JPH0123137B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic diagnostic apparatus, and particularly relates to an improvement in an ultrasonic diagnostic apparatus that can move the focal point of ultrasonic waves in the depth direction.

[Conventional technology]

The azimuth resolution of an ultrasound imaging device used for medical diagnosis and the like is determined by the characteristics of a probe that emits and receives ultrasound beams. FIG. 4 shows a cross section of a transducer of a circular flat probe conventionally used in a mechanical scanning type ultrasonic imaging device and a schematic diagram of its ultrasonic beam. With this probe,
If the diameter of the disk is D and the wavelength of the ultrasonic wave is λ, then
Up to the near-field sound field limit (X _N ) determined by D ² /λ, the width of the ultrasonic beam is approximately the same width as the transducer, and at longer distances the ultrasonic beam spreads with an opening angle of λ/D. In contrast to circular plate probes with such characteristics, a concave focusing probe has been proposed that uses a concave transducer to narrow the ultrasonic beam at a short distance. FIG. 5 schematically shows the cross section of the transducer of the concave focusing probe and the ultrasonic beam. In this way, by using a concave transducer, the ultrasonic beam can be narrowed in a specific region. Also, when receiving reflected echoes in this region, the same characteristics as when emitting ultrasonic waves are obtained. Therefore, it is common practice to use a concave focusing probe to increase the lateral resolution of an ultrasonic imaging device. An apparatus using the above-mentioned type of probe has the disadvantage that, although the resolution improves in a specific region, the resolution rapidly decreases when the device deviates from that region. Therefore, it is not convenient when the measurement area is wide. In order to improve these shortcomings,
By dividing the planar disk vibrator into ring shapes and adding a delay to the received signals from these divided vibrators, it is possible to have a focusing effect similar to that of a concave vibrator, and still achieve the above delay amount. Attempts have been made to change the focal point over time and move the focal point to obtain high resolution over the entire measurement area.
(Ueda, Sato, Maeda, Yamamoto; Transactions of the Institute of Electronics and Communication Engineers,
vol58-A (1975) p729) The same thing is done for rectangular oscillators.

The principle of a method of driving a vibrator that can move these focal points will be explained below using an example using a rectangular vibrator. Consider n rectangular oscillators 1, 2, . . . , n, each narrow and long in width, arranged on the same plane at equal intervals. Figure 6 shows the arrangement state and the focal points P ₁ , P ₂ ,
This shows the relationship of _P3 . Convergence points P ₁ , P ₂ ,
Place P ₃ . An arc is drawn around these points and passing through the centers of the vibrators located at both ends of the vibrator array.
Time τ ₁₁ corresponding to the distance l ₁₁ , l ₂₁ ...l _o1 from the point where the straight line connecting the center of each oscillator and point P ₁ intersects with this circular arc to the center of each oscillator 1, 2, ..., n ,τ ₂₁ …
If a delay time of τ _o1 is given to the received signal from each vibrator and then added, the reflected echo will be focused on the point _P1 . Here, τ _o1 =l _o1 /c, where c is the speed of sound in the medium. In order to focus the reflected echo on point P ₂ , for each oscillator 1, 2, ..., n, τ ₁₂ = l ₁₂ /c, τ ₂₂ = l ₂₂ /c, ... τ _o2 = l _o2 / as above. It is sufficient to perform the addition after giving a delay of c. The same applies when point P ₂ becomes P ₃ . Here l ₁₂ , l ₂₂ ,…, l _o2
is given by the same construction method as that used to find l ₁₁ , l ₂₁ , ..., l _o1 in P ₁ .

FIG. 7 shows an example of a wave receiving circuit in which a transducer array has a focusing effect. Here, 1 is a transducer row consisting of the elongated transducers described earlier, 2 is a circuit that delays the received ultrasonic signal from the transducer, and 3 is an adder. Here, the delay circuits have τ ₁₁ , τ ₂₁ ,...
It is obvious from the previous explanation that when a delay of τ _o1 is given, this transducer array is focused on the reflected echo from point P ₁ . _The delay times of the delay circuits connected to _the oscillators ₁ , _{2 ,} ... _, n are calculated as time _passes , _respectively .
If configured so that τ _oo changes, the focal point of the received wave will be P ₁ →
It moves with time as P ₂ →P ₃ . Ultrasonic waves are emitted from the transducer array 1 into the measurement target, and the focal point of the transducer array is electronically moved according to the above principle as the area where the ultrasound is reflected becomes deeper over time. In this way, resolution can be improved over the entire measurement region. This kind of thinking has been around for a longer time than the above-mentioned literature. (Numa, Hashiguchi; No.
Proceedings of the 23rd Japanese Society of Ultrasound in Medicine, P61, 1972-
5 and Japanese Patent Publication No. 50-12742) In fact, a device based on the above principle has been prototyped, and the results have been reported.The biggest drawback is that the number of transducers is small, and the transducer array is When the width (aperture) is small, the focusing effect in deep regions is reduced, and the effect of moving the focusing point only in the near field limit _XN is large.

[Problem to be solved by the invention]

An example that can explain this is shown in FIG. This is explained earlier when receiving the reflected echo when a 2MHz ultrasonic wave is emitted using a probe with a width of approximately 20mm, which has 40 elongated transducers each having a width of 0.4mm arranged adjacently at a pitch of 0.5mm. Based on this principle, the results of calculating the relationship between resolution and distance from the probe are shown when the focal point is moved over time to improve resolution. Focus points are 5.0, 7.5, 10.0,
It was moved sequentially to 12.5, 15.0, 17.5, and 20.0 cm. Here, the resolution is expressed as the width in the azimuth direction in which the sensitivity decreases by -3 dB from the highest point.

Figure 9 shows a 0.4mm vibrator with the same width as above.
120 transducers are arranged adjacently at a pitch of 60 mm, forming a row of transducers approximately 60 mm wide, with focusing points of 5.0, 7.5, 10.0, 12.5,
The relationship between the resolution and the distance from the probe was determined by numerical calculation when the probe was moved sequentially to 15.0 cm and 17.5 cm. Here, the frequency of ultrasound is 2.0MHz,
The definition of resolution is the same as in the case of FIG. As can be seen from this calculation result, by increasing the number of transducers and widening the width of the probe, it is possible to improve the resolution at distances farther than the probe, but near the probe, the focal point As the depth becomes shallower, the resolution improves only near the focal point; beyond this point, the resolution drops sharply, making it even worse in practice than when the width is narrow. In order to improve this problem, the number of focusing points can be increased, but this becomes a problem due to the complexity of the delay circuit, which not only makes the device large and expensive, but also makes it difficult to implement. Furthermore, as the width of the probe increases, the delay time to be given to the received signal also increases, which is disadvantageous in terms of performance in the actual configuration of the delay circuit. To give specific numbers, the previous transducer is more powerful than the transducer among 40 probes.
In order to focus on a point of 7.5cm, the delay time that should be given to the received signal of the transducer in the center of the probe is approximately 420n.
The width of 120 transducers is 6 compared to sec.
cm probe requires a long delay time of 3800n sec. If we try to provide this with an LC delay line, which is often used in actual circuits, considering that the frequency of the received signal is about 2MHz, the signal attenuation will be large, which is considered to be a problem in terms of performance, and both It is difficult to solve.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a technique for improving the resolution between focal points in an ultrasonic diagnostic apparatus in which the focal point of ultrasonic waves can be moved, and to simplify the circuit configuration thereof. do.

[Means to solve the problem]

The above object is to provide a probe comprising a plurality of narrow rod-shaped transducers arranged, a means for transmitting an ultrasonic beam into a subject using the probe and receiving the reflected wave, and In an ultrasonic diagnostic apparatus having means for electronically focusing an ultrasound beam, and a focusing point moving means for moving a focusing point of the ultrasound beam in a depth direction, a receiver is provided in accordance with the depth of the moving focusing point. probe aperture changing means for changing the aperture of the probe by substantially changing the number of transducers involved in the wave; and data for controlling the operations of the focal point moving means and the probe aperture changing means. This is achieved by an ultrasonic diagnostic apparatus characterized by comprising means for storing the data, and means for reading out the data and supplying it to the focal point moving means and the probe diameter changing means.

The operation of each of the above means will be explained in conjunction with the following examples.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram explaining the principle of the present invention. Here, 1 is similar to the conventional moving focal point probe,
This probe consists of narrow rod-shaped transducers arranged adjacent to each other. Here, the focal point is set as a point over time.
Consider the case of moving from P ₁ to P ₂ and P ₃ . Point P ₁
When focusing, the number of oscillators is determined to obtain the required resolution. That is, the effective width (aperture) of the probe is determined, and the width is defined as W. Also, if the distance from the center O of the probe to P ₁ is R, then the point
Find the point where the circular arc centered on P ₁ and passing through the centers Q ₁ and Q ₁ ' of the transducers at both ends, which define the aperture of the probe, intersects the delay line of the straight line P ₁ O. Let the distance between this point and the center O of the probe be _L1 . This L ₁ is given by the following formula.

L ₁ = √ ² + (2) ² −R …(1) When the distance OP ₁ from the center O of the probe to the focal point P ₁ and the apertures of the probe Q ₁ and Q ₁ ′ are each multiplied by k. The center of the transducer at both ends determines the aperture of the transducer.
Similarly, find the point where the arc passing through Q _k and Q _k ′ and having the focal point P _k as its center intersects with the extension of the straight line OP ₁ . Letting the distance between this point and the center of the probe be Lk, Lk is given by the following equation.

Lk=√() ² +(2) ² −kR =k{√ ² +(2)−R}=kL ₁ …(2) In this way, increasing the distance from the center of the probe to the focal point If the aperture of the probe is made proportionally wider, the above-mentioned distance _L1 will also increase proportionally. Therefore, as the reflection point of the ultrasonic waves emitted from the probe moves over time, the focal point of the received waves of the probe moves,
In order to have a focusing effect equivalent to that of a concave transducer when the aperture of the probe is widened in proportion to the moving distance, the amount of delay that should be given to the received signal from each element of the probe is It can be found by applying the same method to FIG. 2 as found in the figure. Here, a delay was given to each element of the probe to have a focusing property equivalent to that of a concave transducer, but an axicon-type transducer (CB Burckhard et al: ULTRASONICS
54, No. 6, 1628), but only the case shown in FIG. 6 will be described below.

Figure 3 shows the results of numerical calculation of the resolution (-3 dB width) as a function of the distance from the probe when the focal point of the received wave is moved according to the above-mentioned principle. Here, the element width of the probe is 0.4 mm, and the pitch is
It is set to 0.5mm. The ultrasonic frequency is 2.0MHz, and the focal point is 5.0, 7.5, 10.0, 12.5, 15.0, 20.0cm.
When moving the probe sequentially, change the aperture of the probe to 2.0, 3.0,
It is expanded to 4.0, 5.0, 6.0, 7.0, and 8.0cm. As the focal point is moved farther away, the aperture of the probe is widened, so the depth of the focal point is always constant, and constant resolution is obtained over a wide range. Also, if the focusing point is placed 17.5 cm away from the probe, the maximum delay time required is 2280 n sec,
This value is about half the value of the case shown in FIG. 9, so it is an easily achievable value. According to the present invention, since the depth of focus and resolution are uniform over the entire area, uniform image quality can be obtained, and the great feature is that it is only necessary to move the focal point at regular intervals. Furthermore, since ultrasonic waves are attenuated in a living body, the reflected echoes become weaker as the distance from the probe increases. Therefore, in practical devices for biological diagnosis, the gain of the amplifier for the received signal is changed over time, but this is not sufficient. The present invention has the great advantage that the number of transducers involved in wave reception in the probe increases over time, and the received signal also becomes stronger.

FIG. 1 is a circuit diagram of the main part of the present invention. In the figure, 1 is a probe consisting of a number of narrow transducers arranged adjacent to each other, 2 is a delay line with taps, 3 is an adder, 4 is an analog switch, 5 is a shift register, 6 is an amplifier, and 7 is a shifter. register, 8
It is ROM (Read-Only-Memory). In this configuration, the reflected waves from inside the living body received by the probe 1 are transmitted through the amplifiers 6, _{6 -1} , 6 _-2 , which are connected to the respective transducers 1 _-1 , 1 _-2 , ...1 _-o . …6 After being amplified by _-o , it is guided to delay line 2. Delay line 2, 2 _-1 ,
2 _-2 , . . . 2 _-o are provided with taps for setting the delay time corresponding to the line segment L shown in FIG. 2 given to each vibrator. Selection of these taps is performed by opening and closing analog switches 4, _4-1 , _4-2 , . . . 4 _-o . In this figure, when the output of the shift register 7 is 1, the analog switch 4 is closed, and when it is 0, it is opened. The signal from the vibrator 1 _-1 is sent to the adder 3 via the delay line 2 _-1 for the first time. In the case of a transducer in which the convergence point is close to the probe 1 and the aperture may be small, and therefore the received signal is not required, the analog switch 4 is used to prevent the received signal from being applied to the adder 3. The switch 4 can be connected not only to the tap of the delay line 2 but also to ground.

Tap switching of the delay line 2 and control of the aperture of the probe 1 are performed by an analog switch 4, shift registers 5, 7, and ROM 8. Shift register 5 has serial input and parallel output, while shift register 7 has parallel input and parallel output. The contents of the shift register 7 can be rewritten all at once by a control signal, and newly written data is transferred from the shift register 5 connected to the shift register 7 as shown in the figure. . After the contents of the shift register 5 are transferred to the shift register 7, new contents from the ROM 8 are sequentially written to the shift register 5. This operation is performed in the interval during which the analog switch 4 is switched by a clock pulse. ROM
8. Of course, in the reading order, the focusing point and probe aperture (the number and position of the transducers to be operated) must be calculated in advance so that they follow the principle of the present invention explained earlier. It is included as data.

The above explained the case of wave reception, but for wave transmission, the diameter of the probe is changed as the focal point moves, and the ultrasonic beam width can be controlled regardless of the movement of the focal point, as in the case of wave reception. It can be kept constant.
In this embodiment, the output of the amplifier is grounded as a method of not applying the output of the vibrator to the adder, but the present invention is not limited to this, and the method of changing the gain of the amplifier described above may also be used. .

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain uniform resolution over the entire observation area, and when implementing this, the depth of focus of the convergence point is uniform, so the number of focal points to be set is small, and the number of focal points required is small. Since the delay amount of the delay circuit can also be made smaller than that of the conventional method, it is possible to concretely realize the present invention. It also compensates for the loss of sensitivity at long distances from the probe due to attenuation of ultrasound in the living body, and has great practical effects, such as improving SN in this region.

Furthermore, to control the delay line for focusing and the number of oscillators involved in operation, it is possible to store pre-calculated data in a storage means and read it out in the order of operation and use it, significantly reducing the circuit configuration. It can be done easily.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a portion that moves the focal point and changes the number of oscillators according to an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the principle of determining the delay time given to changes in the aperture and focal point of the probe according to the present invention. Figure 3 is an example of calculating the relationship between the distance from the probe and the resolution according to the present invention. Figure 4 is a schematic diagram of an ultrasound beam when using a flat plate transducer, Figure 5 is a schematic diagram of an ultrasound beam when a concave transducer is used, and Figure 6 is a diagram of conventional ultrasound focusing. Figure 7 is a diagram of the principle of the method, Figure 7 is a diagram of the circuit that focuses the ultrasonic waves in Figure 6, and Figure 8 is the diagram of the principle of the ultrasonic wave focusing circuit shown in Figure 6. Figure 9 shows an example of the relationship between distance and resolution obtained by calculation. Figure 9 shows an example of the relationship between distance from the probe and resolution when a wide probe is used and the focal point is moved. This is the diagram I found. 1... Probe, 2... Delay line, 3... Adder,
4...analog switch, 5...shift register, 6...amplifier, 7...shift register, 8...
…ROM.

Claims (1)

[Scope of Claims] 1. A probe consisting of a large number of narrow rod-shaped transducers arranged adjacent to each other, and the probe is used to transmit an ultrasonic beam into a subject and receive the reflected waves. an ultrasonic diagnostic apparatus comprising: a means for electronically focusing the ultrasonic beam; and a focusing point moving means for moving the focusing point of the ultrasonic beam in a depth direction,
a probe diameter changing means for changing the diameter of the probe by substantially changing the number of transducers involved in fast waves or wave reception in accordance with the depth of the moving focal point; and moving the focal point. The method is characterized by comprising means for storing data for controlling the operations of the means and the probe diameter changing means, and means for reading out the data and supplying it to the focusing point moving means and the probe diameter changing means. Ultrasound diagnostic equipment. 2 The data storage means is a ROM (Read-Only-
2. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is a memory.