Acoustic Velocity Measurement for Enhancing Laser UltraSound Imaging Based on Time Domain Synthetic Aperture Focusing Technique

Abstract

A method to enhance laser ultrasound (LUS) image reconstruction with the time-domain synthetic aperture focusing technique (T-SAFT) is presented, in which the acoustic velocity is extracted in situ with curve fitting. The operational principle is provided with the help of a numerical simulation, and the confirmation is provided experimentally. In these experiments, an all-optic LUS system was developed by using lasers for both excitation and detection of ultrasound. The acoustic velocity of a specimen was extracted in situ by fitting a hyperbolic curve to its B-scan image. The needle-like objects embedded within a polydimethylsiloxane (PDMS) block and a chicken breast have been successfully reconstructed using the extracted in situ acoustic velocity. Experimental results suggest that knowing the acoustic velocity in the T-SAFT process is important not only in finding the depth location of the target object but also for producing a high resolution image. This study is expected to pave the wave to the development and usage of all-optic LUS for bio-medical imaging.

Adapting the Time-Domain Synthetic Aperture Focusing Technique (T-SAFT) to Laser Ultrasonics for Imaging the Subsurface Defects

“…Their study included a pulsed laser beam to generate waves that scanned over the test surface, which were produced by conventional ultrasonic transducers. Yoon T et al [28] analyzed the influence of acoustic velocity during the image reconstruction process by using the laser ultrasonic T-SAFT and concluded that accurate acoustic velocity extraction could enhance the visibility in reconstructed images. Ying KN et al [29] investigated the directivity patterns of multi-modes, which were generated via pulsed laser beam, and adapted these multi-modes to generate inspection images via the T-SAFT algorithm.…”

Research on Photoacoustic Synthetic Aperture Focusing Technology Imaging Method of Internal Defects in Cylindrical Components

“…Ying [ 26 ] proposed a Multi-mode Time-domain SAFT algorithm, which can be used to superimpose SAFT images generated by single-mode ultrasound signals to obtain a better defect shape. Yoon [ 27 ] presented a method to enhance laser ultrasound image reconstruction with the time-domain synthetic aperture focusing technique, in which the acoustic velocity is extracted in situ with curve fitting. As for cylindrical components, Li [ 28 ] established a theoretical model of the forward vector algorithm for an ultrasonic immersion curved surface to improve the detection speed.…”