Acculturation and Subclinical Atherosclerosis among U.S. South Asians: Findings from the MASALA study

OBJECTIVE

Longer duration of residence among immigrants to the United States, a proxy measure of acculturation, has been associated with higher subclinical atherosclerosis. South Asian immigrants are the second fastest growing immigrant group in the U.S. but little is known about the effects of acculturation with atherosclerosis in this high cardiovascular risk population.

METHODS

We conducted a cross-sectional analysis using data from a community-based cohort called the Mediators of Atherosclerosis in South Asians Living in America (MASALA) study. Participants (n=900) were between ages of 40-84 years and had no existing cardiovascular disease. We developed a multi-dimensional measure of acculturation in South Asians, called traditional cultural beliefs, and measured other proxy measures of acculturation to determine whether they were associated with higher levels of subclinical atherosclerosis after controlling for socioeconomic, behavior/lifestyle, and cardiovascular risk factors.

RESULTS

Mean duration of residence in the U.S. was 27±11 years and tertiles of strength of traditional cultural beliefs were examined. Longer duration of U.S. residence was associated with higher levels of coronary artery calcium even after adjustment for covariates and lifestyle mediators. The novel measure of strength of traditional cultural beliefs was associated with lower common carotid intima media thickness among those with moderate traditional beliefs only.

CONCLUSIONS

These findings support the need for better conceptualization and measurement of how migration influences cultural beliefs and practices, and their subsequent influence on health behaviors and cardiovascular disease risk.

The Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis (SONIA) Trial

BACKGROUND

Transcranial Doppler ultrasound (TCD) and magnetic resonance angiography (MRA) can identify intracranial atherosclerosis but have not been rigorously validated against the gold standard, catheter angiography. The WASID trial (Warfarin Aspirin Symptomatic Intracranial Disease) required performance of angiography to verify the presence of intracranial stenosis, allowing for prospective evaluation of TCD and MRA. The aims of Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis (SONIA) trial were to define abnormalities on TCD/MRA to see how well they identify 50 to 99% intracranial stenosis of large proximal arteries on catheter angiography.

STUDY DESIGN

SONIA standardized the performance and interpretation of TCD, MRA, and angiography. Study-wide cutpoints defining positive TCD/MRA were used. Hard copy TCD/MRA were centrally read, blind to the results of angiography.

RESULTS

SONIA enrolled 407 patients at 46 sites in the United States. For prospectively tested noninvasive test cutpoints, positive predictive values (PPVs) and negative predictive values (NPVs) were TCD, PPV 36% (95% CI: 27 to 46); NPV, 86% (95% CI: 81 to 89); MRA, PPV 59% (95% CI: 54 to 65); NPV, 91% (95% CI: 89 to 93). For cutpoints modified to maximize PPV, they were TCD, PPV 50% (95% CI: 36 to 64), NPV 85% (95% CI: 81 to 88); MRA PPV 66% (95% CI: 58 to 73), NPV 87% (95% CI: 85 to 89). For each test, a characteristic performance curve showing how the predictive values vary with a changing test cutpoint was obtained.

CONCLUSIONS

Both transcranial Doppler ultrasound and magnetic resonance angiography noninvasively identify 50 to 99% intracranial large vessel stenoses with substantial negative predictive value. The Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis trial methods allow transcranial Doppler ultrasound and magnetic resonance angiography to reliably exclude the presence of intracranial stenosis. Abnormal findings on transcranial Doppler ultrasound or magnetic resonance angiography require a confirmatory test such as angiography to reliably identify stenosis.

Carotid artery tortuosity, kinking, coiling: stroke risk factor, marker, or curiosity?

Although abnormalities in course and geometry (tortuosity, kinking, and coiling) of the internal carotid arteries (ICA) are commonly identified, their etiology and relationship with stroke and stroke risk factors remain unclear This study assessed the clinical and ultrasonographic features of the patients with abnormalities in course and geometry of the ICA. Carotid color duplex ultrasound studies of 345 consecutive patients referred to the Neuroultrasound Lab were prospectively evaluated. Abnormalities in direction and course of the ICA were classified according to the criteria of Weibel-Fields and Metz modified by the authors. Kinking was categorized as mild (> 60 degrees), moderate (30 degrees-60 degrees), and severe (< 30 degrees). Carotid abnormalities (CA) were found in 85/345 (24.6%), 60/85 (70.6%) were female. More CA were seen in females older than 60 y/o (p < 0.001), but there was no gender difference in patients 60 y/o or younger CA were bilateral in 41 patients (48%), but in those with unilateral CA, most were on the left. The most common CA was kinking (71 arteries, 56%), followed by tortuosity (48 arteries, 38%), and coiling (7 arteries, 6%). None of the atherosclerotic vascular diseases or risk factors was associated with CA. Mild atheromatous plaques predominated in patients with CA, but moderate and large plaques were more common in the others (p = 0.001). Maximal systolic velocity at the level of CA was higher in patients with kinking or coiling compared with tortuosity (p = 0.001). Lumen diameter at the level of CA was inversely correlated to the severity of CA (p < 0.001). However, carotid stenosis was equally present in all groups. This study suggests that CA have no clear importance as a stroke risk factor or marker of atherosclerotic vascular disease. Our results suggest that CA do not develop as a consequence of vascular risk factors or atherosclerotic lesions, and they are not related to ischemic stroke, TIA or the presence of carotid stenosis. In women, CA was related with advanced age. It appears that CA frequently identified by color duplex sonography are more of curiosity than a clinically significant finding.

Lateralized auditory spatial perception and the contralaterality of cortical processing as studied with functional magnetic resonance imaging and magnetoencephalography

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were used to study the relationships between lateralized auditory perception in humans and the contralaterality of processing in auditory cortex. Subjects listened to rapidly presented streams of short FM-sweep tone bursts to detect infrequent, slightly deviant tone bursts. The stimulus streams consisted of either monaural stimuli to one ear or the other or binaural stimuli with brief interaural onset delays. The onset delay gives the binaural sounds a lateralized auditory perception and is thought to be a key component of how our brains localize sounds in space. For the monaural stimuli, fMRI revealed a clear contralaterality in auditory cortex, with a contralaterality index (contralateral activity divided by the sum of contralateral and ipsilateral activity) of 67%. In contrast, the fMRI activations from the laterally perceived binaural stimuli indicated little or no contralaterality (index of 51%). The MEG recordings from the same subjects performing the same task converged qualitatively with the fMRI data, confirming a clear monaural contralaterality, with no contralaterality for the laterally perceived binaurals. However, the MEG monaural contralaterality (55%) was less than the fMRI and decreased across the several hundred millisecond poststimulus time period, going from 57% in the M50 latency range (20-70 ms) to 53% in the M200 range (170-250 ms). These data sets provide both quantification of the degree of contralaterality in the auditory pathways and insight into the locus and mechanism of the lateralized perception of spatially lateralized sounds.

Transcranial Doppler ultrasonography: year 2000 update

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.

Motor area activity during mental rotation studied by time-resolved single-trial fMRI

The functional equivalence of overt movements and dynamic imagery is of fundamental importance in neuroscience. Here, we investigated the participation of the neocortical motor areas in a classic task of dynamic imagery, Shepard and Metzler's mental rotation task, by time-resolved single-trial functional Magnetic Resonance Imaging (fMRI). The subjects performed the mental-rotation task 16 times, each time with different object pairs. Functional images were acquired for each pair separately, and the onset times and widths of the activation peaks in each area of interest were compared to the response times. We found a bilateral involvement of the superior parietal lobule, lateral premotor area, and supplementary motor area in all subjects; we found, furthermore, that those areas likely participate in the very act of mental rotation. We also found an activation in the left primary motor cortex, which seemed to be associated with the right-hand button press at the end of the task period.

Comparison of matched BOLD and FAIR 4.0T-fMRI with [15O]water PET brain volumes

Valid comparisons of functional activation volumes from fMRI and PET require accurate registration, matched spatial resolution, and if possible matched noise. We coregistered 4.0T-fMRI and PET volumes, using a series of linear and nonlinear transformations applied to the PET volumes. Because of the limited number of fMRI slices that were available, PET volumes were transformed to the fMRI space. Since 4.0T-fMRI and 4.0T-MRI volumes have significant spatial distortion due to magnet inhomogeneities, high resolution 1.5T-MRI volumes were nonlinearly transformed to 4.0T-MRI volumes as part of the transformation chain. The smoothing effects of these registration transformations were measured, in order to match the spatial resolution of the coregistered fMRI and PET volumes. Spatial resolution of the transformed PET volumes in the fMRI space was degraded by up to 60% due to the transformation process. Due to both the image acquisition characteristics and the coregistration process, the transformed PET volumes had a spatial resolution that was lower than that of tMRI. Therefore, significant smoothing of fMRI volumes was necessary to match their spatial resolution with that of the transformed PET volumes. Matching the spatial resolution of the fMRI volumes to those of the transformed PET volumes was achieved by matching the shape of their point spread functions. In order to do this, Gaussian kernels were employed to smooth the fMRI volumes. We were unable to simultaneously match the resolution and noise of fMRI and PET signals in the motor cortex. Activation maps derived from transformed PET and smoothed fMRI volumes were compared. Contralateral motor cortex was active in all modalities but there were large variations in the size of the activated region and its signal to noise ratio across BOLD, FAIR, and PET images within each subject. Nevertheless, the relative CBF changes measured by FAIR were consistent with those determined by PET.

In vitro measurement of muscle volume with 3-dimensional ultrasound

The aim was to test the accuracy of muscle volume measurements with a new 3-dimensional (3-D) ultrasound system, which allows a freehand scanning of the transducer with an improved quality of the ultrasound images and therefore the outlines of the muscles. Five resected cadaveric hand muscles were insonated and the muscle volumes calculated by 3-D reconstructions of the acquired 2-D ultrasound sections. Intra-reader, inter-reader and follow-up variability were calculated, as well as the volume of the muscle tissue measured by water displacement. In the results, 3-D ultrasound and water displacement measurements showed an average deviation of 10.1%; Data of 3-D ultrasound measurements were: intra-reader variability 2.8%; inter-reader variability 2.4% and follow-up variability 2.3%. 3-D measurements of muscle volume are valid and reliable. Serial sonographic measurements of muscle may be able to quantitate changes in muscle volume that occur in disease and recovery.

Reproducibility of BOLD-based functional MRI obtained at 4 T

The reproducibility of activation patterns in the whole brain obtained by functional magnetic resonance imaging (fMRI) experiments at 4 Tesla was studied with a simple finger-opposition task. Six subjects performed three runs in one session, and each run was analyzed separately with the t-test as a univariate method and Fisher's linear discriminant analysis as a multivariate method. Detrending with a first- and third-order polynomial as well as logarithmic transformation as preprocessing steps for the t-test were tested for their impact on reproducibility. Reproducibility across the whole brain was studied by using scatter plots of statistical values and calculating the correlation coefficient between pairs of activation maps. In order to compare reproducibility of "activated" voxels across runs, subjects and models, 2% of all voxels in the brain with the highest statistical values were classified as activated. The analysis of reproducible activated voxels was performed for the whole brain and within regions of interest. We found considerable variability in reproducibility across subjects, regions of interest, and analysis methods. The t-test on the linear detrended data yielded better reproducibility than Fisher's linear discriminant analysis, and therefore seems to be a robust although conservative method. Preliminary data indicate that these modeling results may be reversed by preprocessing to reduce respiratory and cardiac physiological noise effects. The reproducibility of both the position and number of activated voxels in the sensorimotor cortex was highest, while that of the supplementary motor area was much lower, with reproducibility of the cerebellum falling in between the other two areas.

Magnetic sensor data acquisition for three-dimensional ultrasound of the orbit

PURPOSE

Three-dimensional (3D) B-mode ultrasound imaging is now possible using a magnetic sensor data acquisition system to localise data points, allowing free-hand scanning. We report the first use of this freehand scanning system for insonation of the orbit.

METHODS

We insonated 10 orbits in 5 volunteers (all men; mean age 37 years) with an Acuson 128XP ultrasound system and a 7.5 MHz transducer. Power-Doppler was used to image vascular structures. Data were acquired using a new magnetic sensor system with detectors mounted on the transducer. Free-hand scanning was done using sweeping or fan-like and linear movements over 20-30 s to cover the orbit, with retrospective measurements of orbital structures. A 3D reconstruction was performed via an external workstation.

RESULTS

All orbits were adequately imaged by one data acquisition. Selected intraorbital structures were identified and their course followed, including optic nerve and central vessels, as well as short and long ciliary vessels. The mean transverse area of the optic nerve was 5.6 +/- 1.1 mm2; the diameter of the optic nerve was 3.0 +/- 0.3 mm. The lateral rectus muscle was clearly seen, with a mean diameter of 4.9 +/- 0.3 mm, at the level of optic nerve head.

CONCLUSION

Three-dimensional ultrasound of the orbit allows imaging of the location, course and relationships of intraorbital vessels, the optic nerve and the lateral rectus muscles with one data acquisition, as well as quantitative measurements not possible with 2D images alone. This method allows rapid, free-hand data acquisition, with a multitude of potential clinical applications.

Electrodynamic headphones and woofers for application in magnetic resonance imaging scanners

Electrodynamic speakers compatible with (functional) magnetic resonance imaging (MRI) are described. The speakers magnets are removed, their function is replaced by the scanner's magnetic field, resulting in an uncommon but efficient operation. The method can be used with headphones as well as woofers. Functional MRI is not associated with any known biological risks, but as a method for visualization of task-specific activation of brain regions it is undesirably noisy. Thus, it requires both noise protection and efficient sound transmission systems for delivering acoustic stimuli to subjects. Woofers could possibly be used in active noise-control systems. The speakers described in this paper can be used for either task.

Transcranial 3D B-mode imaging in a case of cerebral hemorrhage

The case of a patient with temporal lobe hemorrhage is presented. This is the first report of use of a new three-dimensional data acquisition system that entails free-hand scanning with three-dimensional transcranial duplex sonography. Three-dimensional image reconstruction reduced the spatial asymmetry inherent in oblique two-dimensional ultrasonography, making evaluation of the precise location, size, and anatomic relations of intracranial hemorrhage easier.

Influence of ECG-triggered data acquisition on reliability for carotid plaque volume measurements with a magnetic sensor three-dimensional ultrasound system

Three-dimensional (3D) ultrasound reconstructions of the carotid arteries are based on multiple sections of two-dimensional data. Some 3D systems use an electrocardiography (ECG)-triggered data acquisition for 3D reconstructions of pulsatile vessels such as carotid arteries. No systematic comparison of 3D data, acquired with and without ECG triggering, has been reported. We used a new magnetic sensor system allowing freehand scanning for data acquisition. Our aim was to test the effect of ECG triggering on the reliability of plaque volume measurements in the carotid arteries. Data acquisition in the carotid arteries in 25 patients (one plaque from each patient) was performed using two different procedures for data acquisition: 1) a magnetic sensor system for a data acquisition without ECG-triggering, and 2) a magnetic sensor system with ECG-triggered data acquisition. All plaque volumes were measured using manual tracing of the outlines of the plaques. The following reliability data (mean values) were obtained: magnetic sensor system without ECG triggering: intrareader variability 13.3%, interreader variability 16.7%, follow-up variability 16.3%; magnetic sensor system with ECG triggering: intrareader variability 4.6%, interreader variability 4.5%, follow-up variability 5.2%. Carotid plaque volume measurements obtained using a magnetic sensor system with freehand scanning and ECG triggering is highly reliable. ECG triggering is necessary, because a magnetic sensor system without ECG triggering resulted in reduced reliability for plaque volume measurements.

Functional magnetic resonance imaging of a human auditory cortex area involved in foreground-background decomposition

Auditory foreground-background decomposition is a pattern recognition process which combines simultaneous and sequential grouping in complex sound sequences. Using functional magnetic resonance imaging with reduced scanner noise and stimulation through a new type of earphones, we investigated the possibility that this process activates topographically distinct areas of human auditory cortex. A basic matching-to-sample task with variable tones (sequential grouping) caused significant activity in three separate landmark-related territories on the supratemporal plane. A similar task in the presence of a strongly masking acoustic background pattern to challenge simultaneous grouping led to the distinction of the subterritory in which foreground signal-related or task-related signal properties were exclusively seen. In contrast to the remainder of territories the level of activity and the periodicity of the signal time-course was resistant to the masking influence of the background. This suggests that auditory foreground-background decomposition involves a specialized non-primary auditory cortex field. Generally, the findings demonstrate functional parcellation of auditory cortex for which the evidence in humans, in contrast to other primates, is only indirect to date.

Intercenter agreement in reading Doppler embolic signals. A multicenter international study

BACKGROUND AND PURPOSE

Different frequencies of asymptomatic Doppler embolic signals have been reported in studies. There has been concern that different criteria for identification may account for some of this variation. A previous reproducibility study between two centers found good agreement, but no studies among large numbers of centers have been performed. We performed an international reproducibility study among nine centers, each of which had published recent studies of embolic signal detection in peer-reviewed journals.

METHODS

Each center performed blinded analysis of a taped audio Doppler signal composed of transcranial Doppler middle cerebral artery recordings from 6 patients with symptomatic carotid artery stenosis. The exact time of any embolic signal was recorded. Six centers also measured the intensity increase of any embolic signals detected. Interobserver agreement was determined by a method based on the proportion of specific agreement.

RESULTS

Seven centers reported between 39 and 55 signals, but one center reported 142 embolic signals. The probability of agreement between observers was .678, which rose to .791 when the data from the highest reporting center were excluded. Introducing a decibel threshold resulted in a significant increase in the probability of agreement; a decibel threshold of > 7 dB resulted in a probability of agreement of .902. Intensity measurements made by different centers were usually highly correlated, but this was not always the case, and 3 of the 15 correlations were not significant. The absolute values of the intensities measured varied between centers by as much as 40%.

CONCLUSIONS

Although most centers report similar numbers of embolic signals, some use less specific criteria and report more events. The use of a decibel threshold improves reproducibility. However, intensity thresholds developed by one center cannot be directly transferred without validation to another center; differing methods of measurement are being used, and this results in different intensity values for the same embolic signals, even when the same equipment is used.

Risk factors differ for carotid artery plaque with and without acoustic shadowing. Atherosclerosis Risk in Communities Study Investigators

To investigate the association of gender, ethnicity, and several cardiovascular risk factors with carotid artery plaque and plaque with acoustic shadowing in a population-based sample, high-resolution B-mode ultrasonography was used to characterize lesions in the common and internal carotid arteries, and at the carotid bifurcation in 12,796 US men and women, aged 45 to 64 years, participating in the Atherosclerosis Risk in Communities Study (ARIC) baseline survey. In multiple logistic regression analyses, male gender (odds ratio and 95% confidence interval: 1.52 [1.39-1.67]) and increased total (1.47 [1.32-1.63]) and low-density-lipoprotein cholesterol (1.49 [1.34-1.65]) levels were statistically significantly associated only with the presence of plaque. In contradistinction, smoking (2.22 [1.79-2.75]) and hypertension (1.54 [1.30-1.82]) were additionally associated with acoustic shadowing. Hyperfibrinogenemia (1.33 [1.12-1.59]) was associated only with lesions accompanied by acoustic shadowing. While ethnicity associations with plaque alone varied across the artery segments, among those with plaque, being white was uniformly associated with acoustic shadowing. After multivariable adjustment, high-density-lipoprotein cholesterol was not associated with either manifestation of atherosclerosis. In conclusion, differences were seen in the associations of established cardiovascular risk factors with discretely characterized carotid artery plaque lesions, according to the presence or absence of acoustic shadowing suggestive of mineralization of plaque.

Reproducibility of extracranial carotid atherosclerotic lesions assessed by B-mode ultrasound: the Atherosclerosis Risk in Communities Study

The reproducibility in the identification of carotid artery lesions using B-mode ultrasound was studied in a large random sample selected from the Atherosclerosis Risk in Communities (ARIC) Study. Carotid lesions were defined as plaque with or without acoustic shadowing (indicative of mineralization). A weighted kappa (kappa w) statistic was used as a chance-adjusted measure of repeatability. In the ARIC baseline survey, the kappa w values for the assessment of lesions on repeat reading were 0.47, 0.60 and 0.69 in the left common carotid artery, the carotid bifurcation and the internal carotid artery, respectively. In a repeat scanning, the kappa w values ranged from 0.59 to 0.79 in the left carotid segments. The results were similar in the left and right carotid arteries. Covariates (age, race, gender, body mass index, study center) did not influence the reproducibility. Similar results were also found in both the baseline survey and the first follow-up examination. In conclusion, reproducibility in the assessment of carotid lesions by B-mode ultrasound can be achieved in multicenter studies at fair to good levels of agreement.

A prospective reevaluation of transient ischemic attacks as a risk factor for death and fatal or nonfatal cardiovascular events

BACKGROUND AND PURPOSE

Transient ischemic attack (TIA) is generally considered a risk factor for death and cardiovascular events. This assumption is based on comparisons of the survival of the TIA population with that of the general population. Such comparisons may provide biased estimates of the risk associated with TIA because the general population is usually more healthy than TIA patients.

METHODS

Using a prospective case-control study design, we report the comparison of a TIA population (n = 280) and a control group (n = 399) with a comparable cardiovascular risk factor burden. Proportional hazards analysis was used to compare survival time and time to fatal or nonfatal stroke and/or myocardial infarction for the two study groups. Comparisons were made without adjustment for risk factors and after adjustment for age, race, sex, and major cardiovascular risk factors.

RESULTS

Before adjustment for age-race-sex or risk factors, TIA proved to be a risk factor for early mortality, stroke, and myocardial infarction (P < .05). Adjustment for age-race-sex disparities between the case and control groups explained much of the differences in mortality, as the hazard ratio was reduced from 2.2 to 1.4. However, adjustment for age-race-sex or age-race-sex and risk factors did not markedly reduce the role of TIA as a risk factor for stroke or myocardial infarction.

CONCLUSIONS

Although TIA proved to be a risk factor for stroke or myocardial infarction, it apparently plays a smaller role in the risk of death.

Bilateral diabetic thigh muscle infarction

A 19-year-old woman with insulin-dependent diabetes mellitus developed pain and tenderness in the medial aspect of the left thigh and calf, followed 1 week later by similar symptoms in the right leg. Technetium 99m pyrophosphate (PYP) radionuclide scans showed increased flow and uptake in the medial thigh muscles. Magnetic resonance imaging (MRI) of the thigh showed increased signal on proton density and T2-weighted images in the medial and lateral thigh compartments. High-resolution B-mode ultrasound showed hyperechoic changes in the anteromedial thigh muscles, with loss of normal myofascial interfaces, and a mixed appearance, bilaterally. Two months later, after the symptoms had begun to resolve, the images had improved. This case documents bilateral diabetic thigh infarction identified by abnormal technetium 99m PYP flow studies, MRI signal, and B-mode ultrasound imaging.