Noncephalic referential recording of the electroencephalogram (EEG) has become increasingly important as the technique of mapping EEG activities over the scalp has begun to be widely used. The noncephalic reference derivation is ideal in this respect, but its practical use has been extremely limited because of its inevitable contamination by a large amplitude electrocardiogram (EKG). To overcome this problem, a method of EKG artifacts elimination in EEG recording with noncephalic reference derivation was proposed by some previous authors. The feature of the method was to obtain the estimated artifact waveform by using a peak synchronous averaging technique. However, the accuracy of this previous method sometimes deteriorates because of the variability in its amplitude and duration of each EKG artifact. This paper proposes a new method for EKG artifact elimination by taking into account its variability. The waveform of EKG artifacts, which was originated from the electrical activities by different cardiac muscles, consisted of several components. According to its characteristic, the waveform was divided into several component waves, and their variability for amplitude and duration were independently estimated by using similarity coefficient methods proposed in the past. The proposed method was applied into EEG records with noncephalic reference derivation acquired from five healthy adults. The accuracy of the elimination was investigated in comparison with the previous EKG elimination technique, and the successful improvement of the elimination was verified. The proposed method could be applied to the recording of short latency evoked potentials that requires a noncephalic reference derivation.

View full abstract

We study Spatio-temporal dynamics of the entrainment of brain waves. The entrainment is induced by an external photo-stimulus to the eyes with a periodic frequency, close to the frequency of the alpha wave. It certainly suggests for an origin of the wave to be a nonlinear oscillator. Dealing with the spatio-ternporal characteristics of such nonlinear oscillators based on entrainment dynamics, we propose a new method by a normalized entrainment map in space. By the use of this method, the following facts are clarified: (1) The frequency range of the entrainment in sinciput is broader than that in occiput; (2) The stronger entrainment by the stimulus is observed for the narrower bandwidth of the alpha peak in the stimulus-free spectrum (the so-called single peak spectrum); and (3) The wider the entrainment, the broader the spectrum in a stimulus-free case (the so-called multipeaks spectrum). These results clearly show that the new method may be useful in understanding the characteristic of the dynamics of the alpha wave as nonlinear oscillator systems.

View full abstract

Because friction between the surfaces of a medical device and biological tissues causes pain, it is generally accepted that a lubrication of the surfaces should reduce pain. Therefore silicone oil is used to lubricate the surface of hypodermic needles, but the safety of using silicone oil has not yet been sufficiently discussed. In this study, we investigated the use of mechanical vibration to reduce friction between the surfaces of medical devices and biological tissues as an alternative to lubricants. The vertical force was electrically measured during the insertion of a hypodermic needle into swine muscle tissue. A robotic arm was used to insert the needle. We used three types of piezoelectric elements: type D (the discal piezoelectric element), type M I (the multilayer piezoelectric element [2×3×20mm]), and type M II (the multilayer piezoelectric element [10×10×20mm]), The frequency dependence of the effect of the vibration was assessed in a range of 0 to 10kHz, and we found that insertion force decreased with an increase in frequency. The vibration by the type M II element most markedly reduced the insertion force at the frequency of 10kHz. Under this condition, the insertion force of the hypodermic needle decreased to 69% of that under nonvibration conditions. Since interstitial fluid has non-Newtonian viscosity that reduced with the shear rate in the fluid, the vibration, which increases with this rate, reduces the resistance of fluid flow between the needle and the biological tissue. Thus insertion force can be reduced by the use of vibration. Moreover, since the effect of non-Newtonian viscosity can be expected in the other biological fluids around medical devices such as enteroscopes, this method of reducing friction by vibration may be widely available.

View full abstract

We have been developing a computer-aided diagnosis (CAD) system for mammograms, and many interesting results have been presented for the detection of mammographic masses, spicules, and clustered microcalcifications. The purpose of this study is to develop a computer-aided sketch (CAS) system for assisting physicians when they draw a sketch during mammogram reading. The sketches are automatically drawn by using defined elements determined from the mammograms. These elements are based on automated detection (segmentation) techniques developed so far in our CAD research. Users (usually physicians) are able to use it easily, and if necessary they are able to modify the automated sketch displayed on the CRT monitor. The modification can be done simply by deleting the computerized region of interest (lesion) and/or manually drawing some lines. Our initial results using 430 digitized images indicated that physicians were for the most part satisfied with the defined regions illustrated by our CAS system. Some differences between the sketches by the physician and by the CAS system were found especially for masses and spicules in regions of high density or low contrast. The reason for this was considered to be mainly because physicians usually draw a sketch depending on their knowledge and experience, even though it is hard to determine any lines in the image. Since the microcalcifications, pectoral muscles, and nipples can be represented by some simple lines, the sketches for these images most often easily matched those of the physicians. Because the sketches provided by the CAS system can be saved as electronic data, it is possible to set up a patient record system more efficiently than the conventional method of drawing sketches on paper by hand. The CAS scheme is useful not only for physicians' simple sketch drawings, but also for an electronic patient record system.

View full abstract

We have been developing automated detection algorithms to detect masses on mammograms. In our algorithm, we devised an adaptive thresholding technique for detecting masses, but there was a problem because our system failed to detect the masses with a partial loss of region. To deal with this problem, we propose a new method in this study. The partial loss mass is identified by similarity with the sector-shaped mass pattern models. To calculate the similarity, four features are applied, such as (1) average of pixel values, (2) standard deviation of pixel values, (3) template matching based on the sector-shaped mass pattern models, and (4) concentration feature by density gradient. Our automated mass detection system was improved by combining a previous method with a new one. To evaluate the new method for detecting the masses with a partial loss of region, we examined 335 mammograms. When the searching area is limited near the chest wall, the TP (True Positive) rate by applying our new method is higher than that by using the previous method with fewer false positives per image. Our system improved this by combining the previous method with the new one; the detection sensitivity of the partial loss masses was improved from 57% to 96%, though the number of false positives was increased to 1.09 per image, from 0.88. These results indicated that the new technique effectively improved the detection performance of our computer-aided diagnosis system.

View full abstract

The authors recorded 19ch event-related potentials (ERPs) during binocular stereoscopic vision by random-dot stereograms (RDSs) from 9 subjects. The stereoscopic vision was invoked by three kinds of RDSs with middle-sized, large, and no disparities. The subjects with liquid crystal glasses were requested to press a button when the stimuli were stereoscopically perceived and to press another button without stereopsis. From the multiple equivalent current dipole source localization (ECDL) of differential waveforms between middle-sized or large, and no disparities, it followed that ECDs for components with negative peaks at 400ms were located at the parietal cortex, and that those for earlier components with a positive peak at 100ms and a negative peak at 250ms were localized to the striate and prestriate cortices, respectively.

View full abstract