Human tissues and organs often exhibit rheological behaviors during their deformation. For surgery simulation and human modeling, we have to identify physical parameters of such deformation in advance. In this paper, we propose an approach to estimate the physical parameters of uniform rheological deformation based on 2D/3D finite element (FE) modelsimul ation. At first, the FE dynamic model was described and simulations were conducted with initial parameters. Then, the identification method was proposed according to analysis of deformation behavior. Finally, identification results were shown and their validity was evaluated by comparing identified parameters and initial ones. This method can be extended to visco-elastic and layered rheological deformation.
The present study was conducted in order to clarify the features of the occurrences of body movement during nighttime sleep and estimate the depth of sleep. Sleep experiments were conducted on seven healthy, non-medicated subjects, aged20-23years (5 males and 2 females) for 7 hours. During sleep, body movement was measured by electroencephalography (electroencephalography body movement: EEGBM) and by a passive infrared type motion sensor (NapVIEW body movement: NapVIEWBM) . Among all subjects, the mean concordance rate between EEGBM and NapVIEWBM was 0.95 ± 0.03. This finding suggests that it is possible to measure body movement with a 90% or greater concordance with EEGBM using a non-contact method, such as NapVIEW. Analysis of the relationship between body movement intervals and depth of sleep showed that the interval between body movements was longer during deep sleep and shorter during light sleep. Sleep state was evaluated based on data obtained by detailed analysis of the interval between body movements. Linear discriminant analysis was conducted on the interval data obtained by NapVIEWBM to divide into a group of light sleep stages and a group of deep sleep stages. A concordance rate of 90.5% between estimated depth of sleep and actual sleep stage was obtained during light sleep, while a concordance rate of 70.8% was obtained during deep sleep. These findings indicate that sleep state can be adequately evaluated based on depth of sleep as indicated by body movement.
This study examined the effect of sitting positions on cerebral activation for people in bed and analyzed postural significance. The subjects were 30 healthy adults. We recorded their EEGs in α and β band and performed a subjective test in supine and sitting positions with the head of the bed elevated at 30° and 80°. First, measurements were made in the supine position for 5 minutes, and the head of the bed was then elevated. Measurement continued in the sitting position for 15 minutes at 3 stages: Stages 1, 2, and 3. Using the supine position as a baseline, we compared the supine and sitting positions. We also compared the two angles, 30° and 80°. The EEG showed a significant increase at the 80° for all measured regions and intervals, and a partially significant increase was noted at 30°. Comparing the effect of different angles confirmed the significance of 80° at Stages 1 and 2. Moreover retention time of cerebral activation at 80° is longer than that at 30°. The subjective test also confirmed a higher degree of awakening in the sitting position and in a bed at 80°. Consequently, the effect of the sitting position verified cerebral activation.
An “active” ultrasound Doppler method was newly developed in order to directly and easily discriminate emboli from micro bubbles flowing in blood vessel. The principle of this method is based on measuring the induced velocities of an embolus and a micro bubble by acoustic radiation force of ultrasound wave. This force is mainly influenced by the difference in characteristic acoustic impedances between emboli or bubbles and ambient fluid. In order to prove the availability of this new discrimination method, micro bubbles, model emboli and the other particles were irradiated by ultrasound wave from a commercial ultrasound diagnostic equipment. Every motion was observed by a high speed video camera and their velocities along sound axis were measured. As a result, it was found that micro bubbles were strongly moved with a velocity along the axis in steady flow while model emboli were hardly moved, and that this “active” ultrasound Doppler method had high availability for a medical diagnosis system to discriminate emboli from micro bubbles flowing in human vessel.
The sinuses of Valsalva are known to contribute to the normal function. Therefore, the Valsalva graft is being widely used in the aortic root replacement. On the other hand, the artificial valve is developed by the regenerative medical techniques in some research groups. These devices are artificial internal organs. It is desirable for the device to equip long-term durability. In this study, we computed the stress and the displacement in the sinus and the valvular leaflet by commercial software, which is composed by finite element method, in order to clear the between shape parameters and durability. As a result, deformations of the sinuses and leaflets are very small against the pressure loading on a model with sinus of Valsalva. And the rupture part of our developing artificial valve overlapped with very high stress region of the computational model. However, we could minimize the stress by fixing the leaflet shapes.
We propose a new method for obtaining narrow-band electrocardiographic potential (ECG) and respiratory variation in infants through their underwear. This method is based on capacitive coupling involving the electrode, the underwear, and the skin. In order to detect ECG signal and respiratory variation individually, a differential separation filter is introduced. The filter divides an input signal into a high frequency component for narrow-band ECG detection and a low frequency component for respiratory variation detection. To evaluate the proposed method, a pilot measuring device was made and tested. As the results, we confirmed the following: (1) Respiratory variation signal obtained with our device was highly correlated (r = 0.995) with that measured simultaneously with a commercial pneumotachograph. (2) Our pilot device succeeded in measuring narrow-band ECG and respiratory variation respectively in 13 of 15 and 11 of 15 measurements of infant aging 53 to 187 days. (3) R-R interval extracted from the narrow-band ECG was 25 times more precise than that calculated from photoplethysmogram. (4) Heart rate variability extracted from the narrow-band ECG was 100 times more precise than that calculated from photoplethysmogram. These results reveal that the proposed method appears promising for application to bedding of infants and neonate as a non-invasive and awareness-free approach for ECG and respiratory variation monitoring during sleep.
Ultrasonic diagnosis requires substantial experiences for both acquiring and reading echography. This paper describes a novel method for synthesizing ultrasound image with artifacts according to user's probe manipulation. The proposed method is a sample-based approach that stores pre-captured real echo images as a volume data set in which each voxel has multi-directional values. Output echography is synthesized by interpolating voxel values, considering spatial arrangement and directivity of the voxel values. Experimental results demonstrated spatially seamless echography synthesis and characteristic artifacts with various probe postures.
In order to study the availability of pulsed magnetic stimulation (pMS) for recovery of acute muscle fatigue, evoked potential were recorded from soleus (slow-twitch fiber type, fatigue-resistant) and extensor digitorum longus (fast-twitch fiber type, fatigue-sensitive) using hypokalemic and normal Wistar rats in vivo. Hypokalemic rats are useful as nerve-muscle disease model. These rats are suffering from hypokalemic periodic paralysis. Muscle fatigue was caused by electric stimulation to the sciatic nerve for 3 min. pMS were delivered every 2 min for 30 s over the lower limb after induced muscle fatigue. pMS were controlled by a Magnetic stimulator with a figure-of-eight coil (Magstim 200, The Magstim Company, UK) . The coil was placed in order to induce a muscle twitch. It was found that a recovery curve in evoked potential for the muscle varied depending on two factors: the type of muscle fibers and the hypokalemic condition. In addition, the recovery curve in evoked potential was improved slightly by pMS. These findings suggest that recovery curves in evoked potential may reflect characteristics of muscle fiber type and hypokalemia, and that pMS may have an effect on recovery of muscle fatigue.
Our goal is to establish an early diagnostic method for dementia by electroencephalography (EEG) usinga working memory task (Sternberg task). We studied four dementia patients and eighteen healthy subjects. In all subjects, the EEG was recorded while performing a Sternbergtask. A power spectrum value was calculated from the recorded brain waves, and EEG topography image was made based on recording from 19 electrodes. The resulting shape of distribution over the activated region of healthy subjects was an oval at around vertex points Fz, Cz, and Pz at frequencies of 4.392 Hz, 4.880 Hz, and 5.368 Hz, respectively. In contrast, the shape of power spectrum distribution in dementia patients was distorted. It is suggested that the difference in the shape of EEG topography is related to the dementia.
It is important to consider a measurement and an evaluation of the postural responses in human to perturbation such as trips or slips. In this study we gave healthy young subjects backward translation of table as horizontal perturbation, and measured the body sway by the perturbation. The sixteen subjects attached the sensor to an ankle joint, a thigh and a back near the center of gravity. They are kept upright position on the table and then given the perturbation. The experiments were performed with 20 trials of different acceleration from 0.6m/s2 to 4.4m/s2 by 0.2m/s2 in gradually increase. As a result, it was classified in three patterns about a process they shifted from an ankle strategy to a stepping strategy by the peak value of the angular velocity, when they are given the perturbation sequentially. It is no correspondence relationship between classified shift process, static balance inspection and perturbation that begin to support by a stepping strategy. The experiment performed with perturbation in gradually increase identified that postural sway increased with magnitude of perturbation and postural strategy shifted gradually. Therefore it suggested that the experiment performed with perturbation in ascending order was useful to see the gradualshift process unlike with the experiment performed randomly.
Mechanical stress is known to alter the electrophysiological property of myocardium and may trigger fatal arrhythmias when an abnormal load is applied to the heart. We developed novel techniques combining experiment and simulation to elucidate the mechanisms of stretch-induced arrhythmias. We applied transient global stretch to arterially perfused rabbit right ventricular wall preparations. The distribution of strain (determined by marker tracking) and membrane potential (measured by optical mapping with the voltage-sensitive dye, di-4-ANEPPS) were simultaneously recorded while accounting for the motion artifact and the 3-D morphology of preparations was examined by the laser scanner. To further investigate the mechanisms of stretch-induced arrhythmogeneicity, we performed a computer simulation based on finite element method (FEM) . Although the uniform stretch was applied globally, the medium stretch (10∼15%) initiated the excitation from a local spot. On the other hand, the large stretch (> = 20%) caused the synchronous excitation of entire preparation. Computer simulation based on the heterogeneous morphology creates the inhomogeneous strain distribution in response to the stretch, and the focal excitation was observed where the tissue thickness was thin. Our computer simulation also indicates that this focal excitation induced by the medium stretch develop to the stretch-induced spiral wave formation. The inhomogeneous structure of the ventricular wall modulated the globally applied stretch to create heterogeneous strain distribution. Global stretch of medium intensity, rather than intense one, may trigger the fatal arrhythmia.
We have been working on development of automated preoperative planning system for total hip arthroplasty. Although we have already developed automated planning procedures for implants which are inserted into the host bone, there were no automated methods to adjust the integrated planning with considering pelvic and femoral side conditions. In this study, we enhanced the automated procedure to integrate both sides of the plannings by minimizing limb length difference and assuring sufficient range of motion. The system simulates all combination of implants and adopts candidates of cup placement to fulfill the restrictions for optimal placement. We applied this algorithm to 15 cases and confirmed that the automated plannings were optimized successfully in 13 cases. This showed a usefulness of the automated method as an assistant tool for surgical planning.
We developed a new magnetic sensor for residual brain tumor using magnetite enveloped by cationic liposome (MCL) . First, we evaluated the dynamic state of MCL on MRI following local injection into the rat brain and confirmed the safety of MCL by observing the rat's behavior and performing histological examination. In this study, 1.5 mg/ml concentration of MCL showed proper contrast-enhancing effect and did not transport to the liver or kidney. Local injection of MCL into the rat brain did not induce abnormal behavior and no abnormal inflammation was observed in histology. These study suggested the possibility of developing a new technique for detecting brain tumor.