To detect the early developmental stages of arteriovenous access (AVA) stenosis in hemodialysis patients, this study explored a stenosis detector based on the Burg method and the fractional-order chaos system (FOCS). The bruit developed by the blood flowing through AVA can be a viable noninvasive strategy for monitoring AVA functions. We used the Burg method of the autoregressive model to estimate the frequency spectra of phonographic signals recorded by an electronic stethoscope in patients' AVAs and to identify the spectral peaks in the region of 25-800 Hz. The frequency spectra differed significantly between normal and stenosis statuses in AVA. We found that the frequency and amplitude in power spectra analysis varied in accordance with the severity of AVA stenosis. However, the correlation of these parameters for classifying the degree of stenosis is limited when only using the Burg method. Therefore, we used an FOCS to monitor the differing frequency spectra between the normal condition and AVA stenosis. The variances of these two conditions were dynamic errors that were the coupling variables that tracked the responses between the master system and the slave system. A total of 42 patients who had received percutaneous transluminal angioplasty (PTA) for their failing AVAs was recruited for this study. In this study, the dynamic error, Index Ψ, was used to calculate the frequency spectrum redistribution in patients undergoing PTA. In addition, ΔImp was the index used to evaluate improvements in the luminal diameter between pre- and post-PTA. Therefore, we used linear regression to model the relationship between ΔImp and Index Ψ. The findings indicate that the proposed method has enhanced efficiency, especially in the venous anastomosis (V-site). The FOCS is a novel and simple algorithm for analyzing the residual AVA stenosis of PTA treatment.
Recently, ultrasound techniques have become an important alternative in the assessment of osteoporosis. The speed of sound (SOS) and broadband ultrasound attenuation (BUA) on calcaneus are commonly used in an ultrasound densitometer for osteoporosis evaluation. However, the quantitative ultrasound (QUS) parameters provided by a densitometer using most commercial ultrasound instruments are based on the assumption of a fixed bone thickness. Information on bone thickness is a critical factor for accurate estimation of SOS through conventional approaches; yet, the thickness of bone tissue is not available through in vivo measurements and it is almost impossible to obtain the thickness of bone tissue via conventional approaches. Therefore, the SOS measurements will be incorrect. The purpose of this work is to develop a two-sided interrogation technique for the SOS measurements that is less susceptible to bone thickness. The results show that this proposed technique can obtain a better SOS estimation on bone tissue. Using bone phantoms that mimic actual tissue, the validity of the approach is confirmed with measurements showing high accuracy (>99%) and low standard deviation (<0.5%). Finally, the measurements of 14 healthy subjects are also reported. The results show that this technique can provide the bone thickness information to reduce the SOS estimation errors compared with the fixed bone thickness assumption.
Quantitative ultrasound (QUS) techniques have recently been widely applied for the characterization of tissues. For example, they can be used for the quantification of Achilles tendon properties based on the broadband ultrasound attenuation (BUA) and the speed of sound (SOS) when the ultrasound wave passes through the tissues. This study is to develop an integrated system to investigate the properties of Achilles tendons using QUS images from UBIS 5000 (DMS, Montpellier, France) and B-mode ultrasound images from HDI 5000 (ATL, Ultramark, USA). Subjects including young (32 females and 17 males; mean age: 23.7 ± 2.0) and middle-aged groups (8 female and 8 males; mean age: 47.3 ± 8.5 s) were recruited and tested for this study. Only subjects who did not exercise regularly and had no record of tendon injury were studied. The results show that the BUA is significantly higher for the young group (45.2 ± 1.6 dB MHz−1) than the middle-age group (40.5 ± 1.9 dB MHz−1), while the SOS is significantly lower for the young (1601.9 ± 11.2 ms−1) compared to the middle-aged (1624.1 ± 8.7 m s−1). On the other hand, the thicknesses of Achilles tendons for both groups (young: 4.31 ± 0.23 mm; middle age: 4.24 ± 0.23 mm) are very similar. For one patient who had an Achilles tendon lengthening (ATL) surgery, the thickness of the Achilles tendon increased from 4 mm to 4.33 mm after the surgery. In addition, the BUA increased by about 7.2% while the SOS decreased by about 0.6%. In conclusion, noninvasive ultrasonic assessment of Achilles tendons is useful for assisting clinical diagnosis and for the evaluation of a therapeutic regimen.
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