||Assessment of Biomechanical Properties of Soft Tissues Using Portable Ultrasound Indentation System
||Department of BioMedical Engineering
The definition of soft tissues is any tissues that connect, support, or surround organs of human. It consists of skin, fat, fiber, tendon, ligament, muscle, and fascia. Diseases of soft tissues include infection, inflammation, rupture, tumor, edema, and hematoma. The status of soft tissues in the human body is often of interest in clinical diagnosis. According to previous studies, we know that, if soft tissues undergo pathological changes, they are usually accompanied by changes in their stiffness and thickness. Palpation is often used to clinically detect changes in soft tissues, but this method is subjective and unquantifiable; we need a quantitative, more accurate system to collocate with palpation. Ultrasound is a good choice because advantages of using it are that it is non-invasive, quantifiable, easy to perform, and cheaper than other instruments. Hence, in this study, we developed a portable ultrasound indentation system with a hand-held probe and used chirp-coded excitation with the Tukey window function as the signal trigger. Chirp-coded excitation with the Tukey window function is an effective method to increase the echo signal-to-noise ratio (eSNR) and transmitted energy because if eSNR is too low, this may affect the output of the signal process and reduce the worth of a technique in clinical diagnosis. If the energy of the transmitted ultrasound signals is too low, it will affect the penetration depth of the ultrasound system. In future studies, we could use this system to detect abnormalities not only in the biceps brachii but also in other soft tissues in the human body. Therefore, we used ultrasound elastography with a 5-MHz single element transducer combined with a load cell, which can measure 0–5 N and record the force when compressing the transducer. We then integrated the ultrasound signals and force values to process the elastic information of the soft tissues. In the in vitro validation, we tested the technique on double layer phantoms with different hardness and stiffness as well as on porcine soft tissues. In the in vivo validation, we tested the biceps brachii in the human body. From the information gained on tissue elasticity, we found that our system was able to distinguish variations in hardness in a double layer phantom along with different layers in the porcine tissues and biceps brachii of the human body.
List of Tables VII
List of Figures VIII
Chapter 1. Introduction 1
1.1 Ultrasound Elastography 1
1.2 Coded Excitation 4
1.3 Literatures Review 6
1.4 Motivation and Aim 11
Chapter 2. Materials and Methods 12
2.1 System Architecture 12
2.1.1 Load Cell 13
2.1.2 Data Acquisition (DAQ) 16
2.1.3 Chirp Pulse 17
2.1.4 Indenter Probe 19
2.2 Experimental Procedures 20
2.2.1 Measurement Method 20
2.2.2 Tissue-mimicking Phantoms 21
2.2.3 Signal Processing 22
2.2.4 Participants 25
Chapter 3. Results and Discussion 27
3.1 System Test 27
3.2 Indentation Probe 28
3.3 Double Layer Phantoms 31
3.4 Porcine Tissue 34
3.5 Normal Subjects 34
Chapter 4. Conclusion 36
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