System for estimating target velocity from pulse echoes in response to their correspondence with predetermined delay trajectories corresponding to different distinct velocities
First Claim
1. The method of estimating the velocity of a target from repetitive echoes received in response to transmission of a plurality of repetitive pulses of propagating signals which comprises the steps ofa. translating said echoes into a series of successive outputs which occur in time relationship dependent upon a set of preselected target trajectories,b. searching for correspondence between the time relationship of said outputs and a plurality of expected time relationships each representing a different preselected target velocity, andc. selecting the one of said preselected velocities wherein said correspondence is greatest as the estimated velocity of said target.
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Abstract
In order to avoid the use of complex transform and correlation techniques for estimating the velocity of a target from which ultrasonic RF bursts are received as return echoes, the time of occurrence of successive returns are compared with a plurality of delay trajectories each representing a different target velocity. The trajectory with which the returns match with minimum variance, or maximum likelihood of being in time coincidence, provides an estimate of the velocity of the target. In different embodiments the RF return, the envelope of the return or the quadrature components thereof are processed to determine to which delay trajectory they are most proximal. The search for the delay trajectory is called a "butterfly search" in two dimensions (slow time or transmitted pulse repetition periods and fast time or range). Each butterfly line corresponds to a distinct linear velocity. The criterion that a signal corresponding to the returns should be equal in amplitude at all points along the correct trajectory may be used for envelope and RF signals. The use of the quadrature components is preferred in noisy environments, such as where the target is the scatterers in blood flow and blood flow velocity is to be determined. In the embodiment using the quadrature components, each butterfly line is searched for corresponding normalized likelihood ratio maxima, since such maxima occur on the correct butterfly line. The butterfly search can be implemented with less computation complexity than correlation or transform operations heretofore used for blood flow velocity estimation, and with fewer repeat pulses, and the results are more accurate in the presence of noise.
33 Citations
38 Claims
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1. The method of estimating the velocity of a target from repetitive echoes received in response to transmission of a plurality of repetitive pulses of propagating signals which comprises the steps of
a. translating said echoes into a series of successive outputs which occur in time relationship dependent upon a set of preselected target trajectories, b. searching for correspondence between the time relationship of said outputs and a plurality of expected time relationships each representing a different preselected target velocity, and c. selecting the one of said preselected velocities wherein said correspondence is greatest as the estimated velocity of said target.
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15. The method of detecting the velocity of a transcutaneous target selected from the group consisting of movement of tissue, organs and blood flow, from ultrasonic echoes received in response to a plurality of repetitive transmissions of ultrasonic pulse signals which comprises the steps of
a. translating said echoes into a plurality of time displaced outputs, which are located in a space having at least two dimensions defined by orthogonal axes one of which is the time of transmission of said ultrasonic pulse signals and the other of which is the time elapsed between transmission of said pulse signals and the reception of said echoes, b. detecting upon which of a plurality of butterfly lines in an array containing a plurality of said lines, said time displaced outputs are most proximal, each of said lines corresponding to a different target velocity, and c. providing as an estimate of the velocity of said target the velocity which corresponds to the line of a plurality of lines which is most proximal to said time displaced output.
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20. Apparatus for estimating the velocity of a target from repetitive echoes received in response to transmission of a plurality of repetitive pulses of propagating signals which comprises
means for translating said echoes into a series of successive outputs which occur in time relationship dependent upon a set of preselected target trajectories, means for searching for correspondence between the time relationship of said outputs and a plurality of expected time relationships each representing a different preselected target velocity, and means for selecting the one of said preselected velocities wherein said correspondence is greatest as the estimated velocity of said target.
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34. Apparatus for detecting the velocity of a transcutaneous target selected from the group consisting of movement of tissue, organs and blood flow, from ultrasonic echoes received in response to a plurality of repetitive transmissions of ultrasonic pulse signals which comprises
means for translating said echoes into a plurality of time displaced outputs, which are located in a space having at least two dimensions defined by orthogonal axes, one of which is the time of transmission of said ultrasonic pulse signals and the other of which is the time elapsed between transmission of said pulse signals and the reception of said echoes, means for detecting upon which of a plurality of butterfly lines in an array containing a plurality of said lines said time displaced outputs are most closely proximal, each of said lines corresponding to a different target velocity, and means for providing as an estimate of the velocity of said target the velocity which corresponds to the line of a plurality of lines which is most proximal to said time displaced outputs.
Specification