Ultrasonic diagnostic apparatus and ultrasonic diagnostic method

1. An ultrasonic diagnostic apparatus comprising:

an ultrasonic probe;

a transmitting and receiving unit which transmits a voltage to the ultrasonic probe to cause the ultrasonic probe to transmit an ultrasonic beam and to receive an echo from a subject with the ultrasonic probe;

a signal processing unit which acquires ultrasonic image data on the subject from an output signal of the transmitting and receiving unit;

a subject recognition unit which sets a plurality of image areas in an image of the subject in the ultrasonic image data acquired by the signal processing unit, calculates a spatial variance value and a first spatial average value of a luminance value of the ultrasonic image data, and a second spatial average value of noise data for each of the image areas, and recognizes whether each of the image areas is a part of the image of the subject based on the spatial variance value, the first spatial average value, and the second spatial average value; and

an optimum voltage computing unit that calculates a sensitivity, which is a difference between the first spatial average value and the second spatial average value, in the image area recognized as the subject by the subject recognition unit, and limits the transmission voltage to the ultrasonic probe based on the sensitivity and a preset threshold value; and

a shape change detection unit which detects a change in shape of the subject from temporally-consecutive image data in the ultrasonic image data;

wherein the optimum voltage computing unit calculates the sensitivity for each of the image areas recognized by the subject recognition unit when the shape change detection unit detects a change in shape of the subject, and limits the transmission voltage to the ultrasonic probe based on the sensitivity and the preset threshold value.

2. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum voltage computing unit calculates an average value of sensitivities in the image area, compares the average value of sensitivities with the threshold value, and if the average value of sensitivities is greater than the threshold value, lowers the transmission voltage to the ultrasonic probe.

3. The ultrasonic diagnostic apparatus according to claim 2 , wherein the optimum voltage computing unit lowers the transmission voltage by a voltage value corresponding to the difference between the average value of sensitivities and the threshold value.

4. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum voltage computing unit calculates the sensitivity each time a scan is made with the ultrasonic beam transmitted from the ultrasonic probe and, on the basis of the sensitivity and the preset threshold value, limits the transmission voltage to the ultrasonic probe.

5. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum voltage computing unit is capable of setting the preset threshold value separately inside and outside a region of interest set in the subject.

6. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum voltage computing unit limits the transmission voltage to the ultrasonic probe in real time or at regular intervals of time.

7. The ultrasonic diagnostic apparatus according to claim 1 , further comprising:

an optimization specifying unit which is for giving an instruction to optimize the transmission voltage to the ultrasonic probe

wherein the optimum voltage computing unit, when receiving an instruction from the optimization specifying unit, calculates a sensitivity in the image area recognized by the subject recognition unit and, on the basis of the sensitivity and the preset threshold value, limits the transmission voltage to the ultrasonic probe.

8. The ultrasonic diagnostic apparatus according to claim 7 , wherein the optimization specifying unit has a switch which is operated manually to give the instruction to the optimum voltage computing unit.

9. The ultrasonic diagnostic apparatus according to claim 1 , wherein the ultrasonic image data is composed of a plurality of temporally-consecutive frame images, and

the shape change detection unit compares temporally-consecutive ones of the frame images in the ultrasonic image data, thereby detecting a change in the shape of the subject.

10. An ultrasonic diagnostic method comprising:

transmitting a voltage to an ultrasonic probe to cause the ultrasonic probe to transmit an ultrasonic beam;

receiving an echo from a subject with the ultrasonic probe;

acquiring ultrasonic image data on the subject with a signal processing unit from an output signal of the ultrasonic probe;

setting a plurality of image areas in an image of the subject in the ultrasonic image data acquired by the signal processing unit, calculating a spatial variance value and a first spatial average value of a luminance value of the ultrasonic image data, and a second spatial average value of noise data for each of the image areas, and recognizing whether each of the image areas is a part of the image of the subject based on the spatial variance value, the first spatial average value, and the second spatial average value; and

calculating a sensitivity, which is a difference between the first spatial average value and the second spatial average value, in the image area recognized as the subject, and limiting the transmission voltage to the ultrasonic probe based on the sensitivity and a preset threshold value; and

detecting a change in shape of the subject from temporally-consecutive image data in the ultrasonic image data;

wherein the calculating calculates the sensitivity for each of the recognized image areas when the detecting a change in shape detects a change in shape of the subject, and limits the transmission voltage to the ultrasonic probe based on the sensitivity and the preset threshold value.

11. The ultrasonic diagnostic method according to claim 10 , wherein the limiting the transmission voltage to the ultrasonic probe includes:

calculating an average value of sensitivities in the image area,

comparing the average value of sensitivities and the threshold value, and

if the average value of sensitivities is greater than the threshold value, lowering the transmission voltage by a voltage value corresponding to the difference between the average value of sensitivities and the threshold value.