| 摘要 |
In a method for calculating the flow velocity of, for example a blood stream, ultrasound pulses are repeatedly transmitted into an examination region with a spacing of a pulse repetition time (Tr). An autocorrelation function (Kii) and a cross correlation function (Kiq) in an environment (Tr+/-1.5 T) around the pulse repetition time (Tr) are formed from the quadrature components (i, q) of echo signals of respectively successive transmission pulses. The shift of the maximum ( DELTA t) of the correlation functions (Kii, Iiq) relative to the pulse repetition time (Tr) as a result of the velocity of the flow is fixed in a region (Bn) wherein the ambiguous, mean Doppler frequency ( omega ) identified in a traditional way lies. The apparatus for the implementation of this method comprises a shift identification circuit for this purpose. This shift identification circuit calculates the shift of the maximum ( DELTA t) of one or both correlation functions (Kii, Kiq) relative to the pulse repetition time (Tr).
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