JPS6384534A - Ultrasonic imaging apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic imaging apparatus that transmits and receives an ultrasonic beam to obtain a tomographic image of a subject.

(Prior art) When an ultrasonic transducer is irradiated onto a subject, an echo returns from a reflector. The time from which this echo originates from the transmitting transducer is expressed by the following equation.

t-2d/v...(1)
However, d...distance to the reflector ■...speed of sound In equation (1), if the depth d of the reflector changes, the time t also changes, and therefore the echo vibrations returning from different depths. Since the time from the time of transmission of the ultrasonic wave is different, if you observe this on a CRT (cathode ray tube) monitor by subtracting n with the horizontal axis as the time axis and modulating the brightness with a Nicol oscillator, you can see that the time of the ultrasonic oscillator is different. A tomographic image of a plane parallel to the irradiation direction is obtained. This is called a B-mode image.

(Problem to be solved by the invention) However, since the B-mode image is also a cross-sectional view of the object in the depth direction, if there is a convergence point of the ultrasound beam at a certain depth, the B-mode image is a cross-sectional view of the object at a depth different from that depth. The echo image becomes out of focus,
The image becomes blurred and becomes a tomographic image that does not clearly show the surrounding area. Furthermore, the ultrasonic transducer that is reflected from deep inside the object and returns has different resolution depending on location due to variations in beam width and propagation attenuation, causing problems in image quality such as shading. Furthermore, since the conventional apparatus can only obtain one cross-sectional Wi image at a time, it is difficult to grasp the three-dimensional shape, size, and positional relationship of the reflector. In order to obtain an image in focus over the entire screen, a C-mode image can be obtained based on echoes from a depth that coincides with the convergence point of the ultrasound beam, but conventional C-mode images focus the ultrasound beam on two Since the image is obtained by scanning each point of a dimensional matrix and displaying the intensity of the echo from each point in two dimensions, the image contains a lot of speckle noise.

The present invention has been made in view of the above points, and its purpose is to prevent i! The object of the present invention is to realize ultrasonic imaging If that can obtain a tomographic image without deterioration of the image.

(Means for Solving the Problems) The present invention, which solves the above problems, provides an ultrasound imaging apparatus that transmits and receives ultrasound beams to obtain tomographic images of a subject, and includes a plurality of ultrasound transducers. , an ultrasonic probe that transmits and receives a flat fan-shaped ultrasonic beam in the scanning direction, means for reciprocating the fan-shaped beam in a direction perpendicular to the plane of the fan, and maintaining a relationship perpendicular to the plane of the fan. means for sequentially changing the scanning direction of the ultrasonic beam while the ultrasonic beam remains in the same position; means for selecting data at an arbitrary depth of the received echo signal; 15i image reconstruction means for reconstructing the image.

(Function) The transmitted beam is scanned by the Si-wave probe that transmits the fan-shaped beam.Ill 1D The tIIID of one circuit scans the transmitted beam in the direction perpendicular to the fan surface, and the beam is superimposed while maintaining the perpendicular relationship to the fan surface. The scanning direction of the acoustic beam is changed sequentially. Receive echo signals from the reflector for each scan, obtain echo signals at a predetermined depth using a range gate, and based on that, image reconstruction vR
A C-mode image is reconstructed according to the position. By providing range gates at multiple points, multiple C-mode images with different depths are obtained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic block diagram of an embodiment of the present invention. In the figure, 1 is an ultrasound probe that sends ultrasound to the subject in front and performs sector scanning to receive echoes from a reflector, with multiple ultrasound transducers arranged in a linear array. It has a structure. 2 is a probe rotation mechanism that rotates the ultrasound probe 1 within the plane of the ultrasound transducer array; 3 is a scan control M+! that controls the probe rotation mechanism 2 and the sector scan control circuit 4; ! At step S, the control unit 5 controls the rotation angle of the ultrasound probe 1 and the sector angle of the sector scan. 6 is the sector scan 1IIlt
I! 1 This is a transmitting/receiving unit that receives a control signal from circuit 4, electrically beam-steering and focusing the transducer ultrasonic wave, and transmits it, and also receives an echo signal that returns from that direction and processes the signal. .

Reference numeral 7 denotes a range gate for collecting a received echo signal on a surface at a predetermined depth perpendicular to the wave transmission direction, and allows the received signal at the time of generation of the range gate vibrator to pass therethrough. The received echo signal that has passed through the range gate 7 is converted into a digital signal by an AD converter 8. Reference numeral 9 denotes an image reconstruction device that takes in the received echo signal converted into a digital signal and reconstructs a C-mode image, which is a tomographic image of a plane perpendicular to the wave transmission/reception direction, by image reconstruction calculation similar to computer tomography. Then, the rotation angle and sector angle of the projection data necessary for reconstruction are given from the control section 5 to reconstruct a C-mode image, and the C-mode image is displayed on the image display device 10.

Next, the operation of the embodiment configured as described above will be explained.

In response to a command from the control unit 5, the fogging scan control unit 3 causes the sector scan control circuit 4 to transmit and receive ultrasonic sector scans by the transmitting/receiving unit 6 and the ultrasound probe 1, and also performs the scanning. The ultrasonic probe 1 is rotated by controlling the probe rotation mechanisms.

The ultrasonic transducer transmitted from the ultrasonic probe 1 becomes an ultrasonic beam having the following shape. That is, the beam is converged in the sector scan direction by the delay circuit built in the transmitter/receiver 6, but forms a fan beam that spreads out in a fan shape in a plane perpendicular to the sector scan direction. The shape of this ultrasonic beam is shown in FIG. In the figure, θ indicates the range of the sector in which the ultrasonic beam is returned, and is an angle with respect to the front direction of the ultrasonic probe 1. φ is the spread angle of the fan beam and is in a plane perpendicular to the sector scan direction.

In other words, a fan with a spread angle φ scans a range of angles θ from the front of the ultrasonic probe 1 to the left and right.

The echo signal from the reflector caused by the ultrasonic beam is received by the ultrasonic probe 1, amplified and detected by the transmitter/receiver 6, and input to the range gate 7. In the range gate 7, only data at a depth F shown in FIG. 2 is allowed to pass through the received echo signal, for example. Therefore, by sector scanning of the fan beam ultrasound, data about the spherical region 20 as shown in FIG. 1 by one transmission and reception of sound waves
9 represents the area of data to be displayed. The following area 20 is the data surface. Reference numeral 21 denotes a portion of a cylindrical or spherical reflector cut by the data surface 20. The echo signal intensity for this reflector 21 is obtained by adding all the echo signals within each rectangular area, so that it becomes as shown in the lower graph of FIG. 3. Such data corresponds to projection data in X-ray CT, etc., so the ultrasound probe 1 is rotated over 180 degrees or 3600 degrees, data on the echo intensity in the stomach at each angle is collected, and these data are combined with By reconstructing the image based on the computed tomography method, a tomographic image of the reflector 21 is obtained. An image reconstructed by computer tomography becomes a good image without speckle noise due to the averaging effect of the projection data.

FIG. 4 shows an example of the waveform of the range gate oscillator that corresponds to the data plane 20 in FIG. This is a range gate vibrator generated at 7. The distance tF between the range gate vibrator 23 and the reverse wave vibrator 22, which are set at the depth F, is expressed by the following formula, similar to the formula (1).

tp-2F/v In FIG. 3, the thickness D of the data surface 20 corresponds to the transducer width of the range gate transducer 23.

, if the range gate 7 collects the received signal at the depth F as described above, m@reconstruction device 1i29 generates Xl
Parallel xI in l1CT! A hyperwave image on a spherical surface having a depth F is reconstructed by a reconstruction method of projection data using a beam, for example, a filtered pack projection method. This reconstructed image is displayed on the image display device 1o.

Here, the reconstructed image is the range gate oscillator 2 shown in FIG.
The time corresponding to the depth F given by 1.3. Since it is calculated from a collection of intensity data of received echo signals, the range gate oscillator is
By creating a plurality of even images such as a, 23b, and 23c, it is possible to easily obtain a plurality of reconstructed images having different depths. In this case, the depths of the plurality of range gates are preferably set within the range of the focal depth of the ultrasound beam.

Between the above bags, the measurement area of the projection data obtained by fan beam sector scanning (q) is rectangular, as is clear from FIG. FIG. 6 shows changes in the measurement area when the probe rotating machine 4'! The measurement area changes at each rotational position.For this reason, complete projection data can be obtained within the inscribed circle of the square measurement area 24. In this case, only incomplete projection data are collected, and reconstruction theory cannot guarantee a correct reconstructed image.This effect causes shading and
It appears as a 121 degree shift. In order to reduce this influence, image reconstruction may be performed by applying weighting to the projection data as shown in FIG. 7, for example. In the figure, if the scan angle is plotted on the X-axis and the weighting is plotted on the y-axis, and the normalized scan range is set between 1 and -1 on the X-axis, the shape of the river is semicircular and can be expressed by the following equation. expressed.

As mentioned above, by applying the method of computer tomography, it is possible to obtain a C-mode image formed by received echo signals at the same distance from the ultrasound probe, which is the transmitting I source. As a result, it has become possible to obtain an image without deterioration in image quality due to defocus due to differences in distance from the sound source, shading due to changes in attenuation amount, or speckle noise.

Note that the present invention is not limited to the above embodiments. For example, the rotation of the beam was done by mechanically rotating the ultrasound probe using a probe rotation mechanism, but the ultrasound probe's ultrasound beams were arranged in a matrix and electrically controlled to rotate the ultrasound probe. can be done.

It is also possible to perform sector scanning mechanically.

Also, since scanning is performed using the sector scan method, projection data can be obtained on the same curved surface even if the probe is rotated, but if the tomographic plane is far away from the ultrasound probe, sector scan Alternatively, even if a linear scan or convex scan method is used, an m-sectional image can be reconstructed because the deviation of the curved surface due to the rotation angle is small. Furthermore, image quality can be improved by introducing XICT techniques such as overscanning to prevent the effects of movement during measurement and the introduction of a quarter offset method to increase spatial resolution.

Furthermore, the range gate was performed using a range gate oscillator, but when reconstructing the image in the image reconstruction device, the range gate was programmed to take data from the point of depth F and the range was set using software. A gate may be provided.

(Effects of the Invention) As described above in detail, according to the present invention, a novel C-mode ultrasonic imaging apparatus applying the method of computer tomography is provided.

By providing multiple range gates in this 1iffi, multiple C-mode ultrasound images can be obtained at the same time, making it easy to understand the three-dimensional shape of the reflector from these images, which is useful for practical purposes. The effect is great.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an embodiment of the present invention, and FIG.
The figure shows the shape of the ultrasound beam, Figure 3 shows the shape of the data surface obtained by scanning the transmitted ultrasound and setting the range gate, Figure 4 shows the waveform of the range gate transducer, and Figure 5 shows the shape of the data surface obtained by scanning the transmitted ultrasound and setting the range gate. The figure is a waveform diagram when multiple range gate oscillators are provided, Figure 6 is an explanatory diagram of changes in the measurement area when the rectangular data surface is rotated, and Figure 7 is the sag applied to the image reconstruction device. FIG. 1... Ultrasonic probe 2... Probe rotation mechanism 3
...Scan control section 4...Sector scan control circuit 5...Control section 6...Transmission/reception section 7...
Range gate 8 - AD converter 9... Image reconstruction device 10... Image display device 20... Data surface 21... Reflector 22... Transmission oscillators 23.23a, 23b, 23c ...Range gate transducer 24.24a...Measurement area Patent applicant Yokogawa Medical Systems Co., Ltd. Figure 2 Scan axis 1; M-sonic probe θ; Sector angle (one side) φ; Beam spread angle α: Probe rotation angle F; Depth 2o; Data surface 21, Reflector 4th figure 22: Hosin oscillator 23, Range gate oscillator 5th figure η, Transmission nogle 7 illusion, Z3b, 23c, ' Range gate Oscillator Figure 6 24.24a; row 1 constant area 7th section?

Claims (2)

[Claims] (1) Ultrasonic imaging equipment that transmits and receives ultrasonic beams to obtain tomographic images of a subject. a sonic probe, means for reciprocally scanning the fan-shaped beam in a direction perpendicular to the plane of the fan, means for sequentially changing the scanning direction of the ultrasonic beam while maintaining a perpendicular relationship to the plane of the fan, and a receiving echo. The method further comprises: means for selecting data at an arbitrary depth of the signal; and image reconstruction means for reconstructing an image from the data obtained by the data selection means using a computer tomography technique. Features of ultrasonic imaging equipment. (2) The means for selecting data selects a plurality of data sets having different depths, and the image reconstruction means obtains a plurality of images based on the plurality of data sets. The ultrasonic imaging device according to item 1.