JPH0333331B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sector electronic scanning ultrasonic diagnostic apparatus.

The directivity of array transducers used in conventional sector electronically scanned ultrasound diagnostic equipment deteriorates as the deflection angle increases. That is,
As the ultrasound beam width increases, the amplitude of the ultrasound beam also decreases. Two problems have been encountered: an increase in the beam width causes a decrease in resolution, and a decrease in the beam amplitude degrades the S/N ratio of the image.

An object of the present invention is to provide a sector electronic scanning ultrasonic diagnostic apparatus that can prevent deterioration of resolution and S/N even when the deflection angle becomes large. The purpose of this is to calculate the voltage to excite each element or the preamp amplification degree of each element based on the directional characteristics of one element that makes up the sector array transducer (phasic array transducer). and includes a storage device that stores this calculated value as a weighting amount,
This is achieved by reading out the weighting amount at the same time as the transmission and reception of the ultrasound beam is switched.

The nature and embodiments of the invention will now be described with reference to the drawings.

FIG. 1 shows an example of the directivity characteristics of a phased array transducer in a conventional sector type electronic scanning ultrasonic diagnostic apparatus. As is clear from this figure, as the deflection angle increases, the half-width of the ultrasound beam (beam width when the amplitude becomes 1/2)
As the beam becomes wider, the beam amplitude also decreases.
This is because the directivity of the elements that make up the array transducer is not sufficiently wide (Broad), and this is due to the electrical and mechanical coupling between the elements arranged on the same support. It is caused by FIG. 2 shows the directivity of one element of a phased array transducer. Note that the dotted line is a theoretical value of an ideal state determined only by the center frequency of the element and the element width. As shown in FIG. 2, the directivity of one element is not wide enough. For this reason, when the deflection angle increases, the overall directional characteristics deteriorate.

The present invention changes the excitation voltage of each element of the array transducer, or It consists of controlling the preamplifier amplification degree in the same way, or controlling both using a similar method. Of course, this weighting amount also includes the amount of compensation for the decrease in beam amplitude. As a conventional technique, a method has been used in which the outputs of each element are combined in a receiving system and then the decrease in amplitude due to an increase in the deflection angle is compensated for. Although this method can compensate for the amplitude, it does not improve the beam characteristics. In addition, conventional weighting methods, such as Dorktyevishev distribution,
All weighting amounts were symmetrically distributed. As described above, it is impossible to bring the directivity of the elements of the array transducer into the ideal state shown by the dotted line in FIG. This is because electrical and mechanical coupling cannot be completely removed because the elements must be placed adjacent to each other on the same support base.

The weighting in each weighting control of the pulsar excitation voltage and preamplifier amplification degree for each element according to the present invention will be explained with reference to FIG. N
is the total number of elements in the array transducer,
A is the midpoint, which is the center of the ultrasound beam. The length AO is the focal length Rf (for electron focusing), and θ ₀ is the deflection angle of the ultrasound beam, θ ₁ , θ ₂ ...
θ _i , θ _N-1 , when the deflection angle θ is ₀ , each element is
This is the central angle (deflection angle of the element) between the central axis of the element and a straight line connecting the center of the element to the focal point O. These central angles are the deflection angle θ ₀ ,
Once the total number of elements N, element pitch P, and focal length Rf are determined, they are determined by calculation, and θ _i =
f(θ ₀ , N, P, Rf). Therefore, for any deflection angle θ ₀ , N θ _i are determined, and the ratio of this θ _i to the peak value is determined from FIG. A weighting amount can be obtained from this ratio and a predetermined distribution function.

FIG. 3 is a block diagram showing one embodiment of the present invention. 10 is an array transducer, 1
2 is Pulsar PS, 14 is Preamplifier PA, 16
18 is a changeover switch SW, 18 is a delay circuit, 20 is a combining circuit, 22 is an ultrasonic beam transmission/reception control circuit, and 24 is a weighting amount storage device. According to this illustrated example, the amplification degree of the preamplifier (PA) 14 may be changed in accordance with the weighting amount. The voltage of the pulser 12 (PS) may be changed along with the amplification degree. Alternatively, only the pulser voltage may be changed. During implementation, the central angle θ _i must be determined in accordance with the number of deflection angles, that is, the number of scanning lines (only the left half is sufficient), and the corresponding weighting amount must be determined from Figure 2. As a result, the configuration of the device becomes extremely complicated. Therefore, if the deflection angle θ ₀ is limited to a certain angle θ _w or more, and the maximum deflection angle θ _nax is θ _w < θ ₀ < θ _nax , the area of this deflection angle θ ₀ is divided into 3 to 4 equal parts. , the weighting amount of each element corresponding to its central angle θ _i is determined from FIG.
The weighting amount of each element with respect to the central angle of each region is stored in the storage device 24, for example, a ROM memory, and the pulsar voltage or preamplifier amplification degree is controlled when transmitting and receiving the ultrasonic beam. Configure.

[Brief explanation of the drawing]

Fig. 1 is a directivity characteristic diagram of a phased array transducer, Fig. 2 is a directivity characteristic diagram of one element, Fig. 3 is a schematic block diagram showing an embodiment of the present invention, and Fig. 4 is a central angle diagram. FIG. 10 is an array transducer, 12 is a pulser, 14 is a preamplifier, 16 is a changeover switch, 22 is a wave transmission/reception control circuit, and 24 is a storage device.

Claims (1)

[Claims] 1 According to the ultrasonic beam deflection angle θ ₀ , the deflection angle θ _i of each element is determined as a function of the beam deflection angle θ ₀ , the total number of elements N, the element pitch P, and the focal length _Rf. The ratio to the peak value is determined by the directivity characteristic of one element constituting the sector array transducer, and the pulser excitation voltage or preamplifier amplification for each element is determined from this ratio and a predetermined distribution function. The weighting amount is read out at the same time as the transmission/reception of the ultrasonic beam is switched, and the pulsar voltage or preamplifier amplification degree for each element is variably controlled. A sector electronic scanning ultrasonic diagnostic device.