Shigeo Ohtsuki

A new echocardiographic method for identifying vortex flow in the left ventricle: numerical validation.

A new mathematical method for estimating velocity vectors from color Doppler datasets is proposed to image blood flow dynamics; this method has been called echodynamography or vector flow mapping (VFM). In this method, the concept of stream function is exploited to expand a 2-D distribution of radial velocities in polar coordinates, observed with color Doppler, to a 2-D distribution of velocity vectors. This study was designed to validate VFM using 3-D numerical flow models. Velocity fields were reconstructed from the virtual color Doppler datasets derived from the models. VFM captured the gross features of flow structures and produced comparable images of the distribution of vorticity, which correlated significantly with the original field (for velocity magnitudes, standard error of estimate = 0.003 to 0.007 m/s; for vorticity, standard error of estimate = 0.35 to 2.01/s). VFM may be sensitive for depicting flow structures derived from color Doppler velocities with reasonable accuracy.

The Flow Velocity Distribution from the Doppler Information on a Plane in Three-Dimensional Flow

In order to observe and estimate the flow of fluid in three-dimensional space, the pulsed Doppler method has been used widely. However, the velocity information acquired is only the velocity component in the beam direction of the wave even if an observation plane is formed by beam scanning. Accordingly, it is difficult to know the velocity distribution in the observation plane in tree-dimensional flow. In this paper, the new idea for processing the velocity distribution in the beam direction on an observation plane for transposing to flux distribution (flow function method) has been introduced. Further, the flow in an observation domain is divided into two kinds of flows, viz., the base flow which indicates the directivity of the flow in the observation domain and the vortex which is considered a two-dimensional flow. By applying the theory of a stream function to the two-dimensional flow, and by using the physical feature of a streamline to the base flow, the velocity component v which intersects perpendicularly to the beam direction is estimated. The flow velocity distribution in a scanning plane (observation plane) can be known from these two components of velocity, viz., beam direction componentu and perpendicular component to the beam directionv. The principle was explained by an example of the blood flow measurement in normal and abnormal heart chamber, by the ultrasonic Doppler method.

Determination of sound speed in biological tissues based on frequency analysis of pulse response

The sound speed in biological tissues provides important diagnostic and treatment planning information. Conventional methods of sound-speed determination generally require that transducers make physical contact with specimens in order to measure thickness and travel time in the time domain. The physical contact may cause deformation and affect blood flow and the measurement of travel time in the time domain may be sensitive to waveform distortion due to tissue inhomogeneity and surface roughness. A method for determination of the sound speed is proposed in which the sound travel time in the sample and the difference in total travel time from the transducer to the rigid reflector due to the presence of the sample are estimated in the frequency domain and which does not require physical contact of ultrasonic probes to living or freshly excised tissue specimens. Ultrasonic speed measurements in silicone rubber and acrylic resin specimens verified the method validity. The standard deviation of the measurements over a 10- x 10-mm area is less than 4 m/s. Sound-speed distribution measurements of porcine muscle are in agreement with previously published results.

Relationship Between Speed of Sound in and Density of Normal and Diseased Rat Livers

Speed of sound is an important acoustic parameter for quantitative characterization of living tissues. In this paper, the relationship between speed of sound in and density of rat liver tissues are investigated. The speed of sound was measured by the nondeformable technique based on frequency-time analysis of a 3.5 MHz pulse response. The speed of sound in normal livers varied minimally between individuals and was not related to body weight or age. In liver tissues which were administered CCl4, the speed of sound was lower than the speed of sound in normal tissues. The relationship between speed of sound and density in normal, fatty and cirrhotic livers can be fitted well on the line which is estimated using the immiscible liquid model assuming a mixture of normal liver and fat tissues. For 3.5 MHz ultrasound, it is considered that the speed of sound in fresh liver with fatty degeneration is responsible for the fat content and is not strongly dependent on the degree of fibrosis.

Spiral systolic blood flow in the ascending aorta and aortic arch analyzed by echo-dynamography

Using echo-dynamography, systolic blood flow structure in the ascending aorta and aortic arch was investigated in 10 healthy volunteers. The blood flow structure was analyzed based on the two-dimensional (2D) and 1D velocity vector distributions, changing acceleration of flow direction (CAFD), vorticity distribution, and Doppler pressure distribution. To justify the results obtained in humans, in vitro experiments were done using straight and curved tube models of 20mm diameter. The distribution of the CAFD showed a spiral staircase pattern along the flow axis line. In addition, the changes in the velocity profile in the short-axis direction, 2D distribution of the vorticity, and velocity vector distribution on the aortic cross-section plane, all confirmed the presence of systolic twisted spiral flow rotating clockwise toward the peripheral part of the ascending aorta. The rotation cycle of this spiral flow correlated inversely with the maximum velocity of the aortic flow, so that this cycle was shorter in early systole and longer in late systole. The model experiments showed similar results. The spiral flow seemed to be produced by several factors: (i) anterior shift of the direction of ejected blood flow due to the anterior displacement of the projection of the aorta; (ii) accelerated high pressure flow ejected antero-upward; (iii) inertia resistance at the peripheral boundary of the sinus of Valsalva; and (iv) reflection caused by the concave spherical structure of the inner surface of the basal part of the aorta. Because the main spiral flow axis line nearly coincided with the center line of the aorta, it is concluded that the occurrence of the spiral flow plays an important role in maintaining the blood flow direction passing through the cylindrical curved aortic arch and thus in keeping the most effective ejection as well as in dispersing the shear stress in the aortic wall.

Physiological basis and clinical significance of left ventricular suction studied using echo-dynamography

BACKGROUND The existence as well as the exact genesis of left ventricular suction during rapid filling phase have been controversial. In the present study, we aimed at resolution of this problem using noninvasive and sophisticated ultrasonic methods. The clinical meaning was also documented. METHODS Ten healthy male volunteers were examined by 2D echocardiography and echo-dynamography which enables us to obtain detailed instantaneous data of blood flow and wall motion simultaneously from the wide range of the left ventricle. The correlation of blood flow and wall motion was also studied. RESULTS Rapid ventricular filling was divided into 2 phases which had different physiology. The early half (early rapid filling: ERF) showed the effect which was alike drawing a piston. This was proved by the shape of the velocity of inflow and the basal muscle contraction which actively assisted extension of the relaxed apical and central parts of the left ventricle, giving the negative pressure which causes the ventricular suction. The later half (late rapid filling: LRF) showed the turning of the fundamental flow and the squeezed basal part just like the sphincter in addition to the expansion of the apical and central portions of the left ventricle, and all of these cooperatively augmented the suction effect. CONCLUSION Ventricular suction does exist to help ventricular filling. Simultaneous appearance of the contraction in the basal part and the relaxation or extension in the apical part during the post-ejection transitional period was made to occur the suction in the LV. And it can be said that the suction appeared in the late stage of systole as the one of the serial systolic phenomena.

A new concept of the contraction–extension property of the left ventricular myocardium

OBJECTIVES Using newly developed ultrasonic technology, we attempted to disclose the characteristics of the left ventricular (LV) contraction-extension (C-E) property, which has an important relationship to LV function. METHODS Strain rate (SR) distribution within the posterior wall and interventricular septum was microscopically measured with a high accuracy of 821μm in spatial resolution by using the phase difference tracking method. The subjects were 10 healthy men (aged 30-50 years). RESULTS The time course of the SR distribution disclosed the characteristic C-E property, i.e. the contraction started from the apex and propagated toward the base on one hand, and from the epicardial side toward the endocardial side on the other hand. Therefore, the contraction of one area and the extension of another area simultaneously appeared through nearly the whole cardiac cycle, with the contracting part positively extending the latter part and vice versa. The time course of these propagations gave rise to the peristalsis and the bellows action of the LV wall, and both contributed to effective LV function. The LV contraction started coinciding in time with the P wave of the electrocardiogram, and the cardiac cycle was composed of 4 phases, including 2 types of transitional phase, as well as the ejection phase and slow filling phase. The sum of the measurement time duration of either the contraction or the extension process occupied nearly equal duration in normal conditions. CONCLUSION The newly developed ultrasonic technology revealed that the SR distribution was important in evaluating the C-E property of the LV myocardium. The harmonious succession of the 4 cardiac phases newly identified seemed to be helpful in understanding the mechanism to keep long-lasting pump function of the LV.

Location of flow axis line in the left ventricle and its interaction with local myocardial motion

BackgroundThe interaction between local myocardial motion and blood flow dynamics should be assessed to evaluate left ventricular pump function.MethodsThe contour map of the absolute value of blood flow velocity in the left ventricle (LV) was drawn. The ridgeline of the contour was defined as the “flow axis line”. LV wall motion was assessed by the tracing endocardial border in consecutive B-mode images and by myocardial tissue velocity distribution obtained by the optical flow method.ResultsThe location of the main flow axis line was affected by the local myocardial movement in the short axis direction. The flow axis line method is superior to the previous investigations on two-dimensional blood flow analysis because it considered three-dimensional blood flow.ConclusionsThe flow axis line represents not only intracardiac blood flow structure but also its interaction with the cardiac wall motion.

Observation of Underwater Ultrasound Propagation in the Sea by Two-Period M-Sequence Signal Method

The velocity of a current going in and out through a strait can be measured by the differences in underwater sound propagation times with and against the current. However, ambient pulsive noises often interfere with the measurements of sound propagation times when a pulsed sound is used. A two-period M-sequence signal method is therefore proposed which is free from ambient pulsive noises. A sound propagation test was carried out. Short term propagation stability and tidal effects on multipath propagation were observed.

Estimation of Doppler shift frequency using selected phase information for high frame rate color flow mapping

PurposeWe describe a new approach to processing signals used to estimate the Doppler shift frequency in high frame-rate color flow mapping with fewer pulse transmissions. When an ultrasound pulse is transmitted to a large number of scatterers, the echoes from the scatterers overlap and interfere with one another. This interference causes the phase of the received echo signal to fluctuate, thus disturbing the estimated shift in Doppler frequency. The technique proposed here eliminates this disturbed phase information, leaving the remaining information for use in estimating the shift in Doppler frequency. The instantaneous frequency of the echo signal can serve as an index of the influence of interference.MethodsTo test this technique in vivo we used radio-frequency echo signals from the carotid artery for simulation and evaluated the error of the estimated Doppler shift frequency in several cases.ConclusionPerformance was enhanced when the number of pulses transmitted was limited and this technique was used.