Conventional ultrasonic motion or flow velocity estimation is limited to the axial velocity component. A novel technique, called "spatial quadrature," for the simultaneous estimation of axial and lateral velocity components is introduced. This technique utilizes even and odd spatial weightings of the point spread function that have a quandrature relationship. These weightings produce modulation in the received echo that can be decoded to quantify lateral motion. This estimator can be implemented for two-dimensional velocity estimation with a conventional transducer array and medical ultrasound scanner, preferably one with parallel receive processing. The technique also can be extended to three-dimensional velocity estimation given an appropriate 2-D transducer and scanner architecture. Discussed are space and frequency domain descriptions of this estimator in the context of a brief overview of 2-D flow estimation methods, including analyses characterizing the performance envelope of this estimator. In addition, the application of this technique in CW and PW regimes, and with both radio frequency and baseband quadrature (I- and-Q) data, are discussed. Phantom studies demonstrate spatial quadrature in 2-D using a clinical scanner.
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