We have proposed a nondestructive inspection method for steel billets using ultrasonic computerized tomography by time of flight (TOF). It has been found that the proposed method may detect defects inside high-attenuation materials with the aid of sequential pulse transmission all around the surface. However, it takes a long time to measure the TOF by this method owing to large numbers of scans and transmissions. In this paper, we propose a TOF measurement method to apply our inspection method to simultaneous TOF measurement in a shape-distorted billet to speed up the inspection. In this method, besides a measurement plane and a reference plane, a standard reference plane is used to compensate not only the effect of the characteristics between a transmitter and a receiver but also the effect of the shape distortion in simultaneous measurement. In this paper, the performance of the present method was verified by numerical simulation and experiment. As a result, the defects in a shape-distorted billet were successfully visualized in simultaneous TOF measurement by the present method. Moreover, it was confirmed that the proposed method diminished the artifacts in the computerized tomography (CT) images by compensating the error caused by multiple simultaneous transmissions. It was revealed that the present method is more robust to noise than the previous method. Therefore, it is expected that the TOF measurement in the nondestructive inspection of a shape-distorted billet can be sped up by the proposed method.

http://iopscience.iop.org/article/10.7567/JJAP.52.07HC09/pdf

Speeding Up of Nondestructive Inspection for Shape-Distorted Billet by Simultaneous Measurement of Time of Flight

Shear wave elastography has attracted attention because of its possibility for quantitative measurement of tissue elasticity. However, conventional methods for shear wave elastography have shortcomings. To solve the shortcomings, we propose a new scheme for shear wave elastography, in which tissue elasticity is measured only at tumors using the shear wave generated by the mode conversion of a longitudinal wave. In this study, as a fundamental examination, we investigate the suitable frequency and incident angle of a longitudinal wave for generating the shear wave through finite element method (FEM) simulations.

http://iopscience.iop.org/article/10.7567/JJAP.52.07HF23/pdf

Finite Element Method Study for Generating Shear Wave by Mode Conversion of Longitudinal Wave at Elasticity Boundary in a Living Body

Development of Blood Vessel Depth Displaying Method for Laparoscopic Surgery Guidance

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Accurate estimate of 2-dimensional motion vector via finite array synthetic aperture reconstruction processing of high-frame-rate speckle echo signal in living tissue

A strategic synthetic aperture radar (SAR) along a flight path has been developed including a potential extensibility in a wide-range target area and an excellent spatial resolution by utilizing two-way range stacking, matched filtering, and chirp signal transmission. For the simultaneous ultrahigh-frame-rate ultrasonic imaging of microdynamics in a living tissue, a one-way synthetic aperture array processing of a real-time-received two-dimensional (2D) echo signal followed by a successive transmission is indispensable, in which the range stacking in SAR should be modified toward the pulsed ultrasonic irradiation generated by the array transducer. Therefore, the modification of the range stacking was proposed for pulsed radiation from a flexible point ultrasonic source. Firstly, a one-way receiving range stacking algorithm was described in a spatiotemporal frequency domain, and it was consequently extended to account for the forward-range- and cross-range-dependent time delay of the 2D echo signal in each range bin for the reconstruction of the target area. The overall system performance for the linear array transducer having 256 elements with a 3.0 MHz center frequency and a 0.25 mm pitch was verified for the reconstructed images in a numerical simulation and a hardware experiment.

Target Area Extension in Synthetic Aperture Array Signal Processing for High-Frame-Rate Estimate of Two-Dimensional Motion Vector In vivo

Ultrahigh speed dynamic elastography has promising potential capabilities in applying clinical diagnosis and therapy of living soft tissues. In order to realize the ultrahigh speed motion tracking at speeds of over thousand frames per second, synthetic aperture (SA) array signal processing technology must be introduced. Furthermore, the overall system performance should overcome the fine quantitative evaluation in accuracy and variance of echo phase changes distributed across a tissue medium. On spatial evaluation of local phase changes caused by pulsed excitation on a tissue phantom, investigation was made with the proposed SA signal system utilizing different virtual point sources that were generated by an array transducer to probe each component of local tissue displacement vectors. The final results derived from the cross-correlation method (CCM) brought about almost the same performance as obtained by the constrained least square method (LSM) extended to successive echo frames. These frames were reconstructed by SA processing after the real-time acquisition triggered by the pulsed irradiation from a point source. The continuous behavior of spatial motion vectors demonstrated the dynamic generation and traveling of the pulsed shear wave at a speed of one thousand frames per second.

Experimental Evaluation of the High-Speed Motion Vector Measurement by Combining Synthetic Aperture Array Processing with Constrained Least Square Method

Target area extension in synthetic aperture array signal processing for high-frame-rate estimate of two-dimensional motion vector in vivo (Special issue: Ultrasonic electronics)

Ryouta Yokoyama

Papers

Experimental Evaluation of the High-Speed Motion Vector Measurement by Combining Synthetic Aperture Array Processing with Constrained Least Square Method

Target Area Extension in Synthetic Aperture Array Signal Processing for High-Frame-Rate Estimate of Two-Dimensional Motion Vector In vivo

Target area extension in synthetic aperture array signal processing for high-frame-rate estimate of two-dimensional motion vector in vivo (Special issue: Ultrasonic electronics)