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

Utility of intravascular ultrasound in intracranial and extracranial neurointerventions: experience at University at Buffalo Neurosurgery-Millard Fillmore Gates Circle Hospital

Intravascular ultrasound (IVUS) generates high-resolution cross-sectional images and sagittal reconstructions of the vessel wall and lumen. As a result, this imaging modality can provide accurate measurements of the degree of vessel stenosis, allow the detection of intraluminal thrombus, and analyze the plaque composition. The IVUS modality is widely used in interventional cardiology, and its use in neurointerventions has gradually increased. With case examples, the authors illustrate the utility of IVUS as an adjunct to conventional angiography for a wide range of intracranial and extracranial neurointerventions.

Relation between anemia and vulnerable coronary plaque components in patients with acute coronary syndrome: virtual histology-intravascular ultrasound analysis

The aim of the present study was to evaluate the plaque components and the predictors of thin-cap fibroatheroma (TCFA) in anemic patients with acute coronary syndrome using virtual histology-intravascular ultrasound (VH-IVUS). Anemia was defined according to criteria of the World Health Organization, (i.e. , hemoglobin levels < 13 g/dL in men and < 12 g/dL in women) and we compared VH-IVUS findings between anemia group (171 patients, 260 lesions) and non-anemia group (569 patients, 881 lesions). Anemia group had greater % necrotic core (NC) volume (21% ± 9% vs 19% ± 9%, P = 0.001) compared with non-anemia group. Hemoglobin level correlated negatively with absolute NC volume (r = -0.235, P < 0.001) and %NC volume (r = -0.209, P < 0.001). Independent predictors of TCFA by multivariate analysis were diabetes mellitus (odds ratio [OR], 2.213; 95% confidence interval [CI], 1.403-3.612, P = 0.006), high-sensitivity C-reactive protein (OR, 1.143; 95% CI, 1.058-1.304, P = 0.012), microalbuminuria (albumin levels of 30 to 300 mg/g of creatinine) (OR, 2.124; 95% CI, 1.041-3.214, P = 0.018), and anemia (OR: 2.112; 95% CI 1.022-3.208, P = 0.028). VH-IVUS analysis demonstrates that anemia at the time of clinical presentation is associated with vulnerable plaque component in patients with acute coronary syndrome.

Positive remodeling is associated with vulnerable coronary plaque components regardless of clinical presentation: virtual histology-intravascular ultrasound analysis

OBJECTIVE

We used virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the relation between coronary artery remodeling pattern and plaque components in 1133 patients.

METHODS

We divided the patients into two groups according to the remodeling pattern as positive remodeling (PR, remodeling index>1.05) (n=192) and intermediate remodeling (IR, remodeling index ≤ 1.05 and ≥ 0.95)/negative remodeling (NR, remodeling index<0.95) (n=941). VH-IVUS analysis classified the color-coded tissue into four major components: green (fibrotic, FT); yellow-green (fibro-fatty); white (dense calcium); and red (necrotic core, NC). Thin-cap fibroatheroma (TCFA) was defined as focal, NC-rich (≥ 10% of the cross-sectional area) plaques being in contact with the lumen in a plaque burden ≥ 40%.

RESULTS

At the minimum lumen site, PR group had greater plaque plus media area (12.8 ± 4.9 vs. 9.9 ± 3.8mm(2), p<0.001) and greater %NC area (21.7 ± 12.3 vs. 18.2 ± 11.6%, p<0.001) and smaller %FT area (57.0 ± 14.5 vs. 59.4 ± 14.6%, p=0.037) compared with IR/NR group. PR group had greater plaque volume (188 ± 150 vs. 135 ± 130 mm(3), p<0.001) and greater %NC volume (19.1 ± 9.6 vs. 16.6 ± 9.2%, p=0.001) and smaller %FT volume (58.3 ± 11.7 vs. 60.6 ± 11.0%, p=0.009) compared with IR/NR group. PR group had more TCFA compared with IR/NR group (21% vs. 13%, p=0.006). Similar findings about plaque components were observed in terms of greater %NC volume and smaller %FT volume in PR group compared with IR/NR group in patients with both acute coronary syndrome and stable angina.

CONCLUSIONS

VH-IVUS analysis demonstrates that PR was associated with more vulnerable plaque components compared with IR/NR regardless of their clinical presentation.

Relationship between microalbuminuria and vulnerable plaque components in patients with acute coronary syndrome and with diabetes mellitus. Virtual histology-intravascular ultrasound

BACKGROUND

The purpose of the present study was to use virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the relationship between microalbuminuria and plaque components in 920 patients.

METHODS AND RESULTS

Patients with albumin levels <30mg/g creatinine were defined as having normoalbuminuria (n=824), and those with albumin levels 30-300mg/g as having microalbuminuria (n=96). The microalbuminuria group contained more patients with acute coronary syndrome (ACS; 72% vs. 61%, P=0.018) and more patients with diabetes (53% vs. 26%, P<0.001). In ACS patients, %necrotic core (NC) volume was significantly greater in the microalbuminuria group compared with the normoalbuminuria group (19±10% vs. 15±9%, P=0.019), but not in patients with stable angina. In ACS patients, thin-cap fibroatheroma (TCFA) was observed more frequently in the microalbuminuria group (36% vs. 18%, P=0.008), and microalbuminuria was the independent predictor of TCFA (odds ratio [OR], 1.106; 95% confidence interval [CI]: 1.025-1.144, P=0.018). In diabetic patients, %NC volume was significantly greater in the microalbuminuria group compared with the normoalbuminuria group (20±9% vs. 16±10%, P=0.017), but not in non-diabetic patients. In diabetic patients, TCFA was observed more frequently in the microalbuminuria group (38% vs. 17%, P=0.002) and microalbuminuria was the independent predictor of TCFA (OR, 1.120; 95%CI: 1.038-1.204, P=0.012).

CONCLUSIONS

Microalbuminuria was associated with a higher number of vulnerable plaque components in ACS and diabetic patients. More intensive medical therapy is needed to stabilize the vulnerable plaque if microalbuminuria is observed in diabetic ACS patients.

Impact of omega-3 polyunsaturated fatty acids on coronary plaque instability: an integrated backscatter intravascular ultrasound study

OBJECTIVE

To assess the impact of omega-3 polyunsaturated fatty acids (ω3 PUFAs) on coronary plaque instability.

METHODS

Serum content of eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA) was measured in 336 of 368 consecutive patients suspected of having coronary artery disease who underwent coronary angiography. Conventional and integrated backscatter intravascular ultrasound (IB-IVUS) parameters were analyzed in 116 patients with 128 coronary plaques, using a 43-MHz (motorized pullback 0.5mm/s) intravascular catheter (View It, Terumo Co., Japan). Lipid-rich plaques were classified into two categories according to their components.

RESULTS

Patients with acute coronary syndrome had significantly lower levels of ω3 PUFAs (especially of EPA and DPA) than those without it. IB-IVUS analyses showed that ω3 PUFAs correlated inversely with % lipid volume and positively with % fibrous volume. Patients with low EPA levels, low DPA levels, and low DHA levels had a significantly higher % lipid volume (p=0.048, p=0.008, and p=0.036, respectively) and a significantly lower % fibrous volume (p=0.035, p=0.008, and p=0.034, respectively) than those with high levels of these fatty acids. Even after adjustment for confounders, the presence of both low EPA and low DPA levels proved to be an independent predictor for lipid-rich plaques in any of the two categories.

CONCLUSIONS

A lower serum content of ω3 PUFAs (especially of EPA and DPA) was significantly associated with lipid-rich plaques, suggesting the contribution to the incidence of acute coronary syndrome.

Intravascular imaging of vulnerable coronary plaque: current and future concepts

Advances in coronary imaging are needed to enable the early detection of plaque segments considered to be 'vulnerable' for causing clinical events. Pathological studies have contributed to our current understanding of these vulnerable or unstable segments of plaque. Intravascular ultrasonography (IVUS) has provided insights into the morphology of atherosclerosis, the mediators of plaque progression and the factors associated with acute coronary syndrome (ACS). In addition, the demonstration of pancoronary arterial instability has highlighted that ACS involves a multifocal disease process. Various second-generation intravascular imaging technologies-employing advanced processing of ultrasound radiofrequency backscatter signals, light-based imaging, spectroscopic imaging and molecular targeting-possess inherent advantages for the identification of meaningful surrogates of plaque instability. The fusion of these imaging technologies within a single imaging catheter is likely to allow for greater synergism in image quality and early disease detection. However, natural-history studies to validate the use of these novel imaging tools for enhanced risk prediction are needed before these strategies can be incorporated into mainstream clinical practice.

Current techniques for MR imaging of atherosclerosis

Vessel wall imaging of large vessels has the potential to identify culprit atherosclerotic plaques that lead to cardiovascular events. Comprehensive assessment of atherosclerotic plaque size, composition, and biological activity is possible with magnetic resonance imaging (MRI). Magnetic resonance imaging of the atherosclerotic plaque has demonstrated high accuracy and measurement reproducibility for plaque size. The accuracy of in vivo multicontrast MRI for identification of plaque composition has been validated against histological findings. Magnetic resonance imaging markers of plaque biological activity such as neovasculature and inflammation have been demonstrated. In contrast to other plaque imaging modalities, MRI can be used to study multiple vascular beds noninvasively over time. In this review, we compare the status of in vivo plaque imaging by MRI to competing imaging modalities. Recent MR technological improvements allow fast, accurate, and reproducible plaque imaging. An overview of current MRI techniques required for carotid plaque imaging including hardware, specialized pulse sequences, and processing algorithms are presented. In addition, the application of these techniques to coronary, aortic, and peripheral vascular beds is reviewed.

Lipid-rich plaques predict non-target-lesion ischemic events in patients undergoing percutaneous coronary intervention

BACKGROUND

Despite growing interest in non-target lesion events in patients undergoing percutaneous coronary intervention (PCI), there has been little discussion of predictors.

METHODS AND RESULTS

A total of 155 consecutive patients who underwent PCI were enrolled. Conventional and integrated backscatter intravascular ultrasound (IB-IVUS) parameters were measured in non-target lesions utilizing a 40-MHz intravascular catheter. Lipid-rich plaques (LRP) were defined as lesions with an increased lipid volume (> median) and greater lipid content. Non-target ischemic events were defined as death, non-fatal myocardial infarction, any repeat revascularization and rehospitalization for angina involving the non-target vessel or the target vessel outside the index lesion. During the follow-up period (median: 1,265 days), non-target events were observed in 16 patients (11%). Using the Cox proportional hazard model, LRP (odds ratio [OR], 6.06; 95% confidence interval [CI]: 1.81-20.4, P = 0.0035), elevated serum C-reactive protein (CRP) levels (OR, 6.83; 95%CI: 2.19-21.3, P = 0.0009) and acute coronary syndrome present at baseline (OR, 4.08; 95%CI: 1.21-13.8, P = 0.024) were significantly and independently associated with non-target events. Synergistic effects of LRP and elevated serum CRP levels for prediction of non-target events (OR, 14.8; 95%CI: 4.57-48.0, P < 0.0001) were found even after adjusting for confounders.

CONCLUSIONS

LRP measured using IB-IVUS proved to be an independent morphologic predictor of non-target ischemic events after PCI, particularly enhancing the risk in patients with elevated serum CRP levels.

Tissue characterization of coronary plaques and assessment of thickness of fibrous cap using integrated backscatter intravascular ultrasound. Comparison with histology and optical coherence tomography

BACKGROUND

The purpose of this study was to develop a new online integrated backscatter intravascular ultrasound (IB-IVUS) system and to validate its ability to measure fibrous cap thickness by comparing IB-IVUS images with those from optical coherence tomography (OCT).

METHODS AND RESULTS

Images were acquired from 125 segments of 26 coronary arteries obtained at autopsy from 11 cadavers. In the training study (n=30), 242 regions-of-interest on color-coded maps were compared with histology. In the validation study, 95 cross-sections were diagnosed by IB-IVUS and histology. In 24 patients with stable angina, 28 arterial cross-sections were imaged by IB-IVUS and OCT in vivo. In the training study, cutoff values of 39 decibels (dB) and 17dB were the optimal predictors of lipid pool/fibrosis and fibrosis/calcification, respectively, with 38-MHz mode; 42dB and 20dB, respectively, with 43-MHz mode. In the validation study, IB classified the fibrous, lipid-rich and fibrocalcific components with an accuracy of 92%, 91% and 95%, respectively. Agreement between the histological and IB-IVUS diagnoses was excellent (Cohen's κ=0.83). There was a correlation between the fibrous cap thickness measured by IB-IVUS and OCT (r=0.74, P<0.001).

CONCLUSIONS

The IB-IVUS system with improved resolution provides high diagnostic accuracy for the analysis of the tissue characteristics of coronary plaques, and enables estimation of the thickness of the fibrous cap in the clinical setting.

A new approach for improving coronary plaque component analysis based on intravascular ultrasound images

Virtual histology intravascular ultrasound (VH-IVUS) is a clinically available technique for atherosclerosis plaque characterization. It, however, suffers from a poor longitudinal resolution due to electrocardiogram (ECG)-gated acquisition. This article presents an effective algorithm for IVUS image-based histology to overcome this limitation. After plaque area extraction within an input IVUS image, a textural analysis procedure consisting of feature extraction and classification steps is proposed. The pixels of the extracted plaque area excluding the shadow region were classified into one of the three plaque components of fibro-fatty (FF), calcification (CA) or necrotic core (NC) tissues. The average classification accuracy for pixel and region based validations is 75% and 87% respectively. Sensitivities (specificities) were 79% (85%) for CA, 81% (90%) for FF and 52% (82%) for NC. The kappa (kappa) = 0.61 and p value = 0.02 indicate good agreement of the proposed method with VH images. Finally, the enhancement in the longitudinal resolution was evaluated by reconstructing the IVUS images between the two sequential IVUS-VH images.

Relation between plaque components and plaque prolapse after drug-eluting stent implantation--virtual histology-intravascular ultrasound

BACKGROUND

It is not well known which plaque components are associated with the development of plaque prolapse (PP) and what are the major components in prolapsed plaque. The relationship between pre-stenting plaque components and post-stenting PP was assessed and the plaque components of prolapsed plaque were evaluated in patients who underwent drug-eluting stent (DES) implantation using virtual histology-intravascular ultrasound (VH-IVUS).

METHODS AND RESULTS

The study group consisted of 132 patients who underwent DES implantation and pre- and post-stenting VH-IVUS. Of these patients, 68 patients had 76 PP lesions and 64 patients had 76 non-PP lesions. Intra-stent PP volume was 3.6+/-1.5 mm(3). Plaque volume was significantly greater and absolute fibrotic (FT) and necrotic core (NC) volumes were significantly greater in PP lesions compared with non-PP lesions. On multivariate analysis, absolute NC (odds ratios [OR]=1.14, P<0.001) and FT volume (OR =1.09, P<0.001) were independently associated with the development of PP. In intra-stent prolapsed plaque the FT component was greatest, but the NC component was also large, and %NC volume correlated positively with Deltacreatine kinase-MB (r=0.489, P<0.001) and Deltatroponin-I (r=0.679, P<0.001), and %FT volume correlated negatively with DeltaCK-MB (r=-0.539, P<0.001) and Deltatroponin-I.

CONCLUSIONS

NC and FT components were associated with development of PP; and NC and FT components in prolapsed plaque were associated with cardiac enzyme elevation after DES implantation.

Relation between functional stenosis and tissue characterization of intermediate coronary plaques in patients with stable coronary heart disease

BACKGROUND

Tissue characteristics of coronary plaques can be evaluated using integrated backscatter intravascular ultrasound (IB-IVUS), while fractional flow reserve (FFRmyo) is an index of functional coronary stenosis. We assessed the relation between functional stenosis and the characteristics of plaque tissue using FFRmyo and IB-IVUS.

METHODS AND RESULTS

A total of 17 lesions with 75%-stenosis assessed visually by coronary angiography from 17 stable angina patients (64.2+/-9.1 years old, 11 males) were studied. IB-IVUS was evaluated in the most stenotic cross-sectional area. Using commercially available software, coronary plaques were assessed for calcification (CA), fibrosis (F), and lipid pool (LP). Lesions were localized in the left anterior descending artery in 11 patients, the left circumflex in 3, and the right coronary artery in 3. On quantitative coronary angiography, the percent diameter stenosis (%DS) was 60.5+/-7.3%. Plaque burden was 71.4+/-9.1%, FFRmyo was 0.74+/-0.13. The tissue component of the plaques was: CA(%), 3.0+/-2.4%; F(%), 60.5+/-9.6%; LP(%), 37.2+/-11.0%. Significant correlation was not observed between %DS or plaque burden and FFRmyo, structural stenosis and plaque characterization, nor between CA(%) and FFRmyo. There was a positive correlation between F(%) and FFRmyo (r=0.62, p<0.01) and a negative correlation between LP(%) and FFRmyo (r=-0.52, p<0.05).

CONCLUSION

Our findings indicate that the tissue characteristics of coronary plaques in intermediate lesion affect functional stenosis.

Intravascular ultrasound: principles and cerebrovascular applications

Intravascular sonography is a valuable tool for the morphologic assessment of coronary atherosclerosis and the effect of pharmacologic and nonpharmacologic interventions on the progression or stabilization of atherosclerosis. An analysis of the different modes, applications, and limitations is provided on the basis of review of existing data from multiple clinical case studies, trials, and mechanistic studies. Intravascular sonography has been used to assess the outcomes of different percutaneous interventions, including angioplasty and stent implantation, and to provide detailed characterization of atherosclerotic lesions, aneurysms, and dissections within the cerebrovascular circulation. Evolution of intravascular sonographic technology has led to the development of more sophisticated diagnostic tools such as color-flow, virtual histology, and integrated backscatter intravascular sonography. The technologic advancement in intravascular sonography has the potential of providing more accurate information prior, during, and after a medical or endovascular intervention. Continued assessment of this diagnostic technique in both the intracranial and extracranial circulation will lead to increased use in clinical practice with the intent to improve outcomes.

Intravascular Ultrasound Analysis of Correlation between Plaque-Morphology and Risk Factors in Peripheral Arterial Disease

OBJECTIVE

To analyze relationships between plaque-morphology classified by intravascular ultrasound (IVUS) and risk factors in patients with peripheral arterial disease (PAD).

METHODS

We performed IVUS in 203 patients with PAD. Multiple regression and logistic analysis were used to assess relationships between plaque-morphology (degree of calcification, presence of a lipid core, intimal flap and thrombus) and risk factors including diabetes mellitus, hypertension, dyslipidemia, estimated glomerular filtration rate (eGFR), HbA1c and the homeostasis model assessment-insulin resistance ratio (HOMA-IR).

RESULTS

IVUS data led to 22% of lesions being classified as soft, 18% as fibrous, 32% as calcified, and 28% as mixed. Calcification was present in the superficial and deep layers in 65% and 35% of cases, respectively, and a lipid core, intimal flap and thrombus were found in 31%, 5.4% and 3.0%, respectively. The calcified angle correlated with HbA1c and eGFR (p < 0.05). Associations were found between deep calcification and HOMA-IR (odds ratio: 4.4, p < 0.05) and a lipid core and hypercholesterolemia (odds ratio: 3.2, p < 0.05). The odds ratio for intimal flap was 15.6 times with hypercholesterolemia (p < 0.05) and 16.9 times with a high HOMA-IR (p < 0.01).

CONCLUSION

Plaque calcification and morphology are associated with chronic kidney disease, insulin resistance and dyslipidemia in PAD patients.

Relationship between thin cap fibroatheroma identified by virtual histology and angioscopic yellow plaque in quantitative analysis with colorimetry

BACKGROUND

Thin cap fibroatheroma (TCFA) is considered to be a vulnerable plaque. Virtual Histology-intravascular ultrasound (VH-IVUS) can precisely identify TCFA in vivo. Intense yellow plaque on angioscopy determined by quantitative colorimetry with L a b color space corresponds with histological TCFA; in particular, a plaque of color b value >23 indicates an atheroma with a fibrous cap thickness <100 mum. In the present study, the relationship between VH-TCFA and angioscopic plaque color determined by colorimetry was investigated.

METHODS AND RESULTS

Fifty-seven culprit plaques in 57 patients were evaluated by VH-IVUS and angioscopy. VH-TCFA was defined as a plaque with a necrotic core >10% of plaque area without overlying fibrous tissue, and angioscopic TCFA was a plaque with b value >23. The frequency of angioscopic TCFA was higher in the VH-TCFA group than in the VH-non-TCFA group (74% vs 23%, P=0.0002). Moreover, yellow color intensity (b value) significantly correlated with plaque classification on VH-IVUS. When TCFA detected with angioscopy was used as the gold standard, the sensitivity, specificity, and accuracy for TCFA with VH-IVUS was 68%, 81%, and 75%, respectively.

CONCLUSIONS

VH-TCFA strongly correlated with angioscopic TCFA determined by a quantitative analysis with colorimetry.