JPS6157016B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image signal processing device that improves the image quality of a display image in an ultrasonic image display device or the like.

In observation devices such as ultrasound diagnostic equipment, radar, and image pickup tubes that scan objects using beams such as ultrasound beams, electromagnetic beams, and electron beams, the original image may be distorted due to the thickness or spread of the beam. It tends to become blurry and degrade the resolution. Now, let the scanning direction be the x direction, and the original image is r(x),
The intensity distribution in the scanning direction of the beam is h(x)
(referred to as a spread function), the obtained image signal s(x) is given by s(x)=∫ ^∞ _−∞ r(u)h(x−u)du (1). Equation (1) is called convolution integral. s(x), r(x),
The Fourier transform of h(x) is expressed as S(nχ)=∫ ^∞ _−∞ s(x)e−i2πn〓x _dx (2) R(nχ)=∫ ^∞ _−∞ r(x)e−i2πn〓x _dx (3) H(nχ)=∫ ^∞ _−∞ h(x)e−i2πn〓x _dx (4) Defined as (n〓 is the spatial frequency), generally S(nχ)=R(nχ)×H( nχ) (5) Therefore, R(nχ)=S(nχ)/H(nχ) (6) is obtained.

In equation (6), if H(nχ) and S(nχ) are known, R(nχ) can be found, so
Fourier transform h(x) and s(x) to R
After determining (nχ), R(nχ) is subjected to inverse Fourier transform to obtain the original image r(x).
In general, strictly implementing the above steps is not only very complicated and requires extensive calculations, but also
Since it is not suitable for real-time processing, the processing function m(x) that satisfies ∫ ^∞ _−∞ m(u)h(x-u)du=δ(x) (7) (δ(x) is a delta function) Approximately find the original image r(x) by convolution integral with the obtained image signal ∫ ^∞ _−∞ s(u)m(x-u)du=r'(x)(8) The value is being calculated. However, even with this procedure, it takes time to recalculate the processing function m(x) for different spread functions h(x), it is difficult to obtain a good approximation, and the distribution of m(x) is
The distribution is several times wider than the distribution of This method has drawbacks such as ghosts appearing in the image signal r'(x) that compensates for the spread of the displayed image, and is not practical.

For this reason, in conventional real-time image processing circuits, for example, Nikkei Electronics
As published in the May 29, 1978 issue (pages 38-40 of the same issue, "Prototype of ultrasonic image display device capable of C-mode display and real-time image processing"), five images were sampled sequentially in the scanning direction. Image signal values s _i-2 , s _i-1 ,...s _i+
2 and a _-2 , a _-1 , ..., a ₂ as compensation (weighting) coefficients. By calculating the approximate value r _i of the original image r(x) and appropriately determining the weighting coefficients a _-2 , a _-1 , ..., a ₂ , difference processing (contour emphasis) and smoothing can be performed. is going on. However, as is clear from the explanation below, equation (9) does not take into account the relationship with the spread function h(x), so although effects such as edge enhancement and smoothing can be expected, equation (9) In principle, it is impossible to expect the value of the compensated image signal r _i thus obtained to sufficiently approximate the original image r(x).

Therefore, an object of the present invention is to eliminate the need for complex calculations such as strict Fourier transform in an image signal processing device in which original image information is input as an image signal via a sensor unit having known one-dimensional spread function characteristics. The object of the present invention is to provide an image signal processing device including a relatively simple, low-cost, and practical image signal compensation circuit.

Another object of the invention is to, with relatively high approximation accuracy,
An object of the present invention is to provide a real-time image signal processing device that can improve image quality or resolution.

Next, the principle of the present invention will be explained using FIGS. 1 and 2, taking an ultrasound image signal as an example.

FIG. 1 is an explanatory diagram of an ultrasonic echo image obtained when a cross section of several threads strung in water is observed using an ultrasonic image diagnostic apparatus called a linear electronic scanning type. In FIG. 1, the direction of the broken line arrow indicates the depth (distance or sweep) direction in which the ultrasonic beam is emitted, and the direction of the solid line arrow indicates the electronic scanning (azimuth or scan) direction. 1 ₁ , 1 ₂ ,
..., 1 ₅ each shows a cross-sectional image of the thread,
As shown in the figure, in the displayed image, the length in the azimuth direction is several times the length in the distance direction due to the spread of the beam. In the case of a linear electronic scanning type, the length in the azimuth direction is said to be 3 to 5 sweeps of the ultrasonic beam. As shown, this length varies in the distance direction and also depending on how the beam is focused.

FIG. 2 shows an example of the functional form of the spread function h(x). Figure 2a shows a type called a rectangular shape, which is close to a real example of an ultrasound echo image.
FIG. 2b shows the case where the spread function h(x) is similar to the error function (Gaussian) curve.

Generally, the spread of the spread function h(x), that is, the blur of the image, is often about several pixels, so
Assuming that the spread is within the range of 2d, the convolution integral equation (1) can be rewritten as follows.

s(x)=∫ (x-u)du =∫ (x-u)du (10) Now, the values obtained by sampling s(x), r(x), and h(x) for each pixel are s _i , r _i , h _i and rewriting equation (10) by setting the spread of the spread function to 2n pixels or less, we get becomes. The present invention focuses on the fact that n is generally a relatively small value (1, 2, 3, etc.), and uses equation (11) to compensate for the image signal value s _i and the spread of the display image one scan ago. It attempts to calculate the current r _i value from the data of the signal value r _i , and it aims to obtain an approximate value of the original image relatively easily without using complicated operations such as strict Fourier transform or processing functions. It is something.

For simplicity in equation (11), h _j =h− _j =0
(j3), h ₁ = h _-1 and h ₂ = h _-2 . Also, h ₀ =
1 Therefore, even if 0h ₁ and h ₂ are 1, generality is not lost.

s _i-2 =h ₂ r _i-4 +h ₁ r _i-3 +r _i-2 +h ₁ r _i-1 h ₂ r _i (12) ∴r _i =1/h ₂ {s _i-2 −h ₁ r _i-1 −r _i-2 −h ₁ r _i-3 −h ₂ r _i-4 } (13) According to equation (13), h ₁ and h ₂ are known, and r _i-4 , r
If _i-3 ,..., r _i-1 have been calculated, in principle s _i
It can be seen that r _i can be found from the data. However, there are practical problems in using equation (13) as is. That is, the value obtained by equation (13) is fine when h ₂ 〓h ₁ 〓h ₀ = 1 as shown in Figure 2a, but in a general example, as shown in Figure 2b, h If ₂ is close to the base of the spread function h(x), sufficient accuracy is often not obtained. Also,
Concerning s _i , there are also concerns about using only one piece of data. Next, based on equation (12),
Examples will show that some practical formulas can be derived in place of equation (13).

Calculating s _i-1 in the same way as equation (12), s _i-1 = h ₂ r _i-3 + h ₁ r _i-2 + r _i-1 + h ₁ r _i + h ₂ r _i+1 (14) ( 14) Subtracting equation (13) from equation s _i-1 s _i-2 = h ₂ r _i+1 + (h ₁ − h ₂ ) r _i + (1− h ₁ ) r _i-1 − ( 1 − h ₁ ) r _i-2 − (h ₁ − h ₂ ) r _i-3 − _{h 2} r _i-4 (15) Similarly, s _i-2 − s i _-3 = h ₂ r _i +( h ₁ - h ₂ ) r _i-1 + (1-h ₁ ) r _i-2 - (1- h ₁ ) r _i-3 - (h ₁ - h ₂ ) r _i-4 - _{h 2} r _{i- 5} (16) By setting h ₁ = h ₂ = 1 (h ₃ = 0) in equation (16), the following equation is obtained.

r′ _i =s _i-2 −s _i-3 +r _i-5 ≒1/2(s _i-1 −s _i-2 +r _i-1 +r _i-4 ) ≒1/3(s _i s _{i- 1} +2r _i-1 +r _i-3 ) (17) This is the case when the spread function h(x) has the form shown in Figure 2a. Similarly, by setting h ₁ =1 (h ₂ =0) in equation (15), the following equation is obtained.

r″ _i = s _i-1 − _{s i-2} + r _i-3 ≒ 1/2 (s _i − s _i-1 + r _i-1 + r _i-2 ) (18) This means that the spread function h(x) is , if it has the shape shown in FIG. 2c.

If the spread function h(x) is
When it is uniquely defined in the form,
Using equation (15) or (16), the calculation equation in the image signal processing device of the present invention can be determined as equation (17) or (18), but in actual cases, the spread function h( x) can have a shape intermediate between those in Figure 2 a and c, and can also change shape within the same screen. In such a case, if the spread function assumed during circuit configuration and the actual spread function differ by a wide range, the position of the displayed image will shift slightly and a harmful ghost image will appear.
Therefore, in one embodiment in which the present invention is applied to a linear electronic scanning ultrasound imaging apparatus, equations (17) and (18) are
The following approximate equation is used, which is a linear combination of equations.

r _i ≒lr″ _i +mr′ _i =l(s _i-1 −s _i-2 +r _i-3 ) +m(s _i-2 −s _i-3 +r _i-5 ) (19) (l+m=1) In the above equation, l and m are compensation coefficients (parameters), which are changed depending on the characteristics of the ultrasonic element (probe) and the pixel position.Incidentally, when l = m, the spread function h(x) is as shown in Figure 2 d. This corresponds to the case where the function form is as shown in Fig. 2b.The values of l and m are determined by measuring the spread function or by trial and error.

To further expand equation (19), if h(x) takes the form as shown in Figure 2 e (h ₀ = 1, h ₁ = h ₂ =
0), we get r _i = s _i −s _i-1 + r _i-1 (20), so r′ _i , r obtained by equations (17), (18), and (20) ″ Using _i and r _i ,
As an approximation formula that further generalizes equation (19), r _i ≒kr _i +lr″ _i +mr′ _i (k+l+m=1) =k(s _i −s _i-1 +r _i-1 ) +l(s _i-1 −s _i-2 +r _i-3 ) +m(s _i-2 −s _i-3 +r _i-5 ) (21) is obtained.As is clear from the above explanation,
Equation (21) was approximately derived assuming that the actual h(x) consists of any of the forms a, c, and e in Figure 2, or a combination thereof, but the equation shown in Figure 1 It is suitable for application to improving the image quality of displayed images of ultrasound echoes in linear electronic scanning ultrasound diagnostic equipment such as
By changing the values of and m depending on the characteristics of the ultrasonic element (probe) and the pixel position, a display image sufficiently close to the original image r(x) can be obtained.

Equation (21) is obtained by calculating equations (17), (18), or (19) for r _i separately for each case where h(x) has the form a, c, or e in Figure 2. r _i was derived assuming that it can be approximated by a linear combination of these, but if the shape of h(x) is the shape shown in Figure 2 b by appropriately selecting the values of parameters k, l, and m, It can also be practically applied (when h ₁ , h ₂ ≠1).

However, it is also possible to derive an arithmetic expression in another form assuming from the beginning that h(x) has the form shown in FIG. 2b, which will be shown below. Similar to equation (15) or (16), s _i −s _i-1 = h ₂ r _i+2 + (h ₁ − h ₂ ) r _i+1 + (1− h ₁ ) r _i −( 1-h ₁ )r _i-1 −(h ₁ −h ₂ )r _i-2 −h ₂ r _i-3 (22) In equation (22), r _i+1 ≒ r _i+2 + r _i /2 and,
Using the approximation of r _i ≒ r _i+1 + r _i-1 /2, r _i ≒ 1/1 + h ₁ + h ₂ {s _i −s _i-1 + (1 + h ₂ )
r _i-1 + (h ₁ - h ₂ ) r _i-2 + h ₂ r _i-3 } is obtained.

In this way, if you select either equation (21) or equation (23) and perform the weighted addition operation, the original image r
Sampled image signal r _i corresponding to (x)
can be found.

When performing calculations using equations (21) to (23), when r _i is at the starting point of the azimuth direction scanning, there are no values of r _i-1 , r _i-2 , etc., so the values are “zero.” ”
This shall apply hereinafter.

Next, we will express the arithmetic expressions in the signal processing of the present invention, exemplified by formulas (13), (21), and (23), in general common expressions and highlight the features of the signal processing of the present invention. Shown. That is, the weighted addition operation used in the image signal processing device of the present invention compensates for the spread of the single or multiple displayed images one scan before, in addition to the single or multiple input image signals..., s _i ,... (calculated) image signal...r _i ,
It can be expressed using the following general expression.

In the above equation, N is a not very large integer (for example, 3 to 5), and a _o and b _o are parameters with positive and negative values, which are determined by the shape of the spread function h(x). Comparing equation (24) with, for example, equation (9) above, the essential feature of the principle of the image signal processing device of the present invention is that the second term on the right side of equation (24), It can be seen that this is due to the addition of .

The principle of image signal processing in the present invention has been described in detail above, but next, as a specific circuit example, equation (21) is applied to an ultrasound echo image signal in a linear electronic scanning ultrasound diagnostic device. An example of processing will be explained below.

Figure 3 is an enlarged view of a part of the screen of the ultrasound echo display image in the linear electronic scanning ultrasound diagnostic device shown in Figure 1. As in Figure 1, the direction of the dashed arrow is the direction of the ultrasound beam. The firing direction is shown, and the solid arrow direction shows the direction of electronic scanning. In the i-th sweep of the ultrasonic beam, the j-th pixel in the depth (distance) direction is p _i ,j.
The reflected wave from the living body corresponding to this p _i ,j pixel is A/D converted, and the _resulting digital signal value (level data) is calculated by compensating for the spread in the transducer scan direction to be determined. The value of the image signal (level data) in the case is r _i ,j, and hereafter j
The constant values of are abbreviated as s _i and r _i , respectively. Similarly, p _i-5 , j; p _i-4 , j; p _i-3 ,
s i _{- 5} , r _{i-5 ; s i-4 , r i-4} ; s _i-3 , _{r i-3} for j; p i- ₂ , j; p _{i-1 , j;, etc.} ;s _i-2 ;
It is assumed that r _i-2 ; s _i-1 ; r _i-1 ;, etc. are made to correspond. As mentioned above, in the linear electronic scanning ultrasonic diagnostic apparatus, the azimuth direction, that is, p _i-5 , j; p _i-
4. Spreading (blurring) of the displayed image due to spreading of the ultrasound beam in the direction in which p _i , j;
can be seen, so the x direction in the spread function h(x) coincides with the azimuthal direction in this case.

FIG. 4 is a block diagram showing one embodiment of a specific circuit. In Fig. 4, 2, 3, and 4 connected in series are shift registers that store image signals (level data) for one sweep of the ultrasound beam, respectively, and convert the reflected waves from the living body into analog and digital. By sequentially inputting level data of digital signals, the shift register 2 has pixels p _i-1 , j; p _i-1 , j ₊₁ ;... p _i ,
1; p _i , 2;...; p _i , j ₋₁ (corresponding to one scanning line segment in the display image; in detail, s _i-1 , j; s _i-1 , j ₊₁ ...; s _i , 1; s _i ,
2;...;s _i ,j _-1 . ) is stored, and when there is further input, an image signal s _i-1 corresponding to p _i-1 , j is output from the output terminal. Similarly, image signals s _i-
2 , s _i-3 are output. 5, 6, and 7 are adders, respectively s _i , s _i-1 ; s _i-1 , s _i-2 ;
and s _i-2 ; s _i-3 ;, subtraction between the inputs is performed to obtain s _i -s _i-1 ; s _{i-1 ,} respectively.
- Output the values of s _i-2 ; s _i-2 , s _i-3 ; Similarly to shift registers 2, 3, and 4, shift registers 8, 9, 10, 11, and 12 are shift registers that store image signals (level data) for one sweep. By sequentially inputting the image signals r _i , j (abbreviated as r _i ) whose expansion in the child scan direction has been compensated for into the shift register 8, the respective outputs r _i-1 , r _i-2 , r _i-3 ,
r _i-4 and r _i-5 are obtained. Adders 13, 14, and 15 add the outputs of shift registers 5 and 8, 6 and 10, and 7 and 12, respectively, to output s _i -s _i-1 +r _i-1 , s _{i- 1} −s _i-2 +
r _i-3 , s _i-2 −s _i-3 +r _i-5 are obtained. 16,1
7 and 18 are compensation coefficient setters consisting of the necessary number of digits that can be manually set arbitrarily according to the characteristics of the ultrasonic element and the pixel position, and output the values of parameters k, l, and m in equation (21). do. 19,2
Multipliers 0 and 21 multiply the values of k, l, and m by the outputs of adders 13, 14, and 15, respectively. Furthermore, the adders 22 and 23 cause the multiplier 19,
By finding the sum of the outputs of 20 and 21 (21)
The calculation based on the formula is completed, and the value of the image signal r _i with compensation for the spread in the transducer scan direction is obtained. In equation (21), there is a restriction condition of k+l+m=1 for the set values of parameters k, l, and m, but in general, it is sufficient to find the relative value of r _i , so the above restriction condition is not necessary. Not. However, when changing the values of k, l, and m depending on the pixel position, an arbitrary constant c
However, it must be set so that k+l+m=c.

Furthermore, since it is undesirable for the input image signals s _i , . . . to contain noise, for example,
Before signal processing according to the present invention is performed using the "image signal processing device" described in No. 64413, etc.,
It is necessary to perform sufficient noise removal processing.

Furthermore, if the input image signals s _i , . In such a case, for example, by setting the values of l and m in equation (21) or h ₁ and h ₂ in equation (23) smaller than the values obtained from the actual h(x) data, It is necessary to mitigate the effects of image signal processing according to the invention and to balance compensatory effects with harmful side effects.

In the above explanation, an example of the circuit when formula (21) is applied has been described, but in general, when formula (24) is applied, which is shown as a general expression of the principle of image signal processing in the present invention. Also,
It goes without saying that this can be achieved with a similar circuit configuration, and it is also possible to perform real-time processing in which the circuit operates every sampling clock period of the image signal with the circuit configuration described above. Not even.

In addition, in the above description, an embodiment has been described for the purpose of improving the resolution in the electronic scanning (azimuth) direction of the ultrasound beam, but it is also Regarding the resolution in the scanning line direction of an image, the present invention can be extended and applied if the shape of the spread function h(x) is determined (by actual measurement or trial and error).

Furthermore, the shape of the spread function h(x) may change depending on the pixel position, but in this case, the above weighted addition operation (Equation (21), Equation (23),
For example, k, l, and m in equation (21); an in equation (24)
By changing values such as and bn depending on the pixel position, it is possible to expand the effective application of the present invention.

In the above explanation, the explanation was limited to the case where it is applied to a linear electronic scanning type ultrasonic diagnostic device, but the present invention is not limited to the linear electronic scanning type, but can also be applied to a system in which the original image information has known one-dimensional spread function characteristics. All imaging devices that form image signals via the image signal processing system, such as sector electronic scanning type and other ultrasonic diagnostic equipment, as well as other ultrasonic equipment such as ultrasonic flaw detection equipment, radar, It can be applied when the thickness of the beam is a problem in devices that generally use a beam to scan an object and output an image signal, such as a tomographic diagnostic device (CT) or a scanning electron microscope image pickup tube. Variations are possible. Therefore, the scope of the claims of the present invention is not limited to the embodiments or applications used in the above description.

As described in detail above, the present invention simplifies image signal processing in an imaging device in which original image information forms an image signal via a system having known one-dimensional spread function characteristics while maintaining the relationship with the spread function. Since the Fourier transform is performed in a linear manner, it accurately compensates for the blurring of the displayed image due to the spread of the ultrasound beam in the electronic scanning (azimuth) direction in linear electronic scanning ultrasound diagnostic equipment, etc., and converts the displayed image into a real image of the subject. It can be sufficiently approximated.

In addition, since calculations with a precision equivalent to strict Fourier transform can be processed in real time with a relatively simple circuit configuration, its practical effects are extremely large when used to improve the image quality or resolution of ultrasound echo display images, etc. There is something.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of an ultrasound echo image obtained when a cross section of several threads stretched in water is observed using a linear electronic scanning ultrasound imaging system, and Figure 2 is an illustration of the spread function h(x). Figure 3 shows an example of the functional form of
The figure is a partially enlarged screen view of an ultrasound echo display image in a linear electronic scanning ultrasound imaging system.
The figure is a block diagram for explaining a characteristic circuit of the image signal processing device according to the present invention. In the figure, h(x)...spread function, s _i ...image signal data before processing, r _i ...image signal data after processing, k・l・m...parameters, 2.3.
4, 8, 9, 10, 11, 12...shift register, 5, 6, 7, 13, 14, 15, 22, 23
... Adder, 16, 17, 18 ... Compensation coefficient setter, 19, 20, 21 ... Multiplier.

Claims (1)

[Scope of Claims] 1. In an image signal processing device in which original image information is input as an image signal via a sensor unit having known one-dimensional spread function characteristics, the image signal is sequentially sampled in the direction of the spread of the one-dimensional spread function. a shift register for accumulating at least one input image signal data; and at least one of the following weighted addition calculation means, which is sampled sequentially in the direction of spread of the one-dimensional spread function.
a shift register that stores image signal data before scanning; a compensation coefficient setter that can be set arbitrarily;
Means for performing a weighted addition operation in real time using at least one input image signal data outputted from the two sets of shift registers, at least one image signal data subjected to a weighted addition operation, and the compensation coefficient. An image signal processing device, characterized in that the weighted addition calculation means is configured to perform at least the following calculations. However, r _i ; image signal data compensated for the spread in the transducer scan direction s _i ; input image signal data N; an integer that is not very large. An image signal processing device characterized in that the direction of expansion of the dimensional spread function is made to match the direction of pixel sweep in original image information. 3. The image signal processing device according to claim 1, wherein the direction of spread of the one-dimensional spread function is orthogonal to the direction of pixel sweep in the original image information. 4. In the image signal processing device according to claim 2 or 3, the values of each of the plurality of compensation coefficients used in the weighted addition calculation are determined in the direction of spread of the one-dimensional spread function or in the direction of the spread of the one-dimensional spread function. An image signal processing device characterized by being configured to change in orthogonal directions. 5. In the image signal processing device according to claim 2 or 3, the values of the plurality of compensation coefficients used in the weighted addition calculation are set in the direction of spread of the one-dimensional spread function and orthogonal thereto. An image signal processing device characterized by being configured to change the image signal in a direction.