abstract: Ultrasound B-mode imaging is an increasingly significant medical imaging modality for clinical applications. Compared to other imaging modalities like computed tomography (CT) or magnetic resonance imaging (MRI), ultrasound imaging has the advantage of being safe, inexpensive, and portable. While two dimensional (2-D) ultrasound imaging is very popular, three dimensional (3-D) ultrasound imaging provides distinct advantages over its 2-D counterpart by providing volumetric imaging, which leads to more accurate analysis of tumor and cysts. However, the amount of received data at the front-end of 3-D system is extremely large, making it impractical for power-constrained portable systems. In this thesis, algorithm and hardware design techniques to support a hand-held 3-D ultrasound imaging system are proposed. Synthetic aperture sequential beamforming (SASB) is chosen since its computations can be split into two stages, where the output generated of Stage 1 is significantly smaller in size compared to the input. This characteristic enables Stage 1 to be done in the front end while Stage 2 can be sent out to be processed elsewhere. The contributions of this thesis are as follows. First, 2-D SASB is extended to 3-D. Techniques to increase the volume rate of 3-D SASB through a new multi-line firing scheme and use of linear chirp as the excitation waveform, are presented. A new sparse array design that not only reduces the number of active transducers but also avoids the imaging degradation caused by grating lobes, is proposed. A combination of these techniques increases the volume rate of 3-D SASB by 4\texttimes{} without introducing extra computations at the front end. Next, algorithmic techniques to further reduce the Stage 1 computations in the front end are presented. These include reducing the number of distinct apodization coefficients and operating with narrow-bit-width fixed-point data. A 3-D die stacked architecture is designed for the front end. This highly parallel architecture enables the signals received by 961 active transducers to be digitalized, routed by a network-on-chip, and processed in parallel. The processed data are accumulated through a bus-based structure. This architecture is synthesized using TSMC 28 nm technology node and the estimated power consumption of the front end is less than 2 W. Finally, the Stage 2 computations are mapped onto a reconfigurable multi-core architecture, TRANSFORMER, which supports different types of on-chip memory banks and run-time reconfigurable connections between general processing elements and memory banks. The matched filtering step and the beamforming step in Stage 2 are mapped onto TRANSFORMER with different memory configurations. Gem5 simulations show that the private cache mode generates shorter execution time and higher computation efficiency compared to other cache modes. The overall execution time for Stage 2 is 14.73 ms. The average power consumption and the average Giga-operations-per-second/Watt in 14 nm technology node are 0.14 W and 103.84, respectively. / Dissertation/Thesis / Doctoral Dissertation Engineering 2019

Shear wave elastography is a medical imaging modality in which tissue elasticity is estimated by measuring the speed of ultrasound-induced shear waves. This study aimed to implement four shear wave generating pushes and compare their performance according to chosen metrics. The focused push, unfocused push, unfocused comb push and line push were implemented on a Verasonics ultrasound system and tested on a polyvinyl alcohol phantom. Shear wave propagation was imaged using angle-compounded ultrafast imaging. Axial particle velocities were estimated using a 2D autocorrelator and then cross-correlated to obtain local shear wave speed estimates. The focused push and line push were found to generate shear waves with 1--3 times higher peak axial particle velocity, implying better signal-to-noise ratios. The focused push, unfocused push and line push were found to exhibit areas 7 mm wide around the pushing beams in which shear wave speed cannot be estimated, whereas the unfocused comb push has no such blind area.

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第17981号 / 人健博第10号 / 新制||人健||1(附属図書館) / 80825 / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 坪山 直生, 教授 椎名 毅, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

Musculoskeletal models and simulations allow for the estimation of forces acting on muscles and joints during human movement and athletic performance. In order to improve the accuracy of these models for a specific application, knowledge about subject-specific in vivo properties of human muscle and tendon is needed. This study presents a method for estimating in vivo mechanical properties of human tendon in the lower leg, using a combination of ultrasound imaging and motion capture. Key mechanical parameters — such as tendon stiffness, moment arm, slack length and force-strain relationship — and the contribution of tendon elongation to ankle mobility of the medial gastrocnemius (MG) and soleus (SOL) aspects of the Achilles tendon were obtained in vivo in 8 typically-developed adults, and the applicability of the method on the tibialis anterior (TA) tendon was investigated. In contrast to previous studies using a comparable method, variable tendon moment arm lengths during passive movement of the ankle joint was taken into consideration. As a novelty, the passive mechanical properties of the Achilles tendon were obtained in vivo in 4 hemiplegic post-stroke subjects and compared to the 8 typically-developed subjects. The estimated mechanical parameters of the MG and SOL aspects of the Achilles tendon were consistent with findings in the literature. In order to estimate stiffness of the TA tendon, it was shown that a larger range of motion (ROM) of the foot during the passive rotation experiments is needed. The comparison between typically-developed and hemiplegic post-stroke subjects revealed significantly lower tendon stiffness and slack angle, and significantly higher contribution of tendon elongation to ankle mobility in the post-stroke group. The developed method enables estimation of in vivo mechanical properties of tendon in the lower leg and contributes to improving the accuracy of subject-specific musculoskeletal models and simulations. / Person-specific biomechanical models

No description available.

Skeletal muscle is a plastic tissue capable of responding to environmental perturbations. Increased loading via resistance exercise (RE) activates muscle protein synthesis (MPS) and, to a lesser extent, muscle protein breakdown (MPB). The ingestion of protein further stimulates MPS and suppresses MPB, inducing a positive net protein balance and protein accretion – i.e., muscle hypertrophy. In contrast, muscle unloading reduces MPS, which is thought to be the key driver underpinning skeletal muscle atrophy. The degree of muscle hypertrophy and atrophy in response to loading and unloading varies significantly between individuals and provides an opportunity to investigate the molecular regulators of skeletal muscle remodelling. To that end, we developed a novel unilateral model in which one leg was subjected to RE to induce hypertrophy (Hyp) and the contralateral limb was immobilized to induce atrophy (At). In study 1, we characterized the morphological changes induced by our HypAt model and validated the use of ultrasonography to measure changes in muscle size in both limbs. We discovered that by assessing the differential change in muscle size between legs we reduced the coefficient of variation between subjects. This enabled a more in-depth means-based characterization of the molecular regulators of skeletal muscle remodelling. Indeed, we discovered significantly more genes regulated by muscle remodelling than similarly-sized studies. We also identified a transcriptional signature that scaled with lean mass gains in three independent cohorts and included RNA species that were only modulated at their untranslated regions. Finally, in study 3 we simultaneously measured MPS and MPB in response to short-term immobilization (4 days) and demonstrated for the first time that MPB is statistically unchanged by unloading. Taken together, these studies contribute significantly to our understanding of skeletal muscle remodelling under different loading states and provide a valuable hypothesis-generating resource for future research in the field. / Thesis / Doctor of Philosophy (PhD) / Adaptations of skeletal muscle to loading and unloading are variable between individuals. Herein, we employed a unilateral approach to better understand the drivers of this variability by assessing the influence of resistance training (RT) and disuse on muscle protein turnover and gene expression. First, we validated the use of ultrasound for measuring changes in muscle size in response to loading and unloading. We then identified thousands of genes regulated by loading status and discovered many that were correlated with lean mass gain – some of which would not have been detected without our model. We also demonstrated that RT-induced increases in muscle protein synthesis were not associated with changes in muscle size; however, reductions in muscle protein synthesis were associated with the degree of muscle atrophy observed in response to disuse. Together, these studies contribute significantly to our understanding of how skeletal muscle size is regulated by muscle loading and unloading.

No description available.

No description available.

No description available.

No description available.