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Thứ Bảy, 29 tháng 12, 2012

Carotid Artery Stiffness Using Ultrasound Radiofrequency Data Technology

Evaluation of Carotid Artery Stiffness in Obese Children Using Ultrasound Radiofrequency Data Technology

Ye Jin,  Yaqing Chen, Qingya Tang, Mingbo Xue, Wenying Li, and Jun Jiang



Objectives—The goals of this study were to investigate the difference in carotid arterial stiffness in obese children compared to healthy children and to study the correlation between carotid arterial stiffness parameters and obesity using ultrasound (US) radiofrequency (RF) data technology.

Methods—Carotid artery stiffness parameters, including the compliance coefficient, stiffness index, and pulse wave velocity, were evaluated in 71 obese patients and 47 healthy controls with US RF data technology. In addition, all participants were evaluated for fat thickness in the paraumbilical abdominal wall and fatty liver using abdominal US.

Results—Compared to the control group, the blood pressure (BP), body mass index (BMI), fat thickness in the paraumbilical abdominal wall, presence of fatty liver, and carotid stiffness parameters (stiffness index and pulse wave velocity) were significantly higher in the obese group, whereas the compliance coefficient was significantly lower in the obese group. Furthermore, the pulse wave velocity was weakly positively correlated with the BMI, systolic BP, diastolic BP, and paraumbilical abdominal wall fat thickness, whereas the compliance coefficient was weakly negatively correlated with the systolic BP, BMI, and paraumbilical abdominal wall fat thickness. The presence of a fatty liver was moderately positively correlated with the BMI and weakly positively correlated with the pulse wave velocity.

Conclusions—Ultrasound RF data technology may be a sensitive noninvasive method that can be used to accurately and quantitatively detect the difference in carotid artery stiffness in obese children compared to healthy children. The detection of carotid functional abnormalities and nonalcoholic fatty liver disease in obese children should allow early therapeutic intervention, which may prevent or delay the development of atherosclerosis in adulthood.


Ultrasound Examinations of the Common Carotid Artery

With the participants in the supine position, the bilateral carotid arteries were scanned from the top to down in the long axis. For longitudinal 2-dimensional US images of the carotid artery, the near and far arterial walls were displayed as two echogenic lines, and the adventitia and intima were separated by the hypoechoic media. The inner most layer (intima) was isoechoic, continuous, and linear. The far arterial wall appeared as a hyperechoic structure. Carotid artery stiffness was measured at the common carotid artery bifurcation level in the long-axis view. The examination site was selected 1.0 cm below the carotid sinus edge. The width of the probe objective frame was set at 1.4 to 1.5 cm.

The position and height of the probe frame were adjusted to adapt the carotid artery to the middle of the frame. The probe beam direction was adjusted to ensure that the sound beam was vertical to the anterior and posterior arterial walls to clearly show the intima and media in the anterior and posterior walls. During the examinations, the participants were asked to hold their breath just before the start of the RF data scan. This scan detects the distension wave, intended as the change in the diameter of the vessel during a cardiac cycle. The difference between the systolic and diastolic diameter values is hereby the distension, and it is the fundamental parameter measured by the quality arterial stiffness software. The wall-tracking feature was active during the scan (Figure 1; see the orange lines across the vessel wall and the green lines associated with wall distension on pulsing). The real distension represented by the green line movements was “amplified,” giving a fast estimation for the user regarding the vessel’s elastic properties and allowing adequate detection (green lines should be as continuous as possible). The distension waveform represented by the movement of the blue lines was displayed at the bottom of the image. The waveform height provided relative information on the shape to ensure that the scan was continuous without artifacts. The premium elaboration capabilities of the MyLab Gold platform allows very fast frame rate acquisition (≈480 Hz), which allows detection without any ambiguity for wall velocities up to 30 m/s (well above the normal 10 m/s). When the instrument displayed6 continuous and stable values (an SD of the measurement ≤20 μm), the image was fixed and stored immediately. The distension value (systolic – diastolic) was determined during each cardiac cycle, and the software calculated the average value of 6 cardiac cycles.

After the 3 BP measurements had been taken, the average of both systolic and diastolic BPs were calculated and entered manually into the quality arterial stiffness vascular calculation software. The average distension value and the brachial systolic and diastolic BPs were used by the software to generate the carotid stiffness parameters, assuming that the arterial pressure at the level of the brachial artery was the same as that at the level of the carotid artery.

The carotid stiffness parameters were presented in the worksheet report (Figure 2). The mean of 3 measurements along with the maximum value were included in the final report.

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