• Annals of Clinical Neurophysiology
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• v.11 no.2
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• pp.54-58
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• 2009

Background: Obstructive sleep apnea (OSA) is associated with several cardiovascular diseases. However, the mechanisms are not completely understood. The measure of common carotid artery intima-media thickness (IMT) has been extensively used as an early marker of atherosclerosis. The aim of this study was to test the hypothesis that early signs of atherosclerosis are present in patients with OSA and correlate with OSA severity Methods: Eleven male patients with OSA were studied by using full standard overnight polysomnography and high-definition echo-tracking device to measure intima-media thickness and carotid artery diameter. Eight healthy volunteers matched for age and sex were studied by portable respiratory monitoring device. All participants were free of hypertension, diabetes, and were not on any medications. Patients with OSA were naive to treatment. Results: All patients and normal controls were male. There was no significant difference of age between patients and controls ($48.4{\pm}8.85$ and $48.0{\pm}9.77$). Significant differences existed between control subjects and patients with mild to moderate and severe OSA (apnea-hypopnea index, $1.51{\pm}1.15$ and $38.51{\pm}19.13$ respectively) in intima-media thickness ($0.59{\pm}0.064$ and $0.93{\pm}0.16$; P=0.0023), and carotid diameter ($5.79{\pm}0.44$ and $6.47{\pm}0.51$; P=0.0227). Multivariate analyses showed that the apnea-hypopnea index correlated independently with intima-media thickness and carotid diameter (r=0.79, P=0.0008, and r=0.47, P=0.0482). Conclusions: Middle-aged patients with OSA who are free of overt cardiovascular diseases have early signs of atherosclerosis, which further supports the hypothesis that OSA plays an independent role in atherosclerosis progression.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2511-2517
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• 2009

Recently, a FMCW radar is used for the various purposes in the short range detection and tracking of targets. The main advantages of a FMCWradar are the comparative simplicity of implementation and the low peak power transmission characterizing the very low probability of signal interception. Since it uses the frequency modulated continuous wave for transmission and demodulation, the received beat frequency represents the range and Doppler information of targets. Detection and extraction of useful information from targets are performed in this beat frequency domain. Therefore, the resolution and accuracy in the estimation of a beat spectrum are very important. However, using the conventional FFT estimation method, the high resolution spectrum estimation with a low sidelobe level is not possible if the acquisition time is very short in receiving target echoes. This kind of problems deteriorates the detection performance of adjacent targets having the large magnitude differences in return echoes and also degrades the reliability of the extracted information. Therefore, in this paper, the model parameter estimation methods such as autoregressive and eigenvector spectrum estimation are applied to mitigate these problems. Also, simulation results are compared and analyzed for further improvement.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.403-411
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• 2023

Functional ultrasound imaging, such as elasticity imaging and micro-blood flow Doppler imaging, enhances diagnostic capability by providing useful mechanical and functional information about tissues. However, the implementation of functional ultrasound imaging poses limitations such as the storage of vast amounts of data in Radio Frequency (RF) data acquisition and processing. In this paper, we propose a sub-Nyquist approach that reduces the amount of acquired axial samples for efficient shear-wave elasticity imaging. The proposed method acquires data at a sampling rate one-third lower than the conventional Nyquist sampling rate and tracks shear-wave signals through RF signals reconstructed using band-pass filtering-based interpolation. In this approach, the RF signal is assumed to have a fractional bandwidth of 67 %. To validate the approach, we reconstruct the shear-wave velocity images using shear-wave tracking data obtained by conventional and proposed approaches, and compare the group velocity, contrast-to-noise ratio, and structural similarity index measurement. We qualitatively and quantitatively demonstrate the potential of sub-Nyquist sampling-based shear-wave elasticity imaging, indicating that our approach could be practically useful in three-dimensional shear-wave elasticity imaging, where a massive amount of ultrasound data is required.