JPS61173386A - Ultrasonic diagnosing device - Google Patents

Abstract

PURPOSE:To reduce image strain and improves S/N by changing the cutoff frequency of the interpoltive function in dependence upon the magnitude of the power of resolution relative to the sampling period. CONSTITUTION:The ultrasonic waves are transmitted from an ultrasonic probe 1 into an object, the received signals are received at 3, added at 4, detected at 5 and taken in at a buffer memory 7A through an A/D converter. In the memory 7A, polar coordinate addresses of echo data are converted into rectiangular coordinate addresses and, in a register group 7B, echo data of picture element units and converted address data are taken from the memory 7A. In a subtractor 7C, differential data from sample lattice points are given as addresses to a ROM7D. The coefficient data showing optimum filter characterstics are selected. The echo data are multiplied in a multiplication unit 7E and the echo data are added by adders 7F, 7G. These added data are processed by a normalizing arithmetic unit 7H and written into a frame memory 71 so as to be displayed in the display system.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an ultrasonic diagnostic apparatus that obtains ultrasonic tomographic images by transmitting and receiving ultrasonic waves by sector scanning. The present invention relates to an ultrasonic diagnostic apparatus designed to reduce distortion and improve 87N.

[Technical background of the invention and its problems]

A so-called sector-scanning ultrasonic diagnostic device obtains an ultrasonic tomographic image by controlling the transmitting and receiving phases of a group of ultrasonic transducers so that the transmitted and received ultrasonic waves are scanned in a fan shape. . In the ultrasonic transmission and reception system for sector scanning,
The reflected sound field distribution whose information is collected is expressed in a polar coordinate system (r, θ), and in the image display system, pixels displayed as an image are expressed in an orthogonal coordinate system (x, y). Therefore, the polar coordinate system (r,
If we try to express the information expressed by the polar coordinate system (rlθ) in the orthogonal coordinate system (x, y), a positional shift will occur as shown in Figure 5 (,), and the information expressed in the polar coordinate system (rlθ) will be expressed in the orthogonal coordinate system (x, y). So-called pixel distortion occurs in the system (z+y), and biological information cannot be expressed correctly.

As a method to eliminate such problems, the fifth method has traditionally been used.
The methods shown in FIG. 5(b) and FIG. 5(c) are used.

That is, in FIG. 5(b), the data of the sample point in the polar coordinate system (r, θ) is directly assigned to the nearest position in the orthogonal coordinate system (x, y). According to this method, errors in the shaded areas in the illustration do not occur, and although the pixel distortion in the above image can be resolved to some extent, errors in the shaded areas in the illustration occur, and it is far from perfect. .

On the other hand, in FIG. 5(c), data at a display point in the orthogonal coordinate system (x, y) is calculated from multiple data of surrounding sample points in the polar coordinate system (1"lθ), For example, the calculation formula shown below is used.

m+n m, n are integers. According to this method, the error can be eliminated to the extent of kana, but in the case of m))n, y#xk. Therefore, although pixel distortion is eliminated, the S/N ratio, which is directly related to the displayed image, is not improved, and an improvement has been desired. [Objective of the Invention] The present invention was made based on the above circumstances. The purpose is to provide an ultrasonic diagnostic apparatus that can reduce pixel distortion in i-ma and sector scanning and improve 8/N.

[Summary of the invention]

In order to achieve such an object, in the present invention, ultrasonic waves are received to the subject by sector scanning, the obtained received signals are added, and the added signal is detected to detect the tomographic image of the subject. An A/D that digitizes the detected signal in an ultrasonic diagnostic device that obtains image information and displays the image.
converting means, and converting the echo data for each pixel of the polar II reference system by the sector scanning output from the A/D converting means and the polar coordinate system address of this echo data from an orthogonal coordinate system address to an orthogonal coordinate system address. a buffer memory in which nine converted address data are written to the same address; and a means for determining the converted address data of this buffer memory (base sound field 14 turns);
a second means in which coefficient data indicating a plurality of filter characteristics is stored in advance and coefficient data is selected based on the sound field pattern data from the first means; and coefficient data selected by the second means. a third means for multiplying the corresponding echo data by the corresponding echo data; a fourth means for setting the sum of the coefficient values of the echo data group output from the means of M3 to 1; The present invention is characterized by comprising a frame memory that captures the echo data for each pixel outputted from the means of item 4 and generates frame image data to be displayed.

[Embodiments of the invention]

First, prior to a detailed explanation of the present invention, the principle of the present invention will be explained.

That is, in general, to reproduce the original image from the % sample value, convolution of the interpolation function (Convol) is performed as shown in the following equation (1).
utlon).

Next, when the sample points of the polar coordinate system (r, θ) of sector scanning are reproduced as the original image on the frame memory of the display system, what is the meaning of each variable in the above equation (1)? I will explain about it.

When the above equation (1) is converted into an equation of the polar coordinate system (r, θ), the following equation (2) is obtained.

In the above equations (1) and (2), /(x,y)J'(r+θ) are the original image data and f
(mX r nY ) + f (mR + nθ) are sample value data, g (x-mX, y-nY) + g (
r-mR+θ-nθ) are interpolation functions, and r and θ are y-y, respectively, for the orthogonal coordinate system (x, y) K on the frame memory, as shown in FIG. 1 (,).

As shown in Figure 1(b), R2O has a polar tilt system (r+
θ) is the basic unit and spatial sampling period.

The interpolation function in the above is a real space expression of the frequency characteristics of the filter, and is the coefficient of the digital filter itself.

When the above equation (2) is Fourier transformed, it becomes the following equation (3).

Here, Q=Rθ.

In order to completely reproduce the original image, the frequency characteristics of the interpolation function are required to be flat, and it is necessary to satisfy the following formula (4): G (u, ma) = Q = R θ (4) In the above, in order to completely reproduce the original image, it is necessary that the frequency characteristics of the interpolation function be flat, but the flat bandwidth does not need to span the entire band. You can set it as follows. In other words, it is sufficient to apply filter characteristics of an interpolation function that has a bandwidth sufficient to express the original image.
Specifically, as shown in Fig. 2(a), for the original image F1 with a wide band, interpolation function 01 having a wide rectangular window is selected, and as shown in Fig. 2(b), the band Original image F with narrow
For b, an interpolation function Gb having a narrow rectangular window may be selected.

Here, in order to reproduce the original image in its perfect form, it is sufficient to select an interpolation function of a rectangular window with a bandwidth equal to the sampling frequency, but in this case, it is necessary to narrow the bandwidth of the rectangular window. By cutting extra frequency components, the S/N is
This makes it possible to improve the

When the above formula (4) is inversely transformed into 7-IJ, the following formula (5) is obtained.
become that way.

Figure 3 (a) and (b) illustrate the above equation (5), which correspond to Figures 2 (,) and (b), respectively. The bandwidth is widened, images are sufficiently averaged, and noise can be reduced. Moreover, since the cutoff frequency u(, maC) exists outside the band of the original image, the original image will not be dulled.Also, in sector scanning, it is independent of the position in the polar coordinate system (r, θ). Assuming that the magnitude of the spread function does not change much in , the spatial frequency characteristics of part A in Fig. 1(a) are low as shown in fs2 Fig. 1(b) K, and the first
The spatial frequency characteristics of section B in Figure (a) are shown in Figure 2 (a).
).

Therefore, in sector scanning, the frequency characteristics of the original image vary greatly depending on the position, so the width of the rectangular window can be made narrower, and the degree of S/N improvement can be increased.

Therefore, whereas in the past, writing processing to pixels on the rask and interpolation processing to empty pixels that were not written at that time were performed separately, in the present invention, the raw echo is stored in the frame memory. Rather than writing data, it performs the processes listed below.

(1) Write the result obtained by performing a convolution operation between the interpolation function and the sample value of the echo data for all pixels in the frame memory (corresponding to equation (2)).

■ The interpolation function in ■ is a function expressed by the above equations (4) and (5).

(2) The cutoff frequency of the interpolation function is changed according to the spread function, that is, the size of the resolution relative to the sampling period, to improve the S/N ratio.

Here, the data written to the frame memory is expressed by the following equation (6) using the echo data xk and the coefficient ak.

Here, in the vicinity of the writing point, a. It is necessary to set the value close to K. If the sound field is small, ak/l10 cannot be set to a very large value, and the above-mentioned interpolation function filter has a bandwidth sufficient to express the original image. There are many cases where you just need to apply the characteristics.

Next, an embodiment of the ultrasonic diagnostic apparatus according to the present invention based on the above principle will be described with reference to FIG.

In FIG. 4, reference numeral 1 denotes an array type ultrasonic probe for sector scanning, for example, which is made up of a plurality of ultrasonic transducers arranged in parallel. 2 is a transmitter that applies delayed excitation pulses to each transducer of the probe I in sector scanning.

A receiver 3 has a reception delay amount set corresponding to the excitation delay amount of the transmitter 2, and receives reception signals in sector scanning from each transducer of the probe 1. Reference numeral 4 denotes an adder that adds the received signals from each vibrator outputted from the adder 3. A detector 5 detects the added reception signal from the adder 4 and obtains one raster worth of tomographic image information in the sector scan.

6 is an analog-to-digital converter (A/D-C) that converts the output from the detector 5 from analog to digital.

7 is DigItal 5can Convert which converts tomographic image information (echo data) digitized by A/D-C1f from ultrasound scan to TV scan.
r (D, S, C), the details of which are configured as follows.

That is, these n, s, c 7 are orthogonal Fil! pixel-by-pixel echo data and its polar coordinate system address for each raster. Parameter memory group (BM) 7A that converts it into a standard address and takes in the converted address (lower several bits and upper several bits below the decimal point), and echo data in pixel units from this 8M7A and its conversion address. A register group (Ram) 7B that sequentially takes in data, a subtractor (Rub) 7C that calculates the difference between the previous and current address data that was not taken into this Ram 7B, and the output of Sub 7C. A read-on memory (ROM) 7D selects one of the pre-stored coefficient data indicating the filter characteristics using the address , and the echo data is multiplied ( A multiplier (Con) 7r that performs convolution), an adder (Add) 7F that adds echo data from multiple modalities that have been subjected to convolution processing by this Con7g, and an adder (Add) that adds only coefficients from multiple modalities. ) 7 G and this Add
7F and 7G are processed so that the added value of the coefficient becomes 1 (normalization arithmetic unit (Nor) 7
H, a frame memory (FM) 71 that generates the normalized echo data from this Nor 7 H as one frame of hate data to be displayed, and an address setter 7J for address conversion in the 8M7AK. Sob 7
The at L/S assignment of C and FM 71 is made up of the address setter 7 and the like.

8 is a display system consisting of a CRT (cathode ray tube) or the like for displaying one frame of a tomographic image generated by FM71.

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

That is, when the transmitter 2 is activated, the ultrasonic probe 1 is excited to perform sector scanning, and ultrasonic waves are transmitted into the subject (not shown), the received signal is received by the receiver 3, and the adder 4 ,
The detector 5 takes in digitized echo data D, S, and C74C via the A/D-C6.

In the 8M7A of D, S, and C7, the echo data in pixel units and the conversion address obtained by converting the polar coordinate system address of the echo data to a rectangular coordinate system address using the address setting device 2J are sequentially taken in, and then the R557B Then 8
The echo data and conversion address data in pixel units are sequentially fetched from M7A.

Sub 7 C calculates the difference between the address of the pixel to be written, which is taken into Res 7 B, and the address of the sample grid point, and reads out the difference data to ROM 7 D while making it correspond to the address set by the address setter 7K. Give it as an address. Here, the above conversion address is given to determine the sound field/mother turn, and coefficient data indicating appropriate filter characteristics is selected from this sound field pattern button. And ROM7D
Multiply (convolve) the coefficient data selected by % Can 7 K with the echo data for each pixel,
The F-data from the plurality of systems subjected to convolution processing by this Con7HIC is added to Add7F and Add7G.

The addition data from Add7F and 7G is N
or7H performs arithmetic processing so that the added value of the coefficient becomes 1, and writes each to the orthogonal coordinate system address of FM71 while corresponding to the address by address setter 7K, a frame image is generated, and the image is displayed on display system 8. Ru.

As described above, according to this embodiment, A/D-(:, 6
Don't just write the echo data from S, C7 to 7M71 (for all pixels of 7M71,
The result obtained by performing a 9-convolution operation on the coefficient data and echo data indicating the filter characteristics by the interpolation function is written. In this case, the interpolation function selected above is a conversion from the polar coordinate system to the orthogonal coordinate system. The sound field determined based on the conversion address is selected based on the turn and is further normalized by a coefficient of 1, so that it is possible to prevent pixel distortion and display an image with an improved S/N ratio. Become.

In the above embodiment, the conversion address written to the ninth BMFA that generates the read address of ROM7D uses the lower number pits and the upper number pits below the decimal point of the conversion result from the polar coordinate system to the orthogonal coordinate system. However, all pits may be used.

The present invention is not limited to the above embodiments, and can be implemented with various modifications without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, received signals obtained by transmitting and receiving ultrasonic waves to and from a subject by sector scanning are added, and the tomographic image information of the subject is obtained by detecting the added signal. In an ultrasonic diagnostic apparatus designed to display an image, the detection signal is digitized by an A/D conversion means, and echo data for each pixel in a polar coordinate system obtained by the sector scanning and outputted from the A/D conversion means. The converted address data obtained by converting the polar coordinate system address of this echo data into a rectangular coordinate system address is written to the same address.9. a first means for determining four turns of the sound field based on the conversion address data of the buffer memory; a second means for selecting coefficient data based on the pattern data; a third means for multiplying the coefficient data selected by the second means by corresponding echo data; and output from the third means. a fourth means for setting the sum of the coefficient values of the echo data group to 1, and frame image data to be displayed by capturing the echo data for each pixel output from the fourth means with a Cartesian coordinate system address set. The result obtained by performing a convolution operation between the interpolation function and the sample value of the echo data is written to every pixel in the frame memory, and the spread Since the power of the interpolation function and the to-off frequency are changed according to the size of the function, that is, the resolution relative to the sampling period, an ultrasonic diagnostic apparatus that can reduce pixel distortion and improve the S/N ratio is achieved. Can be provided.

[Brief explanation of drawings]

, i￥1 to 3 are for detailed explanation of the present invention. Diagram XI shows the polar coordinate system (rlθ
) A diagram to explain the expression, Figure 2 is a diagram to explain the relationship between the original image and the interpolation function, and Figure 3 is a diagram to explain the characteristics of the interpolation function in Figure 2. FIG. 4 is a schematic diagram showing an embodiment of the ultrasonic diagnostic apparatus according to the present invention, and FIG. 5 is a diagram for explaining pixel distortion due to sector scanning. 1... Ultrasonic probe, 2... Transmitter, 3... Receiver, 4... Adder, 5... Detector, 6... Analog/digital converter (A/ D-C), 7-Diglt
al 5can Conve-rt@r (D, S, C
), 7 A-...Pa, F memory (8M), 7L...
Register group (Rss), 7 C-...Subtractor (sub
), 7D...Read-on memory (ROM), 711m
... Multiplier (Con), 7F, 7G... Adder (
＾dd ), 7H... Normalization operator (Nor), 7
I...Frame memory (FM), 8...Display system.

Claims (1)

[Claims] An ultrasonic diagnostic apparatus that adds received signals obtained by receiving ultrasonic waves to a subject by sector scanning, and detects the added signal to obtain tomographic image information of the subject and display the image. , an A/D conversion means for digitizing the detection signal, echo data for each pixel in a polar coordinate system by the sector scanning output from the A/D conversion means, and the address of the polar coordinate system of this echo data in orthogonal coordinates. a buffer memory in which converted address data obtained by converting to a system address is written to the same address; a first means for determining a sound field pattern based on the converted address data in the buffer memory; a second means for selecting coefficient data based on the sound field pattern data from the first means; and a second means for selecting coefficient data based on the sound field pattern data from the first means; A third means to take advantage of
a fourth means for setting the sum of coefficient values of the echo data group output from the third means to 1; and a fourth means for setting the sum of coefficient values of the echo data group output from the third means to 1; An ultrasonic diagnostic apparatus comprising a frame memory that generates frame image data to be captured and displayed.