1. Field of the Invention
This invention relates to an ultrasonic diagnostic apparatus which transmits an ultrasonic beam from an ultrasonic probe to a subject, such as a biological body, receives the echoes from the subject, and obtains ultrasonic image data on the subject, and more particularly to an ultrasonic diagnostic apparatus and an ultrasonic diagnostic method which adjust a transmission voltage sent to an ultrasonic probe to the optimum value.
2. Description of the Related Art
With an ultrasonic diagnostic apparatus, an ultrasonic probe is brought into contact with a subject, such as a biological body. In this state, the ultrasonic probe transmits an ultrasonic beam to the inside of the subject and receives the echoes from the inside of the subject, thereby acquiring ultrasonic image data on the subject. The ultrasonic probe transmits an ultrasonic beam of acoustic power corresponding to a transmission voltage specified by a system control unit of the ultrasonic diagnostic apparatus. As for the transmission voltage to the ultrasonic probe, a transmission voltage preset within an acoustic power limit range by the system control unit is set as the maximum transmission voltage.
The ultrasonic beam is adjusted according to the type of subject, such as an unborn baby or an internal organ, so as not to transmit high acoustic power to the subject. The acoustic power of the ultrasonic beam is adjusted by the user manually operating an acoustic power adjustment switch provided on the panel of the ultrasonic diagnostic apparatus. The acoustic power adjustment of the ultrasonic beam is made in the acoustic power limit range by the manual operation, with the transmission voltage calculated by the system control unit being used as the maximum transmission voltage.
In the ultrasonic diagnostic apparatus, too, the safety of acoustic power of an ultrasonic beam is required. The transmission voltage for the ultrasonic beam is set to a transmission voltage calculated in advance by the system control unit. Accordingly, when an actual subject is diagnosed, the acoustic power of the ultrasonic beam has to be limited for the region which needs no diagnosis in the subject. To limit the acoustic power of the ultrasonic beam, the user operates the acoustic power adjustment switch manually, thereby adjusting the acoustic power of the ultrasonic beam to the optimum value. Such an adjustment of the acoustic power of the ultrasonic beam is made for, for example, each of a plurality of diagnostic regions of the subject.
However, when the user operates the acoustic power adjustment switch manually for each of the plurality of diagnostic regions to optimize the acoustic power of the ultrasonic beam, this decreases the diagnostic throughput of the diagnostic regions. Moreover, since a plurality of diagnostic regions of the subject are diagnosed, the total time required for the diagnostic regions becomes longer. Consequently, the irradiation time of the ultrasonic beam to the subject becomes longer.
The technique for not only controlling a method of driving a plurality of piezoelectric vibrators included in an ultrasonic probe in an ultrasonic Doppler spectrum method so as to follow the heat generation limit or acoustic output limit but also observing the Doppler spectrum with high sensitivity has been disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-305129. Specifically, Jpn. Pat. Appln. KOKAI Publication No. 2005-305129 has disclosed a method of switching between a power mode in which the amplitudes of the driving signals corresponding to a plurality of piezoelectric vibrators are relatively high and a power mode in which the amplitudes of the driving signals are relatively low in synchronization with the biological signal of the subject.
It is an object of the invention to provide an ultrasonic diagnostic apparatus and an ultrasonic diagnostic method which are capable of adjusting a transmission voltage sent to an ultrasonic probe according to a subject to an optimum value automatically.