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Toward Locally Resolved Non-Invasive Sound Velocity Measurement
S62
Ultrasound in Medicine and Biology
Purpose: Sonoporation is a technique to introduce foreign genes or drugs into cells by ultrasound exposure. In this study, complex ultrasound fields inside a small chamber for sonoporation study were visualized using the subtraction Schlieren technique. Material & Methods: A small water chamber with a cross section similar to that of a Petri dish was placed on a disk-shaped transducer. The transducer was driven by long-burst ultrasound of 2 MHz in center frequency. The subtraction Schlieren technique (Kudo, J Phys: Conf Seri 2004, 1: 146–149), which visualizes acoustic fields by software subtraction of two shadowgraphs taken in the presence and absence of ultrasound exposure, was used in this study. Results: Different from conventional Schlieren, image subtraction Schlieren can visualize alternative pressure changes at the ultrasound carrier frequency of 2 MHz. Moving pictures of propagating and standing wave fields were successfully visualized by taking a series of instantaneous field images at gradually increasing delay timing after insonation. Standing wave fields were produced in the presence of ultrasound reflection at the water surface but were disturbed by perturbations of the water surface produced by the radiation force of ultrasound. Conclusion: Measurements of exposure dose are essential for studying therapeutic effects of ultrasound. The experimental results show that image subtraction Schlieren will be a powerful tool for visualization of acoustic fields inside small chambers and for estimation of the effective dose of ultrasound exposure. SS 31.04 Toward Non-Scanning Measurement of Eye Lens Curvature with Ultrasound M. Lenz,1 E. Ku¨hnicke2 1 Fak. Et/it, Ife, TU Dresden, Dresden/DE, 2Fakult€at Elektrotechnik und Informationstechnik, Institut F. Festk€orperelektronik, TU Dresden, Dresden/DE Purpose: The presentation describes a novel method for measuring local object curvature radii that aims at curvature measurements of the eye lens, in particular. The specific characteristic is that the method does not require any scanning. Material & Methods: Instead, an annular array is used. It is positioned in such a way that the acoustical axis passes through the centre of curvature. The phase and amplitude differences on the receiver elements are used to determine curvature: The larger the curvature radii of the spherical reflectors, the smaller are the phase differences between the echo signals arriving at the innermost and the outer transducer elements. The effect can be understood qualitatively by considering the different acoustical path lengths. For the quantitative predictions used in the presentation, wave acoustical methods were used. Results: Measurements using steel spheres with diameters from 12mm to 21mm as reflectors demonstrate proof of concept. Good agreement between measurements and numerical sound field simulations could be achieved. Accuracy is mainly limited by transducer symmetry. Conclusion: The next steps intend to find a more robust transducer setup. Further developments will concentrate on ellipsoidal curvatures, concave curvatures and curvatures of buried layers, which necessitates finer transducer segmentation. SS 31.05 Toward Locally Resolved Non-Invasive Sound Velocity Measurement E. Ku¨hnicke, M. Lenz Fakult€ at Elektrotechnik und Informationstechnik, Institut F. Festk€ orperelektronik, TU Dresden, Dresden/DE Purpose: The presentation describes a novel method that aims at sound velocity measurements in tissues. The purpose of the method is locally resolved tissue characterisation and temperature measurements.
Volume 37, Number 8S, 2011 Material & Methods: Instead of using a reference path for sound velocity determination, the signals reflected by scattering particles are analysed. In the measurements, a strongly focusing transducer emits a sound wave into water containing scatterers. Because the strongest echo signal is generated at the ultrasonic focus, the position of the averaged echo signal amplitude indicates the time of flight to the focus. This knowledge suffices to determine sound velocity, because the time of flight to the focus is solely a function of sound velocity, frequency and transducer parameters. Results: In the measurements, the sound velocity of water was varied between 1431 and 1555 m/s by heating with a thermostat, and a calibration curve for the chosen transducer was generated. With a statistical uncertainty of only 1.4 m/s (0.1%), the calibration curve was highly accurate, so that promising results can be stated. Conclusion: To achieve local resolution of sound velocity, the focus position is to be varied with an annular array by always using a different set of delay times. This is expected to allow simultaneous determination of the scatterer positions in tissue and the average sound velocity between transducer and scatterers in the future. SS 31.06 Measurement of Two-Dimensional Temperature Distribution in Tissue Phantom Caused by Ultrasonic Irradiation Observing by Infrared Camera R. Niikawa, T. Tsuchiya, S. Tanaka, S. Sakuma, N. Endoh Department of Engineering, Kanagawa University, Yokohama/JP Purpose: For the development of safety using ultrasonic diagnosis system, it is important to estimate the temperature distribution in tissue. Many causes of heat generation by the ultrasonic wave occur by absorption effect in the media. Two-dimensional temperature distribution depends on sound field and absorption coefficient. In order to describe the relationship between heat generation and sound field accuracy, we measure 2D temperature distribution in tissue phantom caused by ultrasonic irradiation observing by infrared camera. Material & Methods: We measured 2D temperature distribution in agar phantom by infrared camera (TH5104 NEC Avio Infrared Technologies Co., Ltd.). The size of cubic phantom is 90 x 90 x 90 mm. Sound speed and attenuation coefficient of phantom are 1530 m/s and 1.0 [dB/cm] at 1MHz. The frequency of transducer is 1 MHz and diameter is 25 mm. The sound intensity value on the last maximum point is ISPTP 1.5 [W/cm2] using continuous wave. In this study, by considering the effect of reflected wave from bone, we measure temperature distribution into agar phantom with acrylic plate. The phantom was cut at the center into two pieces. Results: We observe 2D thermal image into agar phantom using infrared camera. The difference of temperature rise between phantom with acrylic and without acrylic at interface of phantom-acrylic of central axis of transducer is about 2.5 C when irradiation time is 45 minutes. We observe width of temperature rise at 1 C in radial direction by thermal image. The values of width of temperature rise are 14.9, 26.3, and 47.9 mm at 15, 30, and 45 minutes, respectively. Conclusion: In this study, we observe 2D thermal image into agar phantom using infrared camera. It is clearly shown that proposal method by infrared camera is efficient to measure the 2D temperature distribution in tissue phantom caused by ultrasonic irradiation. SS 31.07 Temperature Elevation Evaluation of Tissue Exposed by Pulsed Ultrasound with Acoustic Radiation Force N. Nitta,1 N. Kudo,2 I. Akiyama3 1 Human Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba/JP, 2Graduate School of Information Science and Technology, Hokkaido University,
Ultrasound in Medicine and Biology
Purpose: Sonoporation is a technique to introduce foreign genes or drugs into cells by ultrasound exposure. In this study, complex ultrasound fields inside a small chamber for sonoporation study were visualized using the subtraction Schlieren technique. Material & Methods: A small water chamber with a cross section similar to that of a Petri dish was placed on a disk-shaped transducer. The transducer was driven by long-burst ultrasound of 2 MHz in center frequency. The subtraction Schlieren technique (Kudo, J Phys: Conf Seri 2004, 1: 146–149), which visualizes acoustic fields by software subtraction of two shadowgraphs taken in the presence and absence of ultrasound exposure, was used in this study. Results: Different from conventional Schlieren, image subtraction Schlieren can visualize alternative pressure changes at the ultrasound carrier frequency of 2 MHz. Moving pictures of propagating and standing wave fields were successfully visualized by taking a series of instantaneous field images at gradually increasing delay timing after insonation. Standing wave fields were produced in the presence of ultrasound reflection at the water surface but were disturbed by perturbations of the water surface produced by the radiation force of ultrasound. Conclusion: Measurements of exposure dose are essential for studying therapeutic effects of ultrasound. The experimental results show that image subtraction Schlieren will be a powerful tool for visualization of acoustic fields inside small chambers and for estimation of the effective dose of ultrasound exposure. SS 31.04 Toward Non-Scanning Measurement of Eye Lens Curvature with Ultrasound M. Lenz,1 E. Ku¨hnicke2 1 Fak. Et/it, Ife, TU Dresden, Dresden/DE, 2Fakult€at Elektrotechnik und Informationstechnik, Institut F. Festk€orperelektronik, TU Dresden, Dresden/DE Purpose: The presentation describes a novel method for measuring local object curvature radii that aims at curvature measurements of the eye lens, in particular. The specific characteristic is that the method does not require any scanning. Material & Methods: Instead, an annular array is used. It is positioned in such a way that the acoustical axis passes through the centre of curvature. The phase and amplitude differences on the receiver elements are used to determine curvature: The larger the curvature radii of the spherical reflectors, the smaller are the phase differences between the echo signals arriving at the innermost and the outer transducer elements. The effect can be understood qualitatively by considering the different acoustical path lengths. For the quantitative predictions used in the presentation, wave acoustical methods were used. Results: Measurements using steel spheres with diameters from 12mm to 21mm as reflectors demonstrate proof of concept. Good agreement between measurements and numerical sound field simulations could be achieved. Accuracy is mainly limited by transducer symmetry. Conclusion: The next steps intend to find a more robust transducer setup. Further developments will concentrate on ellipsoidal curvatures, concave curvatures and curvatures of buried layers, which necessitates finer transducer segmentation. SS 31.05 Toward Locally Resolved Non-Invasive Sound Velocity Measurement E. Ku¨hnicke, M. Lenz Fakult€ at Elektrotechnik und Informationstechnik, Institut F. Festk€ orperelektronik, TU Dresden, Dresden/DE Purpose: The presentation describes a novel method that aims at sound velocity measurements in tissues. The purpose of the method is locally resolved tissue characterisation and temperature measurements.
Volume 37, Number 8S, 2011 Material & Methods: Instead of using a reference path for sound velocity determination, the signals reflected by scattering particles are analysed. In the measurements, a strongly focusing transducer emits a sound wave into water containing scatterers. Because the strongest echo signal is generated at the ultrasonic focus, the position of the averaged echo signal amplitude indicates the time of flight to the focus. This knowledge suffices to determine sound velocity, because the time of flight to the focus is solely a function of sound velocity, frequency and transducer parameters. Results: In the measurements, the sound velocity of water was varied between 1431 and 1555 m/s by heating with a thermostat, and a calibration curve for the chosen transducer was generated. With a statistical uncertainty of only 1.4 m/s (0.1%), the calibration curve was highly accurate, so that promising results can be stated. Conclusion: To achieve local resolution of sound velocity, the focus position is to be varied with an annular array by always using a different set of delay times. This is expected to allow simultaneous determination of the scatterer positions in tissue and the average sound velocity between transducer and scatterers in the future. SS 31.06 Measurement of Two-Dimensional Temperature Distribution in Tissue Phantom Caused by Ultrasonic Irradiation Observing by Infrared Camera R. Niikawa, T. Tsuchiya, S. Tanaka, S. Sakuma, N. Endoh Department of Engineering, Kanagawa University, Yokohama/JP Purpose: For the development of safety using ultrasonic diagnosis system, it is important to estimate the temperature distribution in tissue. Many causes of heat generation by the ultrasonic wave occur by absorption effect in the media. Two-dimensional temperature distribution depends on sound field and absorption coefficient. In order to describe the relationship between heat generation and sound field accuracy, we measure 2D temperature distribution in tissue phantom caused by ultrasonic irradiation observing by infrared camera. Material & Methods: We measured 2D temperature distribution in agar phantom by infrared camera (TH5104 NEC Avio Infrared Technologies Co., Ltd.). The size of cubic phantom is 90 x 90 x 90 mm. Sound speed and attenuation coefficient of phantom are 1530 m/s and 1.0 [dB/cm] at 1MHz. The frequency of transducer is 1 MHz and diameter is 25 mm. The sound intensity value on the last maximum point is ISPTP 1.5 [W/cm2] using continuous wave. In this study, by considering the effect of reflected wave from bone, we measure temperature distribution into agar phantom with acrylic plate. The phantom was cut at the center into two pieces. Results: We observe 2D thermal image into agar phantom using infrared camera. The difference of temperature rise between phantom with acrylic and without acrylic at interface of phantom-acrylic of central axis of transducer is about 2.5 C when irradiation time is 45 minutes. We observe width of temperature rise at 1 C in radial direction by thermal image. The values of width of temperature rise are 14.9, 26.3, and 47.9 mm at 15, 30, and 45 minutes, respectively. Conclusion: In this study, we observe 2D thermal image into agar phantom using infrared camera. It is clearly shown that proposal method by infrared camera is efficient to measure the 2D temperature distribution in tissue phantom caused by ultrasonic irradiation. SS 31.07 Temperature Elevation Evaluation of Tissue Exposed by Pulsed Ultrasound with Acoustic Radiation Force N. Nitta,1 N. Kudo,2 I. Akiyama3 1 Human Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba/JP, 2Graduate School of Information Science and Technology, Hokkaido University,