Gye Rae Tack

Real-time elderly activity monitoring system based on a tri-axial accelerometer.

Purpose. The purpose of this study is to develop an automatic human movement classification system for the elderly using single waist-mounted tri-axial accelerometer. Methods. Real-time movement classification algorithm was developed using a hierarchical binary tree, which can classify activities of daily living into four general states: (1) resting state such as sitting, lying, and standing; (2) locomotion state such as walking and running; (3) emergency state such as fall and (4) transition state such as sit to stand, stand to sit, stand to lie, lie to stand, sit to lie, and lie to sit. To evaluate the proposed algorithm, experiments were performed on five healthy young subjects with several activities, such as falls, walking, running, etc. Results. The results of experiment showed that successful detection rate of the system for all activities were about 96%. To evaluate long-term monitoring, 3 h experiment in home environment was performed on one healthy subject and 98% of the movement was successfully classified. Conclusions. The results of experiment showed a possible use of this system which can monitor and classify the activities of daily living. For further improvement of the system, it is necessary to include more detailed classification algorithm to distinguish several daily activities.

Stimulation Pattern-Free Control of FES Cycling: Simulation Study

The aim of this paper is to investigate control strategies for functional electrical simulation (FES) cycling, with particular focus on the generation of stimulation intensities for multiple muscles, without any predetermined stimulation pattern. The control system is developed by imitating the biological neuronal control system. Specifically, the control signal on the level of joint torque (quasi-joint torque) is generated from the feedback information of lower extremities. The quasi-joint torque is then distributed to each muscle and the muscle delay is compensated, and finally, the stimulation intensity is determined. Parameters of the control system are optimized by the genetic algorithm with cost function of energy consumption and cadence error. The proposed control system is evaluated by computer simulation. The controller generates efficient stimulation even during the muscle fatigue process and successfully continues cycling without any predetermined stimulation pattern. Moreover, the controller is robust to the parameter error in the muscle delay compensator and also to the disturbances. It is expected that the proposed method would improve the FES cycling performance and relieve patients by eliminating the experimental determination of the stimulation patterns.

Effect of Input Waveform Pattern and Large Blood Vessel Existence on Destruction of Liver Tumor Using Radiofrequency Ablation: Finite Element Analysis

Much research has been directed at improving the effectiveness of the radiofrequency (RF) ablation of hepatocellular carcinomas. In that point of view, this study was performed to provide comprehensive information of the relation between RF waveforms and thermodynamic response of the tissue with the consideration of four different types of RF waveforms (half-sine, half-square, half-exponential, and damped-sine) to maximize the amount of tumor tissue removed while maintaining the advantages of RF ablation. For the aim of this study, finite element models incorporating results from previous numerical models were used and validated with ex vivo experiments. From analyses of the entire results, we concluded that this study may prove valuable as a first step in providing comprehensive information of the relation between various RF waveforms and thermodynamic responses within the tissue during the RF ablation process. This study may also contribute toward studies to determine an optimum RF waveform capable of maximizing the amount of tumor tissue removed while maintaining the advantages of RF ablation.

Prediction of cement volume for vertebroplasty based on imaging and biomechanical results

Control of bone cement volume (PMMA) may be critical for preventing complications in vertebroplasty, the percutaneous injection of PMMA into vertebra. The purpose of this study was to predict the optimal volume of PMMA injection based on CT images. For this, correlation between PMMA volume and textural features of CT images was examined before and after surgery to evaluate the appropriate PMMA amount. The gray level run length analysis was used to determine the textural features of the trabecular bone. Estimation of PMMA volume was done using 3D visualization with semi-automatic segmentation on postoperative CT images. Then, finite element (FE) models were constructed based on the CT image data of patients and PMMA volume. Appropriate material properties for the trabecular bone were assigned by converting BMD to elastic modulus. Structural reinforcement due to the changes in PMMA volume and BMD was assessed in terms of axial displacement of the superior endplate. A strong correlation was found between the injected PMMA volume and the area of the intertrabecular space and that of trabecular bone calculated from the CT images (r-0.90 and −0.90, respectively). FE results suggested that vertebroplasty could effectively reinforce the osteoporotic vertebra regardless of BMD or PMMA volume. Effectiveness of additional PMMA injection tended to decrease. For patients with BMD well lower than 50mg/ml, injection of up to 30% volume of the vertebral body is recommended. However, less than 30% is recommended otherwise to avoid any complications from excessive PMMA because the strength has already reached the normal level.

Performance Evaluation of One-dimensional Fiber-optic Radiation Sensor for Measuring High Energy Electron Beam Using a Charge-coupled Device

In this study, we have fabricated one-dimensional fiber-optic radiation sensor array for high energy electron beam therapy dosimetry. Fiber-optic radiation sensor comprises an organic scintillator as a sensing volume, optical fiber as a light guider and photo-detector as a light measuring device. Usually, photomultiplier tube or photodiode is used as a photo-detector however we have tried to use a charge-coupled device as a scintillating light measuring system for one-dimensional fiber-optic radiation sensor array. This system can take an image of the proximal ends of one-dimensional fiber-optic sensor array and can measure light intensities of individual image of optical fibers simultaneously using simple imaging software. Charge-coupled device as a light measuring detector has many advantages which are easy in multi-dimensional measurements, high spatial resolution and relatively low cost. We have measured one-dimensional electron beam distributions in a PMMA phantom with different energies and field sizes of electron beam using a fiber-optic sensor and a charge-coupled device. Also, the percentage depth dose curves for high energy electron beams are obtained.

Changes in Cognitive Performance Due to Three Types of Emotional Tension

The purpose of this study was to investigate how three types of emotional tension levels affect performance of a cognitive task. Ten university male (age 25.7 ±1.5) and ten female (age 24.5 ±1.8) students participated in this experiment. We used a 3-back task as a cognitive task. Using pictures selected from a group test, three types of tension levels, i.e. tensed, neutral, and relaxed emotions, were induced. The experimental design consisted of six phases; Rest 1 (2 min), Picture 1 (presenting emotion tensioning photos for 2 min), 3-back Task 1 (2 min), Picture 2 (presenting emotion tensioning photos for 2 min), 3-back Task 2 (2 min), and Rest 2 (2 min). Galvanic skin response (GSR) was also measured during all phases of the experiment. The accuracy rate of 3-back task performance was the highest at a neutral emotional state, followed by relaxed and then tensed emotional state. Through this study it could be inferred that tension, induced by stimuli unrelated to cognitive tasks, decreases the performance of cognitive tasks.

Development of an MR-Compatible ECG Amplifier

The purpose of the present study is to develop a magnetic resonance (MR)-compatible electrocardiogram (ECG) amplifier. If ECG signals are measured simultaneously with the acquisition of MR images, there can be a mutual interference effect. The present system was designed to block noises caused by the main magnetic field, gradient magnetic field and radiofrequency (RF) pulse when MR images are acquired. It uses analogue elements in order to remove any possible effect on MR images. In addition, a radio-frequency-interference (RFI)-free optical data link using the pulse-width modulation (PWM) technique is adopted in order to transmit ECG signals measured inside the MR room.

Development of simple camera-based system for lower limb alignment evaluation during cycling

Simple camera-based system for evaluation of lower limb alignment as a part of an automated cycling fitting system was developed and verified in this study. Developed imaging system can evaluate lower limb alignment quantitatively during pedaling using a general camcorder and single marker attached on the knee. Threshold-based marker detection algorithm with YCbCr color space was proposed in this study. Experiment was carried out to compare trajectory data from marker detection algorithm of the developed imaging system with trajectory data from 3-D motion analysis system. Result showed that average error between trajectories was 1.8 mm (0.57%) of range of motion (ROM) of 326 mm in the vertical direction and 2.3 mm (6.16%) of ROM of 37 mm in the medio-lateral direction. There existed significant correlation between two measured values (r=1.00 in the vertical direction and r = 0.926 in the medio-lateral direction). It can be concluded that developed imaging system be applied to evaluate lower limb alignment which is an important factor for bicycle fitting.

AGE–GENDER DIFFERENCE IN THE BIOMECHANICAL FEATURES OF SIT-TO-STAND MOVEMENT

The purpose of this study was to investigate the effects of age and gender on the biomechanical features of sit-to-stand (STS) movement. Twenty young subjects and 20 elderly subjects participated in this study. Nine events during STS movement were defined where joint angles and joint moments were extracted for further analyses. Two-way repeated measures ANOVA was performed for joint angles and joint moments with age and gender as independent factors. Major gender differences were shown in joint angles. Women used a sliding forward strategy more than men (more flexion of ankle and knee joint) during mid-phases of STS movement (p<0.01) and men used an exaggerated trunk flexion strategy more than women (more hip flexion) in later phases of STS movement (p<0.01). Age differences were shown in joint moments. Elderly subjects showed smaller knee extension moment (normalized by body weight) but greater ankle plantar flexion moment than young subjects in mid-to-late phases of STS movement (p<0.001). More anterior positioning of center of mass (COM) in the elderly might be the reason for the strategy difference. That is, the shorter distance of COM from the knee joint would require less knee extension moment, and likewise, the more forward displacement of COM with respect to the ankle joint would need more plantar flexion moment. More anterior positioning of COM in the elderly, compared to the young was reflected on center of pressure (COP), and the forward displacement of COP was correlated well with the higher body mass index (BMI) and shorter thigh length (r=0.359−0.66;p<0.01).

ACCELERATION PATTERN OF THE UPPER BODY DURING LEVEL WALKING IN PATIENTS WITH PARKINSON'S DISEASE

The aim of this study was to investigate the effects of Parkinsons disease (PD) on upper body acceleration patterns during level walking. Twenty-three patients with PD and 29 controls of similar age participated in this study. Subjects walked along a 12 m linear walkway at self-selected comfortable speeds. Upper body accelerations were measured using three-axis accelerometers located at the pelvis, shoulder, and head. Acceleration magnitude, stride-to-stride irregularity, and degree of coupling among three body parts were derived from the acceleration signals. In the vertical (supero-inferior) direction, PD patients exhibited a smaller acceleration magnitude, a more irregular pattern, and less coupling of acceleration among body parts compared to the controls (p<0.05). In the anterio-posterior (AP) direction, acceleration magnitude at the pelvis in PD patients was smaller than that in the controls (p<0.05). In addition, the phase lag of AP head acceleration from shoulder and pelvis was smaller in PD patients than in the controls (p<0.05). These results suggest that PD patients walk with reduced ankle power generation and a more rigid upper body in the AP direction and with more irregular muscle force generation in the SI direction.