutaneous coronary intervention (PCI) with integrated backscatter IVUS (IB-IVUS) guidance. They will be randomly allocated to receive pitavastatin (4mg), or pitavastatin (4mg) plus EPA (1800mg), and prospectively followed for 6-8 months.

RESULTS

The primary endpoint will be changes in tissue characteristics in coronary plaques, evaluated by IB-IVUS, and secondary endpoints will include absolute changes in coronary plaque volume, serum lipid levels, and inflammatory markers. The safety profile will also be evaluated.

CONCLUSIONS

The combination therapy of EPA and pitavastatin for regression of coronary plaque evaluated by IB-IVUS (CHERRY) study will be the first multicenter study using IB-IVUS to investigate the effects of combination therapy with pitavastatin and EPA on coronary plaque volume and tissue characteristics.

Impact of tissue characteristics on luminal narrowing of mild angiographic coronary stenosis: assessment of integrated backscatter intravascular ultrasound

Integrated backscatter intravascular ultrasound (IB-IVUS) is a useful method for analyzing coronary plaque tissue. We evaluated whether tissue composition determined using IB-IVUS is associated with the progression of stenosis in coronary angiography. Sixty-three nontarget coronary lesions in 63 patients with stable angina were evaluated using conventional IVUS and IB-IVUS. IB-IVUS images were analyzed at 1-mm intervals for a length of 10 mm. After calculating the relative areas of the tissue components using the IB-IVUS system, fibrous volume (FV) and lipid volume (LV) were calculated through integration of the slices, after which percentages of per-plaque volume (%FV/PV, %LV/PV) and per-vessel volume (%FV/VV, %LV/VV) were calculated. Progression of coronary stenosis was interpreted from the increase in percent diameter stenosis (%DS) from baseline to the follow-up period (6-9 months) using quantitative coronary angiography. %DS was 24.1 ± 12.8 % at baseline and 23.2 ± 13.7 % at follow-up. Using IB-IVUS, LV was 31.7 ± 10.5 mm(3), and %LV/PV and %LV/VV were 45.6 ± 10.3 % and 20.2 ± 6.0 %, respectively. FV, %FV/PV, and %FV/VV were 35.5 ± 12.1 mm(3), 52.1 ± 9.5 %, and 23.4 ± 7.1 %, respectively. The change in %DS was -0.88 ± 7.25 % and correlated closely with %LV/VV (r = 0.27, P = 0.03) on simple regression. Multivariate regression after adjustment for potentially confounding risk factors showed %LV/VV to be correlated independently with changes in %DS (r = 0.42, P = 0.02). Logistic regression analysis after adjusting for confounding coronary risk factors showed LV (odds ratio 1.08; 95 % confidence interval 1.01-1.16; P = 0.03) and %LV/VV (odds ratio 1.13; 95 % confidence interval 1.01-1.28; P = 0.03) to be independent predictors of the progression of angiographic coronary stenosis. Our findings suggest that angiographic luminal narrowing of the coronary artery is likely associated with tissue characteristics. IB-IVUS may provide information about the natural progression of luminal narrowing in coronary stenosis.

Comparison of Coronary Plaque Components between Non-Culprit Lesions in Patients with Acute Coronary Syndrome and Target Lesions in Patients with Stable Angina: Virtual Histology-Intravascular Ultrasound Analysis

Background and Objectives

The differences in plaque characteristics between non-culprit lesions (NCL) in acute coronary syndrome (ACS) patients (ACS-NCL) and target lesions (TL) in stable angina (SA) patients (SA-TL) are not well understood. We used a virtual histology-intravascular ultrasound (VH-IVUS) to compare the plaque components between ACS-NCL and SA-TL.

Subjects and Methods

We compared VH-IVUS findings between 290 ACS-NCL and 276 SA-TL. VH-IVUS classified the color-coded tissue into four major components: green (fibrotic); yellow-green (fibro-fatty); white {dense calcium (DC)}; and red {necrotic core (NC)}. Thin-cap fibroatheroma (TCFA) was defined as a NC ≥10% of the plaque area in at least 3 consecutive frames without overlying fibrous tissue in the presence of ≥40% plaque burden.

Results

Although the plaque burden was significantly smaller (52±13% vs. 54±14%, p=0.044), ACS-NCL had a greater %NC area (17.9±11.6% vs. 14.3±8.7%, p<0.001) and %DC area (9.7±9.8% vs. 8.1±8.0%, p=0.032) compared with SA-TL at the minimum lumen site. By volumetric analysis, ACS-NCL had a greater %NC volume (15.8±9.2% vs. 13.9±7.4%, p=0.006) compared with SA-TL. TCFA was observed more frequently in ACS-NCL compared with SA-TL (27.6% vs. 18.1%, p=0.032). Independent predictors of TCFA by multivariate analysis were ACS {odds ratio (OR): 2.204, 95% CI: 1.321-3.434, p=0.021} and high-sensitivity C-reactive protein (OR: 1.101; 95% CI 1.058-1.204, p=0.035).

Conclusion

Although the plaque burden was significantly smaller, ACL-NCL had more vulnerable plaque components compared with SA-TL, and ACS and high-sensitivity C-reactive protein were the independent predictors of TCFA.

Prognostic impact of concurrence of metabolic syndrome and chronic kidney disease in patients undergoing coronary intervention: Involvement of coronary plaque composition

BACKGROUND AND PURPOSE

Metabolic syndrome (MetS) and chronic kidney disease (CKD) have both been reported as risk factors for cardiovascular events. The aim of this study was to assess the synergistic effect of MetS and CKD on atherosclerotic plaque and cardiovascular outcomes.

METHODS AND SUBJECTS

A total of 545 consecutive patients who underwent percutaneous coronary intervention (PCI) were divided into 4 groups based on the presence or absence of MetS and CKD. MetS was defined using the criteria of the Adult Treatment Panel III of the US National Cholesterol Education Program. CKD was defined as an estimated glomerular filtration rate of <60ml/min/1.73m(2). We analyzed the incidence of major adverse cardiac events (MACE), including cardiovascular death, nonfatal myocardial infarction, target lesion revascularization, and revascularization for new lesions. We also assessed coronary plaque characteristics of 204 patients using integrated backscatter intravascular ultrasound (IB-IVUS).

RESULTS

MACE occurred more frequently in patients with both MetS and CKD (51.4%) than in the other groups, during the follow-up period (log-rank p<0.001). In the IB-IVUS analyses, patients with both MetS and CKD exhibited greater plaque burden (p=0.003) with higher lipid content (p=0.048) compared to the other groups. In Cox analysis, both MetS and CKD proved to be independent predictors of MACE even after adjustment for confounding factors (p=0.018).

CONCLUSIONS

Comorbidity of MetS and CKD is an independent predictor of adverse cardiovascular outcomes in patients undergoing coronary intervention, an effect that may be attributed to coronary plaque instability.

Comparison between integrated backscatter intravascular ultrasound and 64-slice multi-detector row computed tomography for tissue characterization and volumetric assessment of coronary plaques

Background

The purpose of this study was to determine the cut-off values of Hounsfield units (HU) for the discrimination of plaque components and to evaluate the feasibility of measurement of the volume of plaque components using multi-detector row computed tomography (MDCT).

Methods

Coronary lesions (125 lesions in 125 patients) were visualized by both integrated backscatter intravascular ultrasound (IB-IVUS) and 64-slice MDCT at the same site. The IB values were used as a gold standard to determine the cut off values of HU for the discrimination of plaque components.

Results

Plaques were classified as lipid pool (n =50), fibrosis (n =65) or calcification (n =35) by IB-IVUS. The HU of lipid pool, fibrosis and calcification were 18 ± 18 HU (−19 to 58 HU), 95 ± 24 HU (46 to 154 HU) and 378 ± 99 HU (188 to 605 HU), respectively. Using receiver operating characteristic curve analysis, a threshold of 50 HU was the optimal cutoff values to discriminate lipid pool from fibrosis. Lipid volume measured by MDCT was correlated with that measured by IB-IVUS (r =0.66, p <0.001), whereas fibrous volume was not (r =0.21, p =0.059).

Conclusion

Lipid volume measured by MDCT was moderately correlated with that measured by IB-IVUS. MDCT may be useful for volumetric assessment of the lipid volume of coronary plaques, whereas the assessment of fibrosis volume was unstable.

Relationship among coronary plaque compliance, coronary risk factors and tissue characteristics evaluated by integrated backscatter intravascular ultrasound

BACKGROUND

The purpose of the present study was to evaluate the mechanical properties of coronary plaques and plaque behavior, and to elucidate the relationship among tissue characteristics of coronary plaques, mechanical properties and coronary risk factors using integrated backscatter intravascular ultrasound (IB-IVUS).

METHODS

Non-targeted plaques with moderate stenosis (plaque burden at the minimal lumen site: 50-70%) located proximal to the site of the percutaneous coronary intervention target lesions were evaluated by IB-IVUS. Thirty-six plaques (less calcified group: an arc of calcification ≤10°) in 36 patients and 22 plaques (moderately calcified group: 10° < an arc of calcification ≤60°) in 22 patients were evaluated. External elastic membrane volume (EEMV) compliance, lumen volume (LV) compliance, plaque volume (PV) response (difference between PV in systole and diastole), EEM area stiffness index were measured at the minimal lumen site. Relative lipid volume (lipid volume/internal elastic membrane volume) was calculated by IB-IVUS.

RESULTS

In the less calcified group, there was a significant correlation between EEMV compliance and the relative lipid volume (r = 0.456, p = 0.005). There was a significant inverse correlation between EEM area stiffness index and the relative lipid volume (p = 0.032, r = -0.358). The LV compliance and EEM area stiffness index were significantly different in the diabetes mellitus (DM) group than in the non-DM group (1.32 ± 1.49 vs. 2.47 ± 1.79%/10 mmHg, p =0.014 and 28.3 ± 26.0 vs. 15.7 ± 17.2, p =0.020). The EEMV compliance and EEM area stiffness index were significantly different in the hypertension (HTN) group than in the non-HTN group (0.77 ± 0.68 vs. 1.57 ± 0.95%/10 mmHg, p =0.012 and 26.5 ± 24.3 vs. 13.0 ± 16.7, p =0.020). These relationships were not seen in the moderately calcified group.

CONCLUSION

The present study provided new findings that there was a significant correlation between mechanical properties and tissue characteristics of coronary arteries. In addition, our results suggested that the EEMV compliance and the LV compliance were independent and the compliance was significantly impaired in the patients with DM and/or HTN. Assessment of coronary mechanical properties during PCI may provide us with useful information regarding the risk stratification of patients with coronary heart disease.