JPS6258739B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic apparatus. 2. Description of the Related Art In recent years, ultrasonic diagnostic equipment that scans an ultrasound beam like a radar inside a subject to directly view the internal structure of the subject has come into wide use for medical purposes. The probe used for this is required to be as small and lightweight as possible because it needs to come into contact with the living body, and therefore the driving electric circuit is usually not built into the probe, but is built into the main body of the device including the monitor. This output signal is often installed inside the probe and guided to the probe using a connecting cable. FIG. 1 shows an ultrasonic diagnostic apparatus having such a configuration. In the figure, input and output from a device main body 1 having a drive circuit are applied via a cable 2 to a probe 3 containing a piezoelectric vibrator.
In such a diagnostic device, since the cable 2 is usually shielded to prevent external interference, the ground capacity inevitably increases.

Further, many of the probes 3 include a signal line changeover switch inside, and in that case, an electronic switch is usually used, but the on-low resistance of this switch is a finite value and takes a value that cannot be ignored. When using an electronic switch with a MOS structure, the conduction resistance will be 100Ω to 500Ω and the cable capacity will be 400PF to 1000PF. Furthermore, when a ceramic element is used as the piezoelectric vibrator of the probe, it can be considered electrically almost capacitive, and its equivalent capacitance is 100 to 500 PF.

FIGS. 2A and 2B show the basic configuration of the piezoelectric vibrator drive section and its equivalent circuit in the above-mentioned ultrasonic diagnostic apparatus.

A drive circuit 21 in the main body of the device is applied to a switch 23 through a cable 2, and is switched to drive one of a plurality of vibrators (three in the figure for simplicity of explanation). When an electronic switch is used as the switch 23, its conduction resistance is quite high, typically several hundred ohms, as described above. The equivalent circuit at this time is shown in FIG. 2B. A ground capacitance 31 of a cable is connected in parallel to the drive source 21 and applied to the piezoelectric vibrator 24 via a conduction resistance 32 of a switch 23 .
Since the electric impedance of the vibrator 24 is considered to be approximately capacitance as in the case of a ceramic element, the capacitance 33 is shown here. Normally, the impedance of the drive source 21 is low, so even if the cable capacitance 31 is connected in parallel, it does not have much effect, and the input efficiency to the vibrator 24 is almost determined by the conduction resistance 32 and the vibrator impedance 33. FIG. 3 shows the frequency characteristics of the above-mentioned system. When the conduction resistance is larger than the vibrator impedance, attenuation occurs in the high frequency range, which is the frequency at which the vibrator is used, which is undesirable.

Conventionally, a peaking coil is inserted into the circuit as a resonant reactance in order to improve the above-mentioned attenuation in the high frequency range. FIG. 4A shows an equivalent circuit of the vibrator drive unit when a peaking coil is inserted, and FIG. 4B shows its frequency characteristics.

In the figure, the peaking coil 41 has a conduction resistance 3
2. It is inserted in series with the vibrator capacitor 33 and selected so as to have series resonance at the frequency used. In this case, if the value of the conduction resistance 32 is larger than the impedance of the coil 41 or the vibrator capacitor 33, the characteristics will deteriorate and resonance will not be exhibited. In an actual vibrator, the conduction resistance 32 of the electronic switch is quite large, and therefore does not exhibit sufficient resonance characteristics.

The present invention improves the resonance characteristics by improving the above-mentioned drawbacks, and in the present invention, a peaking coil as a resonant reactance is inserted into the drive source end of the cable (generally inside the drive source body). Therefore, it is possible to compensate for intensity attenuation.

FIG. 5A shows an equivalent circuit of a vibrator driving section employing the present invention, and FIG. 5B shows its frequency characteristics.

In the present invention, the peaking coil 41, which was conventionally installed on the probe side of the cable 2, is replaced with the cable 2.
It has been replaced with the drive source side. When this arrangement is adopted, the ground capacity 31 of the cable and the coil 4
1 is approximately series resonance, and its characteristics are extremely sharp because there is no resistance.
Therefore, this is divided by the conduction resistance 32 and the vibrator capacitance 33, and as a result, as shown in FIG. 5B, the resonance characteristic becomes better than that in FIG. 4B.

Figure 8 shows actual measured values when the following realistic constants are given to the circuit in Figure 5A.Cable capacity 220PF Vibrator capacity 220PF Continuity resistance 200Ω Peaking coil reactance 7μH The conventional example shown by the broken line Compared to the characteristics, the output clearly increases near the frequency used, 3MHz.

As is clear from the above detailed description, by employing the circuit configuration according to the present invention, the resonance characteristics can be improved and the effective output in the frequency band used can be increased.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an ultrasonic diagnostic device in which an ultrasound probe and the main body are connected by a cable, and Figure 2A shows the basic configuration of the piezoelectric transducer drive part of the diagnostic device shown in Figure 1. Figure 4B shows its equivalent circuit diagram, Figure 3 shows the frequency characteristics of the circuit in Figure 2, and Figure 4A shows a conventional piezoelectric vibrator drive unit that uses a peaking coil to improve resonance characteristics. A wiring diagram showing the configuration of
5A is an equivalent circuit diagram of the piezoelectric vibrator drive section of an ultrasonic diagnostic device according to an embodiment of the present invention, B is a diagram showing its characteristics, and FIG. 6 is a diagram of the same device. FIG. 3 is a diagram showing actually measured frequency characteristics in comparison with a conventional one. 1...Diagnostic device main body, 2...Cable, 3...
Ultrasonic probe, 21...Piezoelectric vibrator drive source, 23
...Switch, 24... Piezoelectric vibrator, 31... Ground capacity of cable, 32... Continuity resistance of switch, 33... Equivalent capacitance of piezoelectric vibrator, 41... Peaking coil.

Claims (1)

[Claims] 1. An ultrasonic probe equipped with a plurality of piezoelectric vibrators that emit ultrasonic waves to a subject and receive reflected ultrasonic waves from the subject, and an electronic switch that switches between the piezoelectric vibrators, and this ultrasonic probe. What is claimed is: 1. An ultrasonic diagnostic apparatus in which a device main body including a drive source for driving a child is connected by a cable, wherein a resonant reactance is inserted at the drive source end of the cable.