JPH1098587A - Radiation picture reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of grid non-uniformity and moire in spite of the use of any kind of grid at the time of photographing by changing the frequency characteristics of signal processing means based on the cycles of still grids. SOLUTION: The reduction processing of a frequency component is executed for a read picture signal 4 by an image processing means 1 inclucing a filter and, then, it is converted into a digital picture signal by an AD converter 7. The picture processing means 1 consists of the three signal processing means 2a-2c, that is, the filter and a change-over means 3. The frequency characteristics of the three filters are the ones for satisfactorily reducing the frequency components of 3.4 cycle/mm, 4 cycle/mm and 5 cycle/mm by the respective signal processing means 2a-2c and their frequencies correspond to the cycles of the three kinds of still grids to be used at the time of photographing in this system. Then, the change-over means 3 executes an operation based on the grid cycle signal which indicates the grid cycle inputted by an operator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image reading apparatus, and more particularly to image processing performed on an image read by a radiation image reading apparatus.

[0002]

2. Description of the Related Art Conventionally, a radiographic image recorded on a radiographic film is photoelectrically read to obtain an image signal, and after appropriate image processing is performed on the image signal, the image is reproduced and recorded. I have. In addition, using a stimulable phosphor (stimulable phosphor), a medical radiation image of a human body or the like is temporarily recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is excited by laser light or the like. The light is scanned to generate photostimulated light, and the obtained photostimulated light is read photoelectrically to obtain an image signal. Based on the image signal, a radiation image of a subject is recorded on a recording material such as a photographic light-sensitive material or a CRT. There is also known a radiation image processing system for outputting a visible image to a device such as
No. 55-12492).

On the other hand, when a radiographic image is taken, there is known a method in which a stationary grid having a predetermined pitch is arranged between a subject and a recording medium in order to prevent image quality deterioration due to scattered radiation. . In this case, an image obtained by shooting is an image including a grid image.

When an image including such a grid image is read by the radiation image processing system as described above,
Due to the spatial frequency corresponding to the grid pitch and the sampling frequency when digitizing the image signal,
Grid unevenness or moire may occur in a digital image obtained by reading. Conventionally, a filter, which is one of image processing functions incorporated in a reading apparatus, reduces frequency components corresponding to a grid to prevent such grid unevenness and moiré.

[0005]

However, in general, the pitch of the grid, which most effectively prevents the image quality from deteriorating due to scattered radiation, differs depending on the imaging conditions such as the imaging method, the imaging site or the imaging device. When performing radiography, it is usual to use several types of grids having different pitches depending on the radiography conditions.

On the other hand, the image processing function of the above-mentioned conventional reading apparatus is fixedly incorporated, and its processing characteristics are constant. Therefore, radiation images including grid images of various pitches are input. In such a case, the frequency components corresponding to the pitch of the grid image included in the radiographic image cannot be sufficiently reduced to such a degree that grid unevenness or moire does not occur.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a radiation image reading apparatus capable of preventing grid irregularities and moire from occurring regardless of what kind of grid is used at the time of photographing. It is.

[0008]

SUMMARY OF THE INVENTION A radiation image reading apparatus according to the present invention reduces a frequency component corresponding to a period of the grid with respect to an image signal obtained by reading a radiographic image captured using a stationary grid. A radiation image reading apparatus having image processing means for performing image processing, wherein the image processing means has a frequency characteristic variable signal processing means and a frequency for changing a frequency characteristic of the signal processing means based on a period of the stationary grid. It is characterized by comprising characteristic changing means. Here, the “image signal obtained by reading a radiation image” may be an analog image signal or a digital image signal after AD conversion.

Further, since the period of the stationary grid and the radiographing menu at the time of radiographic image correlation are correlated, the frequency characteristic changing means changes the frequency characteristic in accordance with the radiographic image radiographing menu. May go. Here, the photographing menu means a photographing method (normal photographing, magnifying photographing, tomographic photographing, etc.), a photographing part (head, neck, chest, abdomen, etc.), photographing device, and the like.

Specifically, for example, the signal processing means may be a plurality of processing means for performing signal processing having different frequency characteristics, and the frequency characteristic changing means may be a switching means for switching the plurality of processing means. desirable. Alternatively, the signal processing unit may be a unit having a frequency characteristic defined by a predetermined parameter, and a unit for changing the parameter may be provided as the frequency characteristic changing unit.

[0011]

According to the radiation image reading apparatus of the present invention,
It has different frequency characteristic variable signal processing means, and the frequency characteristics of the signal processing means can be changed according to the period of the stationary grid included in the image signal. Signal processing that sufficiently reduces the frequency components corresponding to the included static grid can be applied to the image signal, thereby achieving high image quality without grid unevenness and moiré regardless of the type of grid used for shooting. Image can be obtained.

In general, the cycle of the static grid used for shooting is determined according to the shooting menu. Therefore, the cycle of the static grid used for shooting is automatically determined in accordance with the shooting menu. If switching to the optimal signal processing means is performed, it is not necessary to input the period of the stationary grid for switching the signal processing means, and the burden on the operator can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a radiation image reading apparatus according to the present invention will be described below with reference to the drawings, together with the problems of the conventional apparatus. The embodiment described below relates to the reader of the radiation image processing system shown in the above-mentioned reference. The reading device is a device that reads a captured image recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet stores radiation energy corresponding to the captured image, The reading device scans this sheet with a laser beam, thereby obtaining a photostimulated light having a light amount corresponding to the stored energy, reading the photoelectrically, and obtaining an image signal representing a captured image, Further, sampling is performed at a density of 10 pixels / mm to generate a digital image signal representing a captured image.

In this radiation image reading apparatus, in order to obtain an appropriate digital image signal, in the above process, for example, conversion of the image signal using a conversion table, classification of the image signal into frequency components, enhancement of predetermined frequency components Alternatively, various image processing such as removal is performed. Such image processing includes a process performed on a signal before digitization and a process performed on a digital image signal after digitization. At any time.

As one of such image processing, there is a processing of reducing a predetermined frequency component using a filter.
The present invention relates to an image processing unit including such a filter in a radiation image reading apparatus, and the image processing unit will be described below. In addition, other image processing,
Since the scanning of the stimulable phosphor sheet is described in the above-mentioned reference, the description is omitted in this specification.

Conventionally, the frequency characteristics of the filter used in the above-described processing have been fixedly determined by the specifications of the reader. In other words, for example, if a filter (anti-aliasing filter) provided for the purpose of reducing the frequency above the Nyquist frequency of an image signal in order to prevent an aliasing error, since the reading density of the reading device is 10 pixels / mm, the Nyquist frequency 5 cycle / mm
What is necessary is just to implement as a filter of the response characteristic which reduces the above-mentioned frequency components, and in the radiation image reading apparatus shown in the above-mentioned reference, this was conventionally implemented as one analog filter. Further, the reduction of the frequency component of the grid for preventing grid unevenness and moiré has been simultaneously performed by the anti-aliasing filter.

However, when performing image processing such as reducing the frequency components corresponding to the static grid included in the image, the cycle of the static grid is not determined by the specifications of the reading apparatus, but is determined by several types at the time of photographing. Since the stationary grid can be used properly, if it is realized as one filter as in the above filter, grid unevenness or moiré can be effectively prevented with respect to a certain grid. A problem that a sufficient effect cannot be obtained. Therefore, in the radiation image reading apparatus of the present invention, the frequency characteristic of the filter can be changed according to the grid cycle.

FIG. 1 is a diagram showing an embodiment of the radiation image reading apparatus of the present invention. As shown in the figure, in the present embodiment, the read image signal 4 is subjected to the above-mentioned frequency component reduction processing by the image processing means 1 including the above-mentioned filter, and then the digital image signal The conversion to.

In the present embodiment, the image processing means 1
It comprises two signal processing means 2 a, 2 b, 2 c, that is, a filter and switching means 3. The frequency characteristics of the three filters are
Each signal processing means 2a is 3.4 cycle / mm, signal processing means 2
b has a characteristic of sufficiently reducing the frequency component of 4 cycle / mm, and the signal processing means 2c has a characteristic of sufficiently reducing the frequency component of 5 cycle / mm. This is the frequency corresponding to the period. The dotted line in the frequency characteristic diagram indicates the Nyquist frequency (5.0 cycle / mm).

The three filters are switched by the switching means 3. At this time, the switching means 3 switches based on a grid cycle signal 5 indicating the grid cycle input by the operator. That is, if the grid cycle signal 5 indicates 3.4 cycle / mm, the signal processing means 2a
, If it indicates 4 cycles / mm, the signal processing means 2b
If it indicates 5 cycle / mm, the signal processing means 2c is selected. Here, the input of the grid cycle by the operator is performed by, for example, prompting the operator to input on the operation screen of the reading device, converting the input value into a signal, and switching the signal.
It may be transmitted to. In addition, it can be realized by any method and means commonly used for inputting operation conditions and the like.

Alternatively, the period of the grid used is
Focusing on the fact that it is determined by the imaging menu specified at the time of imaging the radiation image, the switching means 3 may perform switching in conjunction with the imaging menu. In this case, the switching means 3 stores the correspondence between the shooting menu and the grid cycle in advance, and switches the shooting menu signal 6 generated when the operator selects the shooting menu.
A filter may be selected from the correspondence stored at the time of receiving, or a method of associating at the time of selecting a shooting menu and transmitting the corresponding grid period signal 5 to the switching means 3 may be used. Conceivable.

The number of the signal processing means and the frequency characteristics of the processing performed by each signal processing means may be determined for each radiation image processing system in accordance with the type of stationary grid used for radiography in that system. Of course, the above three signal processing means are only examples.

Next, another embodiment of the present invention will be described with reference to FIG. In the embodiment of FIG. 2, the above-described signal processing is performed on the digital image data after the A / D conversion, and more specifically, the filtering processing by a mask operation is performed. In this case, the frequency characteristic of the processing performed on the image data is determined by the mask parameter. Therefore, in order to change the frequency characteristic according to the cycle of the grid, it is sufficient to change the mask parameter according to the cycle of the grid. In the present embodiment, this processing is performed by the parameter changing means 8. .

That is, the parameter changing means 8 determines a parameter by performing a predetermined operation based on the grid cycle signal 5 indicating the grid cycle input by the operator, or determines an appropriate parameter from a plurality of parameters stored in advance. The determined or selected parameter is transmitted to the signal processing means 2 by selecting a parameter or the like. Note that, as the input method of the grid period signal 5, as in the embodiment of FIG. 1, any commonly used method can be applied. Further, similarly to the embodiment of FIG. 1, the parameters may be determined based on the photographing menu signal 6 instead of the grid period signal 5.

Further, the signal processing unit 2 performs a predetermined filtering process using the mask parameter transmitted from the parameter changing unit 8, so that the frequency component corresponding to the period of the grid is reduced.

As described above, according to the radiation image reading apparatus of the present invention, since the filtering process suitable for the read image is performed, it is possible to effectively prevent grid unevenness and moire.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a radiation image reading apparatus according to the present invention.

FIG. 2 is a diagram showing another embodiment of the radiation image reading apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image processing means 2 Signal processing means 3 Switching means 4 Image signal 5 Grid cycle signal 6 Shooting menu signal 7 AD converter 8 Parameter changing means

Claims (4)

[Claims] 1. A radiation image reading apparatus comprising: an image processing unit configured to perform image processing for reducing a frequency component corresponding to a period of the grid on an image signal obtained by reading a radiation image captured using a stationary grid. In the apparatus, the image processing unit includes a signal processing unit having a variable frequency characteristic, and a frequency characteristic changing unit that changes a frequency characteristic of the signal processing unit based on a cycle of the stationary grid. Reader. 2. The radiation image reading apparatus according to claim 1, wherein the frequency characteristic changing unit changes the frequency characteristic in accordance with an imaging menu at the time of imaging the radiation image. 3. The method according to claim 1, wherein the signal processing unit is a plurality of processing units that perform signal processing with different frequency characteristics, and the frequency characteristic changing unit is a switching unit that switches the plurality of processing units. The radiation image reading device according to claim 1 or 2, wherein: 4. The apparatus according to claim 1, wherein said signal processing means is means having frequency characteristics defined by predetermined parameters, and said frequency characteristic changing means is means for changing said predetermined parameters. 3. The radiation image reading device according to 1 or 2.