Non-invasive evaluation of Poisson's ratio of arterial wall using ultrasound

2016

Applied Sciences

Abstract:Recently, high-frame-rate ultrasound has been extensively studied for measurement of tissue dynamics, such as pulsations of the carotid artery and heart. Motion estimators are very important for such measurements of tissue dynamics. In high-frame-rate ultrasound, the tissue displacement between frames becomes very small owing to the high temporal resolution. Under such conditions, the speckle tracking method requires high levels of interpolation to estimate such a small displacement. A phase-sensitive motion estimator is feasible because it does not suffer from the aliasing effect by such a small displacement and does not require interpolation to estimate a sub-sample displacement. In the present study, two phase-sensitive 2D motion estimators, namely, paired 1D motion estimators and 2D motion estimator with shifted cross spectra, were developed. Phase-sensitive motion estimators using frequency spectra of ultrasonic echoes have already been proposed in previous studies. However, such methods had not taken into account the ambiguity of the frequency of each component of the spectrum. We have proposed a method, which estimates the mean frequency of each component of the spectrum, and the proposed method was validated by a phantom experiment. The experimental results showed that the bias errors in the estimated motion velocities of the phantom were less than or equal to (11.5% in lateral, 2.0% in axial) by the proposed 1D paired motion estimators and (3.0%, 2.0%) by the proposed 2D motion estimators, both of which were significantly smaller than (14.0%, 3.0%) of the conventional phase-sensitive 2D motion estimator.

Section: Introductionmentioning

confidence: 99%

Phase-Sensitive 2D Motion Estimators Using Frequency Spectra of Ultrasonic Echoes

2016

Applied Sciences

“…For some years now, we have been measuring the displacement and change in thickness of the arterial wall caused by the heartbeat using this method [19]- [21]. Elasticity images of the human carotid artery have been obtained by the measured displacement distribution, and the potential for transcutaneous tissue characterization has been shown by classifying the elasticity images using the elasticity reference data obtained by in vitro experiments [22]- [24].…”

Section: Introductionmentioning

confidence: 99%

Modification of the phased-tracking method for reduction of artifacts in estimated artery wall deformation

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

Kanai

2006

Noninvasive measurement of mechanical properties, such as elasticity, of the arterial wall, is useful for diagnosis of atherosclerosis. For assessment of mechanical properties, it is necessary to measure the deformation of the arterial wall. In this study, a modification of the previously proposed phased-tracking method was conducted to improve measurement of the small change in thickness (deformation) of the arterial wall due to the heartbeat. In our previous method, a set of two points along an ultrasonic beam was initially assigned, and the change in thickness of the layer between these two points during an entire cardiac cycle was estimated. In motion estimation with ultrasound, the motion of an interface or a scatterer, which generates an echo, can be obtained by estimating the change in time delay of the echo. For example, in the case of a carotid artery of a healthy subject, there are only two dominant echoes from the lumen-intima and media-adventitia interfaces. Thus, only the displacements of the lumen-intima and media-adventitia interfaces can be estimated, which means that ultrasound can estimate only the change in distance (thickness) between these two interfaces. However, even in this case, our previous method gives different estimates of the change in thickness, depending on the depths (positions in the arterial radial direction) of the two initially assigned points. In this study, modifications of the previous method in terms of the strategy for assignment of layers and the required thickness of an assigned layer were made to reduce such an artificial spatial variation in the estimated changes in thickness. Using the proposed method, errors in estimated changes in thickness were reduced from 21.2 24.1% to 0.19 0.04% (mean standard deviation) in simulation experiments. As in the case of the simulation experiments, the spatial variation in estimated changes in thickness also was reduced in in vivo experiments in a carotid artery of a healthy subject and in vitro experiments using two excised, diseased arteries.

“…For this purpose, we developed the "phased tracking" method, for measurement of the small change in the thickness of the arterial wall (less than 100 µm) due to the heartbeat. [16][17][18][19][20][21][22][23][24][25][26] From basic experiments, the accuracy of measurement of the change in thickness has been found to be less than 1 µm using the phased tracking method. 17,20,21 From the change in thickness measured by using this method, the regional strain and the elasticity of the arterial wall can be noninvasively evaluated.…”

Section: Introductionmentioning

confidence: 99%

Measurement of nonlinear property of artery wall using remote cyclic actuation

Kanai

2006

J Med Ultrasonics