Autoradiographical assessment of inflammation-targeting radioligands for atherosclerosis imaging: potential for plaque phenotype identification.

PURPOSE: Many radioligands have been developed for the visualization of atherosclerosis by targeting inflammation. However, interpretation of in vivo signals is often limited to plaque identification. We evaluated binding of some promising radioligands in an in vitro approach in atherosclerotic plaques with different phenotypes. METHODS: Tissue sections of carotid endarterectomy tissue were characterized as early plaque, fibro-calcific plaque, or phenotypically vulnerable plaque. In vitro binding assays for the radioligands [111In]In-DOTATATE; [111In]In-DOTA-JR11; [67Ga]Ga-Pentixafor; [111In]In-DANBIRT; and [111In]In-EC0800 were conducted, the expression of the radioligand targets was assessed via immunohistochemistry. Radioligand binding and expression of radioligand targets was investigated and compared. RESULTS: In sections characterized as vulnerable plaque, binding was highest for [111In]In-EC0800; followed by [111In]In-DANBIRT; [67Ga]Ga-Pentixafor; [111In]In-DOTA-JR11; and [111In]In-DOTATATE (0.064 ± 0.036; 0.052 ± 0.029; 0.011 ± 0.003; 0.0066 ± 0.0021; 0.00064 ± 0.00014 %Added activity/mm2, respectively). Binding of [111In]In-DANBIRT and [111In]In-EC0800 was highest across plaque phenotypes, binding of [111In]In-DOTA-JR11 and [67Ga]Ga-Pentixafor differed most between plaque phenotypes. Binding of [111In]In-DOTATATE was the lowest across plaque phenotypes. The areas positive for cells expressing the radioligand's target differed between plaque phenotypes for all targets, with lowest percentage area of expression in early plaque sections and highest in phenotypically vulnerable plaque sections. CONCLUSIONS: Radioligands targeting inflammatory cell markers showed different levels of binding in atherosclerotic plaques and among plaque phenotypes. Different radioligands might be used for plaque detection and discerning early from vulnerable plaque. [111In]In-EC0800 and [111In]In-DANBIRT appear most suitable for plaque detection, while [67Ga]Ga-Pentixafor and [111In]In-DOTA-JR11 might be best suited for differentiation between plaque phenotypes.

Automated Quantitative Assessment of Coronary Calcification Using Intravascular Ultrasound.

Coronary calcification represents a challenge in the treatment of coronary artery disease by stent placement. It negatively affects stent expansion and has been related to future adverse cardiac events. Intravascular ultrasound (IVUS) is known for its high sensitivity in detecting coronary calcification. At present, automated quantification of calcium as detected by IVUS is not available. For this reason, we developed and validated an optimized framework for accurate automated detection and quantification of calcified plaque in coronary atherosclerosis as seen by IVUS. Calcified lesions were detected by training a supported vector classifier per IVUS A-line on manually annotated IVUS images, followed by post-processing using regional information. We applied our framework to 35 IVUS pullbacks from each of the three commonly used IVUS systems. Cross-validation accuracy for each system was >0.9, and the testing accuracy was 0.87, 0.89 and 0.89 for the three systems. Using the detection result, we propose an IVUS calcium score, based on the fraction of calcium-positive A-lines in a pullback segment, to quantify the extent of calcified plaque. The high accuracy of the proposed classifier suggests that it may provide a robust and accurate tool to assess the presence and amount of coronary calcification and, thus, may play a role in image-guided coronary interventions.

Real-time photoacoustic assessment of radiofrequency ablation lesion formation in the left atrium.

In interventional electrophysiology, catheter-based radiofrequency (RF) ablation procedures restore cardiac heart rhythm by interrupting aberrant conduction paths. Real-time feedback on lesion formation and post-treatment lesion assessment could overcome procedural challenges related to ablation of underlying structures and lesion gaps. This study aims to evaluate real-time visualization of lesion progression and continuity during intra-atrial ablation with photoacoustic (PA) imaging, using clinically deployable technology. A PA-enabled RF ablation catheter was used to ablate and illuminate porcine left atrium, both excised and intact in a passive beating heart ex-vivo, for photoacoustic signal generation. PA signals were received with an intracardiac echography catheter. Using the ratio of PA images acquired with excitation wavelengths of 790 nm and 930 nm, ablation lesions were successfully imaged through circulating saline and/or blood, and lesion gaps were identified in real-time. PA-based assessment of RF-ablation lesions was successful in a realistic preclinical model of atrial intervention.

Intima heterogeneity in stress assessment of atherosclerotic plaques.

Atherosclerotic plaque rupture is recognized as the primary cause of cardiac and cerebral ischaemic events. High structural plaque stresses have been shown to strongly correlate with plaque rupture. Plaque stresses can be computed with finite-element (FE) models. Current FE models employ homogeneous material properties for the heterogeneous atherosclerotic intima. This study aimed to evaluate the influence of intima heterogeneity on plaque stress computations. Two-dimensional FE models with homogeneous and heterogeneous intima were constructed from histological images of atherosclerotic human coronaries (n = 12). For homogeneous models, a single stiffness value was employed for the entire intima. For heterogeneous models, the intima was subdivided into four clusters based on the histological information and different stiffness values were assigned to the clusters. To cover the reported local intima stiffness range, 100 cluster stiffness combinations were simulated. Peak cap stresses (PCSs) from the homogeneous and heterogeneous models were analysed and compared. By using a global variance-based sensitivity analysis, the influence of the cluster stiffnesses on the PCS variation in the heterogeneous intima models was determined. Per plaque, the median PCS values of the heterogeneous models ranged from 27 to 160 kPa, and the PCS range varied between 43 and 218 kPa. On average, the homogeneous model PCS values differed from the median PCS values of heterogeneous models by 14%. A positive correlation (R2 = 0.72) was found between the homogeneous model PCS and the PCS range of the heterogeneous models. Sensitivity analysis showed that the highest main sensitivity index per plaque ranged from 0.26 to 0.83, and the average was 0.47. Intima heterogeneity resulted in substantial changes in PCS, warranting stress analyses with heterogeneous intima properties for plaque-specific, high accuracy stress assessment. Yet, computations with homogeneous intima assumption are still valuable to perform sensitivity analyses or parametric studies for testing the effect of plaque geometry on PCS. Moreover, homogeneous intima models can help identify low PCS, stable type plaques with thick caps. Yet, for thin cap plaques, accurate stiffness measurements of the clusters in the cap and stress analysis with heterogeneous cap properties are required to characterize the plaque stability.

Carotid Plaque Morphological Classification Compared With Biomechanical Cap Stress: Implications for a Magnetic Resonance Imaging-Based Assessment.

BACKGROUND AND PURPOSE: Two approaches to target plaque vulnerability-a histopathologic classification scheme and a biomechanical analysis-were compared and the implications for noninvasive risk stratification of carotid plaques using magnetic resonance imaging were assessed. METHODS: Seventy-five histological plaque cross sections were obtained from carotid endarterectomy specimens from 34 patients (>70% stenosis) and subjected to both a Virmani histopathologic classification (thin fibrous cap atheroma with <0.2-mm cap thickness, presumed vulnerable) and a peak cap stress computation (<140 kPa: presumed stable; >300 kPa: presumed vulnerable). To demonstrate the implications for noninvasive plaque assessment, numeric simulations of a typical carotid magnetic resonance imaging protocol were performed (0.62×0.62 mm(2) in-plane acquired voxel size) and used to obtain the magnetic resonance imaging-based peak cap stress. RESULTS: Peak cap stress was generally associated with histological classification. However, only 16 of 25 plaque cross sections could be labeled as high-risk (peak cap stress>300 kPa and classified as a thin fibrous cap atheroma). Twenty-eight of 50 plaque cross sections could be labeled as low-risk (a peak cap stress<140 kPa and not a thin fibrous cap atheroma), leading to a κ=0.39. 31 plaques (41%) had a disagreement between both classifications. Because of the limited magnetic resonance imaging voxel size with regard to cap thickness, a noninvasive identification of only a group of low-risk, thick-cap plaques was reliable. CONCLUSIONS: Instead of trying to target only vulnerable plaques, a more reliable noninvasive identification of a select group of stable plaques with a thick cap and low stress might be a more fruitful approach to start reducing surgical interventions on carotid plaques.

Assessment of carotid atherosclerosis, intraplaque neovascularization, and plaque ulceration using quantitative contrast-enhanced ultrasound in asymptomatic patients with diabetes mellitus.

AIMS: Patients with diabetes mellitus (DM) are at severely increased risk of developing atherosclerosis. Intraplaque neovascularization (IPN) and plaque ulceration are markers of the vulnerable plaque, which is at an increased risk of rupture and may lead to cardiovascular events. The aim of this study was to assess the prevalence of subclinical carotid atherosclerosis, intraplaque neovascularization (IPN), and plaque ulceration in asymptomatic patients with DM. METHODS AND RESULTS: A total of 51 asymptomatic patients with DM underwent standard carotid ultrasound in conjunction with contrast-enhanced ultrasound (CEUS) to assess the prevalence of subclinical atherosclerosis, IPN, and plaque ulceration. Subclinical atherosclerosis was defined as the presence of atherosclerotic plaque, according to the Mannheim consensus. Semi-automated quantification software was used to assess IPN in suitable plaques. Plaque ulceration was defined as a disruption of the plaque-lumen border of ≥ 1 × 1 mm. A total of 408 carotid segments in 102 carotid arteries were investigated. Forty-six (90%) patients had subclinical atherosclerotic plaques, with a median plaque thickness of 2.4 mm (inter-quartile range 1.9-3.0). CEUS revealed IPN in 88% of the patients. In 10 carotid segments (8%), the plaque had an ulcerated surface. The presence of IPN could not be predicted by the presence of clinical characteristics including complications of DM (P > 0.05). CONCLUSION: Patients with DM have a high prevalence (90%) of subclinical carotid atherosclerosis. Severe IPN and plaque ulceration, which are markers of the vulnerable plaque type, were detected in, respectively, 13 and 9% of these patients.

Utility of contrast-enhanced ultrasound for the assessment of the carotid artery wall in patients with Takayasu or giant cell arteritis.

AIMS: Carotid contrast-enhanced ultrasound (CEUS) was recently proposed for the evaluation of large-vessel vasculitides (LVV), particularly to assess vascularization within the vessel wall. The aim of this pilot study was to evaluate the potential of carotid colour Doppler ultrasound (CDUS) and CEUS in patients with LVV. METHODS AND RESULTS: This prospective study included seven patients (mean age 48 ± 14 years, all females) with established LVV (Takayasu arteritis or giant cell arteritis). All patients underwent CDUS and CEUS (14 carotid arteries). Intima-media thickness, lumen diameter, Doppler velocities, vessel wall thickening, and lesion thickness were assessed. CEUS was used to improve visualization of the lumen-to-vessel wall border, and to visualize carotid wall vascularization. Four (57%) patients [7 (50%) carotid arteries] exhibited lesions, and the average lesion thickness was 2.0 ± 0.5 mm. According to the Doppler peak systolic velocity, 5 (35%) carotid arteries had a <50% stenosis, 1 (7%) had a 50-70% stenosis, and 1 (7%) had a ≥70% stenosis. The contrast agent improved the image quality and the definition of the lumen-to-vascular wall border. Carotid wall vascularization was observed in 5 (71%) patients [9 (64%) carotid arteries]. Five (36%) carotid arteries had mild-to-moderate vascularization, and 4 (29%) had severe wall vascularization. CONCLUSION: Carotid CDUS allows the assessment of anatomical features of LVV, including vessel wall thickening and degree of stenosis. Carotid CEUS improves the visualization of the lumen border, and allows dynamic assessment of carotid wall vascularization, which is a potential marker of disease activity in patients with LVV.

Assessment of subclinical atherosclerosis and intraplaque neovascularization using quantitative contrast-enhanced ultrasound in patients with familial hypercholesterolemia.

OBJECTIVE: Patients with heterozygous familial hypercholesterolemia (FH) are at severely increased risk of developing atherosclerosis at relatively young age. The aim of this study was to assess the prevalence of subclinical atherosclerosis and intraplaque neovascularization (IPN) in patients with FH, using contrast-enhanced ultrasound (CEUS) of the carotid arteries. METHODS: The study population consisted of 69 consecutive asymptomatic patients with FH (48% women, mean age 55 ± 8 years). All patients underwent carotid ultrasound to evaluate the presence and severity of carotid atherosclerosis, and CEUS to assess IPN. IPN was assessed in near wall plaques using a semi-quantitative grading scale and semi-automated quantification software. RESULTS: Carotid plaque was present in 62 patients (90%). A total of 49 patients had plaques that were eligible for the assessment of IPN: 7 patients (14%) had no IPN, 39 (80%) had mild to moderate IPN and 3 (6%) had severe IPN. Semi-automated quantification software showed no statistical significant difference in the amount of IPN between patients > 50 years and patients ≤ 50 years and between patients with a defective low-density lipoprotein receptor (LDLR) mutation and patients with a negative LDLR mutation. Plaques with irregular or ulcerated surface had significantly more IPN than plaques with a smooth surface (p < 0.05). CONCLUSION: Carotid ultrasound demonstrated atherosclerotic plaque in 90% of asymptomatic patients with FH without known atherosclerosis. IPN assessed with CEUS, was present in 86% of these patients. Irregular and ulcerated plaques exhibited significantly more IPN than plaques with a smooth surface.

Carotid intima-media thickness for cardiovascular risk assessment: systematic review and meta-analysis.

OBJECTIVE: B-mode ultrasound measurement of the carotid intima-media thickness (CIMT) is a widely used marker for atherosclerosis and is associated with future cardiovascular events. This article provides a review and meta-analysis of the published evidence on the association of CIMT with future cardiovascular events and its additional value to traditional cardiovascular risk prediction models. METHODS: A systematic review and meta-analysis of the evidence on the association of CIMT with future cardiovascular events and the additional value of CIMT to traditional cardiovascular risk prediction models was conducted. The association of CIMT with future cardiovascular events and the additional value of CIMT were calculated using random effects analysis. RESULTS: The literature search yielded 1196 articles of which 15 articles provided sufficient data for the meta-analysis. A 1 SD increase in CIMT was predictive for myocardial infarction (HR 1.26, 95% CI 1.20-1.31) and for stroke (HR 1.31, 95% CI 1.26-1.36). A 0.1 mm increase in CIMT was predictive for myocardial infarction (HR 1.15, 95% CI 1.12-1.18) and for stroke (HR 1.17, 95% CI 1.15-1.21). The overall performance of risk prediction models did not significantly increase after addition of CIMT data. The areas under the curve increased from 0.726 to 0.729 (p = 0.8). CONCLUSIONS: CIMT as measured by B-mode ultrasound is associated with future cardiovascular events. However, the addition of CIMT to traditional cardiovascular risk prediction models does not lead to a statistical significantly increase in performance of those models.

Assessment of subclinical atherosclerosis using contrast-enhanced ultrasound.

AIMS: The sensitivity of standard carotid ultrasound and colour Doppler for the detection of subclinical atherosclerotic plaques is suboptimal. The aim of this study is to assess whether contrast-enhanced ultrasound (CEUS) added to standard carotid ultrasound improves the detection of subclinical atherosclerosis. METHODS AND RESULTS: Carotid intima-media thickness (CIMT) measurement, standard carotid ultrasound including colour Doppler imaging, and CEUS were performed in 100 asymptomatic patients with one or more risk factors for atherosclerosis. CEUS was performed using intravenous administration of SonoVue™ contrast agent (Bracco S.p.A., Milan, Italy). CIMT, standard ultrasound, colour Doppler, and CEUS were reviewed by two independent observers. Standard ultrasound, colour Doppler, and CEUS were scored for the presence of atherosclerotic plaques. Subclinical atherosclerosis was diagnosed if patients had a CIMT above their age-corrected threshold value or if atherosclerotic plaques were present on standard carotid ultrasound clips or CEUS clips. McNemar's test was performed to compare between groups. Twenty-one patients (21%) had a thickened CIMT value and were considered to have subclinical atherosclerosis. Standard carotid ultrasound including colour Doppler demonstrated atherosclerotic plaques in 77 patients (77%). The addition of CEUS to the standard ultrasound protocol demonstrated atherosclerotic plaques in 88 patients (88%). The incorporation of CEUS into the standard carotid ultrasound protocol resulted in a significantly improved detection of patients with subclinical atherosclerosis (P < 0.01). CONCLUSION: CEUS has an incremental value for the detection of subclinical atherosclerosis in the carotid arteries. Atherosclerotic plaques which were only detected with CEUS and not with standard carotid ultrasound and colour Doppler imaging were predominantly hypoechoic.

Multilayer transducer for acoustic bladder volume assessment on the basis of nonlinear wave propagation.

Catheterization remains the gold standard for bladder volume assessment, but it is invasive, uncomfortable to the patient and introduces the risk of infections and traumas. Acoustic measurement of the bladder volume reduces the need for a urinary catheter. Recently, a new method to non-invasively measure the volume of liquid filled cavities in vivo on the basis of nonlinear wave propagation has been introduced. To implement this method, two different multilayer ultrasound transducers were developed. Both transducers consisted of a first piezo-electric layer of lead zirconate titanate (PZT) to transmit waves at a fundamental frequency (2 MHz) and a second piezo-electric layer (copolymer) to receive a wide range of frequencies including harmonics. To suppress the inherent susceptibility of the film to electromagnetic waves, one of the two transducers, i.e., an "inverted" multilayer transducer, had the copolymer layer located inside the structure. The other multilayer transducer, i.e., a "normal" multilayer transducer, had the copolymer film located on the outside. Both transducers were compared with a commercially available broadband piezo-composite transducer, with respect to their transmit and receive transfer functions, their pulse-echo responses and their electromagnetic susceptibility (EMS) in reception. It was concluded that to measure up to at least the third harmonic frequency component with good sensitivity in combination with high transmit sensitivity at the fundamental frequency, a multilayer structure is preferred. To optimize for the EMS in reception, and hence also the signal-to-noise ratio, an inverted geometry, as proposed in this paper, was proven to be most effective.

Design of a multilayer transducer for acoustic bladder volume assessment.

Catheterization remains the "gold standard" for bladder volume assessment, but it is invasive and introduces the risk of infections and traumas. Therefore, noninvasive bladder volume measurement methods have gained interest. In a preceding study a new technique to measure the bladder volume on the basis of nonlinear ultrasound wave propagation was validated. This paper describes a first prototype of a dedicated multilayer transducer to implement this approach. It is composed of a PZT transducer for transmission and a PVDF layer for reception. Acoustical measurements in a water tank and phantom measurements showed that there is a relation between bladder volume and the harmonic contents of the echo obtained from a region of interest behind the bladder. Simulations with an equivalent transducer model on the basis of KLM-circuit modeling closely matched with the results from the acoustical measurements. The results demonstrated the feasibility of the multilayer transducer design for bladder volume assessment on the basis of nonlinear wave propagation.

Assessment of vulnerable plaque composition by matching the deformation of a parametric plaque model to measured plaque deformation.

Intravascular ultrasound (IVUS) elastography visualizes local radial strain of arteries in so-called elastograms to detect rupture-prone plaques. However, due to the unknown arterial stress distribution these elastograms cannot be directly interpreted as a morphology and material composition image. To overcome this limitation we have developed a method that reconstructs a Young's modulus image from an elastogram. This method is especially suited for thin-cap fibroatheromas (TCFAs), i.e., plaques with a media region containing a lipid pool covered by a cap. Reconstruction is done by a minimization algorithm that matches the strain image output, calculated with a parametric finite element model (PFEM) representation of a TCFA, to an elastogram by iteratively updating the PFEM geometry and material parameters. These geometry parameters delineate the TCFA media, lipid pool and cap regions by circles. The material parameter for each region is a Young's modulus, EM, EL, and EC, respectively. The method was successfully tested on computer-simulated TCFAs (n = 2), one defined by circles, the other by tracing TCFA histology, and additionally on a physical phantom (n = 1) having a stiff wall (measured EM = 16.8 kPa) with an eccentric soft region (measured EL = 4.2 kPa). Finally, it was applied on human coronary plaques in vitro (n = 1) and in vivo (n = 1). The corresponding simulated and measured elastograms of these plaques showed radial strain values from 0% up to 2% at a pressure differential of 20, 20, 1, 20, and 1 mmHg respectively. The used/reconstructed Young's moduli [kPa] were for the circular plaque EL = 50/66, EM = 1500/1484, EC = 2000/2047, for the traced plaque EL = 25/1, EM = 1000/1148, EC = 1500/1491, for the phantom EL = 4.2/4 kPa, EM = 16.8/16, for the in vitro plaque EL = n.a./29, EM = n.a./647, EC = n.a./1784 kPa and for the in vivo plaque EL = n.a./2, EM = n.a./188, Ec = n.a./188 kPa.

Incidence of high-strain patterns in human coronary arteries: assessment with three-dimensional intravascular palpography and correlation with clinical presentation.

BACKGROUND: Rupture of thin-cap fibroatheromatous plaques is a major cause of acute myocardial infarction (AMI). Such plaques can be identified in vitro by 3D intravascular palpography with high sensitivity and specificity. We used this technique in patients undergoing percutaneous intervention to assess the incidence of mechanically deformable regions. We further explored the relation of such regions to clinical presentation and to C-reactive protein levels. METHOD AND RESULTS: Three-dimensional palpograms were derived from continuous intravascular ultrasound pullbacks. Patients (n=55) were classified by clinical presentation as having stable angina, unstable angina, or AMI. In every patient, 1 coronary artery was scanned (culprit vessel in stable and unstable angina, nonculprit vessel in AMI), and the number of deformable plaques assessed. Stable angina patients had significantly fewer deformable plaques per vessel (0.6+/-0.6) than did unstable angina patients (P=0.0019) (1.6+/-0.7) or AMI patients (P<0.0001) (2.0+/-0.7). Levels of C-reactive protein were positively correlated with the number of mechanically deformable plaques (R2=0.65, P<0.0001). CONCLUSIONS: Three-dimensional intravascular palpography detects strain patterns in human coronary arteries that represent the level of deformation in plaques. The number of highly deformable plaques is correlated with both clinical presentation and levels of C-reactive protein. Further studies will assess the potential role of the technique to identify patients at risk of future clinical events