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Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

流体力学用語集 非線形音響学(Nonlinear acoustics)

The accelerating complexity and variety of medical imaging devices and methods have outpaced the ability to evaluate and optimize their design and clinical use. This is a significant and increasing challenge for both scientific investigations and clinical applications. Evaluations would ideally be done using clinical imaging trials. These experiments, however, are often not practical due to ethical limitations, expense, time requirements, or lack of ground truth. Virtual clinical trials (VCTs) (also known as in silico imaging trials or virtual imaging trials) offer an alternative means to efficiently evaluate medical imaging technologies virtually. They do so by simulating the patients, imaging systems, and interpreters. The field of VCTs has been constantly advanced over the past decades in multiple areas. We summarize the major developments and current status of the field of VCTs in medical imaging. We review the core components of a VCT: computational phantoms, simulators of different imaging modalities, and interpretation models. We also highlight some of the applications of VCTs across various imaging modalities.

Virtual clinical trials in medical imaging: a review

For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed.

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Dual-Frequency Piezoelectric Transducers for Contrast Enhanced Ultrasound Imaging

In modern ultrasound imaging devices, two-dimensional probes and electronic scanning allow volumetric imaging of anatomical structures When dealing with the design of such complex 3-D ultrasound (US) systems, as the number of transducers and channels dramatically increases, new challenges concerning the integration of electronics and the implementation of smart micro-beamforming strategies arise Hence, the possibility to predict the behavior of the whole system is mandatory In this paper, we propose and describe an advanced simulation tool for ultrasound system modeling and simulation, which conjugates the US propagation and scattering, signal transduction, electronic signal conditioning, and beamforming in a single environment In particular, we present the architecture and model of an existing 16-channel integrated receiver, which includes an amplification and micro-beamforming stage, and validate it by comparison with circuit simulations The developed model is then used in conjunction with the transducer and US field models to perform a system simulation, aimed at estimating the performance of an example 3-D US imaging system that uses a capacitive micromachined ultrasonic transducer (CMUT) 2-D phased-array coupled to the modeled reception front-end Results of point spread function (PSF) calculations, as well as synthetic imaging of a virtual phantom, show that this tool is actually able to model the complete US image reconstruction process, and that it could be used to quickly provide valuable system-level feedback for an optimized tuning of electronic design parameters

A volumetric CMUT-based ultrasound imaging system simulator with integrated reception and μ-beamforming electronics models

Abersim, a simulation package for 3D nonlinear acoustic wave propagation of wide-band pulses from arbitrary transducers, is presented This study validates the 3D diffraction and attenuation produced by Abersim, by comparing them to those obtained using Field II For the presented test cases, the axial pressure amplitude and the RMS values deviate less than 07 dB, both for axis-symmetric and array transducers Abersim has a MATLAB programming interface, and is freely available under the GPL license

Abersim: A simulation program for 3D nonlinear acoustic wave propagation for arbitrary pulses and arbitrary transducer geometries

Investigation of transmit and receive performance at the fundamental and third harmonic resonance frequency of a medical ultrasound transducer.

Nonlinear acoustic field simulations can be useful for medical transducer design. An accurate estimation of the electro-mechanical transfer function of the acoustic stack, increases the accuracy of the predicted harmonic fields. In this study, we combined a 2D FEM model (using COMSOL) of the transducer stack, with a two-port model of the electrical transmit circuit, and the simulation program for nonlinear wave propagation Abersim. Example simulations showed the effect on the generated second harmonic field for simulated arrays with different elevation sizes, and different piezoelectric materials. Simulated arrays, (f c = 3 MHz, 64 elements, elevation and azimuth focus = 60 mm) with elevation sizes of 9, 11, and 13 mm, were excited with a square wave 3-half-cycle pulse (f c = 1.9 MHz, amplitude = 80 V pp ) through a transmit circuit consisting of a cable and inductive tuning. Nonlinear propagation through a tissue-like medium (attenuation = 0.3 dB/cm/MHz) resulted in maximum second harmonic pressures of 0.75, 0.93, and 1.1 MPa, for 9, 11 and 13 mm elevation, respectively. Simulations with different piezoelectric materials, showed that the single crystals PMN-33%PT and PZN-8%PT resulted in 7–8 dB higher second harmonic pressures than the PZT ceramics HD3202 and PZ21, for the same transmit conditions without tuning. Inductive tuning increased the efficiency for the PZT-ceramics by 6–8 dB, and for single crystals by 0–2 dB. These examples demonstrated how this comprehensive simulation tool could be used to optimize array design.

Simulation of acoustic fields from arbitrary transducer stacks using a FEM transducer model and nonlinear wave propagation

Acoustic Cluster Therapy (ACT) is a two-component formulation of commercially available microbubbles (Sonazoid; GE Healthcare, Oslo, Norway) and microdroplets (perfluorated oil) currently under development for cancer treatment. The microbubbles and microdroplets have opposite surface charges to form microbubble/microdroplet clusters, which are administered to patients together with a drug. When the clusters and drug reach the target tumour, two ultrasound (US) exposure regimes are used: First, high-frequency (>2.0 MHz) US evaporates the oil and forms ACT bubbles that lodge at the microvascular level. Second, low-frequency (0.5 MHz) US induces stable mechanical oscillations of the ACT bubbles, causing localized micro-streaming, radiation and shear forces that increase the uptake of the drugs to the target tumour. This report describes the design and testing of a dual-frequency transducer and a laboratory setup for pre-clinical in vivo studies of ACT on murine tumour models. The dual-frequency transducer utilizes the 5th harmonic (2.7 MHz) and fundamental (0.5 MHz) of a single piezoceramic disk for the high-frequency and low-frequency regimes, respectively. Two different aperture radii are used to align the high-frequency and low-frequency beam maxima, and the high-frequency -3 dB beam width diameter is 6 mm, corresponding to the largest tumour sizes we expect to treat. The low-frequency -3 dB beam width extends 6 mm. Although unconventional, the 5th harmonic exhibit a 44% efficiency and can therefore be used for transmission of acoustic energy. Moreover, both in vitro and in vivo measurements demonstrate that the 5th harmonic can be used to evaporate the microbubble/microdroplet clusters. For the in vivo measurements, we used the kidneys of non-tumour-bearing mice as tumour surrogates. Based on this, the transducer is deemed suited for pre-clinical in vivo studies of ACT and replaces a cumbersome test setup consisting of two transducers.

A Harmonic Dual-Frequency Transducer for Acoustic Cluster Therapy.

A long-standing challenge in integrity management of gas pipelines is stress corrosion cracking (SCC). Such cracks are difficult to detect, calling for sensitive detection methods with good coverage. Recent advances in gas-coupled broad band ultrasound provide a potential method that is based on guided plate waves. The objective of this work is to describe and experimentally evaluate this method based on Halfwave's ART Scan® tool. A water-immersed 12 mm thick steel plate with machined crack-like, spark eroded notches (SEN) of 2 and 6 mm depth, and 10 and 20 mm lengths, were acoustically investigated with broadband (0.3–1.3 MHz) transducers in a pitch-catch setup. Received signals were acquired at 2D grid locations, and pointwise processing parameters were extracted. Summed signal power and a spectral parameter demonstrated the detection of the SENs. The received energy in a selected frequency band was 2.5 and 5.5 dB lower for the 2 and 6 mm deep SENs, respectively, compared to that of an undamaged part of the plate. Using a tomographic image inversion method, the received signals were combined and converted into images. Results of the 6 mm deep SEN showed good agreement with the actual size and location of the SEN. In conclusion, the potential to detect SCC by using an ART Scan® based set-up, combined with pointwise and image formation processing, was successfully demonstrated on test plates with machined crack-like defects.

Martijn Frijlink

Papers

Abersim: A simulation program for 3D nonlinear acoustic wave propagation for arbitrary pulses and arbitrary transducer geometries

Investigation of transmit and receive performance at the fundamental and third harmonic resonance frequency of a medical ultrasound transducer.

Simulation of acoustic fields from arbitrary transducer stacks using a FEM transducer model and nonlinear wave propagation

A Harmonic Dual-Frequency Transducer for Acoustic Cluster Therapy.

Ultrasonic detection of spark eroded notches in steel plates