Two-Dimensional Tracking of Heart Wall for Detailed Analysis of Heart Function at High Temporal and Spatial Resolutions

Abstract

For noninvasive and quantitative measurements of global two-dimensional (2D) heart wall motion, speckle tracking methods have been developed and applied. These methods overcome the limitation of tissue Doppler imaging (TDI), which is susceptible to aliasing, by directly tracking backscattered echoes by pattern matching techniques, i.e., the cross-correlation or the sum of absolute differences, in real time. In these conventional methods, the frame rate (FR) is limited to about 200 Hz, corresponding to the sampling period of 5 ms. However, myocardial function during the isovolumic contraction period obtained by these conventional speckle tracking methods remains unclear owing to low temporal and spatial resolutions of these methods. Moreover, the accuracy of the speckle tracking method depends on an important parameter, i.e., the size of the correlation kernel. To track backscattered echoes accurately, it is necessary to determine the optimal kernel size. However, the optimal kernel size has not been thoroughly investigated. In this study, correlation kernel size, which determines the tracking accurately, was optimized by evaluating root mean squared (RMS) errors in the lateral and axial displacements of a phantom estimated by speckle tracking methods at high spatial and temporal resolutions. For this purpose, the RF data from the longitudinal-axis cross-sectional view for the interventricular septum (IVS) were acquired on the basis of parallel beam forming (PBF) to improve temporal and spatial resolutions. A wide transmit beam scanned in 7 different directions sparsely and 16 receiving beams were generated for each transmission. The RF data of the phantom and the heart wall were obtained at high spatial (angle intervals of scan lines: 0.375 degrees) and temporal [frame rate (FR): 1020 Hz] resolutions. The determined optimal size of the correlation kernel was 7:9 Â 4:8 mm. Estimated displacements of the phantom were in good agreement with the actual displacement at an RMS error of 0.34 mm. Furthermore, the IVS motion during the isovolumic contraction (IC) was analyzed in detail. The speckle tracking method using the optimal kernel size 7:9 Â 4:8 mm was applied to multiple points in IVS to estimate 2D displacements during the IC period. In this period, a rapid displacement of IVS at a small amplitude of 1.5 mm, which suggests the expansion of the left ventricle and has not been measured by conventional tracking methods at a low temporal resolution, was detected by 2D tracking. Furthermore, the displacement on the apical side was found to be delayed by 10 ms compared with that on the basal side. These results indicate the potential of this method in the high-accuracy estimation of 2D displacements and detailed analyses of physiological function of the myocardium.

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

“…After the development of shear wave elastography by Tanter, et al [11], which was the first practical application of high-frame-rate ultrasound, various studies have been conducted for cardiovascular applications, such as vascular strain and blood flow imaging [12][13][14], pulse wave imaging [15,16], and cardiac strain and blood flow imaging [17][18][19][20][21]. In addition, various studies for improvement of the image quality in high-frame-rate ultrasound have been conducted [22][23][24][25][26].…”

Assessing the atrial electromechanical coupling during atrial focal tachycardia, flutter, and fibrillation using electromechanical wave imaging in humans

“…Over the last few years, ultrasound imaging has been undergoing important technical improvements with the advent of software-based systems that allow ultra-high frame rates: 2000–5000 frames/s are achieved by using defocussed transmissions, as opposed to the 50–200 frames/s used in commercial clinical systems, for the depths needed in transthoracic cardiac applications (Bercoff et al, 2004; Bruneel et al, 1977; Delannoy et al, 1979; Honjo et al, 2010; Papadacci et al, 2014; Provost et al, 2014, 2011c). Such high frame rates allow unprecedented temporal resolution, and, perhaps most importantly, a five-fold improvement in the signal-to-noise ratio of cardiac motion and deformation mapping (Provost et al, 2012).…”

Electromechanical wave imaging for arrhythmias

“…Plane waves are most known for their use in supersonic shear imaging (Bercoff et al, 2004; Montaldo et al, 2009) where they are used for the estimation of one-dimensional (Montaldo et al, 2009) and two-dimensional motion (Tanter et al, 2002). In the heart, motion estimation was performed only recently using wide beams (Honjo et al, 2010). …”