Development of Ultrasound Elasticity Imaging System with Chirp-Coded Excitation for Assessing Biomechanical Properties of Soft Tissue

  • 江 幸容

Student thesis: Master's Thesis

Abstract

Changes in the biomechanical properties of soft tissues generally correlates with the pathological phenomenon Ultrasound elasticity imaging which is a non-invasive method can be used to measure the local biomechanical properties of soft tissue that can be used to assess the pathological changes of soft tissue in clinical diagnosis However the echo signal to noise ratio (eSNR) was diminished due to the attenuation of ultrasonic energy by soft tissues that reduces the quality of elastography To improve the quality of elastography the eSNR and penetrating depth of ultrasound can be increased by the average power of ultrasound which is generated using chirp-coded excitation Moreover the low axial resolution of ultrasound generated by chirp-coded pulse can be increased using a proper compression filter Therefore the main goal of this study is to develop ultrasound elasticity imaging system with chirp-coded excitation for assessing biomechanical properties of soft tissue Furthermore the effects of chirp-coded excitation modulated by a Gaussian window and a Tukey window respectively and short pulse excitation upon the qualities of elastography were discussed The ultrasound elasticity imaging system equipped with a 7 5 MHz single element transducer and polymethylpentene compression plate to measure the strain of soft tissue and the compression force on soft tissue was measured by load cell The strain information of soft tissue was analyzed using cross-correlation (CC) algorithm and absolution difference (AD) algorithm The optimal parameters of CC and AD algorithms used for the ultrasound elasticity imaging system with chirp-coded excitation were analyzed by measuring the signal-to-noise ratio on the elastogram (SNRe) of homogeneous phantom Moreover the ultrasound elasticity imaging system with chirp-coded excitation and short pulse excitation were used to measure the elastically phantom (Young’s modulus of background materials and cylindrical inclusion were 13 27 and 26 86kPa respectively) Qualities of elastography for the elastically phantom were assessed by the accuracy of Young’s modulus and elastographic contrast-to-noise ratio (CNRe) The experimental results shows that the SNRe of elastography measured by short pulsed ultrasound was 11dB As the homogenous phantom was measured by 20 cycles chirp-coded ultrasound modulated by a Tukey window the SNRe of elastography (CC algorithm: 15dB AD algorithm: 13dB) is better than that measured by short pulsed ultrasound The CNRe in elastography which was imaged using chirp-coded pulse can be improved 4 1dB compared with that imaged using short pulse In addition the Young’s modulus of cylindrical inclusion analyzed using CC algorithm was 25 52 kPa and that analyzed using AD algorithm was 22 72 kPa These results demonstrated that the ultrasound elasticity imaging system with chirp-coded excitation modulated by a Tukey window could acquire the high quality and high accuracy elastography
Date of Award2015 Aug 12
Original languageEnglish
SupervisorTainsong Chen (Supervisor)

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