JPS5818095B2 - Ultrasonic diagnostic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic probe that takes into consideration the matching between the acoustic impedance of a transducer and the acoustic impedance on the surface of a subject.

As shown in FIG. 1a, a conventional probe has a transducer 1 as shown in FIG.
The front surface is coated with an epoxy resin coating material 2, and the rear surface is held by an acoustic damper material.

When an ultrasonic probe is placed on the object 3 to transmit and receive ultrasonic waves, the ultrasonic pulse emitted by the transducer 1 is reflected by the reflector 4 inside the object 3, and the probe The wave is received as a reflector echo by the sensor 1.

At this time, if the acoustic impedance of the subject on the surface of the subject differs from the acoustic impedance of the coating material 2, a part of the reflector echo will be reflected into the subject from the boundary surface and projected onto the reflector 4 again. Here, the wave is reflected again and received by the probe 1.

Echoes that are received after being reflected multiple times from the same reflector 4 are called multiple echoes, and the distance to the reflector is displayed multiple times, and if this is large, the target reflector echo is It becomes difficult to distinguish between the two, leading to misdiagnosis.

The time relationship of the above echoes is shown in Figure 1.

B in the figure. is the transmitted pulse, B1 is the reflector echo, B
2 indicates one of the multiple echoes.

Next, the relationship between B1 and B2 will be quantitatively examined.

Generally, the following relational expression is shown for the reflection and transmission of sound waves at the interface between two media with different acoustic impedances.

That is, when transmitting acoustic force P1 from a medium with acoustic impedance Z1 to a medium with acoustic impedance Z2, the transmitted force is B2.
, its transmittance is T1□, and medium 1 is
If the force reflected to is P and the reflectance is R21, then Pr Z-Z 2 Ft21--= (==) ・・・・・・・・・
・ (1) P, Z1+Z2 B2 4Z, Z2 1...-41"-"(Z1+Z2)・-°-<2)
).

In FIG. 1, an echo B is reflected from a reflector 4 inside a subject 3 for a pulse projected from a probe 1.
, and find the multiple echo B2 (using the above notation), B has T1□・T23・R43・Ta2・T”21
・・・－・・・・・・・・・(3) B2=T1□・T2
3・R43・R23・R43・T3□・T2.・・・・・・
...It is expressed as (4).

Therefore, if the ratio of multiple echoes to reflector echoes is r, then...
(5) B, Z2 + Z3 Z4 + Z3.

Here, acoustic impedance Z 1 of vibrator 1 = 32 x 105. &/cr? t-5e
c Acoustic impedance Z2 of epoxy coating material 2
25. I X 105g/'1-sec Acoustic impedance Z3 of object 3 (at surface) = 1.6 X 1
05&/crit -5ec Regarding the acoustic impedance Z4 of the reflector 4, if z4>z3, B, = 0.12, B2 = 0.032, r = '20.27 - (6), +□ , if, 6oB' In this way, the undesired multiple echoes exhibit a considerably large value relative to the desired reflector echoes, resulting in serious inconvenience in diagnosis.

The purpose of the present invention is to eliminate the inconvenience of apricot urine,
By adding an acoustic medium whose acoustic impedance changes continuously to the front of the transducer, when receiving ultrasonic waves,
It was designed to reduce multiple reflections caused by strong reflectors inside the subject.

This will be explained in detail below with reference to the drawings.

In the present invention, as an embodiment of the present invention, instead of the coachib material 2 in FIG. Weird 1
An acoustic medium 2' is used.

The acoustic medium 2' can be formed, for example, by mixing tungsten powder into an epoxy resin adhesive and allowing it to harden naturally.

This is an application of the phenomenon that during the curing, the tungsten in the mixture descends into the adhesive, which has a much smaller specific gravity, but it also takes into account the viscosity of the adhesive, the curing time, the particle size of the tungsten powder, etc. You need to choose.

That is, the composition of the mixed cured product is determined by the following selections:
It goes without saying that the fall of tungsten should be controlled so that the upper part contains almost no tungsten and the lower part has a tungsten content that exhibits the same level of acoustic impedance as in the vibrator.

Reflector echo B when using such an acoustic medium 2'; and multiple echo B2 are (3), (4),
Obtained in the same way as (5) 1 B1=T1□・T23・R43・Ta2・T2□
...(7) Tsuru-T1□'・T2. '・R43・
R23'・R43・T32'・T2,'...(8)r
-/ -R23' R43=(all units') (=) ・
(9)2 B1Z2+Z3Z4+Z3.

1 In this case, the acoustic impedance Z2' is continuously changed from a value comparable to the acoustic impedance Z1 of the vibrator to the value of the acoustic impedance of the epoxy resin adhesive Z2'==32 to 2. 2 X 10” 9/(i・5
If the acoustic medium 2' is formed so that ec-, the other acoustic impedance Z1. Z3. When Z4 is the same as above, corresponding to the numerical example (6) above, BI3-0.95B knee 0.024 r' kn = 0.025
...00)1 is obtained.

Therefore, from (6) and (1,0), the following improvement effect is shown.

B' 0.95. r O,271 -2□云8 B, 0.12 r O,02511□
As explained above, if the probe of the present invention is used,
Since the target reflector echo can be made thicker and the undesired multiple echoes can be made smaller, it is possible to prevent misdiagnosis due to multiple echoes as in the past.

[Brief explanation of the drawing]

Figure 1a is a cross-sectional view showing the situation when the probe is brought into contact with the subject, Figure 1 is a temporal relationship diagram of transmitted pulses and echo pulses, and Figure 2 is a reflection at boundaries with different acoustic impedances.・A drawing for explaining transmission, and FIG. 3 is a drawing for quantitatively explaining reflector echo and multiple echo 1. 1... Vibrator, 2... Coating material,
2'...Acoustic medium.

Claims (1)

[Claims] 1 comprises a vibrator and an acoustic medium provided on one surface of the vibrator and in contact with the surface of the subject; the acoustic impedance of the acoustic medium is equal to the acoustic impedance of the vibrator at a position in contact with the vibrator. The acoustic impedance of the acoustic medium is set to be approximately equal to the acoustic impedance of the surface of the test object at positions where it is in contact with the surface of the test object, and the acoustic impedance of the acoustic medium changes continuously between the position where it is in contact with the transducer and the position where it is in contact with the surface of the test object. An ultrasonic diagnostic probe characterized by: