Ryoichi Sakai

A new noninvasive measurement system for wave intensity : evaluation of carotid arterial wave intensity and reproducibility

Abstract. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. Carotid arterial wave intensity in normal subjects has two positive peaks. The first peak, W1, occurs during early systole, the magnitude of which increases with increases in cardiac contractility. The second peak, W2, which occurs towards the end of ejection, is related to the ability of the left ventricle to actively stop aortic blood flow. Between the two positive peaks, a negative area, NA, is often observed, which signifies reflections from the cerebral circulation. The time interval between the R-wave of ECG and the first peak (R − W1) corresponds to the pre-ejection period, and that between the first and second peaks (W1 − W2) corresponds to ejection time. We developed a new ultrasonic on-line system for obtaining WI and arterial stiffness (β). The purpose of this study was (1) to report normal values of various indices derived from WI and β measured with this system, and (2) to evaluate the intraobserver and interobserver reproducibility of the measurements. The measurement system is composed of a computer, a WI unit, and an ultrasonic machine. The WI unit gives the instantaneous change in diameter of the artery and the instantaneous mean blood velocity through the sampling gate. Using these parameters and blood pressure measured with a cuff-type manometer, the computer gives WI and β. We applied this method to the carotid artery in 135 normal subjects. The mean values of W1, W2, NA, R − W1, and W1 − W2 were 8 940 ± 3 790 mmHg m/s3, 1 840 ± 880 mmHg m/s3, 27 ± 13 mmHg m/s2, 104 ± 14 ms, and 270 ± 19 ms, respectively. These values did not show a significant correlation with age. The mean value of β was 10.4 ± 4.8 and the values significantly correlated with age (men: r = 0.66, P < 0.0001; women: r = 0.81, P < 0.0001). The reproducibility was evaluated by intraobserver intrasession (IA), intraobserver intersession (IE), and interobserver intrasession variability (IO). The reproducibility of R − W1 and W1 − W2 was high: the mean coefficient of variation (mCV) of IA was less than 3%; 95% confidence limits from the mean values (CL) were less than 8% for IE and less than 4% for IO. The reproducibility of W1 and β was good: mCV for IA was less than 10%; CL for IE and IO were less than 17%. W2 and NA showed a higher variability than other indices: mCV for IA was less than 13%, and CL for IE and IO were less than 36%. However, two sessions by the same observer and two sessions by different observers were not biased. Wave intensity measurements with this system are clinically acceptable.

A New Method for Evaluation of Fracture Healing by Echo Tracking

Assessment of bone healing on radiographs depends on the volume and radio-opacity of callus at the healing site, but is not necessarily objective, and there are differences of judgment among observers. To overcome this disadvantage, a clinical system was developed to quantify the stiffness of healing fractures of the tibia in patients by the echo tracking (ET) method in a manner similar to a three-point bending test. The purpose of this study was to ensure that the ET system could clinically assess the progress, delay or arrest of healing. The fibular head and the lateral malleolus were supported. A 7.5-MHz ultrasound probe was placed on the proximal and distal fragments and a load of 25 N was applied. Five tracking points were set along the long axis of the ultrasound probe at intervals of 10 mm. With a multiple ET system, two probes measured the displacement of five tracking points on each of the proximal and distal fragments of the tibia, thereby detecting the bending of the two fragments generated by the load. ET angle was defined as the sum of the inclinations of the proximal and distal fragments. Eight tibial fractures in seven patients treated by a cast or internal fixation were measured over time. In patients with radiographically normal healing, the bending angle decreased exponentially over time. However, in patients with nonunion, the angle remained the same over time. It was demonstrated that the ET method could be clinically applicable to evaluate fracture healing as a versatile, quantitative and noninvasive technique.

2A-1 A New Method for Measuring Bone Strength using Echo-Tracking

To evaluate bone strength, it is significant to measure the degree of deformation or strain of bone under a certain load. However no method has been available to non-invasively measure bone deformation. To obtain bone mechanical properties such as elasticity, viscoelasticity and plasticity, we need to externally apply a load to a bone and to accurately measure the small displacement of a specific point on the surface of the bone. For the displacement measurements, we improved the echo-tracking (ET) system. The ET system consists of a diagnostic ultrasound system with a 7.5 MHz linear probe and a PC. PZF echo signals were sampled at 50 MHz and interpolated to eight times the sampling frequency. Then the PC calculated and displayed the small displacement. Furthermore we developed a multi-point ET system and defined ET strain: ETS = D/L, where L was the distance from the first tracking point to the last, and D was the maximum distance from the spline fitting curve of the displacement to the straight line connecting the first tracking point to the last. Then we conducted in vitro experiments using three-point bending (TPB) tests of a porcine tibia placed on a testing machine. As a reference of the bone strain, we used strain gauges attached to the surface of the bone and compared the ETS. With respect to the displacement, there was excellent linearity between the data obtained by the ET system and the linear potentiometer (r = 0.999). In the TPB tests of the porcine tibia, the strain gauge readings and the ETS also showed excellent linearity (r = 0.998 for both the proximal and the distal strain gauges). The results suggest that our method has great potential of non-invasive quantitative diagnosis for bone healing and bone strength

A minute bone bending angle measurement method using echo-tracking for assessment of bone strength in vivo

The purpose of this study is to develop a new ultrasound diagnostic system for non-invasive and quantitative assessment of mechanical properties of the bone or bone healing. In the previous papers, we reported that we had developed a new ultrasound system to measure a minute bone deformation using a multi-point echo-tracking (ET) and that it had a great potential for non-invasive and quantitative diagnosis of bone healing. In this paper, we present a newly developed measurement system with improved accuracy for assessing deformation of intact tibia in vivo. It consists of a dedicated probe, a transmitting/receiving system and analysis software calculating a minute bending angle of the bone surface under a three-point bending (TPB) test. And, we report results of a performance evaluation of the developed system by using test measurements. Furthermore, we evaluated the reproducibility of the in vivo measurement by repeatedly measuring the bending angle of the tibias of 5 healthy volunteers every week for one month. As a result, the evaluation of the accuracy of the measured bending angle using the metallic plate for calibration showed that the standard deviation (SD) of the measurement in range of 0 to 0.1 degrees was 0.004 degrees. Then, we performed an in vivo measurement of normal tibia. The results showed that the mean bending angle of the normal adult tibias under a load of 25 N and a supporting span of the tibial length of each subject was 0.058 degrees with a SD of 0.01 degrees. In addition, SD of the data for the measurement repeatability was 0.006 degrees. We developed a bending angle measurement system for the human tibia using a TPB test and obtained an excellent accuracy of the system and also confirmed through the measurement of the tibia of human volunteers that the repeatability was sufficient to quantitatively assess bending property of the intact tibia.

Measurement of mechanical properties with respect to gap healing in a rabbit osteotomy model using echo tracking.

The most important issue in the assessment of fracture healing is to acquire information about the restoration of the mechanical integrity of bone. Echo tracking (ET) can noninvasively measure the displacement of a certain point on the bone surface under a load. Echo tracking has been used to assess the bone deformation angle of the fracture healing site. Although this method can be used to evaluate bending stiffness, previous studies have not validated the accuracy of bending stiffness. The purpose of the present study is to ensure the accuracy of bending stiffness as measured by ET. A four-point bending test of the gap-healing model in rabbit tibiae was performed to measure bending stiffness. Echo tracking probes were used to measure stiffness, and the results were compared with results of stiffness measurements performed using laser displacement gauges. The relationship between the stiffness measured by these two devices was completely linear, indicating that the ET method could precisely measure bone stiffness.

12C-4 A Minute Bone Bending Angle Measuring Method Using Echo-Tracking for Assessment of Bone Strength

In the previous paper, we reported that an ultrasound system using multi-point echo-tracking (ET) could have a great potential for non-invasive and quantitative diagnosis of bone healing. In this study, the results of a clinical evaluation of the previous method were reviewed and we further improved the ET system to obtain the higher accuracy. The objective of this study was to develop a new ultrasound diagnostic method and to experimentally confirm an improved accuracy of the ET system. First, we investigated the ET system performance by conducting buckling tests using a synthetic bone model which simulated the mechanical properties of the human tibias. To obtain reference data on bone strain, we attached strain gauges to the surface of the bone model. Second, the system was applied to clinically measure the stiffness of the healing position of the tibia in patients in the consolidation period who underwent lengthening of the tibia using an external fixator. To induce an axial load on the tibia, a force of 100-N was applied on the knee of the patients who assumed sitting position and the ET strain (ETS) was measured by detecting small bending curve generated by the bending of the tibial surface. Six tibiae in four patients were measured during the consolidation period. Third, to obtain better accuracy even at a smaller load magnitude, we changed the measurement algorithm for the ET system by using a three-point bending (TPB) test method. Width of the measurement span was increased from 40 mm to 140 mm and a bending angle of the bone fragments generated by loading on the distal part of the proximal fragment was obtained instead of the ETS. Finally, its accuracy was evaluated by measuring the inclination of a metal plate and by conducting a TPB of the bone model. In the buckling test of the bone model, a high correlation coefficient (r=0.978, p<0.01) was obtained between the strain gauge readings and the results obtained with the previous system. In the clinical application, the system was able to measure the ETS change over time until the stiffness at the bone healing position almost reached a level similar to that of an intact tibia. However, it was desirable to have higher accuracy even at a smaller load for patients. From the results of the ET system with the improved algorithm, the standard deviation for the differences between the inclination angles of the metal plate measured by this system and those measured by a potentiometer was 0.005 degree. In the TPB of the bone model, the bending angle measurement was 0.1 degree at an applied load of 25 N. It was concluded that the improved ET system could measure the mechanical property of an intact bone with sufficient accuracy at a smaller load magnitude.