JPS6237982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic apparatus with improved signal-to-noise ratio.

Ultrasonic waves are transmitted to the subject, the ultrasound echoes reflected from interfaces with different acoustic impedances within the body are received, and the reflected echoes are used to display tomographic images of the subject's internal tissues on a display device such as a CRT. death,
Ultrasonic diagnostic apparatuses that perform medical diagnosis using these displayed images are generally in widespread use. Therefore,
The image quality of the ultrasound tomographic image displayed on the display device must be good. A factor that affects the quality of this ultrasound image is the problem of the SN ratio of the device.
When ultrasound is transmitted into a living tissue such as a subject, reflected waves from interfaces with different internal acoustic impedances are attenuated due to absorption by the internal tissue and spherical diffusion of the ultrasound beam, and the signal component becomes smaller. , Therefore, the signal-to-noise ratio deteriorates, and the image is adversely affected. In addition, noise from each electrical device and component that makes up the ultrasound diagnostic device, or white noise from external lighting equipment, power supply, etc., can also be detected by SN as described above.
This will have a negative impact on the ratio. In order to improve this signal-to-noise ratio, conventional ultrasonic diagnostic apparatuses have been devised in various ways. For example, there are considerations such as adopting a special circuit for the reflected wave receiving amplification section, and consideration when actually assembling electrical components. Furthermore, when selecting individual electrical components, there is a drawback in that each electrical component must be selected with a good signal-to-noise ratio.

In addition, by increasing the power of the transmitted ultrasonic pulse, the power of the ultrasonic echoes reflected from inside the object will naturally increase, and thus it is possible to improve the S/N ratio. It is not preferable to increase the power of the transmitted ultrasonic pulse due to safety considerations for certain human bodies.

In order to solve the above-mentioned drawbacks, the present invention includes a plurality of storage devices to sequentially store image information based on reflected waves from inside the subject without increasing the power of the transmitted ultrasound pulse, and output it to a display device. Sometimes,
The present invention provides an ultrasonic diagnostic device that improves the SN ratio by superimposing information stored in each storage device.

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

In FIG. 1, a reference signal of a constant period is received from an oscillator 1, and a driving pulse is outputted to drive a vibrator (not shown) placed on the contact surface of the probe 2 to the subject. A transmitter/receiver circuit 3 that receives ultrasonic echoes from inside the object and performs processing such as detection.
, an amplifier circuit 4 that amplifies the output from the transmitter/receiver circuit 3, an SN ratio improvement circuit 5 that receives the output from the amplifier circuit 4 as input, and improves the SN ratio; A display device 6 is shown that displays an ultrasonic tomographic image with an improved signal-to-noise ratio.

FIG. 2 shows a specific configuration of the SN ratio improvement circuit 5, which receives an output signal from the amplifier circuit 4 at an input terminal 51 and sends this signal to a storage device selection switch 52 (hereinafter abbreviated as "selection switch"). The signal is transmitted to n frame storage devices 53 connected in parallel. This frame storage device 5
The operation control of No. 3 is performed by the control device 54,
It outputs operation commands for each frame storage device 53, that is, write and read command signals.
Further, all n frame storage devices 53 are connected to an adder 55. The output of the adder 55 is supplied to the display device 6 via the output terminal 56, and displayed on the display device 6 as an ultrasound tomographic image.

Next, the operation of one embodiment of the present invention will be described with reference to FIGS. 3, 4, and 5.

In FIG. 3, a large number of ultrasound echo information inside the subject detected by the ultrasound probe 2 are arranged on the contact surface of the ultrasound probe 2 (for example, an electronic scanning linear probe) to the subject 7. vibrator 21
are sequentially driven electronically to produce m ultrasonic beams 22.
The position of the echo source is detected by the reflected waves from the inside.

In this case, the scanning by the ultrasonic beam 22 is performed (1) sequentially starting from the beam number shown in the diagram. Do this sequentially n times like this. One frame of image information is obtained by this one scan, and each frame of image information is synchronized with the scanning of the ultrasonic beam 22, and the one frame of image information is sent to each of the SN ratio improvement circuits 5 in FIG. 1 using the same scanning method. Write to frame storage device 53. Therefore, one frame of image information obtained by scanning with the ultrasonic beam 22 sequentially transmitted from the i-th ultrasound probe 2 to the i-th frame storage device 53 is stored in the i-th frame storage device 53.

(2) Perform the operation of repeating the indicated beam number n times in succession for each beam number m times. That is, Performing such scanning with an ultrasonic beam,
The obtained image information is stored at a position equal to the ultrasound beam number in the frame storage device 53 whose number is equal to the number of scans of each ultrasound beam 22.
That is, the information obtained by the j-th scan of the ultrasound beam number i is sequentially stored in the i-th position of the j-th frame storage device 53.

The difference between the ultrasonic beam scanning methods (1) and (2) is the time required for echo information from the same region to be stored in all n frame storage devices 53. If the scanning time of one scanning line is t, then
According to method (1), it becomes (n-1) mt, and according to method (2), it becomes (n-1) t. Therefore, in the case of method (2), the error due to temporal fluctuations of the same echo source becomes smaller, and it can be said that method (1) is more advantageous than method (1).

When writing to all n frame storage devices 53 is completed by the methods (1) and (2) described above, the stored contents of the frame storage device 53 are read out to the adder 55. In this case, the echo source inside the human body, that is, the position of the echo, changes over time very slowly and is negligibly small compared to the time required for all the n frame storage devices to store information. If so, the contents of each frame storage device are considered to be substantially the same, and therefore, the adder 55
The image information signal outputted from the image information signal is obtained by superimposing information of approximately the same content corresponding to the number of n frames.

In contrast, noise is voltage (current) that changes completely irregularly, and when expressed as a function of time, en
(t), and when this is expressed as a root mean square value, it becomes 1/T∫ ^T ₀ en ² (t) dt=En ² ...(1). Here, T is a sufficiently long time compared to the average period of the noise. En is the effective value of the noise voltage en(t).

Therefore, independent noise voltages arising from completely different causes in each of n frames are expressed as E _o1 , E _o2 ,
.... E _on , the noise voltage E _o0 superimposed by the adder 55 is E _o0 ² = E _o1 ² + E _o1 ² + ... + E _on ² ... (2) where the noise source is If they are the same, E _o1 ² = E _o2 ² =...=E _on ² ...(3), and therefore the second equation is E _o0 ² = nEn ² i...(4) Therefore, E _o0 =√E _oi (1≦i≦) (5) This indicates that the noise component of the output signal of the adder 55 is √ times the arithmetic component of each frame. On the other hand, the output signal E _s0 from the adder 55 on which the signal components in each frame are superimposed is:
It is n times the signal component E _si of each frame, and E _s0 = nEsi (6) Therefore, the SN ratio of the output signal of the adder 55 is
E _s0 /E _o0 is from equations (5) and (6) becomes. As shown by this, the signal-to-noise ratio of the signal input to the input terminal 51 is considered to be E _Si /E _oi , and is therefore improved by a factor of √ compared to the conventional device.
As a result, the image quality is improved, and as described above, a static ultrasonic tomographic image at an arbitrary time phase can be obtained.

Next, using multiple frame storage devices as in the present invention, in addition to displaying static ultrasound tomographic images with an improved SN ratio as described above, ultrasound images inside the subject can be displayed in real time with an improved SN ratio. It is also possible to display tomographic images.

In FIG. 2, the selection switch 52 is sequentially switched every frame period, and the frame storage device connected to the input terminal 51 by the selection switch 52 reads the already stored information to the adder 55. At the same time, an amount of information corresponding to the next new frame is written, and the other frame storage devices 53 in the OFF state simultaneously read out the stored contents to the adder 55. By sequentially repeating these operations, the storage contents of each frame storage device 53 are superimposed in the adder 55,
As mentioned above, the SN of the output signal from the adder 55
The ratio is improved by n times compared to that of the input signal, and at the same time, it becomes possible to display a tomographic image inside the subject in real time. In this case, as described above, it is assumed that the variation over time of the echo source is negligibly small compared to the n frame period.

FIG. 4 shows another embodiment, and 51 is an amplifier 4.
Input terminal 51, an input terminal that receives an output signal from
Resistors serving as signal dividers 58, 58 are connected to the signal dividers 58, 58, and a frame storage device 57 having an addition function is connected to an intermediate connection point between the signal dividers 58, 58. 56 is an output terminal. The echo information signal equivalent to one frame from within the subject inputted from the input terminal 51 is divided by signal dividers 58 and 58 to keep the signal amplitude below the allowable signal amplitude of the storage device, and is stored in the frame addition storage device 57. At the same time, the signal is added to the next input frame information and stored, and the same operation is repeated for an arbitrary number of frames in subsequent frames. If the signal amplitude that can be stored in the frame storage device 57 having the addition function is sufficiently large, the signal dividers 58, 58 are not necessary.

Still another embodiment is shown in FIG.
is connected to one input terminal of the adder 59, and is connected to the other input terminal of the adder 59 via frame storage devices 60 and 61 connected in series from the output terminal of the adder 59. Further, the output end of the adder 59 is connected to an output terminal 56 to a display device. The image information signal corresponding to one frame input from the input terminal 51 is added and outputted by the adder 59 with the signal stored in the frame storage device 60, and this addition output signal is outputted by the adder 59.
1, and immediately before new frame image information is input from the input terminal 51, the frame storage device 6
The stored contents of 1 are transferred to the frame storage device 60, and the contents of the frame storage device 61 are updated with the output of the adder 59. As in the previous embodiment, an appropriate number of frames of image information signals are added and then output to the display device 6. In this way, as described above, the SN ratio of the output signal to the display device is improved by the square root of the number of addition operation frames. Therefore, the quality of the image displayed on the display device is improved.

Further, in FIG. 5, when one frame is composed of m scanning lines, the frame storage device 60 has a storage capacity equivalent to one frame, and the adder 59 stores the storage capacity. A signal corresponding to one scanning line in one frame stored in the device 60 is added, the added signal corresponding to one scanning line is temporarily stored in the storage device 61, and then the signal corresponding to one frame in the storage device 60 is stored. Among the information, the information in the portion corresponding to the scanning line stored in the storage device 61 is updated. By sequentially repeating such operations for each scanning line, the storage device 61
The storable capacity of is sufficient to be equivalent to one scanning line, and a small capacity is sufficient.

Further, in the case of FIG. 5, if the storage device 60 can perform writing and reading at the same time, the storage device 61 is unnecessary.

As stated above, according to the present invention, echo information obtained by transmitting and receiving ultrasound waves multiple times is added and displayed as a single ultrasound beam.
Images with excellent signal-to-noise ratio can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the ultrasonic diagnostic device of the present invention, Fig. 2 is a diagram showing a specific configuration of a circuit for improving the SN ratio of the above device, and Fig. 3 is a block diagram of an embodiment of the ultrasonic diagnostic device of the present invention. FIGS. 4 and 5 are diagrams showing a scanning method using an ultrasound beam of an ultrasound diagnostic apparatus, and are diagrams showing other embodiments of the present invention. 2...Ultrasonic probe, 5...SN ratio improvement circuit, 52...Storage device selection switch, 53, 6
0, 61...Storage device, 54...Control device, 5
5, 59...addition device, 57...memory addition device.

Claims (1)

[Claims] 1. An ultrasound probe that transmits an ultrasound beam in a predetermined direction inside a subject and receives echoes from interfaces with different acoustic impedances in the subject along the predetermined direction; In the ultrasonic diagnostic apparatus, the ultrasonic diagnostic apparatus includes a transmitting/receiving unit that scans, and a display unit that displays echo signals received by the ultrasonic probe in correspondence with the scanning of the ultrasonic beam. A storage means for storing each echo signal obtained by transmitting an ultrasound beam a plurality of times, an addition means for adding each echo signal stored in this storage means, and the added echo signal is an ultrasonic wave. An ultrasonic diagnostic device characterized by displaying information corresponding to beams.