Computed tomography-assessed variations of the carotid sinus.

PURPOSE AND BACKGROUND: Previous studies have identified variations regarding the morphology and location of the carotid sinus, a phenomenon still not commonly approached or studied on computed tomography angiography (CTA). Detailed characterization of the carotid sinus was performed on CTAs, determining its position, diameter and length. METHODS: The study group included 43 patients with disease-free carotid trunks subjected to cervical CTA. We measured the terminal caliber of the common carotid artery (CCA), as well as the calibers of the internal (ICA) and external carotid arteries (ECA) at their origin. The diameters were correlated with the location and the shape of the carotid sinus. We also measured the length of the sinus dilatation (carotid bulb), in regard to its location on the terminal branches of the common carotid artery. RESULTS: Mean diameters of the studied arteries were 7.39 ± 1.04 mm for the CCA, 6.71 ± 1.49 mm for the ICA and, respectively, 4.27 ± 0.75 mm for the ECA. The classical position of the carotid sinus was seen in 80% of cases, the rest being considered anatomical variants. The length of the carotid bulb on the ICA was 9.99 ± 2.22 mm, showing variability between genders. CONCLUSIONS: The carotid sinus does not always extend to the ICA, presenting different distribution patterns that might be relevant in sinus pathology from a clinical point of view, respectively from a surgical point of view during invasive or minimally invasive interventions on the carotid axis.

Feasibility and effectiveness of palliative intensity-modulated radiotherapy for carotid sinus syndrome secondary to recurrent head and neck cancer.

A 74-year-old man presented with recurrent syncope 3 months after definitive surgery for hypopharyngeal cancer. The patient experienced dizziness and severe hypotension on the movement of the neck and head. CT revealed disease recurrence with masses encasing the left internal carotid artery. The patient was diagnosed with vasodepressor type of tumour-induced carotid sinus syndrome (tiCSS) and was referred for palliative intensity-modulated radiotherapy (IMRT). Ten days after the commencement of IMRT (25 Gy in five fractions), the symptoms of tiCSS improved, and there was no re-exacerbation of the symptoms till the patient died 56 days after the commencement of RT. Palliative IMRT was feasible and effective for recurrent malignant tiCSS. Given the fact that palliative IMRT is minimally invasive, this option could be widely adapted for patients with such poor general condition and prognosis.

Total Atherosclerosis Burden of Baroreceptor-Resident Arteries Independently Predicts Blood Pressure Dipping in Patients With Ischemic Stroke.

Nighttime blood pressure (BP) generally dips by 10% to 20% of the daytime values, and abnormal BP dipping may affect vascular health independently of BP level. The regulation of BP dipping involves arterial baroreflex, whose receptors mainly reside in carotid sinuses and aortic arch. Atherosclerosis in these baroreceptor-resident arteries (BRAs) is frequent among patients with ischemic stroke (IS) and might impair their BP-regulating capacity. We aimed to examine associations between atherosclerosis of BRA and BP dipping in patients with IS. BP dipping ratio was measured by 24-hour ambulatory blood pressure monitoring on the sixth day after IS. With computed tomography angiography, atherosclerosis conditions in 10 segments of carotid sinuses and aortic arch were scored and summed as total atherosclerosis burden of BRA. Among the 245 patients with IS, 78.0% had atherosclerosis in BRA. The total AS burden of BRA was negatively correlated with systolic BP dipping ratio (r=-0.331; P<0.001) and diastolic BP dipping ratio (r=-0.225; P<0.001). After adjusting for age, sex, vascular risk factors, 24-hour BP means, cervical and intracranial atherosclerosis scores, the negative correlations still existed (adjusted ß, -0.259 [95% CI, -0.416 to -0.102] and adjusted ß, -0.178 [95% CI, -0.346 to -0.010], respectively). In conclusion, higher total atherosclerosis burden of BRA was independently indicative of more blunted dipping of systolic BP and diastolic BP in IS. The total atherosclerosis burden of BRA might be important for predicting and managing BP dipping in patients with IS.

Bilateral diagonal earlobe crease

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Carotid canal and optic canal at sphenoid sinus.

In the present study, we investigated the relationship between sphenoid sinus, carotid canal, and optic canal on paranasal sinus computed tomography (PNSCT). This study was performed retrospectively. PNSCT images of 300 adult subjects (159 male, 141 female). Sphenoid sinus (pneumatisation, dominancy, septation, inter-sinus septa deviation), anterior clinoid process pneumatisation, Onodi cell, carotid and optic canals (width, dehiscence, classification) were measured. In males, type 3 pneumatised sphenoid sinus (in both sides) and in females type 2 pneumatised sphenoid sinus (right side) and type 3 pneumatised sphenoid sinus (left side) were detected more. Anterior clinoid pneumatisation was present 47.2% in males and 39.7% in females. In male group, more septation (i.e. 22.6%, ≥ 3 septa) in sphenoid sinus were detected. Onodi cell was present 26.6 and 19.1% in males and females, respectively. Carotid canal protrudation to the sphenoid sinus wall was present 23.9-32.1% in males and 35.5-36.2% in females. Dehiscence in carotid canal was detected more in females (34%) compared to males (22%). Optic canal protrudation was 33.3 and 30.5% in males and females. Type 4 optic canal was detected more in both gender. Optic canal dehiscence was detected 11.3 and 9.9% in males and females. Carotid and optic canal diameters were higher in males. In pneumatised sphenoid sinuses and in females, type 3 carotid canal (Protrudation to SS wall) (bilaterally) and type 1 optic canal type (No indentation) (ipsilateral side) were detected more. In elderly patients, carotid and optic canal width increased. When carotid canal protrudation was detected, there was no indentation in optic canals In pneumatised SS, carotid canal protrudation was observed with a greater risk in surgery. However, type 1 (non indentation) optic canal was present in highly pneumatised SS with lower risk for the surgery. In women, the risk of carotid canal protruding (about 1/3) is greater than that of males, and carotid canal dehiscence rates are also higher in females. Therefore, physicians should be very careful during the preparatory stages of the sphenoid sinus surgery. Otherwise, it may not be possible to prevent lethal carotid artery bleeds.

[Relation between ultrasonographic and morphological characteristics of atherosclerotic plaques of carotid sinus]. / Sviaz' ul'trazvukovykh i morfologicheskikh kharakteristik ateroskleroticheskikh bliashek karotidnogo sinusa.

The authors revealed relation between the structure of an atherosclerotic plaque (ASP) and intensity of the ultrasound signal reflected form the ASP. Our prospective pilot study included a total of 90 patients (71 men and 19 women aged from 47 to 79 years, with the median age 62 years) presenting with atherosclerotic stenosis of the carotid sinus (CS) and undergoing treatment at the Research Centre of Neurology (Moscow) from April 2015 to March 2016. All patients underwent ultrasonographic examination followed by morphological study of the structure of the plaques removed during carotid endarterectomy (CEA). It was revealed that intensity of the ultrasound signal from an ASP depended on the morphological structure of the ASP components: the foci of atheromatosis were associated with an ultrasound range of 1.1-5.6 dB, those of fibrosis - with the range 23.1-30.5 dB, and those of calcinosis - with the range 42.3-44.7 dB (presented are the values from the 15th to 85th percentiles). It was determined that an increase of intensity of the ultrasound signal reflected from the foci of atheromatosis and fibrosis in the ASP was associated with the presence of small calcificates therein, and a decrease of intensity of the ultrasound signal from the portions of fibrosis in the ASP - with large accumulation of lipophages or newly formed vessels in these portions.

Evaluation of spatial distribution and characterization of wall shear stress in carotid sinus based on two-dimensional color Doppler imaging.

OBJECTIVE: This study aims to use a wall shear stress (WSS) quantitative analysis software to analyze and evaluate the carotid sinus WSS spatial distribution and characteristics in intima-media thickness (IMT) normal and thickening group by using two-dimensional color doppler flow imaging (CDFI) so as to assist clinicians to predict the location and risk of plaque formation. METHODS: According to IMT, 50 subjects was selected as IMT thickening group and 50 subjects as IMT normal group from subjects who had a carotid ultrasound examination in Shanghai East hospital during October 2016 to October 2017. This study presents the spatial distribution of the carotid sinus WSS based on the WSS quantitative analysis software and compared the spatial distribution and characteristics of the carotid sinus WSS between IMT thickening group and IMT normal group through two- and three-dimensional WSS maps and a fused WSS image. RESULTS: The distributional regularity of WSS in both two group was: carotid sinus < common carotid artery (CCA) < internal carotid artery (ICA) and posterior-interior wall of the carotid sinus < the anterior-lateral wall of the carotid sinus. Furthermore, the WSS of CCA, ICA, the anterior-lateral proximal wall of the carotid sinus, the anterior-lateral distal wall of the carotid sinus, the posterior-interior proximal wall of the carotid sinus, and the posterior-interior distal wall of the carotid sinus in IMT thickening group was lower than the corresponding part of IMT normal group (P < 0.05). CONCLUSION: In summary, this WSS quantitative analysis framework by two-dimensional CDFI can measure and reflect the carotid sinus WSS spatial distribution and characteristics more accurately and visually. As a convenient tool, it may be used for clinical prediction of the plaque formation in carotid sinus in the future.

Fast Von Mises strain imaging on ultrasound carotid vessel wall by flow driven diffusion method.

The elasticity of the vessel wall is important for the clinical identification of rupture-risks. The Von Mises strain can be a potential index for the indication of carotid vessel pathologies. In this paper, a fast clinically applicable real-time algorithm from time-sequence of B-mode carotid images is developed. Due to the compression induced by the normal cardiac pulsation, tissue motion occurs radially and non-rigidly. To obtain an accurate motion field, we developed a variational functional integrating the optical flow equation and an anisotropic regularizer, and designed a diffusion tensor to encourage coherence diffusion. The motion field is smoothed along the desired motion flow orientation. A fast, additive operator splitting scheme, which is ten times faster than the conventional discrete method, is used for the numerical implementation. To demonstrate the efficiency of the proposed approach, finite element models are set up for normal and pathological carotid vessel walls. The results indicate that the proposed diffusion approach obtains an accurate smooth and continuous motion field and greatly improves the follow up strain estimation using a fast differential strain filter. Furthermore, our approach using the Von Mises strain imaging on clinical ultrasound images of the carotid artery is validated. Participants above 65-years in age suffering from different stages of atherosclerosis in their carotid artery are selected. The results are evaluated by an experienced physician. The evaluation results demonstrate that the Von Mises strain has a good correspondence to the presence of certain suspicious areas in the B-mode images. The proposed method is therefore clinically applicable for the real-time Von Mises strain imaging of carotid vessel walls, and can be of great value as a complementary method to B-mode image for the clinical identification of the risk of plaque vulnerability.

Incidence and predictors of syncope recurrence after cardiac pacing in patients with carotid sinus syndrome.

BACKGROUND: Cardiac pacing is the treatment of choice for cardioinhibitory carotid sinus syndrome (CSS), but syncope recurrence occurs in up to 20% of patients within 3 years. The present study aims at assessing incidence and identifying predictors of syncope recurrence in patients receiving pacing therapy for CSS. METHODS: The Syncope Clinics of two large regional hospitals in Northern Italy, both following European Syncope Guidelines, combined to perform this study. Retrospective analysis of 3127 consecutive patients undergoing carotid sinus massage (CSM) was performed 2004-2014. Ten-second supine and standing CSM was systematically assessed in patients aged >40 years with suspected reflex syncope as part of the initial evaluation. Syncope recurrence was investigated in those paced for CSS having >6 months' available follow-up. Data were collected from clinical records and patient interviews. RESULTS: CSS was diagnosed in 261 patients (8.3%). Pacemakers were implanted in 158, with follow-up data available in 112: 19 (17%) experienced 73 syncope recurrences during a mean follow-up of 89 ±â€¯42 months, yielding an incidence of 0.5 episodes per patient/year. Prodrome, predisposing situations preceding syncope and chronic nitrate therapy were more frequent in patients reporting recurrence. Prodrome and predisposing situations remained independent predictors of post-implantation recurrence on multivariable analysis. CONCLUSIONS: CSS is a frequent cause of syncope, if CSM is performed during the initial evaluation. Most patients treated by pacing remain asymptomatic during long-term follow-up. In those who have recurrence, its incidence is very low. Prodrome and predisposing situations are predictors of post-implantation recurrence, suggesting presence of hypotensive susceptibility.

Association Between Carotid Bulb Diaphragm and Ischemic Stroke in Young Afro-Caribbean Patients: A Population-Based Case-Control Study.

BACKGROUND AND PURPOSE: Carotid bulb diaphragm (CBD) has been described in young carotid ischemic stroke (CIS) patients, especially in blacks. However, the prevalence of CBD in CIS patients is unknown, and whether CBD is a risk factor for CIS remains unclear. We assessed the association between CBD and incident CIS in a population-based study. METHODS: We selected all young (<55 years) CIS patients from a 1-year population-based cohort study in the Afro-Caribbean population of Martinique in 2012. All patients had a comprehensive work-up including a computed tomographic angiography. We calculated CIS associated with ipsilateral CBD incidence with 95% confidence intervals using Poisson distribution. We then selected age- and sex-matched controls among young (<55 years) Afro-Caribbean stroke-free patients admitted for a road crash who routinely had computed tomographic angiography. Odds ratio (ORs) were calculated by conditional logistic regression adjusted for hypertension, dyslipidemia, diabetes and smoking. RESULTS: CIS associated with ipsilateral CBD incidence was 3.8 per 100 000 person-years (95% confidence interval, 1.4-6.1). Prevalence of ipsilateral CBD was 23% in all CIS and 37% in undetermined CIS patients. When restricted to undetermined CIS, CBD prevalence was 24 times higher than that in controls (adjusted OR, 24.1; 95% confidence interval, 1.8-325.6). CONCLUSIONS: CBD is associated with an increased risk of ipsilateral CIS in young Afro-Caribbean population.

The accuracy of anatomical landmarks for locating the carotid sinus.

BACKGROUND: carotid sinus massage (CSM) is a valuable clinical test for carotid sinus syndrome (CSS) and relies on accurately locating the carotid sinus (CS). OBJECTIVE: in this study, we sought to examine the accuracy of using anatomical landmarks for locating the CS. METHODS: consecutive patients (n = 20) were recruited prospectively. Two clinicians, trained in CSM, were asked to locate the CS using anatomical landmarks. A point on the skin overlying the CS was then marked by a vascular technician using ultrasound. Accuracy of techniques was compared using intra-class correlation coefficients and Bland-Altman statistics. RESULTS: anatomical landmarks underestimated the CS location by 1.5 ± 1.3 cm. Error extremes ranged from 4 cm below to 2 cm above CS using anatomical landmarks. A moderate correlation between ultrasound and anatomical landmarks was found, r = 0.371 (P = 0.031). CONCLUSION: this is the first study to characterise the accuracy of standard anatomical landmarks used in CSM. Results suggest that the point of maximal pulsation has the lowest associated error. Future work should examine CSM yield across this and a range of other methodological factors.

Three-dimensional imaging MS of lipids in atherosclerotic plaques: Open-source methods for reconstruction and analysis.

Three-dimensional MALDI imaging MS (IMS) is a growing branch of IMS still requiring developments in methodology and technology to make the technique routinely accessible. Many challenges are simply a matter of producing 3D reconstructions and interpreting them in a timely fashion. In this aim and using analysis of lipids from atherosclerotic plaques from a human carotid and mouse aortic sinuses, we describe 3D reconstruction methods using open-source software that provides high-quality visualization and rapid interpretation through multivariate segmentation of the 3D IMS data. Multiple datasets were generated for each sample and we provide insight into simple means to correlate the separate datasets.

Cardiac Iodine-123-Meta-Iodo-Benzylguanidine Uptake in Carotid Sinus Hypersensitivity.

BACKGROUND: Carotid sinus syndrome is the association of carotid sinus hypersensitivity with syncope, unexplained falls and drop attacks in generally older people. We evaluated cardiac sympathetic innervation in this disorder in individuals with carotid sinus syndrome, asymptomatic carotid sinus hypersensitivity and controls without carotid sinus hypersensitivity. METHODS: Consecutive patients diagnosed with carotid sinus syndrome at a specialist falls and syncope unit were recruited. Asymptomatic carotid sinus hypersensitivity and non-carotid sinus hypersensitivity control participants recruited from a community-dwelling cohort. Cardiac sympathetic innervation was determined using Iodine-123-metaiodobenzylguanidine (123-I-MIBG) scanning. Heart to mediastinal uptake ratio (H:M) were determined for early and late uptake on planar scintigraphy at 20 minutes and 3 hours following intravenous injection of 123-I-MIBG. RESULTS: Forty-two subjects: carotid sinus syndrome (n = 21), asymptomatic carotid sinus hypersensitivity (n = 12) and no carotid sinus hypersensitivity (n = 9) were included. Compared to the non- carotid sinus hypersensitivity control group, the carotid sinus syndrome group had significantly higher early H:M (estimated mean difference, B = 0.40; 95% confidence interval, CI = 0.13 to 0.67, p = 0.005) and late H:M (B = 0.32; 95%CI = 0.03 to 0.62, p = 0.032). There was, however, no significant difference in early H:M (p = 0.326) or late H:M (p = 0.351) between the asymptomatic carotid sinus hypersensitivity group and non- carotid sinus hypersensitivity controls. CONCLUSIONS: Cardiac sympathetic neuronal activity is increased relative to age-matched controls in individuals with carotid sinus syndrome but not those with asymptomatic carotid sinus hypersensitivity. Blood pressure and heart rate measurements alone may therefore represent an over simplification in the assessment for carotid sinus syndrome and the relative increase in cardiac sympathetic innervation provides additional clues to understanding the mechanisms behind the symptomatic presentation of carotid sinus hypersensitivity.

Low-Dose Computed Tomography With Adaptive Statistical Iterative Reconstruction and Low Tube Voltage in Craniocervical Computed Tomographic Angiography: Impact of Body Mass Index.

OBJECTIVES: To assess radiation dose and image quality using Adaptive Statistical Iterative Reconstruction (ASIR) in craniocervical computed tomographic angiography and to further evaluate the impact of body mass index (BMI) on image quality. METHODS: A total of 178 consecutive patients (112 men, 66 women; age range, 25-79 years) were enrolled in this prospective study and randomly divided into 2 groups: group A (conventional group): 120 kV, filtered back-projection reconstruction, and group B (low-dose group): 100 kV, 40% ASIR reconstruction. Radiation dose and image quality between groups A and B were compared. Correlation coefficients were calculated between quantitative image quality measurement and BMI, and between radiation dose and BMI using Pearson correlation. Two experienced radiologists independently evaluated the image quality with 4-point scores, and interrater reliability was calculated using κ analysis. RESULTS: The volume CT dose index, dose-length product, and effective dose of group B were lower than those of group A (each P < 0.01), with decreases of 23.99%, 25.15% and 25.47% respectively. Positive correlations existed between radiation dose and BMI for both groups A and B (each P < 0.01). Group B had lower image noise, higher attenuation, higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), and higher subjective score than did group A (each P < 0.01). Computed tomographic values had negative correlations with BMI for the head, neck, and shoulders in both groups A and B (each P < 0.01). Image noise, SNR, and CNR had no correlations with BMI for the head and neck in both groups (each P > 0.01). On the contrary, image noise had a positive correlation, and SNR and CNR had a negative correlations with BMI for the shoulders in group A (each P < 0.01), but in contrast, no such correlations were found in group B (each P > 0.01). CONCLUSIONS: In craniocervical CTA, ASIR can improve the image quality and reduce radiation dose in patients. Furthermore, ASIR reduced the variances of image quality of different body sizes in the shoulders.

Modified carotid sinus massage using an ultrasonography for maximizing vagal tone: a crossover simulation study.

INTRODUCTION: The aim of this study was to ascertain if a modified carotid sinus massage (CSM) using ultrasonography is superior to the conventional CSM for vagal tone generation. METHODS: This was a prospective, crossover, clinical trial including 30 subjects with sinus rhythm. Participants were paired, and they performed 2 types of CSM to each other. To perform the conventional technique, pressure was exerted at the point where the maximal impulse of the carotid pulse was palpated. In the modified technique, participants localized the point of maximal diameter just above the bifurcation of the common carotid artery using ultrasonography and applied pressure to that point. Mean differences between premaneuver and postmaneuver R-R intervals and heart rates were compared. The distance from the midline of the neck (x distance) to the angle of the mandible (y distance) was measured, and the mean distance between the 2 techniques was compared. RESULTS: The baseline mean premaneuver R-R interval and heart rate did not differ significantly between the 2 techniques. The postmaneuver R-R interval and heart rate as well as the mean R-R interval and heart rate differences were significantly greater in the modified CSM. The mean location determined using the modified CSM was located 0.8 cm lateral and 0.8 cm superior to the mean location of the conventional CSM. CONCLUSION: The modified CSM using ultrasonography might be more useful than the conventional CSM in reverting episodes of paroxysmal supraventricular tachycardia and may be a suitable alternative for treating the same in the emergency department.

Initial experience with therapeutic geometric modification of the carotid bulb for true resistant hypertension.

The contribution of carotid baroreceptor feedback in preventing or potentially contributing to the essential hypertensive cascade is poorly understood. It is clear the carotid sinus nerve action potentials are triggered by carotid bulb stretch rather than pressure and are only sustained during pulsatile increases in pressure. In addition, the carotid baroreceptor negative feedback is gradually extinguished in hypertension patients (a phenomenon known as "resetting"). We report a case of significant reduction in blood pressure in a patient with true resistant hypertension after change in the carotid bulb pulsatile strain patterns following the implant of an intravascular prosthesis.

Novel flow quantification of the carotid bulb and the common carotid artery with vector flow ultrasound.

Abnormal blood flow is usually assessed using spectral Doppler estimation of the peak systolic velocity. The technique, however, only estimates the axial velocity component, and therefore the complexity of blood flow remains hidden in conventional ultrasound examinations. With the vector ultrasound technique transverse oscillation the blood velocities of both the axial and the transverse directions are obtained and the complexity of blood flow can be visualized. The aim of the study was to determine the technical performance and interpretation of vector concentration as a tool for estimation of flow complexity. A secondary aim was to establish accuracy parameters to detect flow changes/patterns in the common carotid artery (CCA) and the carotid bulb (CB). The right carotid bifurcation including the CCA and CB of eight healthy volunteers were scanned in a longitudinal plane with vector flow ultrasound (US) using a commercial vector flow ultrasound scanner (ProFocus, BK Medical, Denmark) with a linear 5 MHz transducer transverse oscillation vector flow software. CCA and CB areas were marked in one cardiac cycle from each volunteer. The complex flow was assessed by medical expert evaluation and by vector concentration calculation. A vortex with complex flow was found in all carotid bulbs, whereas the CCA had mainly laminar flow. The medical experts evaluated the flow to be mainly laminar in the CCA (0.82 ± 0.14) and mainly complex (0.23 ± 0.22) in the CB. Likewise, the estimated vector concentrations in CCA (0.96 ± 0.16) indicated mainly laminar flow and in CB (0.83 ± 0.07) indicated mainly turbulence. Both methods were thus able to clearly distinguish the flow patterns of CCA and CB in systole. Vector concentration from angle-independent vector velocity estimates is a quantitative index, which is simple to calculate and can differentiate between laminar and complex flow.

Associations of common carotid intima-media thickness with coronary heart disease risk factors and events vary with distance from the carotid bulb.

BACKGROUND: Common carotid artery (CCA) intima-media thickness (IMT) can be measured using ultrasound near to or below the carotid bulb. This might affect associations of IMT with coronary heart disease (CHD) risk factors and events. METHODS: IMT measurements were performed near and below the divergence of the CCA bulb in 279 white individuals aged 45 to 54 years free of CHD at baseline and a subset of the Multi-Ethnic Study of Atherosclerosis, a cohort composed of whites, blacks, Chinese, and Hispanic subjects. Participants were followed for an average of 8.2 years. Far wall mean of the maximum IMT (MMaxIMT) and mean of the mean IMT of the right and left CCAs were averaged. Framingham risk factors were used in multivariate linear regression models. Parsimonious Cox proportional regression models included first-time CHD as outcome. RESULTS: Mean of the mean IMT below the bulb was smaller than near the bulb (0.51 ± 0.078 vs 0.56 ± 0.088 mm, P < .001) and had similar associations with risk factors (model R(2) = 0.215 vs 0.186). MMaxIMT below the bulb was associated with risk factors (model R(2) = 0.211), but MMaxIMT near to the bulb was not (R(2) = 0.025). Mean of the mean IMT and MMaxIMT below the bulb were associated with CHD events (hazard ratios, 1.67 [P = .047] and 1.72 [P = .037], respectively) but not when measured near the bulb. CONCLUSIONS: CCA IMT measurements made below the bulb are smaller but have more consistent associations with CHD risk factors and outcomes compared with IMT measured near the bulb.