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difference-frequency ultrasound generation from microbubbles under dual-frequency excitation

Chinese Physics B 2010年第9期19卷 437-442页

作者：马青玉邱媛媛黄蓓章东龚秀芬 School of Physics and Technology Nanjing Normal University Key Laboratory of Modern Acoustics Ministry of EducationInstitute of AcousticsNanjing University

The difference-frequency （DF） ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.

关键词： difference-frequency microbubble dual-frequency excitation parametric effect

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Mid-Infrared Pulsed Laser Lithotripsy with a Tunable Laser Using difference-frequency Generation

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Optics and Photonics Journal 2013年第4期3卷 8-13页

作者： Hisanao Hazama Hiromu Kutsumi Kunio Awazu 1Graduate School of Engineering Osaka University Osaka Japan 2Graduate School of Frontier Biosciences Osaka University Osaka Japan 3The Center for Advanced Medical Engineering and Informatics Osaka University Osaka Japan Graduate School of Engineering Osaka University Osaka Japan Graduate School of Medicine Kobe University Kobe Japan

A novel technique of lithotripsy was investigated with a mid-infrared tunable pulsed laser using difference-frequency generation (DFG). Human gallstone samples obtained from 24 patients were analyzed with their infrared absorption spectra. It was found that the principal components of the gallstones were different for the different patients and that the gallstone samples used in this research could be classified into four groups, i.e., mixed stones, calcium bilirubinate stones, cholesterol stones, and calcium carbonate stones. In addition, some gallstone samples had different compositions within the single stone. The mid-infrared laser tunable within a wavelength range of 5.5 - 10 μm was irradiated to the cholesterol stones at two different wavelengths of 6.83 and 6.03 μm, where the cholesterol stones had relatively strong and weak absorption peaks, respectively. As the result, the cholesterol stones were more efficiently ablated at the wavelength of 6.83 μm with the strong absorption peak. Therefore, it is suggested that the gallstones could be efficiently ablated by tuning the wavelength of the laser to the strong absorption peak of the gallstones. The higher efficiency of the ablation using the characteristic absorption peaks should lead to the safer treatment without damage to the surrounding normal tissues. In order to identify the composition of the gallstones in the patients, endoscopic and spectroscopic diagnosis using the DFG laser and an optical fiber probe made with two hollow optical fibers and a diamond attenuation total reflection prism should be useful. The absorption spectrum of the gallstones in the patients could be measured by measuring the energy of the DFG laser transmitted through the optical fiber probe and by scanning the wavelength of the DFG laser.

关键词： Gallstone Lithotripsy Mid-Infrared Tunable Laser difference-frequency Generation

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