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Feasibility of attenuation images from reflected ultrasound signals
ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM
Experimental two-phase Doppler results obtained for a Doppler phantom are discussed. This investigation was supported by PHS Grant Number 1 R43 CA37433-01, awarded by the National Cancer Institute, DHHS. [l] Nowicki, A. and Reid, J.M., Ultrasound Med. Biol. .L 41-50 (1981). A NEW THEORETICAL FORMULATION OF DOPPLER ULTRASOUND, Mani Azimi and A.C. Kak, Department of Electrical Engineering, Purdue University, West Lafayette, IN 47907. Past theoretical contributions in Doppler ultrasound have heavily borrowed from the electromagnetic case. In these contributions, most points of departure between the ultrasonic and electromagnetic cases were taken care of by heuristic incorporation of factors in the derived formulas. We will present a theory that we believe is more complete in the sense that it specifically accounts for the diffracted fields of the transducer aperture (assumed to be a source of a Gaussian focussed beam), the interaction of these fields with the scattering sites, and the interaction of the transducer aperture with the backscattered fields. The theoretical formulation was used to carry out a series of computer simulation studies on Doppler ultrasound. For example, we studied the effect of system bandwidth on range resolution by employing different pulse shapes, transducer transfer functions, velocity profiles and density profiles of erythrocytes. The control afforded by the theory over different parameters of a focused transducer has also allowed us to study the role of transducer design in the Doppler ultrasound systems. In particular, we investigated the influence of transducer size and the aperture-shading function. These and other computer simulation studies will form a part of our presentation. Work supported by NIH grant HL3192404.
SESSION 3:
ATTENUATION I
FEASIBILITY OF ATTENUATION IMAGES FROM REFLECTED ULTRASOUNDSIGNALS, R. Kuc, Department of Electrical Engineering, Yale University, New Haven, CT 06520. The acoustic attenuation coefficient of soft biological tissue has been observed to have an approximately linear-with-frequency attenuation characteristic, with a slope, denoted by 6, that varies with the disease condition of soft tissue, such as the liver and heart muscle. Hence it would be diagnostically useful to estimate the value of B of small tissue regions, defined by a cell measuring D by D cm in the tomographic scan plane. If D is small enough, 'B-images' could be generated. Two approaches for estimating B are examined: the spectral-shift approach, which estimates B from the downward shift experienced by the propagating pulse spectrum with penetration into the liver, and the B from the slope of the logspectral-difference approach, which estimates spectral differences. Lower bounds on the B estimators are derived by placing the tissue cell in the focal plane of the transducer and posing a mathematical model for reflected ultrasound signals. If B denotes the usable bandwidth in the reflected signals, the bounds are shown to be signals, and (BDls4 for the proportional to (BD)-~ for single reflected signals from a square tissue region. With currently available technology, clinically useful results can be obtained for cell sizes measuring approximately 2 cm on a side. This research was made possible by funding from the National Science Foundation, Grant ECS-7919601.
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Experimental two-phase Doppler results obtained for a Doppler phantom are discussed. This investigation was supported by PHS Grant Number 1 R43 CA37433-01, awarded by the National Cancer Institute, DHHS. [l] Nowicki, A. and Reid, J.M., Ultrasound Med. Biol. .L 41-50 (1981). A NEW THEORETICAL FORMULATION OF DOPPLER ULTRASOUND, Mani Azimi and A.C. Kak, Department of Electrical Engineering, Purdue University, West Lafayette, IN 47907. Past theoretical contributions in Doppler ultrasound have heavily borrowed from the electromagnetic case. In these contributions, most points of departure between the ultrasonic and electromagnetic cases were taken care of by heuristic incorporation of factors in the derived formulas. We will present a theory that we believe is more complete in the sense that it specifically accounts for the diffracted fields of the transducer aperture (assumed to be a source of a Gaussian focussed beam), the interaction of these fields with the scattering sites, and the interaction of the transducer aperture with the backscattered fields. The theoretical formulation was used to carry out a series of computer simulation studies on Doppler ultrasound. For example, we studied the effect of system bandwidth on range resolution by employing different pulse shapes, transducer transfer functions, velocity profiles and density profiles of erythrocytes. The control afforded by the theory over different parameters of a focused transducer has also allowed us to study the role of transducer design in the Doppler ultrasound systems. In particular, we investigated the influence of transducer size and the aperture-shading function. These and other computer simulation studies will form a part of our presentation. Work supported by NIH grant HL3192404.
SESSION 3:
ATTENUATION I
FEASIBILITY OF ATTENUATION IMAGES FROM REFLECTED ULTRASOUNDSIGNALS, R. Kuc, Department of Electrical Engineering, Yale University, New Haven, CT 06520. The acoustic attenuation coefficient of soft biological tissue has been observed to have an approximately linear-with-frequency attenuation characteristic, with a slope, denoted by 6, that varies with the disease condition of soft tissue, such as the liver and heart muscle. Hence it would be diagnostically useful to estimate the value of B of small tissue regions, defined by a cell measuring D by D cm in the tomographic scan plane. If D is small enough, 'B-images' could be generated. Two approaches for estimating B are examined: the spectral-shift approach, which estimates B from the downward shift experienced by the propagating pulse spectrum with penetration into the liver, and the B from the slope of the logspectral-difference approach, which estimates spectral differences. Lower bounds on the B estimators are derived by placing the tissue cell in the focal plane of the transducer and posing a mathematical model for reflected ultrasound signals. If B denotes the usable bandwidth in the reflected signals, the bounds are shown to be signals, and (BDls4 for the proportional to (BD)-~ for single reflected signals from a square tissue region. With currently available technology, clinically useful results can be obtained for cell sizes measuring approximately 2 cm on a side. This research was made possible by funding from the National Science Foundation, Grant ECS-7919601.
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