JPH0969157A - Method for processing radiation image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation image processing method capable of reproducing a noticed part area in the image area of a radiation image formed correspondingly to the transmission quantity of radiant rays transmitted through respective parts of a subject in the excellent state of diagnostic performance and moderating the rugged state of a non-noticed part area. SOLUTION: In the radiation image processing method for applying image processing to the image signal of a radiation image formed correspondingly to the transmission quantity of radiant rays transmitted through respective parts of a subject, the image signal area is divided into plural areas by a feature found from the image signal and image processing conditions are changed among partial areas having different features.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image processing method for performing image processing on an image signal of a radiation image formed corresponding to the amount of radiation transmitted through each part of an object, and more specifically, for example, radiation image conversion. In order to read the radiation image stored and stored in the panel and reproduce the radiation image of the same size with excellent diagnostic performance, the radiation image conversion panel is scanned with excitation light and the storage phosphor layer of the panel stores and stores the radiation image. The present invention relates to a radiation image processing method of taking out radiation image information as stimulated emission light, obtaining an image signal by photoelectric conversion, and then performing image processing on the image signal.

[0002]

2. Description of the Related Art As a radiation image processing method described above, Japanese Patent Laid-Open No. 55-163472 discloses that an image signal obtained by scanning a radiation image conversion panel with excitation light is subjected to frequency processing enhancement with the same enhancement ratio. According to Japanese Patent Laid-Open No. 56-11038, the emphasis ratio is changed according to the radiation intensity of the cause instead of the intensity of the image signal. It is known from Japanese Patent Laid-Open No. 60-188941 to apply changed frequency processing emphasis. It is also known to subject the image signal to filter processing for removing noise other than the above-described frequency processing enhancement.

The method (1) enhances the sharpness of the image in the entire read-out area, but since the image roughness in the low signal portion and the low dose portion is overemphasized, the texture becomes very noticeable. There is a problem that the diagnostic performance is likely to deteriorate. The method of and is to solve the problem of, but instead, it becomes easy to emphasize the roughness in the middle to high signal part other than the low signal part and the low dose part, and the low signal part and the low dose part. Since the degree of emphasis is low, there is a problem that lesions and the like in those parts are easily overlooked.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the above-described conventional radiation image processing method, for example, a notable partial area in an image area read from a radiation image conversion panel. It is an object of the present invention to provide a radiographic image processing method capable of reproducing the image in a state in which it has excellent diagnostic performance, and making the roughness of other non-attention partial regions less noticeable.

[0005]

According to the present invention, there is provided a radiation image processing method for performing image processing on an image signal of a radiation image formed corresponding to an amount of transmission of radiation passing through each part of a subject. Is divided into a plurality of partial areas according to the characteristics obtained from the image signal, and the condition of the image processing is changed between the partial areas having different characteristics, and the object is achieved by this configuration. To do.

[0006]

That is, according to the radiation image processing method of the present invention, the image region of the radiation image formed corresponding to the amount of radiation transmitted through each part of the subject includes a plurality of image signals depending on the characteristics obtained from the image signals. Divided into partial areas,
Since the image processing conditions are changed between the partial regions having different characteristics, it is suitable for the image signal of the notable partial region divided by the features indicated by the image signal cumulative values in the vertical and horizontal directions of the partial regions, for example. By applying frequency processing enhancement with a different enhancement ratio and performing filter processing to remove noise on the image signals of other incidental partial areas, the image of the partial area of interest is hardly enhanced in roughness. On the other hand, the sharpness is emphasized, and the roughness of the images of the other auxiliary partial regions is less noticeable, so the images of the partial regions of interest can be reproduced in a state of excellent diagnostic performance,
Images in other auxiliary partial areas can be reproduced with a reduced impression of roughness given to the entire image.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

FIG. 1 is a structural block diagram showing an example of a radiation image recording apparatus for carrying out the radiation image processing method of the present invention, FIG. 2 is a block circuit diagram of a portion for digitally image processing image data, and FIG. 3 is a radiation image. FIG. 4 is an explanatory diagram showing an example of a partial area determination method, and FIG.
It is a block circuit diagram which shows the structure of PU.

In FIG. 1, an X-ray irradiator 1, which is a radiation source, irradiates an object 2 with X-rays, and the X-rays transmitted through the object 2 are disclosed, for example, in JP-A-59-7500. Upon incidence on a radiation image conversion panel 3 as described in JP 61-72091 A, the panel 3 stores and stores X-ray images in its stimulable phosphor layer. Excitation light source 4
Scans and exposes the radiation image conversion panel 3 storing and storing the X-ray image with an exciting light beam such as visible light or infrared light to stimulate the stimulable phosphor layer to emit light. The stimulated emission light is made incident on the photoelectric converter 6 through the filter 5 for removing other excitation light and the like, whereby the photoelectric converter 6 causes the electric signal of the X-ray image to be converted into an analog / digital (A / D) converter. Output to 7,
The A / D conversion unit 7 converts the digital image data and outputs the digital image data to the image processing device 8.

As shown in FIG. 2, the A / D converter 7 converts the output current of the photoelectric converter 6 into a voltage signal by the current / voltage converter 7A, amplifies the voltage signal by the amplifier 7B, and then A / D
The converter 7C converts the digital image data, and the control circuit 7
It is output to the image processing device 8 via D. Here, the amplifier 7B may be a logarithmic amplifier. The control circuit 7D adjusts the gain of the current / voltage converter 7A and the amplifier 7B, and
The input dynamic range of the D converter is adjusted, the reading gain of the radiation image information is adjusted comprehensively, and the image data is transferred to the image processing device 8 at a predetermined timing.

The image processing apparatus 8 shown in FIG. 1 includes an anatomical area determining means 9 and an image processing means 1 which will be described later and are image area dividing means.
0, specifically, as shown in FIG. 2, it is composed of a central processing unit (hereinafter referred to as CPU) 21 and the following various members connected thereto.

A confirmation monitor 22 which is controlled and displayed by the display controller 23 and a frame memory 24 which is controlled by the frame memory controller 25 and stores image processing data such as digital image data from the A / D converter 7. Are connected in parallel to the CPU 21 via the image bus VB. A keyboard 26 for inputting identification information (name, sex, date of birth, etc.) of the subject 2 and a display device 2 for displaying the input information.
7 and 7 are connected in parallel to the CPU 21 via the interface 28. A timing control unit 29 that outputs a timing control signal to the CPU 21 is also connected via the system bus SB, and the timing control unit 29 transmits the timing control signal to the aforementioned subject 2 for X-ray irradiation of the subject 2 by the adapter 3.
It is also output to the X-ray control unit of the X-ray irradiation device 1 via 0, and is also output to the control circuit 7D of the A / D conversion unit 7 for transferring the above-mentioned digital image data to the image processing device 8.

A magnetic memory 31 for recording unprocessed image data or image processed image data under the control of the magnetic memory control unit 32 is also connected to the CPU 21 in parallel with the timing control unit 29 by the system bus SB. The image data may be recorded in an external optical disk device or magnetic tape device as shown by the broken line in FIG.
Further, in parallel with the timing control unit 29, an I / O interface 33 for an external device such as the image output device 11 and a host computer, and a ROM 34 storing a control program and the like are also connected to the CPU 21.

The CPU 21 is provided with the anatomical region determining means 9 and the image processing means 10 of FIG. 1, reads the control program from the ROM 34 via the system bus SB, and also connects the image bus VB and the frame memory control section 25. The original image data is read from the frame memory 24 via the frame memory 24, and the image areas are divided according to the control program as described below, and the image processing is performed under different conditions between the divided partial areas.

As described above, when the X-ray image read from the radiation image conversion panel 3 is the chest image as shown in FIG. 3A, the image data is like a shaded portion a. There is a completely unnecessary part. Further, when the range requiring diagnosis is the lung field surrounded by a broken line, the intermediate part between the part a and the lung field is also called a semi-unnecessary part. However, like the conventional radiation image processing method described above, when the image data of the entire image is image-processed under uniform conditions, the diagnostic performance in which the lung field of the core is reduced in sharpness and graininess due to semi-unnecessary portions and unnecessary portions The anatomical region determining means 9 determines the lung field region and other regions by the image data read from the radiation image conversion panel 3, and the image processing means 10 By performing image processing on the image data under different conditions in the lung field area and other areas, the sharpness is increased only in the lung field area and the granularity in other areas is increased to improve the diagnostic performance. In addition, it enables reproduction with a reduced impression of roughness on the entire image.

The lung field region determining method of the anatomical region determining means 9 will be described with reference to FIG. 3, and the following (1) to (7) will be described.
The processing is performed to determine.

(1) The entire image data in the range of FIG. 3A has a small influence on the image processing. For example, the upper part and the lower part of the region about 1/3 from the upper and lower ends of the image region are excluded. Then, the vertical projection value (cumulative value in one direction of the image data) of the intermediate portion is obtained as shown in B of FIG.

(2) Center 1/3 of the projection value curve of FIG. 3B (X / 3 to 2X / 3 of FIG. 3A)
Then, the position in the X direction at which the projection value shows the minimum value PC is defined as the column XC of the midline.

(3) 1 / on the right and left sides of the range of FIG. 3A
3 columns (range 0-X / 3 and 2X / 3-X in FIG. 3A)
3B corresponding to the projection value curve of FIG. 3B from the center side to the outside, that is, the left side and the right side, respectively.
R and TL are compared with each other, and XR and XL at the X position where the projection value first becomes less than or equal to threshold values TR and TL described below are determined as the left end and the right end of the lung field region.

The thresholds TR and TL are calculated from the minimum value PC of the median line XC in the projection value curve of FIG. 3B and the local maxima PRX and PLX on the left and right sides thereof by the following formula.

TL = {(K1-1) × PLX + PC} / K1 TR = {(K2-1) × PRX + PC} / K2 Note that K1 and K2 are constants, for example, K1 = K2 = 5.
Is set to

(4) For example, the projection value in the lateral direction of the right chest is obtained as shown in C of FIG. 3 from the image data from the midline XC to the left end of FIG. 3A.

(5) The projection value curve of FIG. 3C is moved upward and downward from the central portion (Y / 2 position in FIG. 3A) to change the projection value of each moving point to a threshold value TT for the upper moving point described later. Or, as compared with the threshold value TB for the downward moving point, the YT at the Y position where the projection value at the upward moving point first becomes equal to or less than the threshold value TT and the YB at the Y position where the projection value at the downward moving point first becomes equal to or less than the threshold value YB. , YT is the upper end of the right lung field, YB
Is determined as the bottom edge.

The threshold values TT and TB are Y / 4 to Y / 2 and Y /
From the maximum values PTX and PBX of the projection values of FIG. 3C which are respectively obtained in the range of 2 to 4Y / 5 and the minimum values PTN and PBN of the projection values which are obtained above or below the Y position of the maximum values respectively, Calculated by the formula.

TT = {(K3-1) × PTX + PTN} / K3 TR = {(K4-1) × PBX + PBN} / K4 Note that K3 and K4 are constants, for example, K3 = 10 and K.
4 = 6 is set.

(6) The upper and lower ends of the left lung field are determined in the same manner as in (4) and (5) for image data from the midline XC to the right end of FIG. 3A.

(7) The obtained upper and lower ends of the right lung field and the left lung field are respectively compared, and the upper end located above and the lower end located below are compared with the upper end and the lower end of the lung field region. To decide.

The lung field region is determined as described above.

Not limited to the above example, the X positions of the minimum projection values to the left of XR and to the right of XL in FIG. 3B are defined as the right and left ends of the lung field region, and the projection values PTN and PBN in FIG. 3C are Y. The upper and lower ends of the lung field region may be obtained by using the positions as the upper and lower ends of the right lung field part or the left lung field part. Further, for example, when the subject 2 is a patient using a pacemaker or a single lung patient, and the images of the lung field greatly differ from left to right, at least one of the upper end and the lower end of the left and right lung field regions is Whether the average value or the value on the center side is determined as the upper end or the lower end, or the lung field region is designated using the image monitor 22 of FIG.
It is possible to prevent the diagnostic performance of the lung field image from deteriorating by determining the lung field region by several different methods and setting the average region or the region closest to the center to the lung field region.

The partial area for improving the sharpness of the image can be determined by binarizing the image data using, for example, the CPU 21 having the configuration shown in FIG. According to this, the original image data is first binarized by being compared with a predetermined threshold value in the binarization unit 42, and an identification code is given to each pixel. For example, the identification code 1 is given to the pixels equal to or more than the threshold value, and the identification code 0 is given to the pixels less than the threshold value.

The threshold is set by the threshold setting unit 41, and the initial value of the threshold is set from the image data of the image area. For example, in order to detect the maximum image data (maximum signal value) of the lung field region as the region of interest, it is necessary to gradually decrease the threshold value for binarization from the larger value toward the optimum threshold value direction. The initial value is determined by adding 100 to the maximum signal value of the 8 × 8 pixels in the substantially central portion of the effective image area that excludes most of the portion outside the subject.

When the threshold value is gradually decreased toward the optimum threshold value, the initial value may be set to a value larger than the optimum threshold value. Therefore, the maximum value of the signal values of the entire image area may be used as the initial value. The difference between the value and the optimum threshold is large and the processing time becomes long, which is not preferable. As another example of the method of setting the initial value, a method of obtaining the maximum value of the image data excluding the blank portions of several lines in the approximate center of the effective image area and setting it to the initial value, the signal in the effective image area There are a method of obtaining a histogram of values and setting a maximum value excluding blank portions of the histogram as an initial value, and a method of setting a signal value of a predetermined percentage of the cumulative histogram as an initial value.

On the contrary, when gradually increasing the threshold value from the smaller value toward the optimum threshold value, it is necessary to set the value smaller than the optimum threshold value to the initial value. Therefore, the minimum value of the predetermined range of the image data is set to the initial value. However, for the same reason as above, it is desirable to set the initial value according to the characteristics of each image.

The binarization processing is performed when there is an unnecessary portion in the radiographic image as described with reference to FIG. Alternatively, the entire image area may not be processed, and only the effective image area may be processed. However, in such a situation, it is preferable to perform the entire image as a target.

The labeling section 43 determines the continuity of the identification code in the image data to which the identification code is added and performs the labeling process. Specifically, for example, when a plurality of pixels having the identification code 1 are adjacent and continuous, the same label A, for example, is given to all the pixels of the continuous pixel group, and the pixels having the identification code 1 are adjacent to each other in other portions. If a plurality of consecutive pixels are consecutive, another label B is given to all the pixels of the consecutive pixel group. This operation is performed for all consecutive pixel groups. here,
The case where a plurality of pixels are adjacent to each other and are continuous includes a case in which pixels adjacent to a predetermined pixel in the vertical and horizontal directions have the same identification code, and a case in which pixels in the diagonal vertical direction in addition to the above direction have the same identification code.

When the labeling process is performed, in addition to the continuity of the identification code, the number of consecutive pixels is added as a criterion, and, for example, n or more (n is an integer of 2 or more) pixels are consecutive. You may give a label only to a pixel group. Also,
Labeling may be performed for both identification codes,
Depending on the purpose, it is preferable to use only one of them. Specifically, when it is desired to obtain the maximum value from the image data, it is better to perform labeling only on the continuous pixel group having the identification code 1, and when obtaining the minimum value, labeling is performed only on the continuous pixel group having the identification code 0. It is better to do

The image area determination unit 44 determines a desired image area from the labeled image areas.
Specifically, for example, a desired continuous pixel group, that is, a desired image region is selected from a plurality of labeled continuous pixel groups, for example, based on information of their positions in a radiation image and signal magnitude. . The selected continuous pixel group is 1
It may be one or plural. When the desired image area is not obtained, the threshold value setting unit 41 changes the threshold value appropriately or greatly according to the information, and the desired image area is selected from the binarization processing by the changed threshold value. Repeat up to. Therefore, the threshold setting unit 41, the binarization unit 42, the labeling unit 43, and the image area determination unit 44.
And correspond to the anatomical region determining unit 9 in the example of FIG. 1 which is the partial region dividing unit.

After determining the partial region for improving the sharpness of the image as described above, the image processing means 10 in FIG. 1 or the image processing unit 45 in FIG. 4 determines whether the lung field region or the selected desired image region is selected. For the image data, for example, the original image data So is an enhancement coefficient K (K is a positive number, preferably 3 or more) and m × m pixels (m is 3 or more) centered on a pixel of the original image data So. Image processing of frequency emphasis conversion to Sh is performed at Sh = So + K (So−Sm) using the average value Sm of the original image data of preferably 15 or less) and other than that, for image data in other image areas. , N × for converting the original image data So into an average value Sn of the original image data of n × n pixels (n is an odd number of 3 or more, preferably 15 or less) centered on the pixel. The image processing is a filtering process i.e. the unsharp mask process is performed.

Not limited to the above example, even if the specific region to be subjected to the frequency emphasis processing is a plurality of regions, even if the emphasis coefficient K or the value of m of the average value Sm is different between the plurality of regions, the other regions are not included. Even if the image processing is the frequency enhancement processing in which the enhancement coefficient K is set to 0 or a value close to 0, the image processing in the specific area sets the enhancement coefficient K to 0 and the image processing in the other areas is the non-sharp mask processing. May be The image data subjected to the image processing as described above by the image processing unit 10 or the image processing unit 45 is output to the image output device 11 or a printer,
The radiographic image is reproduced in which the sharpness of the lung field region or the selected desired region is increased to improve the diagnostic performance, and the graininess of the other parts is increased to reduce the rough impression given to the entire image.

The lung field area and the desired image area are determined using the image data obtained by the "prereading" as disclosed in Japanese Patent Laid-Open No. 58-67240, and the "main reading" is performed.
Image processing may be performed on the image data obtained by changing the image processing conditions between those areas and other areas. Further, although the frequency enhancement processing and the non-sharp mask processing are performed as the image processing in the above embodiment, it goes without saying that the gradation processing may be taken up. Of course, the radiation image is not limited to the front image of the human chest.

As described above, the region of interest is recognized, and the image processing condition, specifically, the frequency processing condition is changed inside and outside the region of interest to improve the diagnostic performance of the region of interest, and to improve the roughness of other portions. Although it reduces the impression, the diagnostic performance can be improved by other methods by applying this. Specifically, by changing the interpolation processing magnification of the interpolation processing inside and outside the region of interest and increasing the resolution only within the region of interest, the diagnostic performance is improved while suppressing an increase in the amount of data to some extent.

Depending on the noise value in the area, the type of filter that makes the roughness less noticeable is changed to improve the diagnostic performance.

Etc. are possible.

Further, in addition to the above, instead of the area, the reading condition / filter size / filter type / filter weighting factor / filter weight / corresponding to changes in signal value / contrast / dispersion value / difference value / noise value / information amount etc. It is possible to improve the diagnostic performance by changing the resolution / interpolation type / modulation degree and the like.

[0045]

According to the radiation image processing method of the present invention,
The image area read out from the radiation image conversion panel is divided into partial areas according to the characteristics obtained from the image signal, and for example, the image signal of the partial area where sharpness should be emphasized is subjected to frequency processing emphasis of an appropriate emphasis ratio. , The image processing conditions are changed between the partial regions having different characteristics so that the image signal of the other auxiliary partial regions is subjected to the filter processing for removing the noise. It is possible to reproduce in a state in which the diagnostic performance is excellent, and in other areas, the state in which the impression of roughness is reduced.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an example of a radiation image recording apparatus that implements a radiation image processing method of the present invention.

FIG. 2 is a block circuit diagram of a device that digitally processes image data.

FIG. 3 is an explanatory diagram showing an example of a method of determining a partial area of a radiation image.

FIG. 4 is a block circuit diagram showing the configuration of a CPU that implements different partial region determination methods.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray irradiation device 2 Subject 3 Radiation image conversion panel 4 Excitation light source 6 Photoelectric converter 7 A / D conversion unit 8 Image processing device 9 Anatomical region determination means 10 Image processing means 11 Image output device 21 CPU 41 Threshold setting unit 42 binarization unit 43 labeling unit 44 image region determination unit 45 image processing unit

Claims (3)

[Claims] 1. A radiation image processing method for performing image processing on an image signal of a radiation image formed corresponding to a transmission amount of radiation passing through each part of an object, wherein a region of the image signal is obtained from the image signal. A radiation image processing method, characterized in that the image processing condition is divided into a plurality of partial regions, and the condition of the image processing is changed between the partial regions having different characteristics. 2. An area of the image signal, a main area in which the image signal of the partial area is subjected to image processing of frequency enhancement processing, and a non-main area in which the image signal of the partial area is subjected to image processing of filtering processing. The radiation image processing method according to claim 1, wherein the radiation image processing method is divided into 3. The area of the image signal is a main area in which the image signal of the partial area is not processed, and a non-main area in which both image signals of the partial area are subjected to image processing of a filtering process. The radiation image processing method according to claim 1, wherein the radiation image processing method is divided into