JPH07155322A - Ultrasonic diagnostic system - Google Patents

Abstract

PURPOSE:To adjust the timing of a transmission pulse so that a focal point can be formed correctly on the desired point of a teste body with respect to an ultrasonic diagnostic device equipped with an ultrasonic wave probe which transmits by converting an inputted electrical signal to an ultrasonic wave and outputs by converting a received ultrasonic wave to an electrical signal. CONSTITUTION:Each transmission pulse is transmitted to each ultrasonic vibrator transducer 1 at such a timing that the time difference between a time in the center of pulse width of transmission pulses can be set equal to the difference between a time required for the progression of an ultrasonic pulse between each of plural ultrasonic vibration transducers 1 and a transmission side focusing position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave provided with an ultrasonic probe for converting an input electric signal into an ultrasonic wave and transmitting the same and converting a received ultrasonic wave into an electric signal and outputting the electric signal. Regarding diagnostic equipment.

[0002]

2. Description of the Related Art Ultrasonic waves are transmitted to a subject, especially a human body,
Ultrasonic waves that facilitate the diagnosis of diseases such as internal organs of the human body by receiving the received signals by receiving the ultrasonic waves that have been reflected back by tissues inside the human body and displaying the received signals. A diagnostic device has been used conventionally, and in this ultrasonic diagnostic device, an electric signal is converted into an ultrasonic wave and transmitted into the subject, and at the same time, an ultrasonic wave reflected in the subject is received and converted into an electric signal. An ultrasonic probe is used as the transducer.

FIG. 1 is a perspective view schematically showing an example of an ultrasonic probe, and FIG. 2 is a block diagram showing a circuit connected to the ultrasonic probe. In the lateral direction (arrangement direction, x direction) of FIG. 1, a large number of ultrasonic transducers 1 made of, for example, piezoelectric ceramics (PZT) are arranged in a strip shape, and a common front surface electrically connected to each other on the front surface side thereof. The electrode 1a is formed and grounded. Further, back electrodes 1b that are independent of each other are formed on the back side of each ultrasonic transducer 1, and each lead wire 2 is formed on each back electrode 1b.
Are connected. A matching layer 3 made of epoxy resin or the like corresponding to each ultrasonic transducer 1 is formed on the front surface side of each ultrasonic transducer 1, and the front surface side further has an alignment direction (x direction). ) Is perpendicular to the minor axis (y
The acoustic lens 4 made of silicone rubber or the like is attached to converge the ultrasonic waves transmitted from the ultrasonic probe in the direction). Further, on the back side of the ultrasonic transducer 1, the backing 5 sandwiches the back electrode 1b for the purpose of shortening the waveform duration of the ultrasonic wave and absorbing the ultrasonic wave transmitted to the back side. Is bound to 1.

In order to transmit an ultrasonic wave into a subject (not shown) such as a human body using the ultrasonic probe constructed as described above, each ultrasonic vibration is transmitted from the transmission circuit 6 shown in FIG. Each transmission pulse is sent out to the child 1, and as a result, a burst wave of ultrasonic waves is transmitted from each ultrasonic transducer 1. Here, the transmission timing of each transmission pulse transmitted from the transmission circuit 6 is controlled so that the ultrasonic wave transmitted from each ultrasonic transducer 1 is focused at a predetermined depth in the subject.

FIG. 3 is a diagram showing the relationship between the timing of sending each transmission pulse and the focus position in the subject. As shown, 128 ultrasonic transducers 1_1, 1_2,
, 1_64, 1_65, ..., 1_128 are linearly arranged, and the ultrasonic transducers 1_1, 1_2 ,.
1_64, 1_65, ..., 1_128 are applied to the body surface of the subject, and an ultrasonic pulse is transmitted inside the subject.
At this time, when focusing on the point A inside the subject, the ultrasonic wave transmitted from the ultrasonic transducer 1_1 travels on the straight line connecting the ultrasonic transducer 1_1 and the point A and intersects the arc a. Ultrasonic transducer 1_6 when the point is reached
An ultrasonic pulse is transmitted from 4, 1_65. Thus, in order to focus on the point A, each ultrasonic transducer 1_
1, 1_2, ..., 1_64, 1_65, ..., 1_128
So that the ultrasonic pulses transmitted from the same reach the arc a at the same time, the ultrasonic transducers arranged in the periphery transmit the ultrasonic pulses at earlier timing. Similarly, when focusing on the points B and C, the ultrasonic transducers 1_1 and 1 are similarly set.
, 1_64, 1_65, ..., 1_128, the transmission timings are adjusted so that the ultrasonic pulses simultaneously reach the arcs b and c, respectively.

Incidentally, here, the ultrasonic transducers 1 arranged are arranged.
_1, 1_2, ..., 1_64, 1_65, ..., 1_12
The case where the points A, B, and C on the straight line extending vertically from the center of 8 are focused has been described.
Arranged ultrasonic transducers 1_1, 1_2, ..., 1_6
, 1_65, ..., 1_128 when focusing on a point on a straight line extending into the subject from a position deviated from the center, or arrayed ultrasonic transducers 1_1, 1_2, ..., 1_
The same applies to the case where a point on a straight line diagonally extending from 64, 1_65, ..., 1_128 into the subject is focused.

Further, in the explanation of FIG. 3, 128 ultrasonic transducers 1_1, 1_2, ..., 1_64, 1_6 arranged in array.
Although it has been described that the ultrasonic pulses are transmitted from all 5, ..., 1_128, normally, in one transmission, only 16 ultrasonic transducers arranged, which form a transmission aperture, are arranged. From the ultrasonic pulse. Returning to FIG. 2, the description will be continued.

The ultrasonic waves transmitted from the ultrasonic probe and reflected inside the subject are received by the ultrasonic transducers 1 and converted into received signals. Each received signal is appropriately amplified by each amplifier 7 and then input to the delay adder circuit 8 where the focus is focused on a fixed or sequentially changed depth position in the subject. Delay addition is performed so that they are connected. Regarding reception, each ultrasonic transducer 1_
1, 1_2, ..., 1_64, 1_65, ..., 1_128
The focus of reception within the subject is determined by the pattern of delay of each received signal received in the above, but the focus formation of reception is a well-known technique and is not directly related to the features of the present invention described later. Here, detailed description of the focus formation on the receiving side is omitted.

The reception signal delayed and added by the delay addition circuit 8 is input to a signal processing circuit (not shown), and an image signal representing an image inside the subject by ultrasonic waves is generated based on this reception signal. For example, CR based on the image signal
The image is displayed on the T display device or the like. FIG. 4 is a sound pressure distribution (a) of ultrasonic waves radiated from the arrayed ultrasonic transducers, a sound pressure profile (b) of an ultrasonic beam cross section in the case of the radiated sound pressure distribution, and the radiated sound pressure. It is the figure which showed the beam width (c) of the arrangement direction with respect to the depth direction in a subject in the case of distribution.

As shown in FIG. 4 (a), when an ultrasonic wave of uniform radiation sound pressure is transmitted at both the central portion and the end portion in the transmission opening in the arrangement direction, the ultrasonic beam in the subject is Figure 4
As shown in FIG. 4B, a large side lobe is generated, and as a result, the ultrasonic beam can be finely focused only in the vicinity of the focal point as shown in FIG. 4C, and the beam diameter becomes considerably wide as a whole.

FIG. 5 is a diagram similar to FIG. 4, except that the radiation sound pressure distribution in the arrangement direction is different. As shown in FIG. 5 (a), if the radiated sound pressure at the center of the transmission aperture is increased and the radiated sound pressure at the ends is reduced, side lobes are reduced as shown in FIG. 5 (b). As shown in FIG. 5C, the beam diameter in the array direction can be narrowed down as a whole, and a high-resolution tomographic image can be obtained.

To realize the radiated sound pressure distribution as shown in FIG. 5, there are a method of controlling the amplitude of the transmission pulse applied to the ultrasonic transducer and a method of controlling the pulse width of the transmission pulse. The former method can be expected to have an obvious effect because the amplitude of the transmission pulse is controlled according to a given weighting function. However, since this transmission pulse has a high voltage of, for example, about 100 volts, the amplitude of the pulse is controlled, that is, the voltage. It is not easy to generate different pulses for the transmitter circuit 6 (see FIG. 2).
There is a problem in terms of cost and heat generation of the power supply. The latter method has an advantage that it can be realized only by changing the logic circuit that determines the pulse width while keeping the power supply of the transmission circuit 6 as it is, as disclosed in JP-A-62-38357.

FIG. 6 is a diagram showing the waveform of the emitted ultrasonic wave and its envelope when the duty of the transmission pulse is changed. Here, the duty of a pulse having a pulse width of τ ₀ = 1 / 2.5 MHz, that is, dτ / τ ₀ × 100
(%) Is changed in the range of 3.2% to 50%. It can be seen that the amplitude of the radiated ultrasonic wave changes depending on the duty, and therefore the control of the pulse width of the transmission pulse is effective as a weighting means.

[0014]

However, as can be seen from FIG. 6, when the pulse width is changed, the timing (phase) of the radiated ultrasonic wave is changed along with the change of the amplitude of the radiated ultrasonic wave, and the pulse width of the transmission pulse is changed. The wider and therefore larger the amplitude of the emitted ultrasonic wave, the more the delayed ultrasonic wave is delayed. This delay acts as an error in focus formation on the transmission side described with reference to FIG. 3 and causes a shift in the focus, resulting in deterioration of the resolution of the ultrasonic diagnostic apparatus.

In view of the above circumstances, it is an object of the present invention to provide an ultrasonic diagnostic apparatus in which a transmission pulse is adjusted so that a focal point is correctly formed at a desired point in a subject.

[0016]

An ultrasonic diagnostic apparatus of the present invention which achieves the above object transmits ultrasonic pulses into a subject and receives ultrasonic waves reflected in the subject to receive signals. An ultrasonic probe composed of a plurality of ultrasonic transducers arranged in a predetermined direction, and ultrasonic pulses emitted from the plurality of ultrasonic transducers form a focus at a predetermined position in the subject. As described above, among the plurality of ultrasonic transducers, transmission control means for transmitting each transmission pulse toward the plurality of ultrasonic transducers forming a predetermined transmission opening at each predetermined timing, inside the subject, The inside of the subject based on the delayed addition means for delaying the received signals and adding them together so as to form a fixed or sequentially moving focal point, and the mutually added received signals output from the delayed addition means Disconnection In an ultrasonic diagnostic apparatus including a display unit for displaying an image, the transmission control unit is an ultrasonic transducer arranged in the central portion of the transmission opening toward each of the plurality of ultrasonic transducers forming the transmission opening. The ultrasonic transducers arranged closer to the end of the transmission opening have a narrower pulse width in each transmission pulse, the time difference between the central times of the pulse widths of the transmission pulses, and the plurality of ultrasonic transducers. It is characterized in that it is transmitted at each timing such that the difference between the times required for the ultrasonic pulse to advance is equal between each of them and the above-mentioned predetermined position (transmission side focal position).

In this case, the transmission control means is arranged so that the pulse width T
And then delaying the first pulse signal by time τ (τ ≦ T / 2) and time T−τ, respectively, to generate second and third pulse signals. It is preferable that the transmission pulse to be sent to the ultrasonic transducer is generated by calculating the logical sum of these second and third pulse signals.

[0018]

In the ultrasonic diagnostic apparatus according to the present invention, the time difference between the central times of the pulse widths of the respective transmission pulses is as described with reference to FIG. Since the transmission pulse is transmitted to each ultrasonic transducer at each timing such that the difference between the time required for the ultrasonic pulse to travel between and becomes equal to the difference between them, the focus is correctly focused on the desired focal position. A tied ultrasonic beam is formed, and as a result, the resolution of the ultrasonic diagnostic apparatus is improved.

In generating each transmission pulse, first, a first pulse signal having a pulse width T is first generated, and then the first pulse signal is generated for each time τ (τ≤
T) and time T−τ to generate the second and third pulse signals, and by adopting a method of calculating the logical sum of these second and third pulse signals,
The transmission pulse is generated with a simple circuit configuration.

The principle of the present invention described above will be described below. Here, in explaining the principle of the present invention,
First, the frequency spectrum of the transmission pulse will be described. FIG. 7 is a schematic diagram of a transmission pulse. Generally, a transmission pulse that drives an ultrasonic transducer having a center frequency f ₀ is
A negative (or positive) rectangular wave train having a pulse interval τ (= 1 / f ₀ ) or a rectangular wave train having positive and negative polarities alternately changing at the pulse interval τ / 2. Now, the individual pulse width is dτ
(D: duty (0 to 0.5)), the central angular frequency is ω
_{When 0} (= 2πf ₀ ), the positive pulse wave number is n, and the negative pulse wave number is m (one of n and m allows n = 0 or m = 0), the frequency spectrum of the transmission pulse is ,

[0021]

[Equation 1]

It becomes From the formula (1), the spectrum at the center frequency is

[0023]

[Equation 2]

It becomes Therefore, the amplitude G of the spectrum at the center frequency is

[0025]

[Equation 3]

[0026] The amplitude G varies depending on the positive and negative wave numbers n and m, but if the amplitude when the duty is 50% (d = 0.5) is normalized as G = 1, the following is found between the duty d and the amplitude G: I have a relationship. d = sin ⁻¹ (G) / π (4) The above equation (4) is used to give a transmission pulse having a magnitude of 1.0 at the center and 0.5 at the end of the transmission aperture at the center frequency. Is a duty of 50% (d = 0.5) in the central part,
Duty 16.7% at the end (d = 0.167 = sin
^-1 (0.5) / π) is shown to be good.

On the other hand, the phase φ at the center frequency is φ = −ω ₀ dτ / 2 = −πd (5) Therefore, when the ultrasonic transducer is driven by changing the transmission pulse width, the radiated ultrasonic wave has a delay T proportional to the duty expressed by the following equation.

T = dτ / 2 (∵−ω ₀ T = φ = −πd) (6) The above relationship is one-wave drive (m or n = 0), both-wave drive (m, n ≠ 0) The same applies to both cases.
Therefore, by generating the transmission pulse so that the centers of the pulse widths of the transmission pulse are aligned with each other, it is possible to remove the delay of the radiated ultrasonic wave regardless of the pulse width (amplitude of the radiated ultrasonic wave) of the transmission pulse. .

FIG. 8 is a diagram schematically showing the above relationship. FIG. 8A shows a single transmission pulse, and FIG.
Shows multiple transmitted pulses in case of single-wave drive, FIG.
(C) shows a plurality of transmission pulses in the case of double-wave drive. As shown in FIGS. 8 (a) to 8 (c), by aligning the times of the center of the pulse width of the transmission pulse, radiated ultrasonic waves that are not delayed even if the pulse width of the transmission pulse is changed are generated. be able to.

Although it has been described in FIG. 8 that the centers of the pulse widths are aligned with each other, in order to focus the inside of the subject,
As described with reference to FIG. 3, it goes without saying that the times between the centers of the pulse widths are adjusted so as to correct the difference in the distance between the ultrasonic transducer and the focal point.

[0031]

EXAMPLES Examples of the present invention will be described below. First, a first embodiment will be described with reference to FIG. For a pulse having a pulse width T, a delay line 11 having a delay time τ and a delay time T
A signal having a pulse width of 2τ is taken out by preparing a delay line 12 of −τ, inputting a pulse to each delay line 11 and 12, and ORing the outputs of the delay lines 11 and 12 by an OR circuit 13. You can In addition, this signal is the value of τ (0 ≦
Even if τ ≦ T / 2) is changed, the center of the pulse width always becomes the same time.

The second embodiment will be described with reference to FIG.
For a pulse having a pulse width T, a delay line 14 having a delay time T
Is prepared, a pulse is input to both ends of the delay line 14, and a signal having a pulse width of 2τ is obtained by extracting a signal from the tap 13a corresponding to the delay time τ of the delay line 14. Further, the center of the pulse width of this signal is always the same time even if the value of τ (0 ≦ τ ≦ T / 2) is changed.

By incorporating the pulse width adjusting circuit shown in FIGS. 9 and 10, for example, into the transmission circuit 6 shown in FIG. 2, the pulse width can be varied while the center of the pulse width is adjusted, and the focus of transmission can be adjusted. An ultrasonic diagnostic apparatus with reduced error and high resolution is realized.

[0034]

As described above, according to the present invention, the delay of the transmitted ultrasonic wave which leads to the deterioration of the resolution of the ultrasonic diagnostic apparatus is compensated. Further, the present invention transmits each of the above-mentioned transmission pulses whose pulse width is narrower in sequence as the ultrasonic transducers arranged closer to the end of the transmission opening than the ultrasonic transducers arranged in the central portion of the transmission opening. Therefore, the ultrasonic radiation pressure is easily weighted.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing an example of an ultrasonic probe.

FIG. 2 is a block diagram showing a circuit connected to an ultrasonic probe.

FIG. 3 is a diagram showing the relationship between the timing of sending each transmission pulse and the focus position in the subject.

FIG. 4 is a sound pressure distribution (a) of ultrasonic waves radiated from the arrayed piezoelectric vibrators, a sound pressure profile (b) of the ultrasonic beam cross section in the case of the sound pressure distribution, and the sound pressure distribution thereof. FIG. 6 is a diagram showing a beam width (c) in the array direction with respect to the depth direction in the subject in the case of.

5 is a diagram similar to FIG. 4, except that the radiated sound pressure distribution is different.

FIG. 6 is a diagram showing a waveform of an emitted ultrasonic wave and its envelope when the duty of a transmission pulse is changed.

FIG. 7 is a schematic diagram of a transmission pulse.

FIG. 8 is a schematic diagram showing a single transmission pulse (a), a plurality of transmission pulses in the case of single-wave drive (b), and a plurality of transmission pulses in the case of double-wave drive (c).

FIG. 9 is a circuit diagram showing a main part of the first embodiment of the present invention.

FIG. 10 is a circuit diagram showing a main part of a second embodiment of the present invention.

[Explanation of symbols]

 1 1_1, 1_2, ..., 1_128 Ultrasonic transducer 6 Transmission circuit 11, 12, 14 Delay circuit 13 OR circuit

Claims (2)

[Claims] 1. A plurality of ultrasonic transducers arranged in a predetermined direction for transmitting ultrasonic pulses into a subject and receiving ultrasonic waves reflected in the subject to obtain respective reception signals. An ultrasonic probe, and a predetermined transmission among the plurality of ultrasonic transducers so that the ultrasonic pulse emitted from the plurality of ultrasonic transducers forms a focus at a predetermined position in the subject. Transmission control means for transmitting each transmission pulse to each of a plurality of ultrasonic transducers forming an aperture at each predetermined timing, and each reception for forming a fixed or sequentially moving focus inside the subject. An ultrasonic diagnostic apparatus comprising: delay adding means for delaying signals and adding the signals to each other; and display means for displaying a tomographic image of the inside of the subject based on the mutually added reception signals output from the delay adding means. To The transmission control means is arranged on the end side of the transmission opening with respect to each of the plurality of ultrasonic transducers forming the transmission opening with respect to the ultrasonic transducer arranged in the central portion of the transmission opening. As for each of the transmission pulses whose pulse width is narrower in sequence as the ultrasonic transducers are changed, the time difference between the central times of the pulse widths of the transmission pulses and the plurality of ultrasonic transducers and the predetermined position are An ultrasonic diagnostic apparatus, wherein the ultrasonic pulse is transmitted at each timing so that the difference between the times required for the ultrasonic pulse to advance becomes equal. 2. The transmission control means, after generating the first pulse signal having the pulse width T, outputs the first pulse signal at time τ (τ ≦ T / 2) and time T-τ, respectively.
By delaying, the second and third pulse signals are generated, and the logical sum of these second and third pulse signals is calculated to generate the transmission pulse to be sent to the ultrasonic transducer. The ultrasonic diagnostic apparatus according to claim 1, which is characterized in that.