| 摘要 |
The ultrasonic receiving circuit (1) has two bandpass filters (11, 19) with different centre frequencies (f1, f2), to which the ultrasonic echo signal (S) is fed as input signal. Each bandpass-filtered signal (S'1, S'2) is fed to an envelope generator (13 or 21) whose output signal (S1 or S2) is fed to the first or the second input (15, 23) of a divider element (17). The output signal (S3) of the divider element (17) is fed to a differentiator (25) for the purpose of forming the time derivative. The output signal (S4) of the differentiator (25) is applied to the first input (27) of a comparator (29) to whose second input (31) a prescribed signal value (X) is applied. Tapped at the output (33) of the comparator (29) is a control signal (S5) which upon overshooting and undershooting of the prescribed value (X) by the output signal (S4) of the differentiator (25) changes its absolute value and thus signals the presence of a contrast medium in the tissue. The advantages of the ultrasonic receiving circuit (1) are a good contrast enhancement, the possibility of isolated representation of spaces filled with contrast medium or through which the latter flows, and the possibility of representation using a real time method. <IMAGE>
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