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Two Dimensional Phase Unwrapping Theory Algorithms And Software

A simple technique designed for visualization of ultrasound fields without Schlieren optics is introduced. An optical system of direct shadowgraphy with diverging light, which consists of a point light source and a shadow screen, constituted the basic system, but the screen was replaced by focusing optics: a camera that makes a virtual screen at its focus plane. The proposed technique visualizes displacement of light deflected by ultrasound, and the use of focusing optics enables flexible settings of the virtual screen position and optical magnification. Insufficient sensitivity of shadowgraphy was overcome by elimination of non-deflecting light using image subtraction of shadowgrams taken with and without ultrasound exposure. A 1-MHz focused transducer for ultrasound therapy and a 20-MHz miniature transducer for intravascular imaging were used for experiments, and alternate pressure change in short-pulsed ultrasound was visualized, indicating the usefulness of the proposed technique for evaluation of medical ultrasound fields.

A Simple Technique for Visualizing Ultrasound Fields Without Schlieren Optics

We propose a noncontact and nondestructive method of imaging by using high-intensity aerial ultrasonic waves and optical equipment. This method identifies defects in an imaged area by analysis of the velocity distribution of vibration on the surface of an object continuously irradiated by aerial ultrasonic waves. In a previous study, a related method was applied but could not exactly image the defect shape and size because the vibration mode at the target's surface is generated by a continuous wave that depends on the boundary between the defective area and the defect-free area. By avoiding this problem, the proposed method allows exact imaging of the defect shape and size. In this report, we simulate results from the proposed underlying principle and conduct an experiment based on the proposed principle.

https://iopscience.iop.org/article/10.7567/JJAP.54.07HC07/pdf

Improved method of imaging defect in noncontact and nondestructive technique by high-intensity aerial burst ultrasonic wave and optical equipment

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

With the development of computational technologies, a single processing method becomes important for the ultrasonic and/or acoustic sensing in air. Generally, in the acoustic sensing, the higher resolution measurement can be enabled as the frequency used is higher. In the long range sensing, however, use of short pulse transmission using high frequencies cannot obtain sufficient SNR signals due to the atmospheric attenuation. That is, the measurable range and measurement resolution are in a trade-off relationship. Whereas a pulse compression technique (PCT) is used to solve this problem, in our previous studies[1-2], the super-resolution signal processing based sensing technique that combines SCM-MUSIC[3] and PCT have been proposed as a method of ultrasonic measurements in liquid. It discussed the possibility to improve the SN ratio and resolution. Above mentioned, use of low frequency signals expands the measurable range. However, sound waves of lower frequencies are diffused widely because common speakers are unidirectional and the directivity at lower frequencies are wider. Therefore, it causes the multipath reflection and the unexpected and undesired echoes generate a virtual image. This problem is remarkable in the case of use of lower frequency signals. Therefore, narrow directivity of a speaker is necessary to implement the long range sensing using lower frequency signals.

https://iopscience.iop.org/article/10.7567/JJAP.56.07JC14/pdf

Experimental evaluation of long-range acoustic sensing using super-directivity speaker and super-resolution signal processing with pulse compression technique

In the development of medical ultrasound techniques, fast and accurate pressure field measurement is important. The most common method of measuring an ultrasound pressure field is by using a mechanically scanned hydrophone, which might disturb the acoustic field, and it takes a long time. In this study, we used an optical shadowgraph method. For quantitative measurement using the shadowgraph, it is important to define precisely the optical propagation length between the phase object and the imaging plane. We used a holographic diffuser as the imaging screen for this purpose. A computed tomography (CT) algorithm was used to reconstruct a pressure field, and the result was compared with that of hydrophone measurement. By combining two shadowgraph results from smaller and larger propagation lengths, the result was very close to that of the hydrophone and was successfully reconstructed in the pressure range where nonlinear deformation was clear.

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Quantitative measurement of focused ultrasound pressure field by background-subtracted shadowgraph using holographic diffuser as screen

A fast and accurate ultrasound pressure field measurement is necessary for the progress of ultrasound application in medicine. In general, a hydrophone is used to measure the ultrasound field, which takes a long measurement time and might disturb the ultrasound field. Hence, we proposed a new method categorized in an optical method called Phase Contrast method to overcome the drawback in the hydrophone method. The proposed method makes use of the spatial DC spectrum formed in the focal plane to measure the modulated optical phase induced by ultrasound propagation in water. In this study, we take into account the decreased intensity of the DC spectrum at high ultrasound intensity to increase the measurement accuracy of the modulated optical phase. Then, we apply a non-continuous phase unwrapping algorithm to unwrap the modulated optical phase at high ultrasound intensity. From, the unwrapped result, we evaluate the quantitativeness of the proposed method.

https://iopscience.iop.org/article/10.7567/JJAP.54.07HC09/pdf

Quantitative measurement of high intensity focused ultrasound pressure field by optical Phase Contrast method applying non-continuous phase unwrapping algorithm

The most common method to measure an ultrasound pressure field, hydrophone scanning, requires a long scanning time and potentially disturbs the field, This may limit the efficiency in development of ultrasonic application in medicine. In this study, an optical phase contrast method, enabling the fast and noninterfering measurement, is proposed. This method measures the modulated phase of light caused by the focused ultrasound pulse pressure field. Then, a CT algorithm to quantitatively reconstruct the 3D pressure field is applied. The result agreed well with the measurement by a hydrophone.

Mohd Syahid

Papers

Quantitative measurement of focused ultrasound pressure field by background-subtracted shadowgraph using holographic diffuser as screen

Quantitative measurement of high intensity focused ultrasound pressure field by optical Phase Contrast method applying non-continuous phase unwrapping algorithm

Quantitative measurement of pulsed ultrasound pressure field using optical phase contrast

Quantitative Measurement of Pulsed Ultrasound Pressure Field Using Optical Phase Contrast