JP2008142178A - Radiological image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the image quality that an operator intends by specifying a region of interest and by performing processing on the entire image by using frequency characteristics conforming to the inside of the region of interest. <P>SOLUTION: When the imaging of a subject is carried out in S101, the original image is displayed on an image display device in S102 in order to determine the need of another imaging from the exposure field, the imaging dose, the patient's position, or the like. The operator specifies the region of interest in the displayed image in S103. Analysis processing on the region of interest is performed in S104, and computing processing of a frequency processing parameter is performed in S105. Frequency processing is performed in S106. An image is output by synthesizing the image decomposed by using the frequency processing parameter computed in S105. The image photographed in S107 is displayed in the image display device after appropriately performing gradation processing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiographic image processing apparatus that performs frequency processing on an image obtained by radiography such as X-rays in order to obtain a target image quality.

  Due to recent advances in digital technology, radiographic images are acquired as digital image signals, image processing such as frequency processing and gradation frequency is performed on these digital image signals, and they are displayed on a display or output to a printer. It has been broken.

  By the way, as a frequency processing technique, for example, Patent Document 1 discloses that an image is decomposed into frequency coefficients of a plurality of frequency bands and image processing is performed for each frequency band. Specifically, sharpening processing or the like is performed by decomposing the image signal into signals of a plurality of frequency bands and multiplying the decomposed frequency coefficients by corresponding weighting coefficients.

  FIG. 11 is a graph showing response characteristics when an image is decomposed for each frequency band LV, where the horizontal axis indicates frequency and the vertical axis indicates response characteristics for each frequency band LV. Response characteristics refer to the rate of change of frequency components for each frequency before and after frequency processing.

  For example, in FIG. 12, when the response characteristic is 1.0, it indicates that the frequency component of the frequency band LV does not change before and after the frequency processing, and when the response characteristic is 1.0 or more, the value of the frequency component is before the frequency processing. It shows that it becomes bigger. On the other hand, a value of 1.0 or less indicates that the frequency component value is smaller than that before the frequency processing.

  Here, if inverse transformation is performed on the decomposed image signal as shown in FIG. 11, the response value in all frequency bands is 1. That is, the image signal does not change before and after the frequency processing, but if the inverse transformation is performed by multiplying each frequency coefficient by an arbitrary weighting factor, the response characteristic can be freely changed, and the sharpening in the frequency processing or Smoothing can be performed.

JP 2002-209113 A

  An object of the present invention is to provide a radiographic image processing apparatus that can obtain an image quality intended by an operator by designating a region of interest and processing the entire image using frequency characteristics suitable for the region of interest. There is to do.

  Technical features of the radiographic image processing apparatus according to the present invention for achieving the above-described object include designation means for designating a region of interest on a radiographic image, setting means for setting a frequency processing parameter using the region of interest, And frequency processing means for performing frequency processing based on the parameters set by the setting means.

  According to the radiographic image processing apparatus according to the present invention, it is possible to simply give instructions for frequency processing in accordance with each detailed request, and to perform radiological examination and diagnosis efficiently. Also, the frequency processing setting can be used by an operator who does not know the concept of frequency.

The present invention will be described in detail based on the illustrated embodiments.
FIG. 1 is a block circuit configuration diagram of an X-ray image processing apparatus 1 of the present embodiment. The X-ray image processing apparatus 1 has an effective image processing function when outputting a captured image on a monitor. A subject P such as a human body is disposed between the X-ray generation circuit 2 and the two-dimensional X-ray sensor 3, and the X-ray generation circuit 2 and the two-dimensional X-ray sensor 3 are connected to the data acquisition circuit 4. The data collection circuit 4 is connected to a preprocessing circuit 5, and the preprocessing circuit 5 is further connected to a CPU bus 6. The CPU bus 6 is connected to a CPU 7, a main memory 8 such as a RAM, an operation panel 9 as an input device, a display 10, a region of interest analysis circuit 11, and a frequency processing parameter calculation circuit 12. Further, a decomposition method setting circuit 13, a frequency component decomposition circuit 14, a restoration circuit 15, a gradation processing circuit 16, and a storage device 17 are connected to the CPU bus 6. Among them, an image processing circuit 18 is configured by the decomposition method setting circuit 13 to the gradation processing circuit 16, and a frequency processing circuit 19 is further configured by the decomposition method setting circuit 13 to the restoration circuit 15.

  In such an X-ray image processing apparatus 1, the main memory 8 stores various data necessary for processing by the CPU 7 and functions as a working memory for the CPU 7. The CPU 7 uses the main memory 8 to perform operation control of the entire apparatus according to the operation from the operation panel 9.

  When an input of a shooting instruction is detected from the user via the operation panel 9, the shooting instruction is transmitted to the data collection circuit 4 by the CPU 7. When receiving an imaging instruction, the data acquisition circuit 4 controls the X-ray generation circuit 2 and the two-dimensional X-ray sensor 3 to execute X-ray imaging. In X-ray imaging, first, the X-ray generation circuit 2 emits an X-ray beam X to the subject P, and the X-ray beam X emitted from the X-ray generation circuit 2 passes through the subject P while being attenuated. The dimensional X-ray sensor 3 is reached. Then, an X-ray image signal is output by the two-dimensional X-ray sensor 3. In this embodiment, since the subject P is a human body, the X-ray image output from the two-dimensional X-ray sensor 3 is a human body image.

  The data acquisition circuit 4 converts the X-ray image signal output from the two-dimensional X-ray sensor 3 into a predetermined digital signal and supplies it to the preprocessing circuit 5 as X-ray image data. The preprocessing circuit 5 performs preprocessing such as offset correction processing and gain correction processing on the signal from the data acquisition circuit 4, that is, X-ray image data. The X-ray image data preprocessed by the preprocessing circuit 5 is transferred as original image data to the main memory 8, the display 10, and the image processing circuit 18 through the CPU bus 6 under the control of the CPU 7.

  Here, the image first transferred to the display 10 is referred to as a preview image for convenience. Unlike the conventional film photographing type X-ray photographing apparatus, the X-ray image processing apparatus 1 in the present embodiment allows the user to quickly confirm the X-ray image by displaying the preview image. Such a preview image plays a role of confirming whether or not X-ray imaging is performed as instructed. In the present embodiment, the operator can instruct frequency processing to be performed later by designating a region of interest on the preview image. At this time, the place where the image is displayed does not necessarily have to be a single display device 10. For example, the display device 10 is on the operation panel 9, and the region of interest can be indicated on the image using the region-of-interest operation panel 9. desirable.

  An image in the designated region of interest is analyzed in the region of interest analysis circuit 11 by a method described later, and a frequency processing parameter to be input to the frequency processing circuit 19 is calculated based on the obtained analysis result. The frequency processing parameter calculation circuit 12 calculates a weighting coefficient for performing frequency processing.

  The frequency processing circuit 19 performs frequency processing that changes the information of the frequency of interest from the image information so as to match human vision by emphasizing the frequency band necessary for diagnosis. On the other hand, the gradation processing circuit 16 performs gradation processing for adjusting the density of the information on the density of interest so that it matches human vision. In the present embodiment, as an input means to the frequency processing circuit 19, an input is performed by designating a region of interest in a captured image using the operation panel 9.

FIG. 2 is an operational process flowchart of the X-ray image processing apparatus 1 according to the present embodiment. First, when photographing of the subject P is executed under the control of the CPU 7 in step S101, the photographed original image is transferred to the display 10 and the image processing circuit 18 via the preprocessing circuit 5.
In step S102, the CPU 7 promptly displays the image thinned out by the preprocessing circuit 5 in order to determine the necessity of re-photographing based on the irradiation field, photographing dose, position of the subject P, and the like. Display on the vessel 10.

  Next, in step S103, the CPU 7 detects a region of interest in the image displayed on the display 10 designated by the operator using the operation panel. It is necessary to specify not only the position but also the size of the region of interest specified here. However, in order to simplify the operation, it is preferable to set the size of the region as a default value. In step S103, the position and size can be displayed after the designation, and can be changed if they differ from the instruction. Since the region of interest is for performing frequency processing, a plurality of regions may be designated.

  In step S104, the region-of-interest analysis circuit 11 performs a region-of-interest analysis process. In step S105, the frequency processing parameter calculation circuit 12 performs frequency processing parameter calculation processing. Although it is preferable to analyze the frequency information of the image in the region of interest, the frequency processing parameter may be calculated by other methods. For example, part information is first recognized from the region of interest, and frequency processing parameters suitable for the relevant part stored in the storage device 17 in advance can be output from the obtained part information. Further, if there is patient information, the past frequency processing parameters of the same patient may be output, or a region button selected at the time of imaging may be input. That is, the region-of-interest analysis circuit 11 includes an output by collation with each database.

  Next, in step S106, the frequency component decomposition circuit 14 performs frequency processing. Further, the restoration circuit 15 synthesizes the image decomposed by the frequency component decomposition circuit 14 using the frequency processing parameter calculated in the previous step S105. The image synthesized in step S107 is displayed on the display 10 after being subjected to gradation processing by the gradation processing circuit 16.

  FIG. 3 is a display screen of the display 10 and assumes a case where a blood vessel part in the lung is desired to be selected as a region of interest. The user uses the operation panel 9 to designate a region of interest in an image displayed on the screen of the display device 10. For example, when looking at the ribs of the chest, the position A, B, C, etc. of the corresponding region in the image is designated by a pointing device on the operation panel 9 or a mouse connected to the operation panel 9. Conventionally, the emphasis frequency band and the emphasis level were input as frequency processing input, but with this conventional input method, it is necessary to repeat and view the frequency graph and the processed image alternately as described above. It is.

  Further, the position and size of the region of interest to be input may be the same as the past image specified in the region of the same part imaged in advance by the same imaging device. Further, as a default of the position of the region of interest, the center region in the captured image that is the center of the image effective area of the two-dimensional X-ray sensor 3 or the center of the X-ray irradiation field area can be set as the region of interest. However, when the central region is used, it is preferable that the X-ray irradiation field areas of various shapes that have been transmitted through various parts be correctly known, and thus be the same as the past image.

  FIG. 4 is an explanatory diagram of analysis processing of each image divided by downsampling or the like. (A) is a frequency band of L1 to L4 in which the horizontal axis is arranged from a low frequency to a high frequency, and the vertical axis represents an analysis value. When the obtained histogram of each frequency band Ln is taken, it can be expressed as shown in FIGS. 4B to 4E, with the horizontal axis being a coefficient and the vertical axis being a frequency.

The coefficients in FIGS. 4B to 4E correspond to pixel values in each image. As can be conceptually understood from this histogram, by taking the variance value σ _Ln of the image of each frequency band, it becomes one index reflecting the information amount of the image of each frequency band. An image with a frequency with no information amount is almost uniform, and random fluctuations due to X-ray quantum noise are shown in the image, whereas an image with a frequency with a large amount of information has a large variance value σ _Ln Because.

In the present embodiment, the value of the variance value σ _Ln in the image obtained from each frequency band Ln is performed in the image of each frequency band Ln. Then, as shown in FIG. 4A, the horizontal axis represents the spatial frequency, and the vertical axis represents the weighting coefficient based on the value of the dispersion value σ _Ln obtained. This graph is one of the outputs of the frequency processing parameter calculation circuit 12. Next, it is converted into each parameter for frequency processing based on this dispersion value σ _Ln and used as a final setting parameter for frequency processing.

  Table 1 shows an output example of final frequency processing parameters, and the weighting coefficient for each frequency band Ln is shown. When all the weighting factors are 1, the image after frequency processing is the same as the image before frequency processing.

Table 1
Frequency band Ln Weight coefficient 1 0.6633
2 1.2921
3 1.4227
4 1.2739
5 1.0886
6 1.0819
7 1.0140
8 1.0263
9 0.9997
10 1.0087

In the embodiment, the variance value σ _Ln is used as the analysis value in each frequency image. However, the present invention is not limited to this variance value σ _Ln . For example, it is needless to say that a coefficient indicating the mode in FIGS. 4B to 4E or a coefficient indicating an intermediate value may be used. A feature of this analysis processing is that the analysis results of the region of interest and the region other than the region of interest are compared using information of a plurality of frequency bands Ln.

  FIG. 5 is a detailed flowchart of the process of the X-ray image processing apparatus 1 shown in steps S104 to S106 of FIG.

  In the region-of-interest analysis process in step S104 in FIG. 5, the region-of-interest analysis circuit 11 performs the region-of-interest analysis process. The region-of-interest analysis processing includes step S1041 for setting an image frequency component decomposition method, step S1042 for analyzing an image component for each frequency band, and step S1043 for analyzing an image component for each frequency of the region of interest.

  In step S1041, an image decomposition method setting process is performed. Specifically, the decomposition method setting circuit 13 selects an image frequency component decomposition method and filter. In the present embodiment, the user can arbitrarily select either decomposition by wavelet transform or decomposition of a Laplacian pyramid.

  In step S1042, the frequency component decomposition circuit 14 performs frequency decomposition of the image by the decomposition method set by the decomposition method setting circuit 13 in the previous step S1041. Processing is performed by a decomposition method corresponding to the detection result of the user selection. When the wavelet transform is selected, the frequency component decomposition circuit 14 separates the input image signal into an even address signal and an odd address signal by a combination of a delay element and a downsampler. Then, the frequency component decomposition circuit 14 performs filter processing on the separated image signal using the two filters p and u.

FIG. 6 is an explanatory diagram of the wavelet transform, and s and d in FIG. 6A represent the low-pass coefficient and the high-pass coefficient when one-level decomposition is performed on the one-dimensional image signal, respectively. Calculated. However, x (n) is an image signal to be converted.
d (n) = x (2n + 1) −floor [{x (2n) + x (2n + 2)} / 2] (1)
s (n) = x (2n) + floor [{d (n-1) + d (n)} / 4] (2)

  Through the above processing, one-dimensional discrete wavelet transform processing is performed on the image signal. The two-dimensional discrete wavelet transform is a one-dimensional transform that is sequentially performed in the horizontal and vertical directions of the image, and details thereof are publicly known, and thus description thereof is omitted here.

  FIG. 6B is a configuration example of a two-level frequency coefficient group obtained by two-dimensional conversion processing, and an image signal is decomposed into frequency coefficients HH1, HL1, LH1,... LL in different frequency bands. . In (b), HH1, HL1, LH1,..., LL (hereinafter referred to as subband) indicate frequency coefficients for each frequency band.

  When the decomposition method setting circuit 13 selects Laplacian pyramid decomposition, the frequency component decomposition circuit 14 performs frequency decomposition on the input image signal using the Laplacian pyramid. FIG. 7 is an explanatory diagram of the decomposition of the Laplacian pyramid. In FIG. 7A, g and b represent a low-resolution approximate image and a high-frequency component coefficient of the image when one-level decomposition is performed, respectively. The low-resolution approximate image g is obtained by filtering the image signal x with a low-pass filter. Processed and obtained by downsampling.

  Further, the high frequency component coefficient b is obtained by up-sampling the image signal x and the low resolution approximate image g and further obtaining a difference between the image processed by the low pass filter. The low-pass filter is, for example, a filter as shown in FIG. 7B, and the Laplacian pyramid repeats this process for the low-resolution approximate image g to obtain image components in each frequency band.

Returning to FIG. 5, in step S <b> 1043, the region-of-interest analysis circuit 11 analyzes the obtained image components for each frequency of the region of interest. Then, as described in FIG. 4, a statistical index such as the variance value σ _Ln is calculated from each frequency image.

  In the frequency processing parameter calculation process in step S105 of FIG. 5, the frequency processing parameter calculation circuit 12 performs a frequency processing parameter calculation process. Specifically, a process of comparing the image component analysis result for each frequency in step S1051 between the entire image and the region of interest and a process of determining a weighting coefficient for frequency processing in each frequency band in step S1052 are performed.

  First, in step S1051, the frequency processing parameter calculation circuit 12 grasps the frequency characteristic of the region of interest by comparing the statistical index value obtained in step S1043 between the entire image and the region of interest. Further, the frequency processing parameter calculation circuit 12 calculates a parameter for performing frequency processing based on the result analyzed by the region-of-interest analysis circuit 11. The frequency processing parameter calculation circuit 12 reads the image signal decomposed by the frequency component decomposition circuit 14 from the main memory 8, and compares statistical index values such as dispersion values in the final frequency images between the entire image and the region of interest. To get by.

  Next, in step S1052, the frequency processing parameter calculation circuit 12 determines a weighting coefficient for frequency processing in each frequency band. Specifically, based on the index value obtained in the previous step S1051, the value of the region of interest is compared with the entire image, and the weighting of the frequency processing parameter in the frequency band where the difference is different is output. Naturally, the frequency processing parameter calculation circuit 12 increases the weight of image information in a frequency band with a large amount of information in the region of interest and outputs it.

  In step S106 of FIG. 5, in step S1061, the frequency component decomposition circuit 14 performs frequency processing based on the obtained frequency processing parameter. The frequency component decomposition circuit 14 multiplies the frequency coefficient of each level by the weight coefficient of each level calculated by the parameter calculation circuit 12.

In step S1062, the restoration circuit 15 performs synthesis processing of each weighted frequency image obtained with the frequency processing parameter obtained in the previous step S1061, that is, inverse transformation of the processing performed in the frequency component decomposition circuit 14. For example, when the discrete wavelet transform is performed in the frequency component decomposition circuit 14, the inverse discrete wavelet transform shown in FIG. 6C is performed. The input frequency coefficient is subjected to two filter processes u and p, and after being up-sampled, is superimposed and an image signal x ′ is output. These processes are performed according to the following equation.
x ′ (2 * n) = s ′ (n) −floor [{d ′ (n−1) + d ′ (n)} / 4] (3)
x '(2 * n + 1) = d' (n) + floor [{x '(2 * n) + x' (2 * n + 2)} / 2] (4)

  Through the above processing, a one-dimensional inverse discrete wavelet transform process is performed on the transform coefficient. The two-dimensional inverse discrete wavelet transform sequentially performs one-dimensional inverse transform in the horizontal and vertical directions of the image, and details thereof are publicly known.

  Further, when the Laplacian pyramid is decomposed in the frequency component decomposition circuit 14, the Laplacian pyramid inverse transformation shown in FIG. 7C is performed. The input high-frequency component coefficient b and the low-resolution approximate image g are upsampled, and an image signal x ′ is output by superimposing the filtered signals by the low-pass filter. By repeating this process for each level, the image can be decoded, and details thereof are publicly known.

  FIG. 8 is an operational process flowchart of the X-ray image processing apparatus 1 when extracting part information corresponding to the region of interest. In FIG. 8, the CPU 7 detects designation of the region of interest input via the operation panel (S201). Further, the CPU 7 extracts part information corresponding to the designated region of interest (S202). Then, according to the conversion table stored in the storage device 17, the CPU 7 extracts a frequency processing parameter corresponding to a frequency band necessary for diagnosis of the corresponding part as a set value (S203). Then, the frequency processing in step S106 is executed.

  Further, as shown in the flowchart of FIG. 9, after specifying the region of interest, the corresponding part information is recognized from the corresponding area, and in addition to the part information, the past diagnosis information of the corresponding part and the patient information are integrated ( Step S303). Furthermore, according to the conversion table stored in the storage device 17, a frequency processing parameter corresponding to a frequency band necessary for diagnosis of the corresponding part may be extracted as a set value (step S304).

  Alternatively, as shown in the flowchart of FIG. 10, after the designation of the region of interest is detected, the frequency band specified in the corresponding region is selected using the past conversion processing table log (step S403), and the same frequency band as the past image is selected. May be used as a frequency processing parameter.

  In this case, the region-of-interest specifying means has almost the same meaning as the imaging region specifying button. However, by designating an area in the image, the name of each imaging part is not required and image processing can be performed, so that usability is improved.

  According to the present embodiment, since the frequency processing instruction method can be performed from the captured image or the preview image, for example, the frequency processing instruction according to each detailed request can be simply performed. For this reason, X-ray inspection and diagnosis can be performed efficiently in various X-ray imaging apparatuses, and the frequency processing setting can be used even by an operator who does not know the concept of frequency. The operator can give instructions.

  The present invention can also be achieved by a computer (or CPU or MPU) reading and executing the program code stored in the storage medium in which the program code of the software realizing the functions of the above-described embodiments is recorded. Needless to say. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, not only the functions of the above-described embodiments are realized by the computer reading and executing the program code, but an OS (operating system) running on the computer is used based on the instruction of the program code. it can. A case where part or all of the actual processing is performed by the OS and the functions of the above-described embodiments are realized by the processing is also included in the embodiment of the present invention.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the program code is processed according to the instruction of the program code. Also good. Further, the embodiment of the present invention also includes a case where the CPU or the like provided in the function expansion board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing. Not too long.

It is a block circuit block diagram of an X-ray image processing apparatus. It is an operation | movement flowchart figure. It is a display screen of a display. It is explanatory drawing of an analysis process. It is an operation | movement flowchart figure. It is explanatory drawing of wavelet transformation. It is explanatory drawing of a Laplacian pyramid. It is an operation | movement flowchart figure. It is an operation | movement flowchart figure. It is an operation | movement flowchart figure. It is a graph of the response characteristic decomposed | disassembled for every frequency band. It is a graph of the response characteristic after restoration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray image processing apparatus 2 X-ray generation circuit 3 Two-dimensional X-ray sensor 4 Data acquisition circuit 5 Pre-processing circuit 6 CPU bus 7 CPU
DESCRIPTION OF SYMBOLS 8 Main memory 9 Operation panel 10 Display 11 Region of interest analysis circuit 12 Frequency processing parameter calculation circuit 13 Decomposition method setting circuit 14 Frequency component decomposition circuit 15 Restoration circuit 16 Gradation processing circuit 17 Storage device 18 Image processing circuit 19 Frequency processing circuit

Claims (10)

  A setting unit configured to detect designation of a region of interest on the radiographic image and set a frequency processing parameter using the designated region of interest; and a frequency processing unit configured to perform frequency processing based on the parameter set by the setting unit. A radiographic image processing apparatus.   The radiation image processing apparatus according to claim 1, wherein a region of interest in a preview image is designated by the setting unit.   The radiographic image processing apparatus according to claim 1, wherein a central region of the image is designated as a region of interest by the setting unit.   The radiation according to claim 1, wherein the setting unit includes a frequency component decomposition unit that decomposes the captured image into frequency component images, and an analysis unit that analyzes the component images in the region of interest. Image processing device.   The radiographic image processing apparatus according to claim 4, wherein the analysis unit analyzes a statistical processing value of a coefficient of each frequency component image.   The radiological image processing apparatus according to claim 4, wherein the analysis unit compares the analysis result with an analysis result of a region of interest and a region including others.   The radiographic image processing apparatus according to claim 1, wherein the setting unit sets a weighting parameter for each frequency component image.   The radiographic image processing apparatus according to claim 1, wherein the frequency processing unit adds the frequency images using the frequency processing parameter.   The radiographic image processing apparatus according to claim 1, wherein the setting unit recognizes part information from the region of interest, and sets a frequency processing parameter from the recognized part information.   The radiographic image processing apparatus according to claim 9, wherein the setting unit sets the frequency processing parameter using the recognized part information and past case information.

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