Pei Jarn Chen

Phonographic signal with a fractional-order chaotic system: a novel and simple algorithm for analyzing residual arteriovenous access stenosis.

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 25–800xa0Hz. 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.

A novel bipolar pulse generator for high-frequency ultrasound system

Pulse generator is the critical component in all ultrasound systems for driving a piezoelectric transducer to medical or nondestructive testing (NDT) applications. The transducer in ultrasound system was driven by a pulse train generator, which delivers high-voltage bipolar or unipolar pulse train. Several recent papers have discussed both the importance and the design of unipolar and bipolar pulse generator for ultrasound applications. Bipolar voltage pulse has lower unwanted DC and low-frequency component could decrease the leakage current. Also, its peak-to-peak pulse voltage could achieve twice of the voltage rating of the coaxial cable connecting the generator and the transducer. In current commercial ultrasound systems, bipolar pulse generators are commonly used; however, it still had some disadvantages like longer pulse length, which limited the driving frequency and affect the signal performance. This paper purposed a novel design of bipolar pulse generator based on a novel dual P-N channel MOSFET and FPGA timing control. It could produce multi-cycle pulses with center frequency over 50 MHz and shorter pulse length. This design also preserved the low-cost advantage compared to other commercial design of bipolar pulse generator. It is suitable for high-frequency ultrasound Doppler and B-mode imaging applications.

Quantitative ultrasound (QUS) assessment of tissue properties for Achilles tendons

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.

Ultrasound elasticity imaging system with chirp-coded excitation for assessing biomechanical properties of elasticity phantom

The biomechanical properties of soft tissues vary with pathological phenomenon. Ultrasound elasticity imaging is a noninvasive method used to analyze the local biomechanical properties of soft tissues in clinical diagnosis. However, the echo signal-to-noise ratio (eSNR) is diminished because of the attenuation of ultrasonic energy by soft tissues. Therefore, to improve the quality of elastography, the eSNR and depth of ultrasound penetration must be increased using chirp-coded excitation. Moreover, the low axial resolution of ultrasound images generated by a chirp-coded pulse must be increased using an appropriate compression filter. The main aim of this study is to develop an ultrasound elasticity imaging system with chirp-coded excitation using a Tukey window for assessing the biomechanical properties of soft tissues. In this study, we propose an ultrasound elasticity imaging system equipped with a 7.5-MHz single-element transducer and polymethylpentene compression plate to measure strains in soft tissues. Soft tissue strains were analyzed using cross correlation (CC) and absolution difference (AD) algorithms. The optimal parameters of CC and AD algorithms used for the ultrasound elasticity imaging system with chirp-coded excitation were determined by measuring the elastographic signal-to-noise ratio (SNRe) of a homogeneous phantom. Moreover, chirp-coded excitation and short pulse excitation were used to measure the elasticity properties of the phantom. The elastographic qualities of the tissue-mimicking phantom were assessed in terms of Young’s modulus and elastographic contrast-to-noise ratio (CNRe). The results show that the developed ultrasound elasticity imaging system with chirp-coded excitation modulated by a Tukey window can acquire accurate, high-quality elastography images.

Development of a FPGA-based quantitative ultrasound system for assessing stress-strain properties of Achilles tendon

Achilles tendon (AT) is the most fragile and vulnerable part in human body. Stress-strain properties and shape changing such as cross-sectional area variations of this tendon are important biomechanical properties used clinically for assessing and monitoring surgical repair or postoperative healing progress. However, so far, there are few methods for non-invasively, precisely and quantitatively assessing in vivo AT mechanism. In this study, we develop a quantitative ultrasound system (QUS) based on FPGA aiming at estimating stress-strain properties of AT via evaluating the broadband ultrasound attenuation (BUA) parameter upon different levels of applied stress on the AT. Twenty fresh ATs of hind porcine trotters were procured from a local abattoir, and were preloaded for 30 cycles with a cyclic loading ranging from 0 to 300 N. The loading force pulled along the tendon fibers, and the changes of AT cross-sectional area were acquired by ultrasound transducer implemented in the palmardorsal direction which was perpendicular to the tendon fibers. BUA has been widely used to estimate the broadband ultrasonic attenuation (dB MHz-1) by calculating the slope of a linear regression fit to the attenuation against frequency plot within a frequency range. The tendons were then strained from 1 to 400 N with single steps of 50 N, and the measurements were repeated for ten times following calculating the average slope of BUA to reduce the interference of noise. Results showed that as the tendon tissue was stretched orthogonally to the beam axis, BUA coefficient decreased linearly with increasing stress (R-square =0.89). This indicated that the BUA coefficient is a potentially useful parameter for quantitative characterization of ATs. The FPGA system proposed for measuring tendon thickness using QUS technique is an easy and objective method to precisely evaluate the tissue thickness, providing a new way for AT to implement high-speed online diagnosis.

Estimation of arteriovenous fistula stenosis by FPGA based Doppler flow imaging system

Arteriovenous fistula (AVF) is a vascular access and very import in hemodialysis that is a treatment for patients suffering from end-stage renal disease. Stenosis is considered the major cause of dysfunction of AVF. Despite the relatively low thrombosis rates of AVF, surveillance programs are necessary for detection of stenosis. However, conventional Doppler ultrasound cannot facilitate the risk assessment of AVF, such as insufficient resolution. The objective of this study was to develop an estimation system using FPGA based color relational analysis (CRA) method for AVF stenosis on hemodialysis patients by quantitative Doppler ultrasound, which provides not only the degrees of stenosis (DOS), but also anatomical locations and blood flow physiology information for clinical physicians, lowing the risk arising from treatment. In this paper we proposed a method based on hemodynamic analysis with dimensionless numbers to capture and further quantify the feature values of Doppler ultrasound extracted from intraluminal blood flow. The ratio of the supracritical Reynolds (Resupra) number and the resistive (Res) index were calculated via the peak-systolic and peak-diastolic velocities of blood flow from the arterial anastomosis sites (A) to the venous anastomosis sites (V) to quantitate the DOS at multiple measurement sites. After that, the results were mapped with a CRA classifier to real-time display the DOS. The examination results from thirty long-term dialysis patients showed that this proposed method performed well in DOS and occlusion site detection, with >95% of accuracy. This study confirmed the CRA method is a potential candidate method to effectively evaluate the AVF caused by long-term dialysis or vascular disease. The proposed system provides useful information with better accuracy and convenience for clinical examination.

Development of a High-Frequency Ultrasound System for High Speed Image Scanning

High-frequency image technique has been widely applied to medical diagnoses recently. As high voltage protection, high speed stage and trigger control circuitry are difficult to implement a high frequency ultrasound imaging system. In this study, we utilized a linear servo with high noise tolerance and a novel multi-depth expression method to overcome those issues in developed high speed image system. B-mode image of the chicken phantom by 25MHz transducer shows the resolution of lateral and axial resolutions are up to 123μm and 59μm respectively. In addition, the experiment demonstrates that the axial resolution and depth of field (DOF) can be improved by time gain compensation (TGC) and multi-depth method. The results indicated that the proposed system could achieve over 24 fps for 1mm scan distance and 100 lines per frame. In the future, the developed system is potential for other clinical applications such as ophthalmology and dermatology.

Development of a Bipolar Pulse Generator for High-Frequency Ultrasound Imaging System

The pulse generator is the critical component in high-frequency ultrasound imaging systems. Currently, there still exist some shortcomings about commercial ultrasound image systems and devices such as 5900 PR …etc.. However, to achieve a higher sensitivity and high performance, a programmable pulser generator is desired to match the requirements of high frequency ultrasound image system. In this study, we utilized a novel bipolar pulse generator method to overcome those issues in developed high resolution image system. As the needs of application in clinic, a real –time of high-frequency ultrasound imaging systems, including pulse generator, high speed scanning mechanism, high voltage protection and FPGA trigger control circuit, was developed in our Laboratory. This paper will focus to compare the performance of the bipolar generator and unipolar generator as used in pulse generator device respectively. Finally, the developed bipolar pulse generator show the better performance than the unipolar generator does. The bipolar system can generate clean N-cycle bipolar pulses and improve the center frequency of transducer up to 60 MHz. The axial resolution of scan system has been improved to around 60 μm. In addition, the result indicated that the proposed bipolar pulser could increase 4 dB for pulse/echo waveforms amplitude.

Quantitative Measurements of Blood Vessels on Human Extremities by Near-Infrared (NIR) Technique

In this paper, a nonradioactive and noninvasive blood vessels image system based on NIR technique was presented for estimating the physiological parameters of the blood vessels, such as blood vessel width (BVW), blood vessel width ratio (BVWR) and blood vessel fractal dimension (BVFD). Our results showed the feasibility of quantifying the vasculature on human extremities using the NIR images.

Development of Website for the Operating Procedure of Software Contained in Medical Devices

Fault or failure of software contained in medical devices will seriously endanger users and should be considered to reduce risk. In software development process, the risk analysis and risk control are very important for software contained in medical devices. In order to promote the quality of software contained in medical devices, a website is designed to provide the operating procedure of software contained in medical devices in this paper. The configuration management of software with operation procedure is managed by website based relational database developed by PHP and MySQL. Software process model, V-mode, is applied to guide software development process and used to promote the reliability of software. Moreover, fault tree analysis and failure mode and effects analysis are used to achieve risk analysis and risk control. The risk of software contained in medical devices can be effectively reduced. Therefore, software verification and validation is also integrated to verify and validate the function of software. Integrated Cephalometric Analysis System had been used to show that proposed approach is feasible.