A brief review of optical techniques for visualizing ultrasound fields is given. Acousto-optic interaction is discussed as a basic principle for visualizing inhomogeneity in refractive index fields. ...Light diffraction and deflection are also discussed as important phenomena, especially for visualization of ultrasound fields. Three techniques, Schlieren, phase contrast, and shadowgraph techniques, used for visualization of ultrasound fields are reviewed with discussion of the differences in optical systems and visualized field images. A newly developed focused shadowgraph technique that achieves sensitive detection with simple optics is introduced, and its usefulness for visualization of very short pulses of diagnostic ultrasound equipment is shown.
Abstract
The relationship between thresholds of free radical generation and atomization under ultrasound exposure was investigated to elucidate the mechanisms of ultrasonic atomization. In the ...experiments to gradually increase the transducer driving voltage, the free radical generation, a quick transition of the water surface shape from a protuberance to a fountain, and atomization had the same threshold. The experiments using the acoustic loading conditions with the different water surface shapes also confirmed this fact. Furthermore, a focused shadowgram of the ultrasound field taken using a small container that mimics the protuberance visualized the generation of spotty-shaped high-intensity nodes inside and near the boundary of the protuberance. These results indicate that the induction of cavitation promoted by the high-intensity nodes triggers the appearance of the fountain that leads to the creation of atomization.
In studies on the bioeffects of ultrasound exposure on cells cultured in a Petri dish, an understanding of the pressure field generated inside the dish is essential to achieve better dosimetry of ...ultrasound exposure. In this study, ultrasound fields generated inside four types of small containers designed to mimic a Petri dish were visualized using the focused shadowgraphy technique. The results revealed that wall propagation and water surface reflection of ultrasound make a complex standing wave field in the entire space of the container, which is very different from a standing wave field predicted by a simple model with reflection at the flat water surface without wall propagation.
The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in ...the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.
In contrast to conventional X-ray therapy, proton beam therapy (PBT) can confine radiation doses to tumours because of the presence of the Bragg peak. However, the precision of the treatment is ...currently limited by the uncertainty in the beam range. Recently, a unique range verification methodology has been proposed based on simulation studies that exploit spherical ionoacoustic waves with resonant frequency (SPIREs). SPIREs are emitted from spherical gold markers in tumours initially introduced for accurate patient positioning when the proton beam is injected. These waves have a remarkable property: their amplitude is linearly correlated with the residual beam range at the marker position. Here, we present proof-of-principle experiments using short-pulsed proton beams at the clinical dose to demonstrate the feasibility of using SPIREs for beam-range verification with submillimetre accuracy. These results should substantially contribute to reducing the range uncertainty in future PBT applications.
•Estimation of the cross-sectional absorption distribution in turbid media.•Estimation from intensity and the path length distribution of backscattered light.•Nonlinear inversion technique with the ...fixed point iteration method.•Solution in practical time and in the robust process against measurement noise.
This report presents a proposal of a new technique to estimate the cross-sectional absorption distribution of turbid media from backscattered light by solving a nonlinear inverse problem. After illuminating a beam of light on the surface of a turbid object and measuring the backscattered light as a function of distance from the light incident point, we divide the object into multiple virtual layers to estimate the absorption distribution. The path lengths of photon propagation in the respective layers are calculated using Monte Carlo simulation. The absorption coefficient of each virtual layer can be estimated from the backscattered intensity and the path length distribution in a depth direction. For solving this inverse problem, the linear calculation results are useful as initial solutions. Then the final solutions are obtained from iteration of the nonlinear calculation. Convergence into a unique solution and robustness of the solution against the measurement noise were confirmed. The effectiveness of the proposed technique was verified through simulation and measurement. By lateral scanning of a source–detector pair, we can reconstruct a cross-sectional image of the turbid medium to the depth to which the detected light reaches.
Background
Proton range uncertainty has been the main factor limiting the ability of proton therapy to concentrate doses to tumors to their full potential. Ionoacoustic (IA) range verification is an ...approach to reducing this uncertainty by detecting thermoacoustic waves emitted from an irradiated volume immediately following a pulsed proton beam delivery; however, the signal weakness has been an obstacle to its clinical application. To increase the signal‐to‐noise ratio (SNR) with the conventional piezoelectric hydrophone (PH), the detector‐sensitive volume needs to be large, but it could narrow the range of available beam angles and disturb real‐time images obtained during beam delivery.
Purpose
To prevent this issue, we investigated a millimeter‐sized optical hydrophone (OH) that exploits the laser interferometric principle. For two types of IA waves γ‐wave emitted from the Bragg peak (BP) and a spherical IA wave with resonant frequency (SPIRE) emitted from the gold fiducial marker (GM), comparisons were made with PH in terms of waveforms, SNR, range detection accuracy, and signal intensity robustness against the small detector misalignment, particularly for SPIRE.
Methods
A 100‐MeV proton beam with a 27 ns pulse width and 4 mm beam size was produced using a fixed‐field alternating gradient accelerator and was irradiated to the water phantom. The GM was set on the beam's central axis. Acrylic plates of various thicknesses, up to 12 mm, were set in front of the phantoms to shift the proton range. OH was set distal and lateral to the beam, and the range was estimated using the time‐of‐flight method for γ‐wave and by comparing with the calibration data (SPIRE intensity versus the distance between the GM and BP) derived from an IA wave transport simulation for SPIRE. The BP dose per pulse was 0.5–0.6 Gy. To measure the variation in SPIRE amplitude against the hydrophone misalignment, the hydrophone was shifted by ± 2 mm at a maximum in lateral directions.
Results
Despite its small size, OH could detect γ‐wave with a higher SNR than the conventional PH (diameter, 29 mm), and a single measurement was sufficient to detect the beam range with a submillimeter accuracy in water. In the SPIRE measurement, OH was far more robust against the detector misalignment than the focused PH (FPH) used in our previous study 5%/mm (OH) versus 80%/mm (FPH), and the correlation between the measured SPIRE intensity and the distance between the GM and BP agreed well with the simulation results. However, the OH sensitivity was lower than the FPH sensitivity, and about 5.6‐Gy dose was required to decrease the intensity variation among measurements to less than 10%.
Conclusion
The miniature OH was found to detect weak IA signals produced by proton beams with a BP dose used in hypofractionated regimens. The OH sensitivity improvement at the MHz regime is worth exploring as the next step.
Glioblastoma is a highly invasive and fatal disease. Temozolomide, a blood–brain barrier (BBB)-penetrant therapeutic agent currently used for glioblastoma, does not exhibit sufficient therapeutic ...effect. Cisplatin (CDDP), a versatile anticancer drug, is not considered a therapeutic option for glioblastoma due to its low BBB permeability. We previously investigated the utility of microbubbles (MBs) in combination with ultrasound (US) in promoting BBB permeability and reported the efficacy of drug delivery to the brain using a minimally invasive approach. This study aimed to evaluate the feasibility of CDDP delivery to the brain using the combination of MBs and US for the treatment of glioblastoma. We used mice that were implanted with glioma-261 GFP-Luc cells expressing luciferase as the glioblastoma model. In this model, after tumor inoculation, the BBB opening was induced using MBs and US, and CDDP was simultaneously administered. We found that the CDDP concentrations were higher at the glioblastoma site where the US was applied, although CDDP normally cannot pass through the BBB. Furthermore, the survival was longer in mice treated with CDDP delivered via MBs and US than in those treated with CDDP alone or those that were left untreated. These results suggest that the combination of MBs and US is an effective antitumor drug delivery system based on BBB opening in glioblastoma therapy.
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