Your Health Is Leaked: PPG Waveform Reconstruction Using Stealthily Recorded Physiological Signals.

In this study, we propose a method to reconstruct photoplethysmogram (PPG) waveforms from other stealthily recorded physiological signals. The proposed method focuses on the frequency characteristics between two physiological signals and reconstructs the target PPG waveform using a regression model. We investigate the feasibility of the proposed method to reconstruct target PPG signals from respiratory (RSP) and PPG signals recorded at non-genuine measurement sites using the two datasets of physiological signals. The results indicate that the proposed method achieves similarities between the target PPG and reconstructed PPG signals with correlation coefficients more than 0.860.

Attack on PPG Biometrics: Presentation Attack by Stealth Recording and Waveform Estimation.

To develop a photoplethysmogram (PPG)-based authentication system with countermeasures, we investigate a "presentation attack" against the authentication. The attack uses the PPG for performing measurements on various sites on each subject's body. It records PPG on a nongenuine measurement site stealthily, generates a spoofing signal based on the recorded PPG, and transmits the signal to the authentication device. To investigate the feasibility of the attack, we developed a PPG-based authentication system. We recorded the PPGs of the subjects' bodies using the developed system and investigated the feasibility of attack in the experiment. The results indicated that an attack can occur with a probability of more than 80 % under ideal conditions.

Photoplethysmographic Subject Identification by Considering Feature Values Derived from Heartbeat and Respiration.

This research proposes a subject identification method using PPG (Photoplethysmogram) signals towards continuous authentication. The proposed method uses feature values derived from heartbeat and respiration extracted from PPG signals by means of frequency filtering and MFCC (Mel-Frequency Cepstrum Coefficients) to identify subjects. An experiment was conducted using an open dataset containing PPG signals to investigate the identification performance of the method. The feature values were extracted from the PPG signals and classifiers were generated to evaluate the performance of the method. As a result, the proposed method was found to be capable of identifying 46 people with the accuracy of 92.9 % by using feature values derived from heartbeat and respiration.

Hemodynamic Sensing of 3-D Fingertip Force by Using Nonpulsatile and Pulsatile Signals in the Proximal Part.

This study proposed a novel sensing method of 3-D contact force at a fingertip by using a photoplethysmogram (PPG) device on the proximal part of a finger. The proposed system detects nonpulsatile and pulsatile components of PPG signals from both sides of the proximal part, extracts 16 feature values related to the contact force, and estimates the 3-D force by using a multiple linear regression model. In the validation experiments, the participants wore a PPG device at the proximal parts of their index fingers and applied a contact force at the fingertips for the 11 types of touch actions. The results indicated that satisfactory agreements are observed between the system outputs and the reference forces by the calibrated force sensor. Moreover, the results revealed that the most effective number of feature values corresponded to six for the higher reproducible sensing. Although the development of the effective calibration method is expected to increase robustness, we realized that the proposed method can potentially be used for a 3-D input user interface.

Estimation of Object Elasticity by Capturing Fingernail Images During Haptic Palpation.

In this study, we present a system that performs natural-touch-based elasticity estimation for an object by using a depth camera. To estimate elasticity, which is defined as an object's Young's modulus, a strain-stress curve is obtained from fingernail images during haptic palpation. From a color image, the proposed system detects a fingernail and extracts 10 feature values related to the contact force; then, it estimates the force using a multiple regression model. Deformation of the object was estimated from the finger's three-dimensional position obtained from both color and depth images. Then, a strain-stress curve was determined using the force and deformation data. Evaluation experiments were designed to obtain the strain-stress curves of five objects from 10 participants; then, the estimation performance was investigated. The results show that the reliable range of sensing was within Young's modulus values of 0.12-5.6 MPa and the precision of the measurement was 55 percent of the estimated elasticity.

Analysis of the tractive force pattern on a knot by force measurement during laparoscopic knot tying.

BACKGROUND: Quantifying surgical skills assists novice surgeons when learning operative techniques. We measured the interaction force at a ligation point and clarified the features of the force pattern among surgeons with different skill levels during laparoscopic knot tying. METHODS: Forty-four surgeons were divided into three groups based on experience: 13 novice (0-5 years), 16 intermediate (6-15 years), and 15 expert (16-30 years). To assess the tractive force direction and volume during knot tying, we used a sensor that measures six force-torque values (x-axis: Fx, y-axis: Fy, z-axis: Fz, and xy-axis: Fxy) attached to a slit Penrose drain. All participants completed one double knot and five single knot sequences. We recorded completion time, force volume (FV), maximum force (MF), time over 1.5 N, duration of non-zero force, and percentage time when vertical force exceeded horizontal force (PTz). RESULTS: There was a significant difference between groups for completion time (p = 0.007); FV (total: p = 0.002; Fx: p = 0.004, Fy: p = 0.007, Fxy: p = 0.004, Fz: p < 0.001, Fxy/Fz: p = 0.003), MF (total: p = 0.004; Fx: p = 0.015, Fy: p = 0.035, Fxy: p = 0.009, Fz: p = 0.001, Fxy/Fz: p = 0.041); time over 1.5 N (p = 0.002); duration of non-zero force (p = 0.029); and PTz (p < 0.001). PTz showed the only significant difference comparing intermediates with experts (intermediates: 13.7 ± 9.0, experts: 4.9 ± 3.2; p < 0.001). CONCLUSIONS: We clarified the characteristics of the force pattern at the ligation point during suturing by surgeons with three levels of experience using a force measurement system. We revealed that both force volume and force direction differed depending on surgeons' skill level during knot tying.

Hemodynamic sensing of 3D fingertip force using PPG device on proximal part.

This research proposed a novel method to estimate the 3D contact force of a fingertip using a photoplethysmogram (PPG) device on the proximal part of a finger. The proposed method detects non-pulsatile and pulsatile components of PPG signals, extracts eight feature values related to the contact force, and estimates the force by multiple linear regression. In the validation experiments, the participants wore a PPG device at the proximal part of the index finger and applied contact force. Then, the relationship between the contact force and PPG feature values was investigated. As a result, the system was found to be capable of estimating the 3D contact force with a root-mean-square error of 3.5 % of the maximum contact force.

Estimation of Finger Joint Angles Based on Electromechanical Sensing of Wrist Shape.

An approach to finger motion capture that places fewer restrictions on the usage environment and actions of the user is an important research topic in biomechanics and human-computer interaction. We proposed a system that electrically detects finger motion from the associated deformation of the wrist and estimates the finger joint angles using multiple regression models. A wrist-mounted sensing device with 16 electrodes detects deformation of the wrist from changes in electrical contact resistance at the skin. In this study, we experimentally investigated the accuracy of finger joint angle estimation, the adequacy of two multiple regression models, and the resolution of the estimation of total finger joint angles. In experiments, both the finger joint angles and the system output voltage were recorded as subjects performed flexion/extension of the fingers. These data were used for calibration using the least-squares method. The system was found to be capable of estimating the total finger joint angle with a root-mean-square error of 29-34 degrees. A multiple regression model with a second-order polynomial basis function was shown to be suitable for the estimation of all total finger joint angles, but not those of the thumb.

Noninvasive simultaneous measurement of blood pressure and blood flow velocity for hemodynamic analysis.

We describe a noninvasive and simultaneous measurement method of beat-by-beat blood pressure and blood flow velocity waveforms in the radial artery using tonometry and Doppler flowmetry. We conducted a subjective experiment in which hold-down pressure of tonometry was controlled for determining optimal hold-down pressure and the measurement accuracy under the optimal hold-down pressure was evaluated. As a result, blood pressure and blood flow velocity could be measured simultaneously without the influence of the hold-down pressure on the blood flow velocity. It was possible to analyze hemodynamic indicators, such as wave intensity and vascular impedance, with blood pressure and blood flow using the system. The proposed system for detecting unexpected fluctuations in blood pressure and the involved mechanisms may contribute to the treatment of cardiovascular diseases.

Electrotactile Augmentation for Carving Guidance.

In this study, we presented an efficient and unobtrusive tactile feedback system, which is used to train dental technicians in carving tasks using a wax stick and knife. First, we developed a method for generating performance metrics using a model-based estimation of clearance angles between an object's surface and the carving blade. The calculated clearance angles are compared with desired angles obtained from expert operators. Then, angular errors are presented as tactile cues to the user's finger pads through electrical stimuli at the middle phalanx of the index finger and the thumb. Subsequently, we conducted a feasibility test with novice dental technicians, who showed improvement in initial clearance angles of carving strokes. Moreover, the results showed significant reduction in the occurrence rate of poor-carving when using the proposed system. From these results, we concluded that electrotactile augmentation can provide effective guidance for carving tasks.

Postoperative gluteal skin damage associated with latent development of gluteal muscle damage.

Preceding this study, we observed two cases of concurrent postoperative gluteal skin and muscle damage with extremely high serum creatine kinase (CK) levels, both of which were unrelated to pressure-induced tissue injury. However, postoperative gluteal skin damage accompanied by gluteal muscle damage has not been previously reported and the association between gluteal skin damage, gluteal muscle damage and pressure-induced tissue injury has not previously been investigated. Therefore, we conducted this study to determine the postoperative incidence of gluteal skin damage associated with gluteal muscle damage and assess associations with postoperative serum CK levels and pressure-induced tissue injury. We prospectively evaluated postoperative incidence of gluteal skin damage and measured serum CK levels in 929 consecutive patients who underwent abdominal, urological or gynecological surgery at our hospital. Magnetic resonance imaging (MRI) of the pelvis was performed in 67 patients who consented. As a result, two of 929 patients developed postoperative gluteal skin damage accompanied by gluteal muscle damage. Gluteal muscle damage without gluteal skin damage was observed in 23 of the 67 patients who underwent MRI, and volumes of damaged gluteal muscle and postoperative serum CK levels were positively correlated. Both gluteal skin and muscle damage were distinguishable from pressure-induced tissue injury. Based on the results of this study, we could confirm the occurrence of postoperative gluteal skin damage, distinct from pressure sores, accompanied by gluteal muscle damage. We also revealed latent development of postoperative gluteal muscle damage, distinguishable from compression-induced tissue injury, without accompanying gluteal skin damage.

Material Roughness Modulation via Electrotactile Augmentation.

Tactile exploration of a material's texture using a bare finger pad is a daily human activity. However, modern tactile displays do not allow users to experience the natural sensations of a material when artificial sensations are presented. We propose an electrotactile augmentation technique capable of superimposing vibrotactile sensations in a finger pad, thereby allowing the texture modulation of real materials. Users attach two stimulus electrodes to the middle phalanx of a finger and a grounded electrode at the base of the finger in order to evoke nerve activity. This paper evaluates the proposed electrotactile augmentation for roughness modulation of real materials. First, we introduce the principle of the electrotactile display, which presents artificial sensations at the finger pad. We then confirm that the perceived frequency of mechanical vibration at the finger pad can be shifted using electrotactile augmentation. Finally, we discuss a user study, wherein participants rated the roughness of real materials explored using the proposed system. Experimental results indicate that fine- and macro-roughness perceptions of real materials can be altered using electrotactile augmentation.

Finger motion capture from wrist-electrode contact resistance.

Hand motion capture is an important yet challenging topic for biomechanics and human computer interaction. We proposed a novel electrical sensing technology for capturing the finger angles from the variation of the wrist shape. The proposed device detects the signal related to the wrist-electrode contact resistances, which change according to the variation of the wrist shape accompanying finger movements. The developed sensing device consists of a wrist band, sixteen electrodes and a sensing circuit of contact resistances. We investigated the relationships between the finger angles and the system outputs by using a glove-type joint angle sensor. As a result, we confirmed high correlations of the system outputs with the finger angles for several electrodes. Therefore, we conclude that the proposed system can be used for the estimation of the finger joint angles.

Unobtrusive tactile sensing based on electromechanical boundary estimation.

Unobtrusive tactile sensing is an important yet challenging topic for medical and robotic fields. We proposed a novel tactile sensing technology for obtaining the force of an interaction and the position at which it makes contact with an object of arbitrary shape without any mechanical obstructions. The proposed sensing method is based on electromechanical boundary estimation from the potential distribution, which is related to the contact state of the two objects with a potential applied. To evaluate the sensing method, we investigated the error of positional estimation and the relationship between force and sensor output. The experimental results indicated that the contact position can be estimated with a correctable systematic error several mm.We also confirmed a high correlation between the interacting force and the system output.

Development of a novel marking system for laparoscopic gastrectomy using endoclips with radio frequency identification tags: feasibility study in a canine model.

BACKGROUND: Intraoperative identification of early gastric cancer is difficult to conduct during laparoscopic procedures. In this study, we investigated the feasibility and accuracy of a newly developed marking system using endoclips with radio frequency identification (RFID) tags in a canine model. METHODS: RFID is a wireless near field communication technology. Among the open frequency bands available for medical use, 13.56 MHz is suitable for a surgical marking system because of the similar and linear signal decay both in air and in biological tissues. The proposed system consists of four parts: (a) endoclips with RFID tags, (b) endo-clip applier equipment, (c) laparoscopic locating probe, and (d) signal processing units with audio interface. In the experimental setting using canine models, RFID-tagged endoclips were applied to the mucosa of each dog's stomach. During the subsequent operation, the clips with RFID tags placed in five dogs were located by the detection of the RFID signal from the tag (RFID group), and the conventional clips in the other six dogs were located by finger palpation (FP group). The detected sites were marked by ablation on the serosal surface. Distance between the clips and the metal pin needles indicating ablated sites were measured with X-ray radiographs of the resected specimen. RESULTS: All clips were successfully detected by the marking system in the RFID group (10/10) and by finger palpation in the FP group (17/17). The medians of detection times were 31.5 and 25.0 s, respectively; the distances were 5.63 and 7.62 mm, respectively. The differences were not statistically significant. No adverse event related to the procedures was observed. CONCLUSIONS: Endoclips with RFID tags were located by our novel marking system in an experimental laparoscopic setting using canine stomachs with substantial accuracy comparable to conventional endoclips located by finger palpation through an open approach.

A novel surgical marking system for small peripheral lung nodules based on radio frequency identification technology: Feasibility study in a canine model.

OBJECTIVE: We investigated the feasibility and accuracy of a novel surgical marking system based on radiofrequency identification (RFID) technology for the localization of small peripheral lung nodules (SPLNs) in a canine model. METHODS: The system consists of 4 components: (1) micro RFID tags (13.56 MHz, 1.0 × 1.0 × 0.8 mm), (2) a tag delivery system with a bronchoscope, (3) a wand-shaped locating probe (10-mm diameter), and (4) a signal processing unit with audio interface. Before the operation, pseudolesions mimicking SPLNs were prepared in 7 dogs by injecting colored collagen. By use of a computed tomographic (CT) guide, an RFID tag was placed via a bronchoscope close to each target lesion. This was then followed by scanning with the locating probe, and wedge resection was performed when possible. Operators can locate the tag by following the sound emitted by the system, which exhibits tone changes according to the tag-probe distance. The primary outcome measure was the rate of wedge resection with good margins. RESULTS: A total of 10 pseudolesions imitating SPLNs were selected as targets. During thoracoscopic procedures, 9 of 10 tags were detected by the system within a median of 27 seconds. Wedge resections were performed for these 9 lesions with a median margin of 11 mm. The single failure was caused by tag dislocation to the central airway. CONCLUSIONS: Successful localization and wedge resection of pseudolesions with appropriate margins were accomplished in an experimental setting. Our RFID marking system has future applications for accurately locating SPLNs in a clinical setting.

Smart sensing of tool/tissue interaction by resistive coupling.

A smart sensing of tool-tissue interaction is required to monitor the surgical task without disturbing the tool manipulation. We proposed a new tactile sensing method that enables us to detect the tool-tissue interaction with a simple hardware by resistive coupling. The system consists of two electrodes, a bridge circuit and a differential amplifier for the robust sensing of the contact resistance between the tool and tissue. In order to evaluate the sensing method, we investigated the relationship between the sensor output and the deformation of a wet sponge sample by retraction task. According to the model fitting of the deformation-output profile, we concluded that the proposed sensor provide enough reproducibility in the simple situation. Furthermore, we confirmed that the developed sensor works with a biological sample.

3D simulation of platelet aggregation in cryosurgery.

In cryosurgery for cancer treatment, cells are injured not only by freezing but also by vascular stasis. The vascular stasis caused by thrombosis necrotizes the surrounding non-targeted cells due to the lack of oxygen and nourishment. Inhibition of thrombus formation, which is the former phase of the vascular stasis, is required to prevent damaging normal cells around a tumorDForegoing studies simulated platelet aggregation based on distance between platelets. However, in cryosurgery, temperature dependency of blood-clotting factors' activity is required to be considered. The authors constructed a three-dimensional model consisting of vascular and extra- vascular tissues, and simulated heat transform and platelet aggregation. Heat transform was analyzed by boundary fitted coordinates method, and platelet aggregation was analyzed by particle method. The probability of bonding between platelets is derived from chemical reaction kinetics. The results showed larger size of simulated thrombus on higher temperature. The simulation with varied temperature around destructed area showed platelet aggregation depending on temperature.

Novel algorithm for real-time onset detection of surface electromyography in step-tracking wrist movements.

We present a novel algorithm for real-time detection of the onset of surface electromyography signal in step-tracking wrist movements. The method identifies abrupt increase of the quasi-tension signal calculated from sEMG resulting from the step-by-step recruitment of activated motor units. We assessed the performance of our proposed algorithm using both simulated and real sEMG signals, and compared with two existing detection methods. Evaluation with simulated sEMG showed that the detection accuracy of our method is robust to different signal-to-noise ratios, and that it outperforms the existing methods in terms of bias when the noise is large (low SNR). Evaluation with real sEMG analysis also indicated better detection performance compared to existing methods.

Voice response system of color and pattern on clothes for visually handicapped person.

For visually handicapped people, a mental support is important in their independent daily life and participation in a society. It is expected to develop a system which can recognize colors and patterns on clothes so that they can go out with less concerns. We have worked on a basic study into such a system, and developed a prototype system which can stably recognize colors and patterns and immediately provide these information in voice, when a user faces it to clothes. In the results of evaluation experiments it is shown that the prototype system is superior to the system in the basic study at the accuracy rate for the recognition of color and pattern.