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

Robust carotid artery recognition in longitudinal B-mode ultrasound images

Automatic segmentation of the arterial lumen from ultrasound images is an important task in clinical diagnosis. Carotid artery recognition, the first task in lumen segmentation, should be performed in a fully automated, fast, and reliable way to further facilitate the low-level task of arterial delineation. In this paper, a user-independent, real-time algorithm is introduced for carotid artery localization in longitudinal B-mode ultrasound images. The proposed technique acts directly on the raw image, and exploits basic statistics along with anatomical knowledge. The method's evaluation and parameter value optimization were performed on a threefold cross validation basis. In addition, the introduced algorithm was systematically compared with another algorithm for common carotid artery recognition in B-mode scans, separately for multi-frame and single-frame data. The data sets used included 2,149 images from 100 subjects taken from three different institutions and covering a wide range of possible lumen and surrounding tissue representations. Using the optimized values, the carotid artery was recognized in all the processed images in both multi-frame and single-frame data. Thus, the introduced technique will further reinforce automatic segmentation in longitudinal B-mode ultrasound images.

Oxidative balance in lymphocytes from patients with nonalcoholic steatohepatitis

Oxidative stress is linked to several human diseases, including nonalcoholic steatohepatitis (NASH). In this study, lymphocytes were used as a model to study this disease. These cells offer several advantages for cellular and molecular studies such as easy accessibility, and they are easily accessible and constitute a "time-persistent" system capable of reflecting the condition of the whole organism. Lymphocytes from patients with NASH display oxidative stress features. Among the possible causes for the overproduction of reactive oxygen species in NASH lymphocytes, there might be alterations of enzymatic pathways, auto-oxidation of glucose and mitochondrial superoxide production, which, in turn, would lead to protein oxidative damage. Increased oxidative stress in lymphocytes from patients with NASH may result in a pro-oxidative environment, which, in turn, could modify the pathway of the enzymatic activities. The data confirm that an imbalance between pro-oxidant and antioxidant defense mechanisms may be an important factor in NASH.

The association between functional and morphological assessments of endothelial function in patients with rheumatoid arthritis: a cross-sectional study

Introduction

Patients with rheumatoid arthritis (RA) are at an increased risk for cardiovascular disease (CVD). One of the earliest manifestations of CVD is endothelial dysfunction (ED), which can lead to functional and morphological vascular abnormalities. Several non-invasive assessments of vascular function and morphology can be utilised to assess vascular health, but little is known about the association between each of these assessments in patients with RA, and they tend to be used interchangeably in the literature. The objective of the present study was to examine associations between measures of vascular function and morphology in patients with RA.

Methods

A total of 201 RA patients (155 females, median (25^th to 75^th percentile) age: 67 (59 to 73)) underwent assessments of microvascular endothelium-dependent and endothelium-independent function (laser Doppler imaging with iontophoresis of acetylcholine and sodium-nitroprusside respectively), macrovascular endothelium-dependent and endothelium-independent function (flow-mediated dilatation and glyceryl-trinitrate-mediated dilation respectively), and vascular morphology (pulse wave analysis, carotid intima-media thickness (cIMT), and carotid plaque).

Results

Spearman's correlations revealed that from the functional parameters, only macrovascular endothelium-independent function was inversely associated with cIMT (-0.294 (P < 0.001)) after applying the Bonferroni correction for multiple comparisons. For carotid plaque, t tests showed that macrovascular endothelium-independent function was lower in patients with plaque than without (15.5 ± 8.3 vs. 23.1 ± 9.1%, P = 0.002, respectively).

Conclusions

With the exception of macrovascular endothelium-independent function, all other measures of vascular function were not associated with vascular morphology. This suggests that different assessments of vascular function and morphology in patients with RA reflect quite distinct mechanisms and phases of the atherosclerotic process and should not be used interchangeably.

Serum levels of monobenzylphthalate (MBzP) is related to carotid atherosclerosis in the elderly

BACKGROUND AND OBJECTIVE

Background exposure to environmental contaminants has recently emerged as a new risk factor for cardiovascular disease in general and to atheroclerosis in particular. This cross-sectional study was performed to evaluate if serum concentrations of the phthalate metabolite monobenzylphthalate (MBzP) are related to atheroclerosis in the carotid arteries.

METHODS

In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (1003 subjects all aged 70) the prevalence of overt plaques and echogenicity (gray-scale median, GSM) of carotid artery plaques were recorded by ultrasound in both of the carotid arteries. The intima-media thickness (IMT) and echogenicity (IM-GSM) of the intima-media complex were also measured. The phthalate metabolite MBzP was analyzed in serum by a liquid chromatograph/tandem mass spectrometer.

RESULTS

The circulating level of the phthalate MBzP was related to intima-media thickness (IMT) when adjusting for gender, blood pressure, body mass index (BMI), waist circumference, HDL- and LDL-cholesterol, serum triglycerides, blood glucose and smoking (p=0.034). High levels of MBzP were also strongly associated with an echogenic IM-GSM and plaque GSM (p=0.0001 for both outcomes after adjustment) but not to plaque prevalence (p=0.42).

CONCLUSION

The phthalate metabolite MBzP was strongly related to the echogenicity of intima-media and plaques and also to IMT, independently of traditional CV risk factors. This suggests a role for the phthalate MBzP in the development of atherosclerosis.

Thromboxane prostaglandin receptor antagonist and carotid atherosclerosis progression in patients with cerebrovascular disease of ischemic origin: a randomized controlled trial

BACKGROUND AND PURPOSE

Thromboxane prostaglandin receptors have been implicated to be involved in the atherosclerotic process. We assessed whether Terutroban, a thromboxane prostaglandin receptor antagonist, affects the progression of atherosclerosis, as measured by common carotid intima-media thickness and carotid plaques.

METHODS

A substudy was performed among 1141 participants of the aspirin-controlled 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. Common carotid intima-media thickness and carotid plaque occurrence was measured during a 3-year period.

RESULTS

Baseline characteristics did not differ between Terutroban (n=592) and aspirin (n=549) treated patients and were similar as in the main study. Mean study and treatment duration were similar (28 and 25 months, respectively). In the Terutroban group, the annualized rate of change in common carotid intima-media thickness was 0.006 mm per year (95% confidence interval, -0.004 to 0.016) and -0.005 mm per year (95% confidence interval, -0.015 to 0.005) in the aspirin group. There was no statistically significant difference between the groups in the annualized rate of change of common carotid intima-media thickness (0.011 mm per year; 95% confidence interval, -0.003 to 0.025). At 12 months of follow-up, 66% of Terutroban patients had no emergent plaques, 31% had 1 to 2 emergent plaques, and 3% had ≥3 emergent plaques. In the aspirin group, the corresponding percentages were 64%, 32%, and 4%. Over time, there was no statistically significant difference in the number of emergent carotid plaques between treatment modalities (rate ratio, 0.91; 95% confidence interval, 0.77-1.07).

CONCLUSIONS

Compared with aspirin, Terutroban did not beneficially affect progression of carotid atherosclerosis among well-treated patients with a history of ischemic stroke or transient ischemic attacks with an internal carotid stenosis <70%.

CLINICAL TRIAL REGISTRATION URL

http://www.controlled-trials.com. Unique identifier: ISRCTN66157730.

Attenuated brain-derived neurotrophic factor and hypertrophic remodelling: the SABPA study

Brain-derived neurotrophic factor (BDNF) has been linked to neurological pathologies, but its role in cardiometabolic disturbances is limited. We aimed to assess the association between serum BDNF levels and structural endothelial dysfunction (ED) as determined by cross-sectional wall area (CSWA) and albumin/creatinine ratio (ACR) in black Africans. Ambulatory blood pressure (BP) and ultrasound CSWA values were obtained from 82 males and 90 females. Fasting blood and 8 h overnight urine samples were collected to determine serum BDNF and cardiometabolic risk markers, that is, glycated haemoglobin (HbA1c), lipids, inflammation and ACR. BDNF median split × gender interaction effects for structural ED justified stratification of BDNF into low and high (⩽/>1.37 ng ml(-1)) gender groups. BDNF values (0.86-1.98 ng ml(-1)) were substantially lower than reference ranges (6.97-42.6 ng ml(-1)) in the African gender cohort, independent of age and body mass index. No relationship was revealed between BDNF and renal function and was opposed by an inverse relationship between BDNF and CSWA (r=-0.17; P=0.03) in the African cohort. Linear regression analyses revealed a positive relationship between systolic BP and structural remodelling in the total cohort and low-BDNF gender groups. In the high-BDNF females, HbA1C was associated with structural remodelling. Attenuated or possible downregulated BDNF levels were associated with hypertrophic remodelling, and may be a compensatory mechanism for the higher BP in Africans. In addition, metabolic risk and hypertrophic remodelling in women with high BDNF underpin different underlying mechanisms for impaired neurotrophin homeostasis in men and women.

The impact of variability in ultrasound settings on the measured echolucency of the carotid intima-media

BACKGROUND

B-mode ultrasound measurements of the echolucency of the carotid intima-media may hold information on cardiovascular risk. The information obtained from this measurement may depend on which gain settings are used. We studied the effect of gain settings on echolucency measurements and its consequences on risk factor relations and treatment effects.

METHODS

We used two approaches. In the first, we examined the relationship between calibration, gain and common grey-scale median (GSM) from repeated ultrasound images obtained from four healthy individuals at gain settings ranging from -20 to 20 dB. In the second, we evaluated the effect of gain settings on the relation of risk factors and statin treatment with common GSM, using images from 325 participants of the Measuring Effects on Intima-Media Thickness: an Evaluation of Rosuvastatin (METEOR) study with documented gain settings. Echolucency of the carotid intima-media was measured from ultrasound images using PaintShop Pro and Artery Measurement Software and expressed as GSM.

RESULTS

In healthy individuals, common GSM increased with increments in gain setting, primarily when the measurements were not calibrated. In the METEOR study sample, age and sex were significantly related to gain setting. The risk factor relations with common GSM were of the same magnitude and direction after adjustment for gain setting. Furthermore, adjustment for gain setting did not alter the rates of GSM change over time.

CONCLUSION

Extreme variability in gain settings has a major impact on the echolucency measurements of the far wall common carotid intima-media. Calibration should be used to adjust for these effects of gain settings. Variability in gain settings, however, seems limited in real practice and did not change the direction and magnitude of the relations under study. However, as age and sex are major determinants of gain settings, adjustment for or stratification by age and sex is recommended in studies into echolucency of the carotid intima-media in situations in which gain settings are unknown.

Metformin for non-diabetic patients with coronary heart disease (the CAMERA study): a randomised controlled trial

BACKGROUND

Metformin reduces cardiovascular risk in patients with type 2 diabetes seemingly independent of lowering blood glucose concentration. We assessed the cardiovascular effects of metformin in individuals without type 2 diabetes.

METHODS

We did a single-centre, double-blind, placebo-controlled trial at the Glasgow Clinical Research Facility (Glasgow, UK). We enrolled patients taking statins who did not have type 2 diabetes but who did have coronary heart disease and large waist circumferences. Participants were randomly assigned (1:1) by computer to either metformin (850 mg twice daily) or matching placebo in block sizes of four. Patients, investigators, trial staff, and statisticians were masked to treatment allocation. The primary endpoint was progression of mean distal carotid intima-media thickness (cIMT) over 18 months in the modified intention-to-treat population. Secondary endpoints were changes in carotid plaque score (in six regions), measures of glycaemia (HbA1c, fasting glucose, and insulin concentrations, and Homeostasis Model Assessment of Insulin Resistance [HOMA-IR]), and concentrations of lipids, high sensitivity C-reactive protein, and tissue plasminogen activator. The trial was registered at ClinicalTrials.gov, number NCT00723307.

FINDINGS

We screened 356 patients, of whom we enrolled 173 (86 in the metformin group, 87 in the placebo group). Average age was 63 years. At baseline, mean cIMT was 0·717 mm (SD 0·129) and mean carotid plaque score was 2·43 (SD 1·55). cIMT progression did not differ significantly between groups (slope difference 0·007 mm per year, 95% CI -0·006 to 0·020; p=0·29). Change of carotid plaque score did not differ significantly between groups (0·01 per year, 95% CI -0·23 to 0·26; p=0·92). Patients taking metformin had lower HbA1c, insulin, HOMA-IR, and tissue plasminogen activator compared with those taking placebo, but there were no significant differences for total cholesterol, HDL-cholesterol, non-HDL-cholesterol, triglycerides, high sensitivity C-reactive protein, or fasting glucose. 138 adverse events occurred in 64 patients in the metformin group versus 120 in 60 patients in the placebo group. Diarrhoea and nausea or vomiting were more common in the metformin group than in the placebo group (28 vs 5).

INTERPRETATION

Metformin had no effect on cIMT and little or no effect on several surrogate markers of cardiovascular disease in non-diabetic patients with high cardiovascular risk, taking statins. Further evidence is needed before metformin can be recommended for cardiovascular benefit in this population.

FUNDING

Chief Scientist Office (Scotland).

The relationship between carotid intima-media thickness and global atherosclerosis

Background

The aim of this study was to investigate the relationship between (i) carotid intima–media thickness (CIMT) at baseline as well as (ii) change in CIMT over 5 years (ΔCIMT) and atherosclerotically induced luminal narrowing in non-coronary arterial territories assessed by whole-body magnetic resonance angiography (WBMRA).

Methods and results

In subgroups of the Prospective Investigation of Vasculature in Uppsala Seniors (PIVUS) study, US measurements of CIMT in the common carotid arteries were analysed at 70 and 75 years and ΔCIMT was calculated (n = 272). WBMRA, assessing arterial stenosis in five different territories by which also a total atherosclerotic score (TAS) was calculated, was performed at 70 years (n = 306).

Results

Carotid intima–media thickness in the carotid artery at baseline was correlated with TAS (P = 0·0001) when adjusted to a set of traditional risk factors for atherosclerosis, as well as to stenosis in two of the different investigated territories (aorta and lower leg, P = 0·013 and P = 0·004), but there was no significant correlation between ΔCIMT and TAS (P = 0·41).

Conclusions

In the present study, CIMT, but not ΔCIMT over 5 years, in the carotid artery was related to overall stenoses in the body, as assessed by WBMRA. These findings support CIMT as a general marker for atherosclerosis.

An integrated system for the segmentation of atherosclerotic carotid plaque ultrasound video

The robust border identification of atherosclerotic carotid plaque, the corresponding degree of stenosis of the common carotid artery (CCA), and also the characteristics of the arterial wall, including plaque size, composition, and elasticity, have significant clinical relevance for the assessment of future cardiovascular events. To facilitate the follow-up and analysis of the carotid stenosis in serial clinical investigations, we propose and evaluate an integrated system for the segmentation of atherosclerotic carotid plaque in ultrasound videos of the CCA based on video frame normalization, speckle reduction filtering, M-mode state-based identification, parametric active contours, and snake segmentation. Initially, the cardiac cycle in each video is identified and the video M-mode is generated, thus identifying systolic and diastolic states. The video is then segmented for a time period of at least one full cardiac cycle. The algorithm is initialized in the first video frame of the cardiac cycle, with human assistance if needed, and the moving atherosclerotic plaque borders are tracked and segmented in the subsequent frames. Two different initialization methods are investigated in which initial contours are estimated every 20 video frames. In the first initialization method, the initial snake contour is estimated using morphology operators; in the second initialization method, the Chan-Vese active contour model is used. The performance of the algorithm is evaluated on 43 real CCA digitized videos from B-mode longitudinal ultrasound segments and is compared with the manual segmentations of an expert, available every 20 frames in a time span of 3 to 5 s, covering, in general, 2 cardiac cycles. The segmentation results were very satisfactory, according to the expert objective evaluation, for the two different methods investigated, with true-negative fractions (TNF-specificity) of 83.7 ± 7.6% and 84.3 ± 7.5%; true-positive fractions (TPF-sensitivity) of 85.42 ± 8.1% and 86.1 ± 8.0%; and between the ground truth and the proposed segmentation method, kappa indices (KI) of 84.6% and 85.3% and overlap indices of 74.7% and 75.4%. The segmentation contours were also used to compute the cardiac state identification and radial, longitudinal, and shear strain indices for the CCA wall and plaque between the asymptomatic and symptomatic groups were investigated. The results of this study show that the integrated system investigated in this study can be successfully used for the automated video segmentation of the CCA plaque in ultrasound videos.

Flow-mediated vasodilation was found to be an independent predictor of changes in the carotid plaque status during a 5-year follow-up

AIM

It has previously been shown that flow-mediated vasodilation is a predictor of the progression of the intima-media thickness (IMT). In the present study, the degree of endothelium-dependent vasodilation in both resistance and conduit arteries was evaluated as a predictor of the IMT and plaque progression.

METHODS

In the population-based Prospective Study of the Vasculature in Uppsala Seniors(PIVUS) trial(1,016 subjects all 70 years of age), the invasive forearm technique using acetylcholine administered in the brachial artery (resistance artery, EDV) and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (conduit artery, FMD) were evaluated. The IMT and number of carotid arteries with plaques (0, 1 or 2) were recorded using ultrasound at the baseline investigation and the follow-up visit conducted five years later.

RESULTS

A total of 760 subjects had valid measurements of the IMT and carotid artery plaques at both the investigations conducted at 70 and 75 years of age. Neither the FMD nor EDV significantly predicted the change in IMT over five years. However, the FMD, but not EDV, was associated with the change in carotid plaque burden during the follow-up period, independent of classical risk factors, such as gender, waist circumference, fasting blood glucose, systolic and diastolic blood pressure, HDL- and LDL-cholesterol, serum triglycerides, BMI and smoking (OR 0.81 for a 1 SD change in FMD, 95%CI 0.68 to 0.95, p=0.010).

CONCLUSIONS

The FMD was found to be a predictor of changes in the carotid plaque status, but not IMT, during the 5-year follow-up period, independent of classical cardiovascular risk factors.

Automated boundary extraction of the spinal canal in MRI based on dynamic programming

The spinal cord is the only communication link between the brain and the body. The abnormalities in it can lead to severe pain and sometimes to paralysis. Due to the growing gap between the number of available radiologists and the number of required radiologists, the need for computer-aided diagnosis and characterization is increasing. To ease this gap, we have developed a computer-aided diagnosis and characterization framework in lumbar spine that includes the spinal cord, vertebrae, and intervertebral discs. In this paper, we propose two spinal cord boundary extraction methods that fit into our framework based on dynamic programming in lumbar spine MRI. Our method incorporates the intensity of the image and the gradient of the image into a dynamic programming scheme and works in a fully-automatic fashion. The boundaries generated by our method is compared against reference boundaries in terms of Fréchet distance which is known to be a metric for shape analysis. The experimental results from 65 clinical data show that our method finds the spinal canal boundary correctly achieving a mean Fréchet distance of 13.5 pixels. For almost all data, the extracted boundary falls within the spinal cord. So, it can be used as a landmark when marking background regions and finding regions of interest.

Long-term exposure to black carbon and carotid intima-media thickness: the normative aging study

BACKGROUND

Evidence suggests that air pollution is associated with atherosclerosis and that traffic-related particles are a particularly important contributor to the association.

OBJECTIVES

We investigated the association between long-term exposure to black carbon, a correlate of traffic particles, and intima-media thickness of the common carotid artery (CIMT) in elderly men residing in the greater Boston, Massachusetts, area.

METHODS

We estimated 1-year average exposures to black carbon at the home addresses of Normative Aging Study participants before their first CIMT measurement. The association between estimated black carbon levels and CIMT was estimated using mixed effects models to account for repeated outcome measures. In secondary analyses, we examined whether living close to a major road or average daily traffic within 100 m of residence was associated with CIMT.

RESULTS

There were 380 participants (97% self-reported white race) with an initial visit between 2004 and 2008. Two or three follow-up CIMT measurements 1.5 years apart were available for 340 (89%) and 260 (68%) men, respectively. At first examination, the average ± SD age was 76 ± 6.4 years and the mean ± SD CIMT was 0.99 ± 0.18 mm. A one-interquartile range increase in 1-year average black carbon (0.26 µg/m3) was associated with a 1.1% higher CIMT (95% CI: 0.4, 1.7%) based on a fully adjusted model.

CONCLUSIONS

Annual mean black carbon concentration based on spatially resolved exposure estimates was associated with CIMT in a population of elderly men. These findings support an association between long-term air pollution exposure and atherosclerosis.

Segmentation of the common carotid artery walls based on a frequency implementation of active contours: segmentation of the common carotid artery walls

Atherosclerosis is one of the most extended cardiovascular diseases nowadays. Although it may be unnoticed during years, it also may suddenly trigger severe illnesses such as stroke, embolisms or ischemia. Therefore, an early detection of atherosclerosis can prevent adult population from suffering more serious pathologies. The intima-media thickness (IMT) of the common carotid artery (CCA) has been used as an early and reliable indicator of atherosclerosis for years. The IMT is manually computed from ultrasound images, a process that can be repeated as many times as necessary (over different ultrasound images of the same patient), but also prone to errors. With the aim to reduce the inter-observer variability and the subjectivity of the measurement, a fully automatic computer-based method based on ultrasound image processing and a frequency-domain implementation of active contours is proposed. The images used in this work were obtained with the same ultrasound scanner (Philips iU22 Ultrasound System) but with different spatial resolutions. The proposed solution does not extract only the IMT but also the CCA diameter, which is not as relevant as the IMT to predict future atherosclerosis evolution but it is a statistically interesting piece of information for the doctors to determine the cardiovascular risk. The results of the proposed method have been validated by doctors, and these results are visually and numerically satisfactory when considering the medical measurements as ground truth, with a maximum deviation of only 3.4 pixels (0.0248 mm) for IMT.

Evidence for a genetic link between bone and vascular measures in African ancestry families

Bone mineral density (BMD) has been inversely associated with subclinical and clinical cardiovascular disease (CVD) in population studies, but the potential mechanisms underlying this relationship are unclear. To test if there is a genetic basis underlying this association, we determined the phenotypic and genetic correlations between BMD and carotid artery ultrasound measures in families. Dual-energy X-ray absorptiometry and peripheral quantitative computed tomography were used to measure BMD in 461 individuals with African ancestry belonging to seven large, multigenerational families (mean family size 66; 3414 total relative pairs). Carotid artery ultrasound was used to measure adventitial diameter (AD) and intima-media thickness (IMT). Phenotypic and genetic correlations between BMD and carotid measures were determined using pedigree-based maximum likelihood methods. We adjusted for potential confounding factors, including age, sex, body weight, height, menopausal status, smoking, alcohol intake, walking for exercise, diabetes, hypertension, serum lipid and lipoprotein levels, inflammation markers, and kidney function. We found statistically significant phenotypic (ρ = -0.19) and genetic (ρG  = -0.70) correlations (p < 0.05 for both) between lumbar spine BMD and AD in fully adjusted models. There was also a significant genetic correlation between trabecular BMD at the radius and IMT in fully adjusted models (ρG  = -0.398; p < 0.05). Our findings indicate that the previously observed association between osteoporosis and CVD in population-based studies may be partly mediated by genetic factors and that the pleiotropic effects of these genes may operate independently of traditional risk pathways.

Fully automated on-screen carotid intima-media thickness measurement: a screening tool for subclinical atherosclerosis

PURPOSE

Carotid intima-media thickness (CIMT) is generally considered an appropriate direct vascular method for cardiovascular risk assessment. The objective of this study was to evaluate the feasibility and reproducibility of a newly developed automated on-screen carotid ultrasound with respect to manual measurement with a conventional system.

METHODS

We assessed CIMT in 50 consecutive patients (age 62 ± 5 years, range 21-79 years, 36 men) twice, using a newly developed automated ultrasound (CardioHealth Station) and a conventional system with manual measurement (Acuson, Sequoia). For each patient, three frozen frames of the distal 10 mm of the right and left common carotid arteries were acquired on the two systems, by operators blinded to each other. The average of the mean value of three readings of each system was calculated.

RESULTS

The intraclass correlation coefficient of the interoperator variability was 0.95 and 0.94 for the automated and manual measurements, respectively. The comparative coefficient of variation of the interoperator variability was 8.2 and 8.7% for the automated and manual measurements, respectively. There was no clinically relevant difference between measurements obtained by the two systems (intraclass correlation coefficient = 0.98). The acquisition time of the automated system was significantly shorter than the conventional system (p < 0.01).

CONCLUSIONS

Fully automated on-screen measurements of CIMT are feasible, faster, and as reproducible as conventional manual measurements and may be suitable and cost-effective for screening application in community medicine.

Carotid artery segmentation in ultrasound images and measurement of intima-media thickness

Background. The segmentation of the common carotid artery (CCA) wall is imperative for the determination of the intima-media thickness (IMT) on B-mode ultrasound (US) images. The IMT is considered an important indicator in the evaluation of the risk for the development of atherosclerosis. In this paper, authors have discussed the relevance of measurements in clinical practices and the challenges that one has to face while approaching the segmentation of carotid artery on ultrasound images. The paper presents an overall review of commonly used methods for the CCA segmentation and IMT measurement along with the different performance metrics that have been proposed and used for performance validation. Summary and future directions are given in the conclusion.

End-organ damage in urbanized Africans with low plasma renin levels: the SABPA study

The purpose of this study was to evaluate whether active renin concentration is associated with markers of end-organ damage in urbanized Africans. This study forms part of the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study. For this study, 81 men and 74 women were divided into low- and high-renin groups. Ambulatory blood pressure measurements were conducted. A resting 12-lead ECG was determined in order to determine the gender-specific Cornell voltage. Cardiovascular variables were continuously recorded with the Finometer. Carotid-dorsalis pedis pulse wave velocity was obtained with the Complior acquisition system. The carotid intima-media thickness (CIMT) was obtained with the SonoSite MicroMaxx. Blood samples were collected; serum and plasma were stored at -80 °C for analysis. Anthropometric measurements were taken using standard methods. A general health questionnaire was also completed. The urinary creatinine was determined with a calorimetric method and albumin with a turbidimetric method. The serum sodium and potassium were determined by making use of the Konelab TM 20i Sequential Multiple Analyzer Computer (SMAC). The concentration of active renin in the plasma was analyzed by making use of a high-sensitivity radio-immunometric assay. A negative association (r=-0.29, p<0.01) exists between renal function (ACR) and plasma renin in the low-renin group (<6.18 pg/mL), which was not observed in Africans with high-renin levels. It seems evident that low renin in black South Africans may result in sub-clinical renal damage and impaired vascular function in a group of urbanized black South Africans.

Ultrasound common carotid artery segmentation based on active shape model

Carotid atherosclerosis is a major reason of stroke, a leading cause of death and disability. In this paper, a segmentation method based on Active Shape Model (ASM) is developed and evaluated to outline common carotid artery (CCA) for carotid atherosclerosis computer-aided evaluation and diagnosis. The proposed method is used to segment both media-adventitia-boundary (MAB) and lumen-intima-boundary (LIB) on transverse views slices from three-dimensional ultrasound (3D US) images. The data set consists of sixty-eight, 17 × 2 × 2, 3D US volume data acquired from the left and right carotid arteries of seventeen patients (eight treated with 80 mg atorvastatin and nine with placebo), who had carotid stenosis of 60% or more, at baseline and after three months of treatment. Manually outlined boundaries by expert are adopted as the ground truth for evaluation. For the MAB and LIB segmentations, respectively, the algorithm yielded Dice Similarity Coefficient (DSC) of 94.4% ± 3.2% and 92.8% ± 3.3%, mean absolute distances (MAD) of 0.26 ± 0.18 mm and 0.33 ± 0.21 mm, and maximum absolute distances (MAXD) of 0.75 ± 0.46 mm and 0.84 ± 0.39 mm. It took 4.3 ± 0.5 mins to segment single 3D US images, while it took 11.7 ± 1.2 mins for manual segmentation. The method would promote the translation of carotid 3D US to clinical care for the monitoring of the atherosclerotic disease progression and regression.

Ultrasound contrast image segmentation using a modified level set method

Manual segmentation of ultrasound contrast images is time-consuming and inevitable to variability, and computer-based segmentation algorithms often require user interaction. This paper proposes a novel level set model for fully automated segmentation of vascular ultrasound contrast images. The initial contour of arterial boundaries is acquired based on an automatic procedure. The level set model moves the initial contour towards the boundaries of arterial inner wall based on minimization of the energy function. The traditional energy function is improved by introducing an edge detector based on image gradient and the standard difference image. Both spatial and temporal information of the image are considered, and the robustness and accuracy of the level set model is enhanced. Ultrasonic contrast images of living mouse are acquitted with high frequency ultrasound system. Images of carotid arteries are processed with our method. The segmentation results using the proposed method are evaluated against two observers' hand-outlined boundaries, showing that computer-generated boundaries agree well with the observers' hand-outlined boundaries as much as the different observers agree with each other.

Exploring the link between cardiovascular reactivity and end-organ damage in African and Caucasian men: the SABPA study

BACKGROUND

Heart failure in the African population is reaching alarming levels. Increased afterload as a result of increased vasoconstriction during stress may lead to impaired ventricular function and stroke volume (SV) as well as vascular hypertrophy. In this study, we challenged the cardiovascular system in order to evaluate the possible contribution of indicators of α-adrenergic vasoconstriction (i.e., vascular resistance and SV reactivity) on left ventricular mass and carotid intima-media thickness (CIMT) in African and Caucasian men.

METHODS

We evaluated 101 African and 101 Caucasian male schoolteachers. Ambulatory blood pressure measurements were taken. Total peripheral resistance, Windkessel compliance and SV, and resting and reactivity values were obtained using a Finometer device while the Stroop color word conflict test was being applied. The electrocardiogram was recorded to obtain the Cornell product as indication of left ventricular mass. The CIMT was measured and the cross-sectional wall area (CSWA) calculated.

RESULTS

African men showed higher total vascular resistance resting values as well as higher positive reactivity values compared with Caucasian men. The SV decreased significantly during stress in African men while resting blood pressure and the Cornell product value increased. SV showed a consistent association with left ventricular mass (β = -0.21; P = 0.04) and CSWA (β = -0.24; P = 0.01) in single and multiple regression analyses. No such associations were evident in the Caucasian men.

CONCLUSIONS

African men showed a suppressed SV, possibly as a result of an increased ventricular afterload leading to end-organ damage.

Fully automated segmentation and tracking of the intima media thickness in ultrasound video sequences of the common carotid artery

The robust identification and measurement of the intima media thickness (IMT) has a high clinical relevance because it represents one of the most precise predictors used in the assessment of potential future cardiovascular events. To facilitate the analysis of arterial wall thickening in serial clinical investigations, in this paper we have developed a novel fully automatic algorithm for the segmentation, measurement, and tracking of the intima media complex (IMC) in B-mode ultrasound video sequences. The proposed algorithm entails a two-stage image analysis process that initially addresses the segmentation of the IMC in the first frame of the ultrasound video sequence using a model-based approach; in the second step, a novel customized tracking procedure is applied to robustly detect the IMC in the subsequent frames. For the video tracking procedure, we introduce a spatially coherent algorithm called adaptive normalized correlation that prevents the tracking process from converging to wrong arterial interfaces. This represents the main contribution of this paper and was developed to deal with inconsistencies in the appearance of the IMC over the cardiac cycle. The quantitative evaluation has been carried out on 40 ultrasound video sequences of the common carotid artery (CCA) by comparing the results returned by the developed algorithm with respect to ground truth data that has been manually annotated by clinical experts. The measured IMT(mean) ± standard deviation recorded by the proposed algorithm is 0.60 mm ± 0.10, with a mean coefficient of variation (CV) of 2.05%, whereas the corresponding result obtained for the manually annotated ground truth data is 0.60 mm ± 0.11 with a mean CV equal to 5.60%. The numerical results reported in this paper indicate that the proposed algorithm is able to correctly segment and track the IMC in ultrasound CCA video sequences, and we were encouraged by the stability of our technique when applied to data captured under different imaging conditions. Future clinical studies will focus on the evaluation of patients that are affected by advanced cardiovascular conditions such as focal thickening and arterial plaques.

The echogenicity of the intima-media complex in the common carotid artery is related to insulin resistance measured by the hyperinsulinemic clamp in elderly men

The echogenicity of the intima-media complex (IM-GSM) has recently been shown to be related to the echogenicity in carotid artery plaque and to predict cardiovascular (CV) mortality. The present study aims to evaluate the relationship between metabolic CV risk factors, with special emphasis on insulin resistance, and IM-GSM in the carotid artery. Carotid artery ultrasound with grey-scale median analysis of the intima-media complex, IM-GSM, was performed in a population sample of 480 men aged 75 years. In these subjects, a euglycemic hyperinsulinemic clamp to investigate insulin resistance was performed together with measurements of conventional CV risk factors at the age of 70. The metabolic syndrome (MetS) was defined by the NCEP/ATPIII-criteria. In univariate analysis, IM-GSM in the common carotid artery was inversely correlated with the intima-media thickness (IMT), body mass index (BMI), waist/hip ratio, fasting glucose, serum triglycerides, low HDL cholesterol and insulin resistance at the clamp (r = -0·24, P<0·001). In multiple regression analysis, only insulin resistance at the clamp and BMI were independently related to IM-GSM. Subjects with the MetS (22%) showed a reduced IM-GSM when compared to those without (64 ± 20 SD versus 68 ± 19, P<0·05). Because the echogenicity of the intima-media complex in the carotid artery is related to obesity and insulin resistance at clamp independently of IMT, this new vascular characteristic would serve as a marker of vascular alterations induced by insulin resistance and the MetS and has the advantage to be obtainable in almost all subjects.

Increased age, high body mass index and low HDL-C levels are related to an echolucent carotid intima-media: the METEOR study

INTRODUCTION

Echolucent plaques are related to a higher cardiovascular risk. Studies to investigate the relationship between echolucency and cardiovascular risk in the early stages of atherosclerosis are limited. We studied the relationship between cardiovascular risk factors and echolucency of the carotid intima-media in low-risk individuals.

METHODS

Data were analysed from the Measuring Effects on Intima-Media Thickness: an Evaluation of Rosuvastatin (METEOR) study, a randomized placebo-controlled trial including 984 individuals which showed that rosuvastatin attenuated the rate of change of carotid intima-media thickness (CIMT). In this post hoc analysis, duplicate baseline ultrasound images from the far wall of the left and right common carotid arteries were used for the evaluation of the echolucency of the carotid intima-media, measured by grey-scale median (GSM) on a scale of 0-256. Low GSM values reflect echolucent, whereas high values reflect echogenic structures. The relationship between baseline GSM and cardiovascular risk factors was evaluated using linear regression models.

RESULTS

Mean baseline GSM (± SD) was 84 ± 29. Lower GSM of the carotid intima-media was associated with older age, high body mass index (BMI) and low levels of high-density lipoprotein cholesterol (HDL-C) [beta -4.49, 95% confidence interval (CI) -6.50 to -2.49; beta -4.51, 95% CI -6.43 to -2.60; beta 2.45, 95% CI 0.47 to 4.42, respectively]. Common CIMT was inversely related to GSM of the carotid intima-media (beta -3.94, 95% CI -1.98 to -5.89).

CONCLUSION

Older age, high BMI and low levels of HDL-C are related to echolucency of the carotid intima-media. Hence, echolucency of the carotid intima-media may be used as a marker of cardiovascular risk profile to provide more information than thickness alone.

Constrained snake vs. conventional snake for carotid ultrasound automated IMT measurements on multi-center data sets

Accurate intima-media thickness (IMT) measurement of the carotid artery from minimal plaque ultrasound images is a relevant clinical need, since IMT increase is related to the progression of atherosclerosis. In this paper, we describe a novel dual snake-based model for the high-performance carotid IMT measurement, called Carotid Measurement Using Dual Snakes (CMUDS). Snakes (which are deformable contours) adapt to the lumen-intima (LI) and media-adventitia (MA) interfaces, thus enabling the IMT computation as distance between the LI and MA snakes. However, traditional snakes might be unable to maintain a correct distance and in some spatial location along the artery, it might even collapse between them or diverge. The technical improvement of this work is the definition of a dual snake-based constrained system, which prevents the LI and MA snakes from collapsing or bleeding, thus optimizing the IMT estimation. The CMUDS system consists of two parametric models automatically initialized using the far adventitia border which we automatically traced by using a previously developed multi-resolution approach. The dual snakes evolve simultaneously and are constrained by the distances between them, ensuring the regularization of LI/MA topology. We benchmarked our automated CMUDS with the previous conventional semi-automated snake system called Carotid Measurement Using Single Snake (CMUSS). Two independent readers manually traced the LIMA boundaries of a multi-institutional, multi-ethnic, and multi-scanner database of 665 CCA longitudinal 2D images. We evaluated our system performance by comparing it with the gold standard as traced by clinical readers. CMUDS and CMUSS correctly processed 100% of the 665 images. Comparing the performance with respect to the two readers, our automatically measured IMT was on average very close to that of the two readers (IMT measurement biases for CMUSS was equal to -0.011±0.329mm and -0.045±0.317mm, respectively, while for CMUDS, it was 0.030±0.284mm and -0.004±0.273mm, respectively). The Figure-of-Merit of the system was 98.5% and 94.4% for CMUSS, while 96.0% and 99.6% for CMUDS, respectively. Results showed that the dual-snake system CMUDS reduced the IMT measurement error accuracy (Wilcoxon, p<0.02) and the IMT error variability (Fisher, p<3×10(-2)). We propose the CMUDS technique for use in large multi-centric studies, where the need for a standard, accurate, and automated IMT measurement technique is required.

Progress in atherosclerotic plaque imaging

Cardiovascular diseases are the primary cause of mortality in the industrialized world, and arterial obstruction, triggered by rupture-prone atherosclerotic plaques, lead to myocardial infarction and cerebral stroke. Vulnerable plaques do not necessarily occur with flow-limiting stenosis, thus conventional luminographic assessment of the pathology fails to identify unstable lesions. In this review we discuss the currently available imaging modalities used to investigate morphological features and biological characteristics of the atherosclerotic plaque. The different imaging modalities such as ultrasound, magnetic resonance imaging, computed tomography, nuclear imaging and their intravascular applications are illustrated, highlighting their specific diagnostic potential. Clinically available and upcoming methodologies are also reviewed along with the related challenges in their clinical translation, concerning the specific invasiveness, accuracy and cost-effectiveness of these methods.

Effect of rosuvastatin on the echolucency of the common carotid intima-media in low-risk individuals: the METEOR trial

BACKGROUND

The echolucency of the carotid intima-media is related to increased cardiovascular risk factor levels, morbidity, and mortality. The aim of this study was to assess the effect of statins on the echolucency of the common carotid intima-media in a low-risk population.

METHODS

Data from the Measuring Effects on Intima-Media Thickness: An Evaluation of Rosuvastatin study were used. Ultrasound images from the far walls of the left and right common carotid arteries were used for evaluation of the echolucency of the carotid intima-media, measured by grayscale median (GSM). Low GSM values reflect echolucent structures, whereas high values reflect echogenic structures. The primary end point was the difference in the annual rate of change in GSM between rosuvastatin and placebo.

RESULTS

Two-year change in GSM did not significantly differ between rosuvastatin and placebo in the total population, with a mean difference in the rate of change in GSM of 1.13 (95% confidence interval, -1.00 to 3.25). The effect of rosuvastatin differed across quintiles of baseline GSM values (P for interaction = .01). In the lowest quintile (n = 175) (i.e., in those with the most echolucent intima-media), the difference in the rate of change in GSM between rosuvastatin and placebo was 4.18 (95% confidence interval, -0.23 to 8.58). Increases in GSM were significantly related to decreasing low-density lipoprotein cholesterol levels in the lowest quintile (β = 0.76; 95% confidence interval, 0.26 to 1.25).

CONCLUSIONS

Treatment with rosuvastatin did not affect the echolucency of the arterial wall in all low-risk individuals. However, a potential effect of rosuvastatin on the echolucency of the common carotid intima-media is most likely to be found in individuals with echolucent arterial walls at baseline.

Arterial structure and function in mild primary hyperparathyroidism is not directly related to parathyroid hormone, calcium, or vitamin D

Objective

Elevated levels of calcium and parathyroid hormone (PTH), characteristics of primary hyperparathyroidism (PHPT), may be associated with cardiovascular morbidity and mortality in the general population. We evaluated the possible vascular effects of these risk factors in patients with mild PHPT by using standard methods and new imaging techniques.

Design

A prospective case-control study.

Subjects and Methods

Forty-eight patients with mild PHPT without any known cardiovascular risk factors were studied at baseline and at one year after parathyroidectomy (PTX) in comparison with 48 healthy age- and gender-matched controls. We measured biochemical variables, augmentation index (AIx), aortic pulse wave velocity (PWV_ao), radial (IMT_rad) and common carotid artery (IMT_cca) intima media thicknesses, and the grayscale median (IM-GSM) of the latter.

Results

No significant differences were observed between PHPT patients and controls at baseline for AIx (28.6±12.2 vs. 27.7±12.8%), IMT_rad (0.271±0.060 vs. 0.255±0.053 mm), IMT_cca (0.688±0.113 vs. 0.680±0.135 mm), or IM-GSM (82.3±17.2 vs. 86.5±15.3), while PWV_ao was slightly higher in patients (8.68±1.50 vs. 8.13±1.55, p<0.05). Systolic blood pressure (SBP), calcium, and PTH were higher in patients compared with controls, and decreased after PTX, while vitamin D was lower in patients and increased after PTX. While AIx, PWV_ao, IMT_rad, and IMT_cca were related to SBP, neither correlated to vitamin D levels. Only PWV_ao correlated weakly to plasma PTH (r = 0.29, p<0.01) and ionized calcium (r = 0.22, p<0.05) but showed no relation when age and SBP were adjusted for.

Conclusion

We found normal arterial function despite high calcium, PTH, and low vitamin D levels, in patients with mild PHPT without cardiovascular risk factors. The cardiovascular risk associated with low vitamin D and/or high PTH and calcium levels may be explained by their coupling to blood pressure and other risk factors rather than direct effects on arterial structure.

The metabolic syndrome and progression of carotid atherosclerosis over 13 years. The Tromsø study

Background

The metabolic syndrome (MetS) is associated with increased risk of cardiovascular disease. In this study, we examine if metabolic syndrome predicts progression of atherosclerosis over 13 years.

Methods

Participants were 1442 men and 1532 women in the population-based Tromsø Study who underwent carotid ultrasound examinations at baseline in the 4^th (1994–5) and at follow-up in the 6^th survey (2007–8). Of these, 278 men and 273 women fulfilled the criteria for the MetS, defined according to a modified version of the National Cholesterol Education Program Adult Treatment Panel III (NCEP, ATPIII). Carotid atherosclerosis was assessed as total plaque area (TPA) and mean intima-media thickness (IMT) at follow-up and as change in IMT and TPA from baseline to follow-up. Associations between MetS and its components and carotid atherosclerosis were assessed in linear regression models adjusted for age, total cholesterol and daily smoking, stratified by sex.

Results

IMT and TPA levels at follow-up (p < 0.0001) and progression of TPA (p = 0.02) were higher in the MetS group compared to the non-MetS group. In stepwise multivariable models, MetS was associated with TPA (β = 0.372 mm², p = 0.009) and IMT (β = 0.051 mm, p < 0.0001) in men, and with IMT (β = 0.045 mm, p = 0.001) in women after 13 years of follow-up, but not with progression of IMT or TPA. In analyses stratified by age, MetS predicted progression of IMT (β = 0.043 mm, p = 0.046) and TPA (β = 1.02 mm^2, p = 0.002) in men below 50 years of age. Hypertension was predictive of follow-up TPA and IMT in both genders and of progression of TPA in women. Impaired glucose tolerance was associated with follow up levels of IMT and TPA as well as progression in IMT in men. None of the other components of MetS were associated with progression of atherosclerosis.

Conclusions

Subjects with MetS had higher levels of IMT and TPA at follow up than those without MetS. Mets predicted progression of IMT and TPA in those below 50 years of age, but not in other age groups, indicating that MetS may be involved in the initiation of the atherosclerotic process.

Alkaline phosphatase and arterial structure and function in hypertensive African men: the SABPA study

BACKGROUND

Vascular calcification is believed to be due to the conversion of vascular smooth muscle cells into osteoblast-like cells and is associated with mortality. Since hypertension and related mortality in Africans is a concern, we investigated associations between a marker of osteoblastic activity, alkaline phosphatase (ALP), and measures of arterial structure and function in hypertensive African men.

METHODS

This study included 79 participants. We conducted 24h ambulatory blood pressure and carotid intima-media thickness (cIMT) measurements. cIMT was obtained with an intra-observer variability of 0.04 mm and the cross-sectional wall area (CSWA) was calculated. ALP was measured in serum.

RESULTS

ALP was within its reference range (101.6 vs. 30.0-120.0 U/L), however cIMT was higher when this group was stratified and compared to gender and age-specific reference values. In univariate and partial regressions, and confirmed with multiple regression analyses, 24h systolic blood pressure (β=0.289, p=0.018), 24h pulse pressure (β=0.387, p=0.002), but not 24h diastolic blood pressure (β=0.073, p=0.58), were positively associated with ALP. In addition, mean cIMT (β=0.322, p=0.006) and CSWA (β=0.285, p=0.013) also correlated positively with ALP after adjusting for significant covariates, and after excluding participants with diabetes, renal dysfunction or a HIV positive status.

CONCLUSION

Serum alkaline phosphatase is adversely associated with measures of arterial structure and function in hypertensive African men.

Three-dimensional expansion of a dynamic programming method for boundary detection and its application to sequential magnetic resonance imaging (MRI)

This study proposes a fast 3D dynamic programming expansion to find a shortest surface in a 3D matrix. This algorithm can detect boundaries in an image sequence. Using phantom image studies with added uniform distributed noise from different SNRs, the unsigned error of this proposed method is investigated. Comparing the automated results to the gold standard, the best averaged relative unsigned error of the proposed method is 0.77% (SNR = 20 dB), and its corresponding parameter values are reported. We further apply this method to detect the boundary of the real superficial femoral artery (SFA) in MRI sequences without a contrast injection. The manual tracings on the SFA boundaries are performed by well-trained experts to be the gold standard. The comparisons between the manual tracings and automated results are made on 16 MRI sequences (800 total images). The average unsigned error rate is 2.4% (SD = 2.0%). The results demonstrate that the proposed method can perform qualitatively better than the 2D dynamic programming for vessel boundary detection on MRI sequences.

Double product and end-organ damage in African and Caucasian men: the SABPA study

BACKGROUND

Increasing urbanisation in sub-Saharan African countries is causing a rapid increase in cardiovascular disease. Evidence suggests that Africans have higher blood pressures and a higher prevalence of hypertension-related cardiovascular morbidity and mortality, compared to Caucasians. We investigated double product (systolic blood pressure × heart rate), a substantial measure of cardiac workload, as a possible cardiovascular risk factor in African and Caucasian men.

MATERIAL AND METHODS

The study consisted of 101 urbanised African and 101 Caucasian male school teachers. We measured 24h ambulatory blood pressure and the carotid cross-sectional wall area, and determined left ventricular hypertrophy electrocardiographically by means of the Cornell product. Urinary albumin and creatinine were analysed to obtain the albumin-to-creatinine ratio.

RESULTS

Africans had higher 24h, daytime and nighttime systolic- and diastolic blood pressure, heart rate and resultant double product compared to the Caucasians. In addition, markers of end-organ damage, albumin-to-creatinine ratio and left ventricular hypertrophy were higher in the Africans while cross-sectional wall area did not differ. In Africans after single partial and multiple regression analysis, 24h systolic blood pressure, but not double product or heart rate, correlated positively with markers of end-organ damage (cross-sectional wall area: β=0.398, P=0.005; left ventricular hypertrophy: β=0.455, P<0.001; albumin-to-creatinine ratio: β=0.280, P=0.012). No associations were evident in Caucasian men.

CONCLUSIONS

Double product may not be a good marker of increased cardiovascular risk when compared to systolic blood pressure in African and Caucasian men.

Automatic segmentation of carotid B-mode images using fuzzy classification

This paper presents a new method for the automatic segmentation of the common carotid artery in B-mode images. This method uses the instantaneous coefficient of variation edge detector, fuzzy classification of edges and dynamic programming. Several discriminating features of the intima and adventitia boundaries are considered, like the edge strength, the intensity gradient orientation, the valley shaped intensity profile and contextual information of the region delimited by those boundaries. The adopted fuzzy classification of edges helps avoiding low-pass filtering. The method is suited to real-time processing and user interaction is not required. Both the near and far wall boundaries can be detected in arteries with plaques of different types and sizes. Both expert manual and automatic tracings are significantly better for the far wall, due to the better visibility of the intima and adventitia boundaries. The automatic detection of the far wall shows an accuracy similar to the manual detections. For this wall, the error coefficient of variation for the mean intima-media thickness is in the range [5.6, 6.6 %] for automatic detections and in [6.7, 7.1 %] for manual ones. In the case of the near wall, the same coefficient of variation is in [11.2, 13.0 %] for automatic detections and in [5.9, 9.0 %] for manual detections. The mean intima-media thickness measurement errors observed for the far wall [Formula: see text] are among the best values reported for other fully automatic approaches. The application of this approach in clinical practice is encouraged by the results for the far wall and the short processing time (mean of 2.1 s per image).

Manual or semi-automated edge detection of the maximal far wall common carotid intima-media thickness: a direct comparison

BACKGROUND

Automated edge detection is thought to be superior to manual edge detection in quantification of the far wall common carotid intima-media thickness (CIMT), yet published evidence making a direct comparison is not available.

METHODS

Data were used from the METEOR study, a randomized placebo-controlled trial among 984 individuals showing that rosuvastatin attenuated the rate of change of 2 year change in CIMT among low-risk individuals with subclinical atherosclerosis. For this post hoc analysis, CIMT images of the far wall of the common carotid artery were evaluated using manual and semi-automated edge detection and reproducibility, relation to cardiovascular risk factors, rates of change over time and effects of lipid-lowering therapy were assessed.

RESULTS

Reproducibility was high for both reading methods. Direction, magnitude and statistical significance of risk factor relations were similar across methods. Rate of change in CIMT in participants assigned to placebo was 0.0066 mm per year (SE: 0.0027) for manually and 0.0072 mm per year (SE: 0.0029) for semi-automatically read images. The effect of lipid-lowering therapy on CIMT changes was -0.0103 mm per year (SE: 0.0032) for manual reading and -0.0111 mm per year (SE: 0.0034) for semi-automated reading.

CONCLUSION

Manual and semi-automated readings of the maximal far wall of the common CIMT images both result in high reproducibility, show similar risk factor relations, rates of change and treatment effects. Hence, choices between semi-automated and manual reading software for CIMT studies likely should be based on logistical and cost considerations rather than differences in expected data quality when the choice is made to use far wall common CIMT measurements.

Circulating levels of metals are related to carotid atherosclerosis in elderly

The aim of this study was to investigate if blood levels of trace and/or heavy metals are related to atherosclerosis in a cross-sectional study in elderly. In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (1016 subjects, all aged 70), the prevalence of carotid artery plaques was recorded by ultrasound. The numbers of carotid arteries with plaques (0, 1 or 2) were recorded. Also the thickness (IMT) and gray scale (IM-GSM) of the intima-media complex were measured together with plaque echogenicity. Eleven heavy metals and trace elements were analyzed in whole blood, using inductively coupled plasma-sector field mass spectrometry. Nickel levels were related to the number of carotid arteries with plaques in an inverted U-shaped manner after multiple adjustment for gender, waist circumference, body mass index, fasting blood glucose, systolic and diastolic blood pressure, HDL and LDL cholesterol, serum triglycerides, smoking, antihypertensive treatment and statin use (p=0.026). IM-GSM and plaque echogenicity were both inversely related to chromium in a linear fashion, and to aluminum in an inverted U-shaped manner (both p<0.0001 for IM-GSM). The relationships between metals and IMT were modest. Circulating levels of some metals, like nickel, aluminum and chromium, were related to atherosclerotic plaques or the echogenicity of the IM-GSM and overt plaques independently of cardiovascular risk factors, including lipids.

Automated localisation and boundary identification of superficial femoral artery on MRI sequences

In this paper, an automated method to localise the right superficial femoral artery (SFA) and identify its boundary on magnetic resonance imaging (MRI) sequences without contrast medium injection is proposed. Some anatomical knowledge combined with the mathematical morphology is used to distinguish SFA from other vessels. Afterwards, the directional gradient, continuity and the local contrast are applied as features to identify the artery's boundary using dynamic programming. The accuracy analysis shows that the system has average unsigned errors 3.1 ± 3.1% on five sequences compared to experts' manual tracings.

Circulating levels of persistent organic pollutants (POPs) and carotid atherosclerosis in the elderly

BACKGROUND AND OBJECTIVE

Increased circulating levels of persistent organic pollutants (POPs) have been associated with myocardial infarction. Because myocardial infarction is an atherosclerotic disease, we investigated, in a cross-sectional study, whether POP levels are related to atherosclerosis.

METHODS

In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (n = 1,016 participants 70 years of age), the prevalence of carotid artery plaques was determined by ultrasound. The number of carotid arteries with plaques (0, 1, or 2) was recorded. Also, the intima-media thickness (IMT) and gray scale median of the intima-media complex (IM-GSM) were measured. Twenty-three POPs, comprising 16 polychlorinated biphenyls (PCBs), 5 pesticides, 1 dioxin, and 1 brominated compound (brominated diphenyl ether congener BDE-47), were analyzed by high-resolution chromatography coupled to high-resolution mass spectrometry.

RESULTS

Seven of the POPs (PCB congeners 153, 156, 157, 170, 180, 206, and 209) were significantly associated with the number of carotid arteries with plaques even after adjusting for multiple risk factors (sex, waist circumference, body mass index, fasting blood glucose, systolic and diastolic blood pressure, high-density lipoprotein and low-density lipoprotein cholesterol, serum triglycerides, smoking, antihypertensive treatment, and statin use; p = 0.002-0.0001). Highly chlorinated PCBs (congeners 194, 206, and 209) were associated with an echolucent IM-GSM (p < 0.0001 after adjustment), whereas associations between POPs and IMT were modest.

CONCLUSIONS

Circulating levels of PCBs were associated with atherosclerotic plaques and echogenicity of the intima-media complex independent of cardiovascular risk factors, including lipids. This suggests that POPs may be a risk factor for myocardial infarction, but associations need to be confirmed in prospective studies.

Is there an underestimation of intima-media thickness based on M-mode ultrasound technique in the abdominal aorta?

Measuring intima-media thickness (IMT) in the common carotid artery (CCA) is a valuable resource for the evaluation of subclinical atherosclerosis. The main objective of this study was to explore whether a B-mode ultrasound technique, Philips ATL, and an M-mode ultrasound technique, Wall Track System (WTS), show interchangeable results when measured in CCA and the abdominal aorta (AA). A total of 24 healthy, young subjects were examined. IMT and lumen diameter (LD) of the AA and the CCA were measured twice by two skilled ultrasonographers with two different ultrasound equipment B-mode: (Philips, ATL and M-mode: WTS).The intra-observer variability of IMT in CCA and AA using B-mode showed a coefficient of variation 8% and 9%, and with M-mode 11% and 15%, respectively. Interobserver variability of IMT in CCA and AA using B-mode was 6% and 12%, and with M-mode 11% and 18%, respectively. CCA IMT was 0·53 ± 0·07 and 0·53 ± 0·09 mm using B-mode and M-mode, respectively. However, in AA, IMT was 0·61 ± 0·05 and 0·54 ± 0·10 mm using B-mode and M-mode, respectively. Thus, AA IMT was 11·5% thicker using B-mode (P < 0·01). We received adequate IMT readings from the carotid artery as well as the AA using two commonly used B-mode and M-mode techniques. B-mode technique seems to show less variability, especially in the AA. More importantly, the two techniques measured different IMT thickness in the aorta, emphasizing the importance of using similar technique when comparing the impact of absolute values of IMT on cardiovascular disease.

AUTOMATIC COMPUTER-BASED TRACINGS (ACT) IN LONGITUDINAL 2-D ULTRASOUND IMAGES USING DIFFERENT SCANNERS

Objective. The aim of this paper is to show an algorithm for the automatic computer-based tracing (ACT) of common carotid artery (CCA) in longitudinal B-mode ultrasound images characterized by four main features: (i) user-independence; (ii) suitability to normal and pathological images; (iii) robustness to noise; and (iv) independent of ultrasound OEM scanner.

Methods. Three hundred longitudinal B-mode images (100 normal CCAs, 100 CCAs with increased intima-media thickness, 60 stable plaques, and 40 echolucent plaques) were acquired using three different (GE, Siemens, and Biosound) OEM ultrasound image scanners. The algorithm processed each image to delineate the region of interest containing the CCA. Output of the algorithm are three segmentation lines representing (a) distal (far) and (b) near adventitia layers, and (c) lumen of the CCA. Three operators qualitatively scored the ACTs.

Results. The CCA was correctly automatically traced in all the 300 B-mode images. The performance was independent on the image scanner used to acquire the image or on the type of the CCA (healthy versus pathologic). Eight ACTs out of 300 received a poor score after visual inspection due to an automated adventitia tracing that did not correctly follow the CCA wall in a small portion of the image.

Conclusions. The proposed algorithm is robust in ACTs of CCA since it is independent of scanner and normal/abnormal wall. This approach could constitute a general basis for a completely automated segmentation procedure.

Speed improvement of B-snake algorithm using dynamic programming optimization

This paper presents a novel approach to contour approximation carried out by means of the B-snake algorithm and the dynamic programming (DP) optimization technique. Using the proposed strategy for contour point search procedure, computing complexity is reduced to O(N×M(2)), whereas the standard DP method has an O(N×M(4)) complexity, with N being the number of contour sample points and M being the number of candidates in the search space. The storage requirement was also decreased from N×M(3) to N×M memory elements. Some experiments on noise corrupted synthetic image, magnetic resonance, and computer tomography medical images have shown that the proposed approach results are equivalent to those obtained by the standard DP algorithm.