||Assessment of the Biomechanical Properties of Soft Tissues by Ultrasound Techniques
||Department of BioMedical Engineering
目前臨床上已發展出許多可以代替傳統觸診的方法，利用超音波的物理特性與應力值作為判斷的依據，進一步把軟組織的彈性進行量化，但目前相關演算法皆以傳統的交互相關技術(cross-correlation)或是半自動的量測方法(quasi-automatic measurement)估計超音波訊號的位移情形，但這些方法不僅在位移估計上不準確又含有個人的主觀意識等缺點。因此本研究提出究一套可攜式的即時量測系統，除擷取超音波訊號外並同步紀錄施加在探頭上的力量值，再利用多步的交互相關技術(coarse-to-fine algorithm)來追蹤超音波訊號在壓縮前後的位移，並計算出物體內部的彈性與應力分布狀況，可以更有效評估軟組織生物特性與結構。本系統以5 MHz的超音波探頭作為基準，利用回波訊號來估計軟組織的厚度與形變量；以量測範圍為0到222牛頓的荷重傳感器記錄施加在探測器上的力量值。最後，將這兩筆訊號透過LabVIEW軟體來進行即時分析並將結果顯示為應變圖與超音波彈性成像。
Biomechanical properties of soft tissues are changing with pathological conditions. However, the manual palpation relying on the judgment of the operator was widely used for estimating tissue elasticity. The way is inherent subjectivity and low sensitivity. Hence, in our study, a portable ultrasound indentation system for assessing the biomechanical properties of soft tissues was developed. The system is able to measure the tissue displacement and force signals simultaneously. The 5 MHz transducer was used in this study. The thickness and deformation of the soft tissue were decided from the ultrasound echo signal. A load cell, with a measurement range of 222N, was used to record the force applied on the probe. Moreover, the signals can be processed by the software (LabVIEW 2010) and real-time displayed the strain images and the elastograms.
The similar ultrasound indentation systems have been developed for many years. However, these studies estimated the displacement of ultrasound echo signal by using traditional cross-correlation method or the quasi-automatic measurement method containing a number of drawbacks. Hence, our study utilized coarse-to-fine algorithm, improving the displacement and strain estimates, to track the ultrasound echo signal to obtain tissue deformation.
A validation experiment was performed on tissue-mimicking phantoms and pork tissues. From the result of phantoms including hard substance, we could know the real position within phantom of the hard substance. From the experimental results of pork tissues, the elastography of pork tissue showed the relative hardness between different layers.
List of Figures V
List of Tables VII
Chapter 1. Introduction 1
1.1 Ultrasound Elastography 1
1.2 The Elasticity Estimation Methods 2
1.3 Literature Review 3
1.4 Motivation and the Aim of this Study 11
Chapter 2. Materials and Methods 13
2.1 System Architecture 13
2.1.1 Load Cell 14
2.1.2 Data Acquisition (DAQ) 18
2.1.3 Ultrasound Processing Card 18
2.2 The Elasticity Measurement 19
2.3 Phantoms Preparation 23
2.4 Experiment Procedures 24
2.4.1 Measurement Methods 26
2.4.2 Signal Processing 27
Chapter 3. Results and Discussion 30
3.1 Strain-Stress Curve 30
3.2 Elastography 32
3.2.1 Multilayer Phantom 32
3.2.2 Phantom Including Hard Substance 37
3.2.3 Pork Tissues 40
Chapter 4. Conclusion 43
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