Jpn. J. Appl. Phys. Vol. 38 (1999) pp. 3403–3408 Part 1, No. 5B, May 1999 c 1999 Publication Board, Japanese Journal of Applied Physics In Vivo Measurement of Small Velocity Signals and Change in Thickness of the Heart Walls Hiroshi KANAI ∗1 , Yoshiro KOIWA ∗2 , Yoshiko SAITO ∗3 , Ikuko SUSUKIDA ∗4 and Motonao TANAKA ∗5 Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan (Received November 27, 1998; accepted for publication January 18, 1999) We have previously developed a new method for accurately tracking the movement of the heart wall based on both the phase and magnitude of the demodulated signals to determine the instantaneous position of an object. By this method, velocity signals of the heart wall with small amplitudes less than several micrometers on the motion resulting from a heartbeat can be accurately detected. Moreover, the method has been applied to multiple points preset in the heart wall along an ultrasonic beam so that the spatial distributions of the local change in thickness during one cardiac cycle is determined. In this paper, the method is applied to the free wall of the right ventricle (RV),the interventricular septum (IVS), and the posterior wall of the left ventricle (LV). From the relationships among the results for these parts of the heart, new findings which characterize the velocity signals and the change in thickness in each cardiac period are described. This method offers potential for quantitative myocardial diagnosis. KEYWORDS: velocity signal measurement, local change in thickness, myocardial contraction/relaxation, myocardial motility, cardiac cycle ∗1 Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. E-mail address: hkanai@ecei.tohoku.ac.jp ∗2 First Department of Internal Medicine, School of Medicine, Tohoku Uni- versity, Sendai 980-8575, Japan. ∗3 Third Department of Internal Medicine, School of Medicine, Tohoku Uni- versity, Sendai 980-8575, Japan. ∗4 Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. ∗5 Tohoku Welfare Pension Hospital, Takasago 10, Fukumuro, Miyagino-ku, Sendai 983, Japan. 3403 1. Introduction In the free wall of the right ventricle (RV), the interventric- ular septum (IVS), and the posterior wall of the left ventri- cle (LV) shown in Fig. 1(a), thickening and thinning period- ically occur during myocardial contraction and relaxation as illustrated in Figs. 1(b) and 1(c). This thickening and thin- ning at each local area in the heart wall corresponds to the regional myocardial motility, which originates from the slid- ing of the myosin and actin fibers. To noninvasively realize evaluation of this motility using ultrasound, it is necessary to track the instantaneous positions x A (t ) and x B (t ) of the two points A and B which are preset at the end-diastole along an ultrasonic beam in the heart wall. Then, the change in thickness, h AB (t ), between these two points A and B from their thickness, h 0 , at the end-diastole is obtained from the difference between x A (t ) and x B (t ) as illustrated in Fig. 1(c) if the ultrasonic beam is almost perpendicular to the wall dur- ing the cardiac cycle. 1, 2) Such noninvasive measurement of the change in thickness of the regional area in the heart wall during each cardiac cycle provides essential tools for the di- agnosis of heart diseases. Though M-mode echocardiography offers an advantage in critically looking at the motion pattern of the LV, its spatial resolution along the ultrasonic beam is limited to a few wave- lengths, namely, only up to 1 mm for ultrasound of 3 MHz because an M-mode image is displayed based on the ampli- tude of the reflected ultrasound. On the other hand, there have been numerous elaborate techniques proposed for non- invasive measurement of the velocity of the blood flow in the heart or the arteries based on the Doppler effect. 3) Moreover, several methods, including the phase-locked-loop (PLL) tech- niques, have been proposed to measure rough changes in the diameter of the arterial walls by tracking arterial wall dis- the change in thickness, which are measured by our method. For this purpose, in this study, the developed method was ap- plied to the free wall of the RV, the IVS, and the posterior wall of the LV of a healthy young male volunteer and the IVS of a male patient with dilated-cardiomyopathy (DCM). From the relationship among the results for the three heart walls and the differences between the subjects, new findings which charac- terize the velocity signals and the change in thickness in each period during one cardiac cycle are described. 2. Principles of Measurement of Change in Thickness of the Wall By referring to the M-mode image, which is reconstructed from the A/D converted data, we manually preset two points, A and B , in the heart wall or arterial wall along an ultrasonic placement in real time. 4, 5) For the accurate detection of velocity signals, that is, the in- stantaneous movement on or in the heart wall, we have devel- oped the following “phased tracking method”. 2) This method has been confirmed by experiments using a water tank and has been applied to the in vivo detection of small velocity sig- nals, with sufficient reproducibility, on the wall of the human heart. 2) The detected velocity signals show rapid motion in- cluding high frequency components with small amplitudes, which are difficult to recognize by M-mode echocardiogra- phy. Moreover, the method has been applied to multiple points preset along an ultrasonic beam in the LV wall so that the in- stantaneous object positions, {x i (t )}, and the velocity signals, {v(x i ; t )}, are obtained for these multiple points, {i }, in the LV wall. 1) From the results, by deleting the parallel component, the thickness change components during myocardial contrac- tion/relaxation are detected. Then, their spatial distribution is obtained and is superimposed on the M-mode image using a color code. Spectrum analysis was first applied to the resultant nonin- vasively detected signals to identify the frequency band for the components from 25 Hz to 90 Hz due to the myocardial thickening and thinning. Such analysis shows the novel pos- sibility of diagnosis of the local myocardium. 1, 2) For such waveform analysis and/or spectrum analysis, however, it is significant to characterize each of six periods in one cardiac cycle using the results of the velocity signals and