In Vivo Measurement of Small Velocity Signals and Change in Thickness of the Heart Walls

Self Cite

Section: Methodsmentioning

confidence: 99%

Minute Mechanical-Excitation Wave-Front Propagation in Human Myocardial Tissue

Kanai

Tanaka

2011

Self Cite

“…However, the velocities v l0 ðn; ; dÞ and v d0 ðn; ; dÞ of the silicone rubber in the lateral and axial directions were much lower than the maximum velocities of the actual heart wall motion (about 70 mm/s for both) obtained in separate in vivo experiments by the 1D phased-tracking method. 11,25,26) Therefore, 2D displacements of silicone rubber between two frames (ÁN F ) in the lateral and axial directions, x l ðn; ; dÞ and x d ðn; ; dÞ, were respectively set to be similar to those of the heart wall by increasing the frame interval ÁN F for calculating correlation function as follows. The frame interval ÁN F was set at 25 (corresponding 24 ms) in the basic experiment so that the 2D displacements of the silicone rubber between frames (ÁN F Á ÁT) correspond to the fast motion of the heart wall between two consecutive frames, corresponding to 0.98 ms (ÁN F ¼ 1) in in vivo experiments.…”

Section: Reconstructive Interpolationmentioning

confidence: 99%

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

Honjo

Hasegawa

Kanai

2010

Self Cite

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.

“…As the myocardial SRs are calculated using the velocities obtained at multiple positions in the heart wall, local velocity estimation is essential for the local measurement of SR. In previous studies, 7,30,[33][34][35] the transmural SR distribution was measured at different depths in the heart wall with high temporal resolution using the phased-tracking method. 36) However, it has been difficult for the conventional velocity estimator 36) to measure the minute changes in the spatially local myocardial thickness because the estimated velocity is averaged spatially by the cross-correlation function.…”

Section: Introductionmentioning

confidence: 99%

Measurement of propagation of local and minute contractile response in layered myocardium

Obara

Mori

Arakawa

et al. 2021

Self Cite

The in vivo measurement of the contractile response caused by electrical excitation has been studied to detect myocardial ischemia in its early stages. In the present study, we used our previously proposed local velocity estimator to measure the two-dimensional distribution of the strain rate using high-density beam scanning to obtain propagation of the local and minute contractile response in the heart walls of healthy humans. Alternate layers of contraction and relaxation were observed around the time phase representing the onset of the conduction of electrical excitation. The contraction propagated along the direction of the myocardial fiber in the myocardial layer. These results indicated that the electrical excitation conducted in each myocardial layer and the transmural shearing deformation occurred at the boundary between alternate layers of contraction and relaxation. The measurement of the propagation of the local and minute contractile response can reveal the effective contraction with the transmural shearing deformation.