Ultrasonic diagnostic apparatus and method for processing ultrasonic signal

1. An ultrasonic diagnostic apparatus, comprising:

a transducer including plural elements that send an ultrasonic wave to an object to be inspected and receive the ultrasonic wave reflected from the object to be inspected;

an analog to digital converter that digitizes each of plural received signals received by the plural elements;

a first mixer that multiplies a signal output from the analog to digital converter and a first digital reference signal;

a first filter that extracts a signal having a predetermined center frequency from a signal output from the first mixer;

a digital delay unit that delays signals output from the first filter;

an adder that adds plural signals output from the digital delay unit;

a second mixer that multiplies a signal output from the adder and a second digital reference signal;

an envelope detector that detects a signal output from the second mixer;

a scan converter that converts a signal output from the envelope detector to a picture signal; and

a display that displays a signal output from the scan converter.

2. An ultrasonic diagnostic apparatus, comprising:

a transducer including plural elements that send an ultrasonic wave to an object to be inspected and receive the ultrasonic wave reflected from the object to be inspected;

an analog to digital converter that digitizes each of plural received signals received by the plural elements;

a first mixer that multiplies a signal output from the analog to digital converter and a first digital reference signal;

a first filter that extracts a signal having a predetermined center frequency from a signal output from the first mixer;

a digital delay unit that delays a signal output from the first filter;

an adder that that adds plural signals output from the digital delay unit; and

plural signal processing circuits connected to the output terminal of the adder in parallel,

wherein each signal processing circuit comprises:

a second mixer that multiplies a signal output from the adder and a second digital reference signal;

a second filter that extracts a signal having a predetermined center frequency from a signal output from the second mixer;

an envelope detector that detects a signal output from the second filter;

a scan converter that converts a signal output from the envelope detector to a picture signal; and

a display that displays a signal output from the scan converter,

wherein, in each signal processing circuit, the second filter extracts a signal having a predetermined center frequency different from a center frequency of other ones of the signal processing circuits, from the signal output from the second mixer.

3. An ultrasonic diagnostic apparatus according to claim 2 , wherein the plural signal processing circuits include a first signal processing circuit and a second signal processing circuit, where the first signal processing circuit and the second signal processing circuit respectively comprise a second mixer that multiplies a signal output from the adder and a second digital reference signal, a second filter that extracts a signal having a predetermined center frequency from a signal output from the second mixer, an envelope detector that detects a signal output from the second filter, a scan converter that converts a signal output from the envelope detector to a picture signal, and a display that displays a signal output from the scan converter, and wherein, in the first and second signal processing circuits, each second filter extracts a signal having a predetermined center frequency different between the first and second signal processing circuits from a signal output from the second mixer, and images of a first center frequency and a second center frequency are acquired in parallel.

4. An ultrasonic diagnostic apparatus according to claim 3 , wherein the frequency of the first digital reference signal is set between the first center frequency and the second center frequency.

5. An ultrasonic diagnostic apparatus according to claim 3 , wherein one of the first and second center frequency is a harmonic of the other of the first and second center frequency.

6. An ultrasonic diagnostic apparatus according to claim 2 , wherein images having different center frequencies are displayed on the same display or on different displays.

7. An ultrasonic diagnostic apparatus according to claim 1 or 2 , wherein the sum of the frequency of the first digital reference signal and the frequency of the second digital reference signal is equalized to a center frequency of a received signal to be imaged.

8. An ultrasonic diagnostic apparatus, comprising:

a transducer including plural elements;

a selecting/driving circuit that selects plural n pieces of elements (n=1, 2, - - - , N) for sending an ultrasonic wave having a center frequency ω s to an object to be inspected and receiving the ultrasonic wave having the center frequency ω s reflected from the object to be inspected;

analog to digital converters provided corresponding to the plural n pieces of elements (n=1, 2, - - - , N) for digitizing a received signal received by the element;

first mixers provided corresponding to the analog to digital converters corresponding to the elements for multiplying a signal output from each analog to digital converter and a first digital reference signal having a frequency ω m different from the center frequency ω s ;

first filters provided corresponding to the first mixers corresponding to the elements for extracting a signal having a frequency (ω m −ω s ) from a signal output from each first mixer;

digital delay units provided corresponding to the first filters corresponding to the elements for multiplying a signal output from each first filter and delayed by propagation delay time τ n different in every element from the sending of the ultrasonic wave to the receiving of it by exp(−jω m τ n );

an adder corresponding to the plural n pieces of elements (n=1, 2, - - - , N) for adding signals output from the digital delay units;

a second mixer that multiplies a signal output from the adder and a second digital reference signal having a frequency (ω s −ω m );

an envelope detector that detects a signal output from the second mixer;

a scan converter that converts a signal output from the envelope detector to a picture signal; and

a display that displays a signal output from the scan converter,

wherein a received signal having the center frequency ω s is imaged and displayed.

9. A method of processing an ultrasonic signal, comprising the steps of:

selecting plural n pieces of elements (n= 1, 2, - - - , N) of a transducer including plural elements for sending an ultrasonic wave having a center frequency ω s to an object to be inspected and receiving the ultrasonic wave reflected from the object to be inspected and having the center frequency ω s and driving them;

digitizing plural received signals received by the elements in analog to digital converters provided corresponding to the plural n pieces of elements (n=1, 2, - - - , N);

multiplying a signal output from each analog to digital converter and a first digital reference signal having a frequency ω m different from the center frequency ω s in the first mixers provided corresponding to the analog to digital converters corresponding to the plural n pieces of elements (n=1, 2, - - - , N);

extracting a signal having a frequency (ω m −ω s ) from a signal output from each first mixer in first filters provided corresponding to the first mixers corresponding to the elements;

multiplying a signal acquired by delaying a signal output from each first filter by propagation delay time τ n different every element from the sending of the ultrasonic wave to the receiving of it by exp(−jω m τ n ) in digital delay time units provided corresponding to the first filters corresponding to the elements;

adding signals output from the digital delay units corresponding to the plural n pieces of elements (n= 1, 2, - - - , N) in an adder;

multiplying a signal output from the adder and a second digital reference signal having a frequency (ω s −ω m ) in a second mixer;

detecting a signal output from the second mixer in an envelope detector;

converting a signal output from the envelope detector to a picture signal in a scan converter; and

displaying a signal output from the scan converter on a display,

wherein the received signal having the center frequency ω s is imaged and displayed.