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A novel method for estimating ultrasonic attenuation from pulse-echo ultrasound using the phase of the reflected wave
ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM
A NOVEL METHODFOR ESTIMATING ULTRASONIC ATTENUATION FROM PULSE-ECHO ULTRASOUND USING THE PHASE OF THE REFLECTED WAVE, John R. Klepper', John M. Reid', Hirohide Miwa3, Takaki Shimura3 and Keiiohi Murakami3,11nstitute of Applied Physiology and Medicine, Seattle, WA 98122, 2Drexel University, Philadelphia, PA 19104, and 3Fujitsu Laboratories, Ltd., Kawasaki, Japan. Estimation of the ultrasonic attenuation of soft tissue by pulse-echo ultrasound has been reported by many authors using Fourier spectrum analysis or zero-crossing techniques. Both of these methods rely upon estimating the center frequency of a Gaussian shaped pulse. Relatively poor resolution results from these methods because of the need to process data from a finite time window in order to estimate the center frequency In this paper, we show that the attenuation of the reflected signals. slope coefficient may be instantaneously estimated from a continuous measure of the phase of the received signal, without the need of calculating the Fourier spectrum or averaging over a finite time window. The received pulse-echo signals are mixed with two continuously running oscillators which are 90" out of phase. After low pass filtering, two base band quadrature signals, termed I and Q, result. It is shown that the difference between the reference oscillator frequency and the centroid frequency of the received broadband pulse is equal to the arctangent Thus, a continuous measure of the unwrapped phase results in an (Q/I). instantaneous estimate of the center frequency of the received signals. Alternatively, continuous adjustment of the frequency of the reference oscillators can be made in a feedback loop to keep the output phase constant, with the result that the reference frequency is equal to the centroid of the received spectrum. Either method may be implemented in analog electronics to allow real time estimation of the attenuation slope coefficient. on freshly excised rabbit liver and --In vitro experiments tissue equivalent phantoms result in a significant improvement in resolution over that obtained using FFT techniques.
ON-LINE ESTIMATION OF ATTENUATION USING A ZERO-CROSSING DENSITY MEASUREMENTSYSTEM, M. Nassi, A. Rossetti, S. Shaffer, D. Pettibone, M. Siegenthaler and B. Carvey, Ultrasound Research Dept., Diasonics, Inc., Milipitas, CA 95035. A standard real-time ultrasound B-scanner has been modified to allow an on-line estimation of the rate of center frequency downshift with depth for --in vivo liver studies of attenuation. The estimation is simplified by using a zero-crossing density analysis [l]. Center frequency (rms) values are estimated at each depth segment (0.25 - 0.50 cm) and for all the vectors included in a region of interest (ROI), selected while in normal real-time imaging mode. This data is used to calculate a mean rms frequency value at each depth increment. A linear least-squares fit is then applied to the data rendering the rate of center frequency downshift with depth. The system completes the analysis and displays the attenuation coefficient estimate and a plot of the regression line in less than 100 ms. The advantages and potentially-limiting assumptions of this method will be evaluated and compared with other proposed attenuation estimation methods [21. Data is acquired from phantoms and in vivo cases. This data is analyzed on-line with the zero-crossing system and also stored by a digitized-rf acquisition system, which has been integrated in the same scanner for off-line analysis. [ll Flax, S.W., Pelt, N.J., Glover, G.H., Gutmann, F.D. and McLachlan, M., Ulrasonic Imaging 5, 95-116 (1983). [2] Nassi, M., Havlice, J., Sommer, G., Stern, R. and Shaffer, S., Ultrasonic Imaging 5, 172-173 (1983) (Abstract only).
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A NOVEL METHODFOR ESTIMATING ULTRASONIC ATTENUATION FROM PULSE-ECHO ULTRASOUND USING THE PHASE OF THE REFLECTED WAVE, John R. Klepper', John M. Reid', Hirohide Miwa3, Takaki Shimura3 and Keiiohi Murakami3,11nstitute of Applied Physiology and Medicine, Seattle, WA 98122, 2Drexel University, Philadelphia, PA 19104, and 3Fujitsu Laboratories, Ltd., Kawasaki, Japan. Estimation of the ultrasonic attenuation of soft tissue by pulse-echo ultrasound has been reported by many authors using Fourier spectrum analysis or zero-crossing techniques. Both of these methods rely upon estimating the center frequency of a Gaussian shaped pulse. Relatively poor resolution results from these methods because of the need to process data from a finite time window in order to estimate the center frequency In this paper, we show that the attenuation of the reflected signals. slope coefficient may be instantaneously estimated from a continuous measure of the phase of the received signal, without the need of calculating the Fourier spectrum or averaging over a finite time window. The received pulse-echo signals are mixed with two continuously running oscillators which are 90" out of phase. After low pass filtering, two base band quadrature signals, termed I and Q, result. It is shown that the difference between the reference oscillator frequency and the centroid frequency of the received broadband pulse is equal to the arctangent Thus, a continuous measure of the unwrapped phase results in an (Q/I). instantaneous estimate of the center frequency of the received signals. Alternatively, continuous adjustment of the frequency of the reference oscillators can be made in a feedback loop to keep the output phase constant, with the result that the reference frequency is equal to the centroid of the received spectrum. Either method may be implemented in analog electronics to allow real time estimation of the attenuation slope coefficient. on freshly excised rabbit liver and --In vitro experiments tissue equivalent phantoms result in a significant improvement in resolution over that obtained using FFT techniques.
ON-LINE ESTIMATION OF ATTENUATION USING A ZERO-CROSSING DENSITY MEASUREMENTSYSTEM, M. Nassi, A. Rossetti, S. Shaffer, D. Pettibone, M. Siegenthaler and B. Carvey, Ultrasound Research Dept., Diasonics, Inc., Milipitas, CA 95035. A standard real-time ultrasound B-scanner has been modified to allow an on-line estimation of the rate of center frequency downshift with depth for --in vivo liver studies of attenuation. The estimation is simplified by using a zero-crossing density analysis [l]. Center frequency (rms) values are estimated at each depth segment (0.25 - 0.50 cm) and for all the vectors included in a region of interest (ROI), selected while in normal real-time imaging mode. This data is used to calculate a mean rms frequency value at each depth increment. A linear least-squares fit is then applied to the data rendering the rate of center frequency downshift with depth. The system completes the analysis and displays the attenuation coefficient estimate and a plot of the regression line in less than 100 ms. The advantages and potentially-limiting assumptions of this method will be evaluated and compared with other proposed attenuation estimation methods [21. Data is acquired from phantoms and in vivo cases. This data is analyzed on-line with the zero-crossing system and also stored by a digitized-rf acquisition system, which has been integrated in the same scanner for off-line analysis. [ll Flax, S.W., Pelt, N.J., Glover, G.H., Gutmann, F.D. and McLachlan, M., Ulrasonic Imaging 5, 95-116 (1983). [2] Nassi, M., Havlice, J., Sommer, G., Stern, R. and Shaffer, S., Ultrasonic Imaging 5, 172-173 (1983) (Abstract only).
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