A multiscale dynamic programming procedure for boundary detection in ultrasonic artery images

Number of teeth is related to atherosclerotic plaque in the carotid arteries in an elderly population

BACKGROUND

Periodontal disease has been associated with cardiovascular disorders with an atherosclerotic background, and number of teeth (NT) has been suggested as a possible risk indicator for cardiovascular disease. The objective of this study is to investigate whether NT was related to the intima-media thickness (IMT) and to atherosclerotic plaque in carotid arteries in an elderly population.

METHODS

In a population-based study including 1,016 participants aged 70 years, the NT was self-reported by 947 of the participants. Carotid artery IMT was evaluated by ultrasound. The occurrence of plaque was also measured. Logistic regression was used to analyze the associations between NT and the number of carotid arteries with plaque.

RESULTS

A significant inverse relationship was found between the NT and the number of carotid arteries with plaque after adjustment for age, sex, smoking, body mass index, waist/hip ratio, blood glucose, triglycerides, cholesterol, C-reactive protein, leukocyte count, blood pressure, and Framingham risk score, with odds ratio of 0.89, 95% confidence interval of 0.82 to 0.98, and P = 0.016. The relationship was fairly linear, suggesting a dose-response relationship. When NT was divided into quintiles using the first one as referent, the relationship persisted for all quintiles except for the second one. However, no relationship to IMT was seen.

CONCLUSION

The present study further emphasizes that tooth loss could be an easily obtained risk indicator for atherosclerosis.

Blood pressure variability is significantly associated with ECG left ventricular mass in normotensive Africans: the SABPA Study

The prognostic significance of blood pressure (BP) variability has lately enjoyed considerable attention. The need for early markers of cardiovascular dysfunction is imperative in black South Africans who have a significant risk for cardiovascular disease. We therefore compared 24-h BP variability with various traditional and advanced BP measurements, regarding their association with sub-clinical organ damage in black and white South Africans. The study included 409 African and Caucasian teachers aged 25-60 yrs. We measured office BP, 1-min continuous (finger) BP, ambulatory BP, BP reactivity and determined weighted 24-h BP variability. Albumin-to-creatinine ratio, Cornell product and carotid cross-sectional wall area (CSWA) were measures of organ damage. Africans had higher 24-h BP, BP variability, BP reactivity and sub-clinical organ damage (P<0.001). Correlations of BP variability with organ damage were overall weak when compared with other BP measurements. In normotensive groups, we found an independent association of 24-h systolic BP (SBP) variability with Cornell product only in Africans (r=0.37; P=0.01), confirmed in multiple regression models, with 24-h SBP included in the model. Only in hypertensive Caucasians, a significant correlation between CSWA and 24-h SBP variability was evident (r=0.30; P=0.01), although CSWA indicated stronger correlations with office or 24-h SBP than 24-h SBP variability. To conclude, 24-h SBP variability could potentially be an effective measure for the early detection of normotensive Africans at increased risk for the development of cardiovascular complications. Its usefulness based on associations with target organ damage in hypertensive groups seems to be less than traditional office or 24-h BP measurements.

Circulating levels of bisphenol A and phthalates are related to carotid atherosclerosis in the elderly

BACKGROUND AND OBJECTIVE

Bisphenol A (BPA) levels have previously been associated with coronary heart disease (CHD). Since CHD is an atherosclerotic disease, we investigated if circulating levels of BPA and phthalate metabolites are related to atherosclerosis in a cross-sectional study.

METHODS

In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (1016 subjects all aged 70), the prevalence of overt plaques and echogenectity (grey scale median, GSM) of carotid artery plaques were recorded by ultrasound in both of the carotid arteries. The thickness (IMT) and echogenicity (IM-GSM) of the intima-media complex were also measured. Bisphenol A (BPA) and 10 phthalate metabolites were analyzed in serum by a API 4000 liquid chromatograph/tandem mass spectrometer.

RESULTS

Mono-methyl phthalate (MMP) was related to carotid plaques in an inverted U-shaped manner. This pattern was significant after adjustment for gender, body mass index, blood glucose, blood pressure, HDL and LDL-cholesterol, serum triglycerides, smoking, antihypertensive treatment and statin use (p=0.004). High levels of BPA, mono-isobutyl phthalate (MiBP) and MMP were associated with an echogenic IM-GSM and plaque GSM, while high levels of mono-2-ethylhexyl phthalate (MEHP) were associated with an echolucent IM-GSM and plaque GSM (p<0.0001 after adjustment).

CONCLUSION

The phthalate metabolite MMP was related to atherosclerotic plaques in an inverted U-shaped manner independently of CV risk factors. Some phthalates and BPA were also related to the echogenicity of the plaques, suggesting a role for plaque-associated chemicals in atherosclerosis.

Effect of 3 y of folic acid supplementation on the progression of carotid intima-media thickness and carotid arterial stiffness in older adults

BACKGROUND

Observational studies have shown that low folate and elevated homocysteine concentrations are risk factors for vascular disease in the general population. Randomized controlled trials in vascular patients have failed to show that folic acid reduces the risk of recurrent vascular disease, whereas such trials are lacking in the general population.

OBJECTIVE

The objective was to determine whether folic acid supplementation reduces the progression of atherosclerosis as measured by common carotid intima-media thickness (CIMT)-a validated marker of atherosclerosis and predictor of vascular disease risk.

DESIGN

A randomized, double-blind, placebo-controlled study in 819 men and postmenopausal women aged 50-70 y, free-living in the Netherlands, and with a total homocysteine concentration ≥13 μmol/L at screening was conducted. Participants received either 800 μg folic acid or placebo daily for 3 y. Rate of change in CIMT and arterial distensibility were the primary and secondary outcomes, respectively.

RESULTS

Compared with placebo, serum folate increased by 577% and plasma total homocysteine concentrations decreased by 26% after 3 y of folic acid supplementation. The mean (±SE) rate of change in CIMT was 1.9 ± 0.9 μm/y in the folic acid arm and 1.3 ± 0.8 μm/y in the placebo arm (mean difference: 0.7 μm/y; 95% CI: -1.8, 3.1 μm/y; P = 0.59). No difference was observed (P = 0.23) between the rates of change in distensibility in the folic acid arm (-0.53 ± 0.06 × 10(-3) kPa(-1)) and in the placebo arm (-0.62 ± 0.06 × 10(-3) kPa(-1)).

CONCLUSION

Despite a considerable increase in folate concentrations and a reduction in total homocysteine concentrations, 3-y folic acid supplementation did not slow down atherosclerotic progression or arterial stiffening. This trial was registered at clinicaltrials.gov as NCT00110604.

Associations of cholesterol and glucose with cardiovascular dysfunction in black Africans: the SABPA study

The aim was to determine whether blood glucose or cholesterol is the more prominent contributor to cardiovascular dysfunction in 101 African men and 99 African women. We measured ambulatory daytime blood pressure (BP), carotid intima-media thickness (CIMT), and determined blood glucose and lipids in serum. High-density lipoprotein cholesterol (HDL) (p = 0.002) and HDL: total cholesterol (HDL:TC) (p ≤ 0.001) were significantly lower, while serum glucose (p ≤ 0.001) was significantly higher in men. In single, partial, and multiple regression analysis, BP correlated positively with blood glucose in men. Furthermore, CIMT (B = -0.50; p = 0.009) correlated negatively with HDL:TC in men. While in women CIMT (B = 0.346; p = 0.015) correlated positively with glucose. In conclusion, subclinical atherosclerosis is significantly related to an unfavorable HDL profile in men, whereas in women, this link is stronger with fasting glucose.

A fully automated method using active contours for the evaluation of the intima-media thickness in carotid US images

The thickness of the intima-media complex (IMC) of the common carotid artery (CCA) wall is important in the evaluation of the risk for the development of atherosclerosis. This paper presents a fully automated algorithm for the segmentation of the IMC. The segmentation of the IMC of the CCA wall is important for the evaluation of the intima media thickness (IMT) on B-mode ultrasound images. The presented algorithm is based on active contours and active contours without edges. It begins with image normalization, followed by speckle removal. The level set formulation of Chan and Vese using random initialization provides a segmentation of the CCA ultrasound (US) images into different distinct regions, one of which corresponds to the carotid wall region above the lumen whilst another corresponds to the carotid wall region below the lumen and includes the IMC. The results of the corresponding segmentation combined with anatomical information provide a very accurate outline of the lumen-intima boundary. This outline serves as an excellent initialization for segmentation of the IMC using parametric active contours. The method lends itself to the development of a fully automated method for the delineation of the IMC. The mean and standard deviation of the thickness of the automatically segmented regions are 0.65 mm +/-0.17 mm and the corresponding values for the ground truth IMT are 0.66 mm +/-0.18 mm. The Wilcoxon rank sum test shows no significant difference.

Segmentation of ultrasound images of the carotid using RANSAC and cubic splines

A new algorithm is proposed for the semi-automatic segmentation of the near-end and the far-end adventitia boundary of the common carotid artery in ultrasound images. It uses the random sample consensus method to estimate the most significant cubic splines fitting the edge map of a longitudinal section. The consensus of the geometric model (a spline) is evaluated through a new gain function, which integrates the responses to different discriminating features of the carotid boundary: the proximity of the geometric model to any edge or to valley shaped edges; the consistency between the orientation of the normal to the geometric model and the intensity gradient; and the distance to a rough estimate of the lumen boundary. A set of 50 longitudinal B-mode images of the common carotid and their manual segmentations performed by two medical experts were used to assess the performance of the method. The image set was taken from 25 different subjects, most of them having plaques of different classes (class II to class IV), sizes and shapes. The quantitative evaluation showed promising results, having detection errors similar to the ones observed in manual segmentations for 95% of the far-end boundaries and 73% of the near-end boundaries.

Conventional and behavioral risk factors explain differences in sub-clinical vascular disease between black and Caucasian South Africans: the SABPA study

OBJECTIVES

There is an emerging burden of cardiovascular disease among urban black Africans in South Africa, which has been largely explained by the transition from traditional African lifestyles to more westernized behavior. We examined the role of health behaviors in explaining the excess burden of sub clinical vascular disease seen in black Africans compared to Caucasians.

METHODS

This was a cross-sectional study, comprising of urban African teachers (n=192 black, 206 Caucasian) working for one of the four Kenneth Kaunda Education districts in the North West Province, South Africa. Conventional cardiovascular risk factors, 24 h ambulatory blood pressure and objectively measured physical activity (Actical® accelerometers), smoking (confirmed by serum cotinine), and alcohol (serum gamma glutamyl transferase) were assessed. The main outcome was a marker of sub-clinical vascular disease, mean carotid intima media thickness (mCIMT), measured using high resolution ultrasound.

RESULTS

Compared with Caucasians, the black Africans demonstrated higher mCIMT (age and sex adjusted β=0.044, 95% CI, 0.024-0.064 mm). The blacks also had higher 24h systolic and diastolic blood pressure, triglycerides, adiposity, and C-reactive protein. In addition, blacks were less physically active (790.0 kcal/d vs 947.3 kcal/d, p<0.001), more likely to smoke (25% vs 16.3%, p=0.002), and demonstrated higher alcohol abuse (gamma glutamyl transferase, 66.6 μ/L vs 27.2 μ/L, p<0.001) compared with Caucasians. The difference in mCIMT between blacks and Caucasians was attenuated by 34% when conventional risk factors were added to the model and a further 18% when health behaviors were included.

CONCLUSION

There is an excess burden of sub clinical vascular disease seen in black Africans compared to Caucasians, which can be largely explained by health behaviors and conventional risk factors.

A state of the art review on intima-media thickness (IMT) measurement and wall segmentation techniques for carotid ultrasound

Last 10 years have witnessed the growth of many computer applications for the segmentation of the vessel wall in ultrasound imaging. Epidemiological studies showed that the thickness of the major arteries is an early and effective marker of onset of cardiovascular diseases. Ultrasound imaging, being real-time, economic, reliable, safe, and now seems to become a standard in vascular assessment methodology. This review is an attempt to discuss the most performing methodologies that have been developed so far to perform computer-based segmentation and intima-media thickness (IMT) measurement of the carotid arteries in ultrasound images. First we will present the rationale and the clinical relevance of computer-based measurements in clinical practice, followed by the challenges that one has to face when approaching the segmentation of ultrasound vascular images. The core of the paper is the presentation, discussion, benchmarking and evaluation of different segmentation techniques, including: edge-detection, active contours, dynamic programming, local statistics, Hough transform, statistical modeling, and integration of these approaches. Also, we will discuss and compare the different performance metrics that have been proposed and used to perform the validation. Best performing user-dependent techniques show an average IMT measurement error of about 1μm when compared to human tracings [57], whereas completely automated techniques show errors of about 10μm. The review ends with a discussion about the current standards in carotid wall segmentation and in an overview of the future perspectives, which may include the adoption of advanced and intelligent strategies to let the computer technique measure the IMT in the image portion where measurement is more reliable.

Automated detection of the arterial inner walls of the common carotid artery based on dynamic B-mode signals

In this paper we propose a novel scheme able to automatically detect the intima and adventitia of both near and far walls of the common carotid artery in dynamic B-mode RF (radiofrequency) image sequences, with and without plaques. Via this automated system the lumen diameter changes along the heart cycle can be detected. Three image sequences have been tested and all results are compared to manual tracings made by two professional experts. The average errors for near and far wall detection are 0.058 mm and 0.067 mm, respectively. This system is able to analyze arterial plaques dynamically which is impossible to do manually due to the tremendous human workload involved.

Rationale, design and population baseline characteristics of the PERFORM vascular project: an ancillary study of the Prevention of cerebrovascular and cardiovascular Events of ischemic origin with teRutroban in patients with a history oF ischemic strOke or tRansient ischeMic attack (PERFORM) trial

Purpose

PERFORM is exploring the efficacy of terutroban versus aspirin for secondary prevention in patients with a history of ischemic stroke or transient ischemic attacks (TIAs). The PERFORM Vascular Project will evaluate the effect of terutroban on progression of atherosclerosis, as assessed by change in carotid intima-media thickness (CIMT) in a subgroup of patients.

Methods and results

The Vascular Project includes structural (CIMT, carotid plaques) and functional (carotid stiffness) vascular studies in all patients showing at least one carotid plaque at entry. Expected mean follow-up is 36 months. Primary endpoint is rate of change of CIMT. Secondary endpoints include emergent plaques and assessment of carotid stiffness. 1,100 patients are required for 90% statistical power to detect treatment-related CIMT difference of 0.025 mm. The first patient was randomized in April 2006.

Conclusions

The PERFORM Vascular Project will investigate terutroban’s effect on vascular structure and function in patients with a history of ischemic stroke or TIAs.

Multiscale amplitude-modulation frequency-modulation (AM-FM) texture analysis of ultrasound images of the intima and media layers of the carotid artery

The intima-media thickness (IMT) of the common carotid artery (CCA) is widely used as an early indicator of cardiovascular disease (CVD). Clinically, there is strong interest in identifying how the composition and texture of the media layer (ML) can be associated with the risk of stroke. In this study, we use 2-D amplitude-modulation frequency-modulation (AM-FM) analysis of the intima-media complex (IMC), the ML, and intima layer (IL) of the CCA to detect texture changes as a function of age and sex. The study was performed on 100 ultrasound images acquired from asymptomatic subjects at risk of atherosclerosis. To investigate texture variations associated with age, we separated them into three age groups: 1) patients younger than 50; 2) patients aged between 50 and 60 years old; and 3) patients over 60 years old. We also separated the patients by sex. The IMC, ML, and IL were segmented manually by a neurovascular expert and also by a snake-based segmentation system. To reject strong edge artifacts, we prefilter with an AM-FM filterbank that is centered along the horizontal frequency axis (parallel to the long axis of the IMC, ML, and IL), while removing the low-pass filter estimates and frequency bands with large, vertical frequency components. To investigate significant texture changes, we extract the instantaneous amplitude (IA) and the magnitude of the instantaneous frequency (IF) over each layer component, for low-, medium-, and high-frequency AM-FM components. We detected significant texture differences between the higher risk age group of >60 years versus the lower risk age group of <50 and the 50-60 group. In particular, between the <50 and >60 groups, we found significant differences in the medium-scale IA extracted from the IMC. Between the >60 and the 50-60 groups, we found significant texture changes in the low-scale IA and high-scale IF magnitude extracted from the IMC, and the low-scale IA extracted from the IL. Also, we noted that the IA for the ML showed significant differences between males and females for all age groups. The AM--FM features provide complimentary information to classical texture analysis features like the gray-scale median, contrast, and coarseness. These findings provide evidence that AM--FM texture features can be associated with the progression of cardiovascular risk for disease and the risk of stroke with age. However, a larger scale study is needed to establish the application in clinical practice.

Ultrasound protocols to measure carotid intima-media thickness in trials; comparison of reproducibility, rate of progression, and effect of intervention in subjects with familial hypercholesterolemia and subjects with mixed dyslipidemia

BACKGROUND

Current ultrasound protocols to measure carotid intima-media thickness (CIMT) in trials rather differ. The ideal protocol combines high reproducibility with a high precision in the measurement of the rate of change in CIMT over time and with a precise estimate of a treatment effect. To study these aspects, a post-hoc analysis was performed using data from two randomized double-blind, placebo-controlled trials: one among 872 subjects with familial hypercholesterolemia (FH) and the other among 752 subjects with mixed dyslipidemia (MD), respectively. Participants were randomized to torcetrapib or placebo on top of optimal atorvastatin therapy.

METHODS

CIMT information was collected from the left and right carotid artery from two walls (the near and far wall) of three segments (common carotid, bifurcation, and internal carotid artery) at four different angles (right: 90, 120, 150, and 180 degrees on Meijer's carotid arc; left: 270, 240, 210, and 180 degrees, respectively). Based on combinations of these measurements, 60 different protocols were constructed to estimate a CIMT measure per participant (20 protocols for mean common CIMT, 40 protocols for mean maximum CIMT). For each protocol we assessed reproducibility (intra-class correlation coefficient (ICC), mean difference of duplicate base-line scans); 2-year progression rate in the atorvastatin group with its standard error (SE); and treatment effect (difference in rate of change in CIMT between torcetrapib and placebo) with its SE.

RESULTS

Reproducibility: ICC ranged from 0.77 to 0.91 among FH patients and from 0.68 to 0.86 among MD patients. CIMT progression rates ranged from -0.0030 to 0.0020 mm/year in the FH trial and from 0.00084 to 0.01057 mm/year in the MD trial, with SE ranging from 0.00054 to 0.00162 and from 0.00083 to 0.00229, respectively. The difference in CIMT progression rate between treatment arms ranged from -0.00133 to 0.00400 mm/year in the FH trial and from -0.00231 to 0.00486 mm/year in the MD trial. The protocol with the highest reproducibility, highest CIMT progression/precision ratio, and the highest treatment effect/precision ratio were those measuring mean common CIMT with measurements of the near and far wall at multiple angles. When the interest is in the mean maximum CIMT, protocols using multiple segments and angles performed the best.

CONCLUSION

Our findings support the position that the number and specific combination of segments, angles, and walls interrogated are associated with differences in reproducibility, magnitude, and precision of progression of CIMT over time, and treatment effect. The best protocols were mean common CIMT protocols in which both the near and far walls are measured at multiple angles.

Plasma renin responses to mental stress and carotid intima-media thickness in black Africans: the SABPA study

The renin-angiotensin-aldosterone system can be activated by sympathetic nervous input and is thought to have an important role in the prevalence of hypertension and cardiovascular risk in black Africans. We examined (1) the association between plasma renin responses to mental stress and a marker of sub-clinical atherosclerosis; and (2) associations between resting renin and 24-h ambulatory blood pressure. Participants were 143 urbanized black African men and women (43.1 ± 7.7 years) drawn from a study of Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA). After an overnight fast, participants completed the Stroop mental stress task. Blood samples were drawn during baseline and 10 min after the task to assess the concentration of active renin in plasma. Blood pressure assessments included continuous Finometer measures during the stress testing and 24-h ambulatory monitoring. Carotid intima-media thickness (CIMT) was measured using high-resolution ultrasound. Approximately 50% of the sample responded to the task with an increase in renin concentration. Multiple linear regression analysis revealed an association between the renin stress response and CIMT (β = 0.024, 95% confidence interval, 0.004-0.043), after adjustment for conventional risk factors, blood pressure stress responses and basal levels of renin activity (R(2) for model = 0.37). In addition, resting renin was inversely associated with ambulatory blood pressure. In summary, heightened release of renin during a laboratory mental stressor was associated with a marker of sub-clinical atherosclerosis; thus, it may be a potential mechanism in explaining the increased burden of cardiovascular disease in urbanized black Africans.

Boundary detection in carotid ultrasound images using dynamic programming and a directional Haar-like filter

The intima-media thickness (IMT) of the carotid artery, obtained from B-mode ultrasound images, has recently been proposed as one of the most useful indices of atherosclerosis and can also be used to predict major cardiovascular events. Ultrasonic measurements of the IMT are conventionally obtained by time-consuming manual tracing of the interfaces between tissue layers. We propose a computerized method to detect the boundary of the intima-media complex using a directional Haar-like filter that can account for the slope of the boundary in an image. The directional Haar-like filter extracts a directional boundary feature as an image feature in the region of interest, which is used to compute a cost function. A cost function includes not only the directional Haar-like filtering value but also the geometric continuity that is computed for every pixel in the region of interest. The optimal boundary pixels are detected by using a dynamic programming approach that searches for the pixel that minimizes the cost function in each column of the image. We compared the performance of the proposed method with that of manual methods performed by two radiologists. The results showed that our approach produces very similar results to those based on manual tracing, and there was no statistically significant difference between the IMT measurements segmented manually and those analyzed using our method.

Associations of circulating adiponectin with measures of vascular function and morphology

CONTEXT

Some previous studies have reported an association between circulating adiponectin and selected measures of vascular function and morphology, but most of these studies have been performed in small samples of patients with preexisting disease.

OBJECTIVE

We aimed to evaluate associations between circulating adiponectin and comprehensive measures of vascular function and morphology in a large sample of individuals from the community.

DESIGN, SETTINGS, AND PARTICIPANTS

We conducted a cross-sectional investigation of 981 70-yr-old participants (50% women) of the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS).

MAIN OUTCOME MEASURES

Measures of outcome included vascular function [common carotid artery (CCA) distensibility, flow-mediated dilation, endothelium-dependent and endothelium-independent vasodilation using invasive methods] and vascular morphology [intima-media (IM) thickness, plaque presence, gray scale median (GSM) in the IM and plaques].

RESULTS

In age- and sex-adjusted models, adiponectin was positively associated with IM-GSM, plaque GSM, CCA distensibility, endothelium-dependent and endothelium-independent vasodilation. In multivariable models (with additional adjustment for body mass index; systolic blood pressure; antihypertensive, antidiabetic, and lipid-lowering medication; fasting blood glucose; total cholesterol; high-density lipoprotein cholesterol; creatinine; and smoking), adiponectin remained positively associated with IM-GSM [beta = 2.06; 95% confidence interval (CI), 0.54, 3.58], plaque GSM (beta = 3.11; 95% CI, 0.36, 5.86), and CCA distensibility (beta = 0.04; 95% CI, 0.00, 0.07).

CONCLUSIONS

Serum levels of adiponectin were positively associated with IM-GSM and plaque GSM (indicating lower fat content in the IM and plaques) and CCA distensibility (indicating higher wall elasticity), independent of potential confounders. Our results imply that adiponectin is associated with less arterial pathology.

Intima-media thickness: setting a standard for a completely automated method of ultrasound measurement

The intima-media thickness (IMT) of the common carotid artery is a widely used clinical marker of severe cardiovascular diseases. IMT is usually manually measured on longitudinal B-mode ultrasound images. Many computer-based techniques for IMT measurement have been proposed to overcome the limits of manual segmentation. Most of these, however, require a certain degree of user interaction. In this paper we describe a new, completely automated layer extraction technique (named CALEXia) for the segmentation and IMT measurement of the carotid wall in ultrasound images. CALEXia is based on an integrated approach consisting of feature extraction, line fitting, and classification that enables the automated tracing of the carotid adventitial walls. IMT is then measured by relying on a fuzzy K-means classifier. We tested CALEXia on a database of 200 images. We compared CALEXia?s performance with those of a previously developed methodology that was based on signal analysis (CULEXsa). Three trained operators manually segmented the images and the average profiles were considered as the ground truth. The average error from CALEXia for lumen-intima (LI) and media- adventitia (MA) interface tracings were 1.46 +/- 1.51 pixel (0.091 +/- 0.093 mm) and 0.40 +/- 0.87 pixel (0.025 +/- 0.055 mm), respectively. The corresponding errors for CULEXsa were 0.55 +/- 0.51 pixels (0.035 +/- 0.032 mm) and 0.59 +/- 0.46 pixels (0.037 +/- 0.029 mm). The IMT measurement error was equal to 0.87 +/- 0.56 pixel (0.054 +/- 0.035 mm) for CALEXia and 0.12 +/- 0.14 pixel (0.01 +/- 0.01 mm) for CULEXsa. Thus, CALEXia showed limited performance in segmenting the LI interface, but outperformed CULEXsa in the MA interface and in the number of images correctly processed (190 for CALEXia and 184 for CULEXsa). Based upon two complementary strategies, we anticipate fusing them for further IMT improvements.

A review of noninvasive ultrasound image processing methods in the analysis of carotid plaque morphology for the assessment of stroke risk

Noninvasive ultrasound imaging of carotid plaques allows for the development of plaque-image analysis methods associated with the risk of stroke. This paper presents several plaque-image analysis methods that have been developed over the past years. The paper begins with a review of clinical methods for visual classification that have led to standardized methods for image acquisition, describes methods for image segmentation and denoising, and provides an overview of the several texture-feature extraction and classification methods that have been applied. We provide a summary of emerging trends in 3-D imaging methods and plaque-motion analysis. Finally, we provide a discussion of the emerging trends and future directions in our concluding remarks.

Completeness of carotid intima media thickness measurements depends on body composition: the RADIANCE 1 and 2 trials

AIM

Ultrasound protocols to measure carotid intima media thickness (CIMT) differ considerably with regard to the inclusion of the number of carotid segments and angles used. Detailed information on the completeness of CIMT information is often lacking in published reports, and at most, overall percentages are presented. We therefore decided to study the completeness of CIMT measurements and its relation with vascular risk factors using data from two CIMT intervention studies: one among familial hypercholesterolemia (FH) patients, the Rating Atherosclerotic Disease change by Imaging With A New CETP Inhibitor (RADIANCE 1), and one among mixed dyslipidemia (MD) patients, the Rating Atherosclerotic Disease change by Imaging With A New CETP Inhibitor (RADIANCE 2).

METHODS

We used baseline ultrasound scans from the RADIANCE 1 (n=872) and RADIANCE 2 (n=752) studies. CIMT images were recorded for 12 artery-wall combinations (near and far walls of the left and right common carotid artery (CCA), bifurcation (BIF) and internal carotid artery (ICA) segments) at 4 set angles, resulting in 48 possible measurements per patient. The presence or absence of CIMT measurements was assessed per artery-wall combination and per angle. The relation between completeness and patient characteristics was evaluated with logistic regression analysis.

RESULTS

In 89% of the FH patients, information on CIMT could be obtained on all twelve carotid segments, and in 7.6%, eleven segments had CIMT information (nearly complete 96.6%). For MD patients this was 74.6% and 17.9%, respectively (nearly complete: 92.5%). Increased body mass index and increased waist circumference were significantly (p=0.01) related to less complete data in FH patients. For MD patients, relations were seen with increased waist circumference (p<0.01). Segment-specific data indicated that in FH patients, completeness was less for the near wall of the left (96%) and right internal carotid artery (94%) as compared to other segments (all >98%). In MD patients, completeness was lower for the near wall of both the right and left carotid arteries: 86.0% and 90.8%, respectively, as compared to other segments (all >97%).

CONCLUSIONS

With the current ultrasound protocols it is possible to obtain a very high level of completeness. Apart from the population studied, body mass index and waist circumference are important in achieving complete CIMT measurements.

Blood glutathione and subclinical atherosclerosis in African men: the SABPA Study

BACKGROUND

Sub-Saharan Africans face an increasing burden of hypertension and related cardiac and cerebrovascular morbidity and mortality, making the identification of factors leading to early vascular abnormalities imperative.

METHODS

We investigated the possible influence of the antioxidant glutathione (GSH) on early subclinical atherosclerosis in 63 hypertensive (aged 45.2 years) and 34 normotensive (aged 38.9 years; P < 0.001) nondiabetic African men. We measured ambulatory daytime systolic and diastolic blood pressure (SBP, DBP) as well as daytime mean arterial pressure (MAP), carotid intima-media thickness (CIMT), and calculated the cross-sectional wall area. We determined the reduced form of GSH in whole blood and blood glucose in serum.

RESULTS

Blood glucose (110 vs. 92 mg/dl; P < 0.001) and CIMT (0.75 vs. 0.61 mm; P < 0.001) were higher in hypertensives compared to normotensives. No significant difference existed for GSH. Associations in normotensives suggested the hypotensive effect of GSH after single (SBP: r = -0.35, P < or = 0.05; DBP: r = -0.37, P < or = 0.05; MAP: r = -0.38, P < or = 0.05) and multiple (SBP: B = -0.015, P < 0.05; DBP: B = -0.011, P < 0.05; MAP: B = -0.012, P < 0.05) regression analyses. In hypertensives, CIMT (B = -0.00027, P < 0.01) and cross-sectional wall area (CSWA) (B = -0.0066, P < 0.05) correlated negatively with GSH. These findings were consistent after excluding 10 human immunodeficiency virus (HIV)-positive hypertensive subjects.

CONCLUSIONS

In hypertensive African men, CIMT is negatively associated with GSH, suggesting a possible contributory role of attenuated GSH levels in the development of subclinical atherosclerosis.

Brachial artery hyperemic blood flow velocities are related to carotid atherosclerosis

OBJECTIVE

Cardiovascular (CV) risk relates to the blood flow velocity pattern in the brachial artery during hyperemia, especially to the hyperaemic systolic to diastolic mean blood flow velocity (SDFV) ratio. Here, we investigated the relations between SDFV in the brachial artery and different characteristics of carotid atherosclerosis.

MATERIAL AND METHODS

Data were collected from 1016 70-year-olds participating in the Prospective Investigation of Uppsala Seniors study. Doppler recordings of blood flow velocity during hyperemia were analysed in the brachial artery. In the carotid artery, intima-media thickness (IMT) was recorded together with an assessment of echogenicity by the Grey scale median (GSM) method in both overt plaques and in the intima-media complex (IM-GSM).

RESULTS

The SDFV ratio was related to the number of carotid arteries affected by plaque (P = 0.018) and inversely to plaque echogenicity (P = 0.0003). The SDFV ratio was also related to IMT (P = 0.0022) and inversely to IM-GSM (P = 0.0001). These relations were statistically significant also after adjusting for major CV risk factors, individually as well as summarised as the Framingham risk score.

CONCLUSION

Our results indicate that the hyperemic systolic to diastolic blood flow velocity ratio in the brachial artery is related to atherosclerosis in the carotid artery.

The carotid artery plaque size and echogenicity are related to different cardiovascular risk factors in the elderly: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

Carotid plaques can be characterised by ultrasound by size and echogenicity. Both size and echogenicity are predictors of cardiovascular events. The aim of this study was to examine whether traditional risk factors and markers of inflammation and oxidation were associated with plaque size and echogenicity. Computerised analysis of carotid plaque size and echogenicity (grey scale median, GSM) were performed by ultrasound in a population-based health survey in 1,016 subjects aged 70 years (PIVUS study). Information on cardiovascular risk factors was collected, together with markers of inflammation and oxidation. Increased Framingham risk score, systolic blood pressure, higher BMI and decreased HDL, lower glutathione levels were related to echolucent plaques. Previous or present smoking was common with significantly more pack-years related to the echorich plaques. Plaque size was associated with increased Framingham risk score, systolic blood pressure, blood glucose levels, smoking, ApoB/A1 ratio, OxLDL, TNF alpha, HOMA insulin resistance, leucocyte count, decreased BCD-LDL and low levels of l-selectin. Low HDL, increased BMI and decreased glutathione levels were associated with the echolucency of carotid plaques, implying metabolic factors to play a role for plaque composition. Markers of inflammation were related to plaque size alone, implying inflammation to be predominantly associated with the amount of atherosclerosis. These results suggest that plaque size and echogenicity are influenced by different risk factors.

Detections of arterial wall in sonographic artery images using dual dynamic programming

We propose a novel dual dynamic programming (DDP) technique for detecting intimal and adventitial layers of the common carotid artery of the B-mode sonographic images. This method embeds the anatomic knowledge into its structure so that the robustness against the speckles is increased. Moreover, it inherits the property of getting the optimal solution as the traditional dynamic programming (TDP). Our experimental study shows that the DDP technique achieves a detection performance comparable to manual tracing achieved by physicians. The results demonstrate that it has the potential to perform qualitatively better than applying TDP twice in intimal and adventitial layer detection on sonographic B-mode images.

An echolucent carotid artery intima-media complex is a new and independent predictor of mortality in an elderly male cohort

BACKGROUND

The echogenicity of atherosclerotic plaques is a measure of their lipid content and predicts cardiovascular disease. We hypothesized that the echogenicity of the non-plaque-affected arterial wall may be prognostically important as well, and more easily used as not all subjects carry plaques. We investigated the prognostic value of intima-media (IM) echogenicity (measured as the grey scale median [GSM]) for mortality compared with intima-media thickness (IMT) in a population-based sample of elderly men.

METHODS

A cohort from a community-based sample of 491 men was investigated with carotid artery ultrasound at age 75. IMT and GSM for IM and plaques were measured in the far wall of the common carotid artery being apparently free of plaque. Cox proportional hazard analysis models were used to investigate linear and non-linear relations of IM-GSM to mortality, adjusted for IMT, body mass index, cholesterol, HDL-cholesterol, triglycerides, systolic blood pressure, antihypertensive treatment, CRP, diabetes, current smoking, pack years of smoking, and previous cardiovascular disease.

RESULTS

Seventy-seven subjects died during a median follow-up time of 5.1 years. Participants were divided in tertiles by IM-GSM. In unadjusted analysis, IM-GSM predicted mortality in a U-shaped manner. In Cox proportional hazard analyses, an echolucent IM-GSM was a predictor of all-cause mortality (HR: 3.23; CI: 1.60-6.54; p<0.05) and CVD mortality (n=30, HR: 8.29; CI: 2.03-33.92; p<0.05) independently of IMT and established risk factors. These associations were still significant following adjustment for plaque occurrence and plaque echogenicity.

CONCLUSION

An echolucent intima-media complex is a predictor of all-cause and CVD mortality in elderly men independently of plaque occurrence, plaque GSM, IMT and established risk factors, suggesting the echogenicity of the apparently plaque-free intima-media complex provides novel prognostic information regarding mortality after age 75.

An automatic 2D CAD algorithm for the segmentation of the IMT in ultrasound carotid artery images

Common carotid intima-media thickness (IMT) is a reliable measure of early atherosclerosis - its accurate measurement can be used in the process of evaluating the presence and tracking the progression of disease. The aim of this study is to introduce a novel unsupervised Computer Aided Detection (CAD) algorithm that is able to identify and measure the IMT in 2D ultrasound carotid images. The developed technique relies on a suite of image processing algorithms that embeds a statistical model to identify the two interfaces that form the IMT without any user intervention. The proposed image segmentation scheme is based on a spatially continuous vascular model and consists of several steps including data preprocessing, edge filtering, model selection, edge reconstruction and data refinement. To conduct a quantitative evaluation each image was manually segmented by clinical experts and performance metrics between the segmentation results obtained by the proposed method and the ground truth data were calculated. The experimental results show that the proposed CAD system is robust in accurately estimating the IMT in ultrasound carotid data.

Echogenecity of the carotid intima-media complex is related to cardiovascular risk factors, dyslipidemia, oxidative stress and inflammation: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Increased carotid artery intima-media thickness (IMT), measured by ultrasound, is related to an increased risk of cardiovascular disease. Since presence of echolucent plaques increases the risk further, we investigated if echogenecity of the carotid intima-media complex is related to markers of cardiovascular risk. Our aim was therefore to investigate if intima-media echogenecity is related to cardiovascular risk factors, or to markers of inflammation and oxidation in an exploratory investigation.

METHODS

The PIVUS cohort study is an observational study of 1016 (509 women and 507 men) randomly chosen individuals aged 70 living in Uppsala, Sweden. Carotid artery ultrasound measurements were performed. IMT and the grey scale median (GSM) value were calculated in the intima-media complex (IM-GSM) in the far wall of the common carotid artery. Traditional risk factors were evaluated together with indices of oxidative stress and inflammation.

RESULTS

In the multiple regression analysis, HDL-cholesterol, body mass index, conjugated diens, glutathione, e-selectin and TNF alfa were significantly related to IM-GSM. IMT was independently related to blood pressure, smoking and body mass index.

CONCLUSION

The echolucency of the carotid intima-media was related to several cardiovascular risk factors not related to IMT, such as dyslipidemia, oxidative stress and inflammation. Since the echogenecity of the carotid intima-media complex was related to different risk factors compared to carotid IMT, it is worthwhile to further explore the usefulness of this new marker of the vascular wall.

Computer aided evaluation of ankylosing spondylitis using high-resolution CT

Ankylosing Spondylitis is a disease characterized by abnormal bone structures (syndesmophytes) growing at intervertebral disk spaces. Because this growth is so slow as to be undetectable on plain radiographs taken over years, it is desirable to resort to computerized techniques to complement qualitative human judgment with precise quantitative measures. We developed an algorithm with minimal user intervention that provides such measures using high-resolution computed tomography (CT) images. To the best of our knowledge it is the first time that determination of the disease's status is attempted by direct measurement of the syndesmophytes. The first part of our algorithm segments the whole vertebral body using a 3-D multiscale cascade of successive level sets. The second part extracts the continuous ridgeline of the vertebral body where syndesmophytes are located. For that we designed a novel level set implementation capable of evolving on the isosurface of an object represented by a triangular mesh using curvature features. The third part of the algorithm segments the syndesmophytes from the vertebral body using local cutting planes and quantitates them. We present experimental work done with 10 patients from each of which we processed five vertebrae. The results of our algorithm were validated by comparison with a semi-quantitative evaluation made by a medical expert who visually inspected the CT scans. Correlation between the two evaluations was found to be 0.936 ( p < 10(-18)) .

Real-time measurement system for evaluation of the carotid intima-media thickness with a robust edge operator

OBJECTIVE

The purpose of this report is to describe an automatic real-time system for evaluation of the carotid intima-media thickness (CIMT) characterized by 3 main features: minimal interobserver and intraobserver variability, real-time capabilities, and great robustness against noise.

METHODS

One hundred fifty carotid B-mode ultrasound images were used to validate the system. Two skilled operators were involved in the analysis. Agreement with the gold standard, defined as the mean of 2 manual measurements of a skilled operator, and the interobserver and intraobserver variability were quantitatively evaluated by regression analysis and Bland-Altman statistics.

RESULTS

The automatic measure of the CIMT showed a mean bias +/- SD of 0.001 +/- 0.035 mm toward the manual measurement. The intraobserver variability, evaluated with Bland-Altman plots, showed a bias that was not significantly different from 0, whereas the SD of the differences was greater in the manual analysis (0.038 mm) than in the automatic analysis (0.006 mm). For interobserver variability, the automatic measurement had a bias that was not significantly different from 0, with a satisfactory SD of the differences (0.01 mm), whereas in the manual measurement, a little bias was present (0.012 mm), and the SD of the differences was noticeably greater (0.044 mm).

CONCLUSIONS

The CIMT has been accepted as a noninvasive marker of early vascular alteration. At present, the manual approach is largely used to estimate CIMT values. However, that method is highly operator dependent and time-consuming. For these reasons, we developed a new system for the CIMT measurement that conjugates precision with real-time analysis, thus providing considerable advantages in clinical practice.

A practical protocol to measure common carotid artery intima-media thickness

OBJECTIVE

To describe and test a practical protocol to measure common carotid intima-media thickness that uses the combined values of two longitudinal examination angles to increase sensitivity.

METHOD

Between February and September 2005, 206 patients underwent duplex scan examination of carotid vessels, and the intima-media thickness of 407 common carotids were measured in three angles: transversal, longitudinal posterolateral, and anterolateral, with three intima-media thickness measurements for each near and far wall. In addition to numbers obtained from the three angles of measurement, a fourth visual perspective was obtained by combining the intima-media thickness results of posterolateral and anterolateral longitudinal views and considering the thickest wall measurement.

RESULTS

Two hundred seventy (66.3%) carotid arteries had an intima-media thickness thicker than 1mm. The mean intima-media thickness values achieved by the different incidences were 1.26+/-0.6 mm (transversal), 1.17+/-0.54 mm (longitudinal anterolateral), and 1.18+/-0.58 mm (longitudinal posterolateral). A significant difference in intima-media thickness measurement values was observed when the three angles of examination plus the combined positive results of both longitudinal angles were compared by ANOVA (P=0.005). The LSD Post-Hoc test determined that the combined longitudinal view results were similar to the transversal views (P=0.28) and had greater intima-media thickness means than isolated anterolateral or posterolateral longitudinal views (P=0.02 and 0.05, respectively).

CONCLUSIONS

The protocol presented is a practical method for obtaining common carotid artery intima-media thickness measurements. The combined longitudinal posterolateral and anterolateral longitudinal views provide a more sensitive evaluation of the inner layers of the carotid walls than isolated longitudinal views.

Pulse pressure amplification and risk of cardiovascular disease

BACKGROUND

Whether pulse pressure amplification (PPA) relates to established markers of cardiovascular risk is unknown. The purpose of this study was to investigate the relationship between PPA and cardiovascular risk factors and cardiovascular risk in a population-based sample of 40- to 80-year old men.

METHODS

A cross-sectional, single-center study was performed in 400 men aged 40-80 years. PPA was calculated as a ratio (brachial pulse pressure/central pulse pressure). Detailed information on vascular risk factors was obtained. Aortic pulse wave velocity (PWV) and common carotid intima-media thickness (CIMT), as markers of vascular risk, were measured. We calculated the absolute 10-year risk of coronary heart disease using the Framingham risk score. Regression analysis was used to evaluate the relations under study.

RESULTS

In models adjusted for age, mean arterial pressure (MAP), heart rate, and height, significant inverse relations with PPA were found for waist-to-hip ratio, triglycerides, smoking, pack-years, and hypertension. Furthermore, an increased PPA was significantly inversely related to aortic PWV, common CIMT, and history of symptomatic vascular disease. Finally, the Framingham risk score decreased with increasing PPA.

CONCLUSION

Our study shows that a higher PPA reflects a lower vascular risk in men between 40 and 80 years of age, as shown by a better cardiovascular risk profile, a reduced PWV, common CIMT, and a lower Framingham risk of coronary heart disease.

A new method based on dynamic programming for boundary detection in ultrasound image sequences

Dynamic programming has previously been used when measuring Lumen Diameter (LD) and Intima-Media Thickness (IMT) in single frame ultrasound carotid artery images [1]. An extension to multiframe detection of that procedure is proposed in this paper. Our new method transforms a three dimensional problem into multiple two dimensional problems that can again be solved by dynamic programming. First, several 'candidate boundaries' are detected in each image. Then, one boundary from each image in the sequence is selected in such a way that the sequence of boundaries is optimal among the considered possibilities. A model of the movements of the boundaries is used in the second step. Our proposed method shows promising performance on both synthetic and real ultrasound data.

The echogenecity of the intima–media complex in the common carotid artery is closely related to the echogenecity in plaques

OBJECTIVE

The echogenecity measured by ultrasound of atherosclerotic plaques is related to future cardiovascular events. The aim of the present study is to relate the grey scale median of the intima-media complex (IM-GSM) of the common carotid artery (CCA) to the echogenecity of carotid plaques.

MATERIAL AND RESULTS

In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, a population-based study of 1016 subjects aged 70, carotid artery intima-media thickness (IMT) and IM-GSM were evaluated by ultrasound and computerized analysis. Also the occurrence of plaque and plaque GSM were measured. The echogenecity of the plaques was also visually estimated by the Gray-Weale classification. In subjects with a carotid plaque (n=582), IM-GSM in CCA was correlated to GSM in the plaque (r=0.60, p<0.0001) independently of plaque size and IMT. IM-GSM in CCA was also correlated to the visually estimated echogenecity (p<0.0001 for trend).

CONCLUSION

IM-GSM of the CCA is closely related to the echogenecity in overt carotid plaques, regardless if evaluated by the same computerized method or evaluated visually. This finding suggests that IM-GSM of CCA could be an important and easily measurable characteristic of the carotid artery wall that could be obtained in almost all subjects and not only those with an overt plaque.

Brachial artery intima-media thickness and echogenicity in relation to lipids and markers of oxidative stress in elderly subjects:--the prospective investigation of the vasculature in Uppsala Seniors (PIVUS) Study

The aim of the present study was to relate brachial artery intima-media thickness (IMT) and the grey scale median of the intima-media complex (IM-GSM) to traditional cardiovascular risk factors and markers of inflammation and oxidative stress. In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, a population-based study of 1016 subjects aged 70, brachial artery IMT and IM-GSM, who were evaluated by ultrasound. Lipids, thirteen markers of inflammation and nine markers of oxidative stress were measured. The Framingham risk score was related to IMT (p < 0.0001), but not to the IM-GSM. In univariate analysis, HDL-cholesterol, serum triglycerides, fasting glucose, smoking, HOMA insulin resistance index and oxidized LDL levels were related to IMT. HDL and LDL-cholesterol, triglycerides, VCAM-1, e-selectin, leukocyte count, conjugated diens, baseline conjugated diens (BCD)-LDL, antibodies to oxLDL, the GSSG/GSH glutathione ratio and homocysteine were related to IM-GSM. In multiple regression models, HDL-cholesterol, fasting glucose and oxLDL levels were the independently related to IMT (p = 0.01-0.04), while serum triglycerides, BCD-LDL and the GSSG/GSH ratio were independently related to IM-GSM (p = 0.0001-0.004). In conclusion, in addition to traditional lipid variables, markers of oxidative stress were associated with both thickness and echogenicity of the brachial artery intima-media complex. Thus, both thickness and echogenicity of the brachial artery intima-media complex might be useful biomarkers in the future.

Robust border enhancement and detection for measurement of fetal nuchal translucency in ultrasound images

Ultrasonic measurement of nuchal translucency (NT) thickness in the first trimester of pregnancy has recently been proposed as the most useful marker in early screening for fetal chromosomal abnormalities. However, manual tracing of the two echogenic lines in the image, using on-screen calipers, is hampered by weak edges, together with noise and other artifacts, leading to variable results and inefficiency. Our semi-automatic method of fetal NT thickness measurement uses a coherence-enhancing diffusion filter to enhance the border and reduce noise, followed by detection of the NT by minimization of a cost function, that combines intensity, edge strength and continuity, using dynamic programming. This method has been validated by determining the correlation between manual and semi-automatic measurements.

Torcetrapib and carotid intima-media thickness in mixed dyslipidaemia (RADIANCE 2 study): a randomised, double-blind trial

BACKGROUND

Patients with mixed dyslipidaemia have raised triglycerides, low high-density lipoprotein (HDL) cholesterol, and high low-density lipoprotein (LDL) cholesterol. Augmentation of HDL cholesterol by inhibition of the cholesteryl ester transfer protein (CETP) could benefit these patients. We aimed to investigate the effect of the CETP inhibitor, torcetrapib, on carotid atherosclerosis progression in patients with mixed dyslipidaemia.

METHODS

We did a randomised double-blind trial at 64 centres in North America and Europe. 752 eligible participants completed an atorvastatin-only run-in period for dose titration, after which they all continued to receive atorvastatin at the titrated dose. 377 of these patients were randomly assigned to receive 60 mg of torcetrapib per day and 375 to placebo. We made carotid ultrasound images at baseline and at 6-month intervals for 24 months. The primary endpoint was the yearly rate of change in the maximum intima-media thickness of 12 carotid segments. Analysis was restricted to 683 patients who had at least one dose of treatment and had at least one follow-up carotid intima-media measurement; they were analysed as randomised. Mean follow-up for these patients was 22 (SD 4.8) months. This trial is registered with ClinicalTrials.gov, number NCT00134238.

FINDINGS

The change in maximum carotid intima-media thickness was 0.025 (SD 0.005) mm per year in patients given torcetrapib with atorvastatin and 0.030 (0.005) mm per year in those given atorvastatin alone (difference -0.005 mm per year, 95% CI -0.018 to 0.008, p=0.46). Patients in the combined-treatment group had a 63.4% relative increase in HDL cholesterol (p<0.0001) and an 17.7% relative decrease in LDL cholesterol (p<0.0001), compared with controls. Systolic blood pressure increased by 6.6 mm Hg in the combined-treatment group and 1.5 mm Hg in the atorvastatin-only group (difference 5.4 mm Hg, 95% CI 4.3-6.4, p<0.0001).

INTERPRETATION

Although torcetrapib substantially raised HDL cholesterol and lowered LDL cholesterol, it also increased systolic blood pressure, and did not affect the yearly rate of change in the maximum intima-media thickness of 12 carotid segments. Torcetrapib showed no clinical benefit in this or other studies, and will not be developed further.

Effect of torcetrapib on carotid atherosclerosis in familial hypercholesterolemia

BACKGROUND

Torcetrapib, an inhibitor of cholesteryl ester transfer protein, may reduce atherosclerotic vascular disease by increasing levels of high-density lipoprotein (HDL) cholesterol.

METHODS

A total of 850 patients with heterozygous familial hypercholesterolemia underwent B-mode ultrasonography at baseline and at follow-up to measure changes in carotid intima-media thickness. The patients completed an atorvastatin run-in period and were subsequently randomly assigned to receive either atorvastatin monotherapy or atorvastatin combined with 60 mg of torcetrapib for 2 years.

RESULTS

After 24 months, in the atorvastatin-only group, the mean (+/-SD) HDL cholesterol level was 52.4+/-13.5 mg per deciliter and the mean low-density lipoprotein (LDL) cholesterol level was 143.2+/-42.2 mg per deciliter, as compared with 81.5+/-22.6 mg per deciliter and 115.1+/-48.5 mg per deciliter, respectively, in the torcetrapib-atorvastatin group. During the study, average systolic blood pressure increased by 2.8 mm Hg in the torcetrapib-atorvastatin group, as compared with the atorvastatin-only group. The increase in maximum carotid intima-media thickness, the primary measure of efficacy, was 0.0053+/-0.0028 mm per year in the atorvastatin-only group and 0.0047+/-0.0028 mm per year in the torcetrapib-atorvastatin group (P=0.87). The secondary efficacy measure, annualized change in mean carotid intima-media thickness for the common carotid artery, indicated a decrease of 0.0014 mm per year in the atorvastatin-only group, as compared with an increase of 0.0038 mm per year in the torcetrapib-atorvastatin group (P=0.005).

CONCLUSIONS

In patients with familial hypercholesterolemia, the use of torcetrapib with atorvastatin, as compared with atorvastatin alone, did not result in further reduction of progression of atherosclerosis, as assessed by a combined measure of carotid arterial-wall thickness, and was associated with progression of disease in the common carotid segment. These effects occurred despite a large increase in HDL cholesterol levels and a substantial decrease in levels of LDL cholesterol and triglycerides. (ClinicalTrials.gov number, NCT00136981 [ClinicalTrials.gov].).

Detailed exploration of the endothelium: parameterization of flow-mediated dilation through principal component analysis

Endothelial dysfunction is associated with cardiovascular diseases and their risk factors (CVRF), and flow-mediated dilation (FMD) is increasingly used to explore it. In this test, artery diameter changes after post-ischaemic hyperaemia are classically quantified using maximum peak vasodilation (FMDc). To obtain more detailed descriptors of FMD we applied principal component analysis (PCA) to diameter-time curves (absolute), vasodilation-time curves (relative) and blood-velocity-time curves. Furthermore, combined PCA of vessel size and blood-velocity curves allowed exploring links between flow and dilation. Vessel diameter data for PCA (post-ischaemic: 140 s) were acquired from brachial ultrasound image sequences of 173 healthy male subjects using a computerized technique previously reported by our team based on image registration (Frangi et al 2003 IEEE Trans. Med. Imaging 22 1458). PCA provides a set of axes (called eigenmodes) that captures the underlying variation present in a database of waveforms so that the first few eigenmodes retain most of the variation. These eigenmodes can be used to synthesize each waveform analysed by means of only a few parameters, as well as potentially any signal of the same type derived from tests of new patients. The eigenmodes obtained seemed related to visual features of the waveform of the FMD process. Subsequently, we used eigenmodes to parameterize our data. Most of the main parameters (13 out of 15) correlated with FMDc. Furthermore, not all parameters correlated with the same CVRF tested, that is, serum lipids (i.e., high LDL-c associated with slow vessel return to a baseline, while low HDL-c associated with a lower vasodilation in response to similar velocity stimulus), thus suggesting that this parameterization allows a more detailed and factored description of the process than FMDc.

Snakes based segmentation of the common carotid artery intima media

Ultrasound measurements of the human carotid artery walls are conventionally obtained by manually tracing interfaces between tissue layers. In this study we present a snakes segmentation technique for detecting the intima-media layer of the far wall of the common carotid artery (CCA) in longitudinal ultrasound images, by applying snakes, after normalization, speckle reduction, and normalization and speckle reduction. The proposed technique utilizes an improved snake initialization method, and an improved validation of the segmentation method. We have tested and clinically validated the segmentation technique on 100 longitudinal ultrasound images of the carotid artery based on manual measurements by two vascular experts, and a set of different evaluation criteria based on statistical measures and univariate statistical analysis. The results showed that there was no significant difference between all the snakes segmentation measurements and the manual measurements. For the normalized despeckled images, better snakes segmentation results with an intra-observer error of 0.08, a coefficient of variation of 12.5%, best Bland-Altman plot with smaller differences between experts (0.01, 0.09 for Expert1 and Expert 2, respectively), and a Hausdorff distance of 5.2, were obtained. Therefore, the pre-processing of ultrasound images of the carotid artery with normalization and speckle reduction, followed by the snakes segmentation algorithm can be used successfully in the measurement of IMT complementing the manual measurements. The present results are an expansion of data published earlier as an extended abstract in IFMBE Proceedings (Loizou et al. IEEE Int X Mediterr Conf Medicon Med Biol Eng POS-03 499:1-4, 2004).

Modification of the phased-tracking method for reduction of artifacts in estimated artery wall deformation

Noninvasive measurement of mechanical properties, such as elasticity, of the arterial wall, is useful for diagnosis of atherosclerosis. For assessment of mechanical properties, it is necessary to measure the deformation of the arterial wall. In this study, a modification of the previously proposed phased-tracking method was conducted to improve measurement of the small change in thickness (deformation) of the arterial wall due to the heartbeat. In our previous method, a set of two points along an ultrasonic beam was initially assigned, and the change in thickness of the layer between these two points during an entire cardiac cycle was estimated. In motion estimation with ultrasound, the motion of an interface or a scatterer, which generates an echo, can be obtained by estimating the change in time delay of the echo. For example, in the case of a carotid artery of a healthy subject, there are only two dominant echoes from the lumen-intima and media-adventitia interfaces. Thus, only the displacements of the lumen-intima and media-adventitia interfaces can be estimated, which means that ultrasound can estimate only the change in distance (thickness) between these two interfaces. However, even in this case, our previous method gives different estimates of the change in thickness, depending on the depths (positions in the arterial radial direction) of the two initially assigned points. In this study, modifications of the previous method in terms of the strategy for assignment of layers and the required thickness of an assigned layer were made to reduce such an artificial spatial variation in the estimated changes in thickness. Using the proposed method, errors in estimated changes in thickness were reduced from 21.2 +/- 24.1% to 0.19 +/- 0.04% (mean +/- standard deviation) in simulation experiments. As in the case of the simulation experiments, the spatial variation in estimated changes in thickness also was reduced in in vivo experiments in a carotid artery of a healthy subject and in vitro experiments using two excised, diseased arteries.

Plaque development, vessel curvature, and wall shear stress in coronary arteries assessed by X-ray angiography and intravascular ultrasound

The relationships among vascular geometry, hemodynamics, and plaque development in the coronary arteries are complex and not yet well understood. This paper reports a methodology for the quantitative analysis of in vivo coronary morphology and hemodynamics, with particular emphasis placed on the critical issues of image segmentation and the automated classification of disease severity. We were motivated by the observation that plaque more often developed at the inner curvature of a vessel, presumably due to the relatively lower wall shear stress at these locations. The presented studies are based on our validated methodology for the three-dimensional fusion of intravascular ultrasound (IVUS) and X-ray angiography, introducing a novel approach for IVUS segmentation that incorporates a robust, knowledge-based cost function and a fully optimal, three-dimensional segmentation algorithm. Our first study shows that circumferential plaque distribution depends on local vessel curvature in the majority of vessels. The second study analyzes the correlation between plaque distribution and wall shear stress in a set of 48 in vivo vessel segments. The results were conclusive for both studies, with a stronger correlation of circumferential plaque thickness with local curvature than with wall shear stress. The inverse relationship between local wall shear stress and plaque thickness was significantly more pronounced (p<0.025) in vessel cross sections exhibiting compensatory enlargement (positive remodeling) without luminal narrowing than when the full spectrum of disease severity was considered. The inverse relationship was no longer observed in vessels where less than 35% of vessel cross sections remained without luminal narrowing. The findings of this study confirm, in vivo, the hypothesis that relatively lower wall shear stress is associated with early plaque development.

Cardiovascular disease and cognitive performance in middle-aged and elderly men

BACKGROUND

Decline of cognitive function with age may be due, in part, to atherosclerotic changes. The aim of the present study was to determine the relative contribution of cardiovascular disease (CVD) to cognitive functioning in middle-aged and elderly men.

METHODS

In a cross-sectional study, cognitive tests were administered to 400 independently living men aged 40-80 years. Compound scores were calculated for memory function, processing capacity/speed, and executive function. The MMSE was used as a measure of global cognitive function. Carotid intima-media thickness, pulse wave velocity and ankle brachial blood pressure index were assessed as measures of sub-clinical CVD. The adjusted association of sub-clinical and prevalent CVD with neuropsychological test scores in the total group and in subgroups was assessed by linear regression analysis.

RESULTS

Increased IMT was associated with lower scores on memory performance, and increased PWV was associated with lower scores on processing capacity and executive functioning. Compared with subjects with no CVD, both sub-clinical and prevalent cardiovascular diseases were related to a lower memory performance, beta's (95% CI) were -0.45 (-0.83, -0.07) and -0.45 (-0.84, 0.01), respectively. These associations were present in both middle-aged and elderly men. Furthermore, we observed that for subjects who had sub-clinical or prevalent cardiovascular disease the distribution of MMSE-scores was shifted toward lower values; the distributions were statistically different (p=0.003).

CONCLUSIONS

The results of this study support a relation of sub-clinical CVD with cognitive functioning in middle-aged and elderly men. These results suggest that actions to prevent cognitive decline by preventing atherosclerosis should be taken before middle age.