JPH04337874A - Processor for radiation picture signal - Google Patents

Abstract

PURPOSE:To improve the contrast of a signal in a high spatial frequency area and to improve diagnosis performance by reducing the amplitude of the low spatial frequency component of a radiation picture signal and relatively emphasizing the frequency of the signal in the high spatial frequency area. CONSTITUTION:An image pickup means obtains a digital radiation picture corresponding to the transmission line amount of respective parts in a subject. A picture processor 7 is provided with a function as a low frequency reduction means. The picture processor 7 stores the digital radiation picture signal inputted from a photoelectric conversion device 5 and obtains a non-sharp mask signal (Su) corresponding to a prescribed frequency from the above stored data. When the stored original digital radiation picture signal is set to So and a reduction coefficient to K (0<k<=1), the digital radiation picture signal (S) where amplitude is less than the prescribed low spatial frequency is reduced is obtained by operating S=So-K.Su. Then, the signal S is picture-processed such as a gradation processing and it is outputted to a radiation picture reproduction device 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image signal processing apparatus, and more particularly to image processing (frequency processing) in a medical radiography system.

0002

2. Description of the Related Art Radiographic images such as X-ray images are often used for medical purposes. One method for obtaining this radiographic image is the so-called radiographic method, in which radiation passing through the subject is irradiated onto a phosphor layer (phosphor screen), and this visible light is irradiated onto a film coated with a silver salt photosensitive material for development. be.

[0003] In recent years, with the advancement of radiographic imaging technology,
Methods have been devised to scan the radiograph, read the radiographic image information recorded thereon, convert it into a digital signal, and then reproduce it on a CRT or photosensitive material. As a result, more diagnostic information can be obtained from a single radiograph, resulting in improved diagnostic performance and reduced exposure dose. This method is also expected to improve the efficiency of storing and retrieving radiation image information.

[0004] In the radiation image information reading device using the photographic film, the photographic film on which the radiation image is recorded is exposed and scanned with reading light, and the reflected or transmitted light is detected by a photodetector and converted into an electrical signal. It is done. Also,
On the other hand, methods for obtaining radiographic image information without using radiographic films made of silver salt photosensitive materials have been devised. This method involves causing radiation passing through the subject to be absorbed by some type of phosphor, and then exciting this phosphor with, for example, light or thermal energy, so that the phosphor accumulates due to said absorption. There are devices that emit radiation energy as fluorescence and detect this fluorescence to create an image. Specifically, for example, U.S. Patent Nos. 3 and 8
No. 59,527 or Japanese Unexamined Patent Publication No. 55-12144. These methods use a radiation image conversion method using a stimulable phosphor and visible light or infrared rays as stimulable excitation light, and use a radiation image conversion panel with a stimulable phosphor layer formed on a support. Then, the radiation that has passed through the object is applied to the photostimulable phosphor layer of this radiation image conversion panel, and radiation energy corresponding to the radiation transparency of each part of the object is accumulated to form a latent image. By scanning the stimulable phosphor layer with the stimulated excitation light, the radiation energy accumulated in each part of the radiation image conversion panel is emitted and converted into light, and the optical signal is multiplied by photoelectrons depending on the intensity of this light. Radiation image information is obtained by detecting with a photoelectric conversion element such as a tube or photodiode.

[0005] In another method, radiation transmitted through an object is absorbed by a semiconductor panel having a uniformly charged photoconductor layer of selenium, silicon, etc. to form an electrostatic latent image. There is a method that electrically detects an electrostatic latent image on the semiconductor panel and converts it into an image by scanning the semiconductor panel with light (see, for example, Japanese Patent Laid-Open No. 54-31219).

The radiographic image information obtained in this way may be processed as is or processed into a silver halide film, subjected to image processing such as spatial frequency processing and gradation processing in order to further improve the diagnostic properties of the X-ray images. It is output to a CRT or the like and visualized, or it is stored in an image storage device such as a semiconductor storage device, a time storage device, or an optical disk storage device, and then, if necessary, it is taken out from these image storage devices and stored on a silver halide film. It is output to a CRT or the like and visualized.

As one of the spatial frequency processing methods, an unsharp mask signal Sus for each pixel is obtained, and S'=Sorg+β(Sorg-Sus ) is known to enhance the sharpness of an image by performing spatial frequency enhancement, so-called edge enhancement.
2-62373, etc.).

[0008]

However, the above spatial frequency processing method has the problem that the number of calculations is large and it is difficult to perform image processing in real time. In addition, since the above method emphasizes the high spatial frequency region, there is a problem that image noise is emphasized, resulting in image quality deterioration due to image noise.
This method has the disadvantage that image quality deteriorates significantly in areas where the radiation dose is low (signal is low).

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a new frequency processing device with simple calculation processing and improved processing speed. Also,
SUMMARY OF THE INVENTION An object of the present invention is to provide a new frequency processing device that does not cause image quality deterioration due to noise in small portions of a signal even if the contrast (sharpness) in a high frequency region is improved. A further object of the present invention is to provide a new frequency processing device that improves image quality deterioration due to noise in small portions of signals while maintaining contrast in high frequency regions.

0010

[Means for Solving the Problems] Therefore, a radiation image signal processing apparatus according to the present invention is constructed as shown in FIG. In FIG. 1, the imaging means detects the amount of radiation that has passed through the subject and converts it into a digital radiation image signal, and the low frequency component attenuation means detects the amount of radiation that has passed through the subject and converts it into a digital radiation image signal, and the low frequency component attenuation means detects the amount of radiation that has passed through the subject and converts it into a digital radiation image signal. Attenuate the amplitude.

[0011] Here, the low frequency component attenuation means obtains an unsharp mask signal corresponding to a predetermined low spatial frequency from the digital radiation image signal obtained by the imaging means, and applies a predetermined attenuation to the unsharp mask signal. It is preferable that the amplitude of components below the predetermined low spatial frequency be attenuated by subtracting a value multiplied by a coefficient from the digital radiation image signal obtained from the imaging means.

0012

[Operation] According to this configuration, the amplitude of the low spatial frequency region of the digital radiation image signal is attenuated compared to the amplitude of the high spatial frequency region, so that the signal in the high spatial frequency region can be relatively emphasized in frequency. Can be done. This improves the contrast (sharpness) of the signal in the high spatial frequency region, making it possible to reproduce images suitable for diagnosis.

Furthermore, since the signal in the low spatial frequency region is attenuated, the range of change in the radiation transmittance of the subject is reduced in a pseudo manner, and changes in the dark and dark parts having a relatively large area in the radiographic image are reduced. Width can be reduced. This improves contrast (sharpness) in high spatial frequency regions.
This makes it possible to simultaneously regenerate parts of the subject that are easy to transmit radiation and parts that are difficult to transmit radiation into a state that is easy to observe, without reducing the amount of radiation. Furthermore, this improves the S/N ratio of the portion of the subject that is difficult for radiation to pass through, and improves image quality deterioration due to noise.

In order to attenuate the amplitude of the low spatial frequency region of the digital radiation image signal, an unsharp mask signal corresponding to a predetermined low spatial frequency is obtained from the digital radiation image signal, and a predetermined attenuation coefficient is applied to this unsharp mask signal. By subtracting the value obtained by multiplying by .

[0015]

[Examples] Examples of the present invention will be described below. FIG. 2 showing one embodiment is a basic configuration diagram of a radiation image capturing and reproducing device including a radiation image signal processing device according to the present invention.
An example of application to radiography of the human body for medical purposes will be shown.

Here, the radiation generating device 1 irradiates radiation such as X-rays toward a subject 2 (such as a human chest). A photostimulable fluorescent plate 3 is provided on the side facing the radiation generating device 1 across the subject 2, and this photostimulable fluorescent plate 3 changes the radiation of the subject 2 relative to the amount of radiation emitted from the radiation generating device 1. Energy according to the transmittance distribution (passing dose) is accumulated and recorded in the photostimulable phosphor layer, and the object 2
form a latent image.

The stimulable phosphor plate 3 is provided with a stimulable phosphor layer on a support by vapor phase deposition of the stimulable phosphor or coating of a stimulable phosphor paint. The body layer is shielded or covered by a protective member to block out environmental influences and damage. As the stimulable phosphor material, for example, a material as disclosed in Japanese Patent Application Laid-Open No. 61-72091 or Japanese Patent Application Laid-Open No. 59-75200 is used.

On the other hand, reading of image information from the photostimulable fluorescent plate 3 on which radiation image information of a subject has been accumulated and recorded as described above is carried out as follows. That is, the stimulated excitation light source (gas laser, solid-state laser, semiconductor laser, etc.) 4 generates an excitation light beam whose emission intensity is controlled,
The excitation light beam scans the photostimulable fluorescent plate 3 on which radiation image information of the subject is accumulated and recorded, and the radiation energy (latent image) accumulated in the photostimulable fluorescent plate 3 is generated.
is emitted as fluorescence (stimulated luminescence).

The photoelectric conversion device 5 includes a filter 6 that passes only the fluorescent light (stimulated luminescence) emitted by scanning the photostimulable fluorescent plate 3 with an excitation light beam. Light is received through the incoming light and photoelectrically converted into a current signal corresponding to the incident light for each scanning point, thereby obtaining a radiation image signal for each scanning point. The analog radiation image signal photoelectrically read by the photoelectric conversion device 5 is sequentially A/D converted by an A/D converter (not shown).
/D conversion and output as a digital radiation image signal to an image processing device 7 equipped with a microcomputer. Therefore, in this embodiment, the photostimulable fluorescent plate 3, the photostimulable excitation light source 4, and the photoelectric conversion device 5 constitute an imaging means.

The image processing device 7 performs image processing such as gradation processing on the digital radiographic image signal, and also performs arithmetic processing for attenuating the amplitude of low spatial frequency components according to the present invention, thereby converting the digital radiation image signal into a photoelectric conversion device. The digital radiation image signal from 5 is converted into a form suitable for diagnosis and then output to the radiation image reproduction device 8. Therefore, in this embodiment, the image processing device 7 has the function of low frequency component attenuation means.

The radiation image reproducing device 8 is a printer or a CR.
The digital radiographic image signal processed by the image processing device 7 is input to the monitor such as T, and the captured radiographic image is visualized as a hard copy or a playback screen. Incidentally, together with the radiographic image reproducing device 8, or together with the radiographic image reproducing device 8.
Instead, a storage device (filing system) such as a semiconductor storage device may be provided to store the read radiation image signal.

Furthermore, in this embodiment, a digital radiographic image signal was obtained by reading the radiographic image information accumulated and recorded on the photostimulable fluorescent plate 3 as described above.
A configuration may be adopted in which the passing dose is directly detected by a semiconductor detector such as a CCD line sensor to obtain a digital radiation image signal. Alternatively, a digital radiation image signal may be obtained by irradiating a screen film with radiation that has passed through the subject, developing the film, and reading the image on the film with a reading device. The configuration of the imaging means for obtaining an image signal is not limited to the above embodiment.

The process of attenuating the amplitude of low spatial frequency components performed by the image processing device 7 will now be described. The image processing device 7 stores the digital radiation image signal input from the photoelectric conversion device 5, and obtains an unsharp mask signal Su corresponding to a predetermined low frequency from this stored data. Then, when the stored original digital radiation image signal is So and the attenuation coefficient is K (0<K≦1), by performing the calculation S=So−K・Su, the predetermined low space is A digital radiation image signal S in which the amplitude of components below the frequency is attenuated is obtained, and this signal S is subjected to image processing such as gradation processing and then output to the radiation image reproduction device 8.

The gradation processing is necessary for displaying a radiation image in a diagnostically favorable state, and is used in combination with the spatial frequency processing as described above. here,
The gradation processing may be performed after the spatial frequency processing, but it may also be performed before the spatial frequency processing, and the gradation processing itself converts the analog signal before A/D conversion or after D/A conversion into an analog signal. It may be processed by a circuit, or the digital signal may be digitally processed on a computer.

[0025] In the process of obtaining the digital radiation image signal S in which the amplitude of components below the predetermined low spatial frequency is attenuated, in order to normalize the value of the modulation transfer function near zero spatial frequency, the following procedure is performed. Processing may be performed using a formula. S'=So/(1-K)-K・Su/(1-K) The unsharp mask signal Su is 0.5 cycles/mm.
It is preferable to use an unsharp mask signal such that the modulation transfer function is 0.5 or less at a spatial frequency of 0.01 cycles/mm. With the above, 0.5 cycles/
It is more preferable to use a non-sharp mask signal whose modulation transfer function is 0.5 or less at a spatial frequency of mm.

The unsharp mask signal Su can be created as follows. The first and most basic method is to store the original digital radiation image signal So, read out the signals at each scanning point along with peripheral data according to the size of the non-sharp mask, and calculate the average value (simply There is a method of obtaining the unsharp mask signal Su as an average (average or various weighted averages).

Second, after the original signal So is read out from the stimulable fluorescent plate 3 with a small diameter beam from the stimulable excitation light source 4, image information still remains on the stimulable fluorescent plate 3. In this case, there is a method of reading out the signals of each scanning point by averaging them together with the signals of the surrounding areas using a light beam with a large diameter matching the size of the unsharp mask signal.

Furthermore, the third method utilizes the fact that the beam diameter of the readout light beam gradually widens due to scattering in the phosphor layer, and the original signal is generated by the light emission signal from the incident side of the light beam. There is a method of creating a non-sharp mask signal Su by creating a signal So and emitting light on the side through which the light beam passes. In this case, the size of the unsharp mask signal can be controlled by changing the degree of light scattering of the phosphor layer or by changing the size of the aperture that receives the light.

The fourth method is to perform low-pass filter processing on the analog signal in the beam scanning direction (main scanning direction), and to average the digital radiation signal after A/D conversion in the sub-scanning direction. be. Here, when attenuating the amplitude of a component below a predetermined low spatial frequency using the unsharp mask signal Su, if the modulation transfer function M0 near zero spatial frequency before the amplitude is attenuated is used as a reference,
It is preferable to attenuate so that the value becomes 0.2 ≦M0≦0.9 in order to provide an image suitable for diagnosis;
．． More preferably, 3≦M0≦0.8. Furthermore, when 0.68≦M0≦0.80, the obtained image can be used for diagnosis without any discomfort compared to a system using a conventional screen film.

Therefore, the attenuation coefficient K is 0.1≦K≦0
．． 8, more preferably 0.2≦K≦0
．． 7 is more preferable. Moreover, the most preferable range of the attenuation coefficient K is 0.20≦K≦0.32. In addition, the shape of the unsharp mask signal (see FIG. 3) determined by the spatial frequency fc below 0.5 cycles/mm at which the modulation transfer function is set to 0.5, or the value of the attenuation coefficient K must be specified before processing. These values can be input individually using an external input device, or can be input selectively when a region to be imaged, etc. is specified from among multiple preset values depending on the body region or case. A possible method is to analyze the read image data and automatically set a preferable value.

As described above, the unsharp mask signal Su
If the value obtained by multiplying by the attenuation coefficient K is subtracted from the original digital radiation image signal So (see Figure 3), the amplitude of the signal component below a predetermined low spatial frequency will be reduced to the original signal, as shown in Figure 4. An attenuated image signal can be obtained. If the amplitude of signal components below a predetermined low spatial frequency is attenuated, areas that are easily transparent to radiation and areas that are difficult to transmit, such as the lung field and mediastinum in the case of chest imaging of a human body, can be attenuated. Even if they exist at the same time, the image after signal processing becomes an image in which the range of change in radiation transmittance is reduced in a pseudo manner.

[0032] Therefore, it is possible to simultaneously reproduce a state where it is easy to observe the parts where radiation easily transmits and the parts where it is difficult to transmit radiation. Since the amplitude remains the same as the original, contrast in the high spatial frequency region is ensured, and diagnostic information such as blood vessels and small lesions is not destroyed by the frequency processing, making it possible to obtain images with excellent diagnostic properties. Can be done.

Furthermore, when the amplitude is attenuated to a relatively high spatial frequency region, the amplitude of the signal in the high spatial frequency region becomes medium-low.
It becomes relatively large compared to the low frequency region, and the edge portion of the image becomes an emphasized image. Therefore, such frequency processing can apparently improve the contrast (sharpness) of an image. Next, a more specific state of the frequency processing will be described with reference to FIGS. 3, 4, and 5.

So in FIG. 3 shows the spatial frequency response characteristic of the digital radiation image signal obtained when the radiation image accumulated on the stimulable phosphor plate 3 is sampled at 100 μm/pixel. be. In addition, Su is
It shows the spatial frequency response characteristics of a Gaussian distribution unsharp mask signal set so that the modulation transfer function at 0.5 cycles/mm is 0.5 or less. In this example, 100
When the above image sampled at μm/1 pixel is averaged over 80 pixels×80 pixels, a non-sharp mask signal is created by weighting it in a Gaussian distribution. In the figure, fc is the spatial frequency when the modulation transfer function is 0.5.

Note that the creation of the unsharp mask signal Su is as follows:
The weighting may be omitted and simple averaging may be taken, and the spatial frequency response characteristic of the rectangular unsharp mask signal in that case is shown in FIG. However, the shape of the non-sharp mask is
It is not necessary to make it square like 80 pixels x 80 pixels,
It may be rectangular. FIG. 4 shows the calculation result S of (So-K・Su), and in this example, the attenuation coefficient K is set to 0.
．． 3. Further, the attenuation coefficient K is normally fixed to a predetermined value, but if it is changed according to the magnitude of the original digital radiation image signal So or the unsharp mask signal Su, it is possible to The degree of amplitude attenuation of the signal in the low spatial frequency region can be changed depending on the region, and images with improved diagnostic performance can be provided.

[0036]

As explained above, according to the present invention, by attenuating the amplitude of the low spatial frequency component of a radiation image signal, it is possible to frequency-emphasize a signal in a relatively high spatial frequency region, and The signal contrast in the frequency domain is improved. In addition, attenuating the amplitude of the low spatial frequency component pseudo-reduces the range of change in radiation transmittance of the subject, making it possible to simultaneously observe parts of the subject that are easy to transmit radiation and parts that are difficult to transmit radiation. This makes it possible to easily regenerate the data. Therefore, particularly in medical radiation images, it is possible to obtain reproduced images suitable for diagnosis, and there is an effect that diagnostic performance using radiation images can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing the spatial frequency response characteristics of the original radiation image signal So and the unsharp mask signal.

FIG. 4 is a diagram showing a spatial frequency response characteristic resulting from attenuating the amplitude of a low spatial frequency component.

FIG. 5 is a diagram showing a spatial frequency response characteristic when a non-sharp mask signal is created by simple averaging without weighting.

[Explanation of symbols]

1 Radiation generator 2. Subject 3. Stimulable fluorescent plate 4. Stimulative excitation light source 5 Photoelectric conversion device 7 Image processing device 8 Radiographic image reproduction device.

Claims (2)

[Claims] 1. Imaging means for detecting the amount of radiation passing through a subject and converting it into a digital radiation image signal, and a low frequency component for attenuating the amplitude of the low spatial frequency component of the digital radiation image signal obtained by the imaging means. A radiation image signal processing device comprising: attenuation means. 2. The low frequency component attenuation means obtains an unsharp mask signal corresponding to a predetermined low spatial frequency from the digital radiation image signal obtained by the imaging means, and applies a predetermined attenuation coefficient to the unsharp mask signal. 2. The digital radiation image signal according to claim 1, wherein the amplitude of the component below the predetermined low spatial frequency is attenuated by subtracting a value obtained by multiplying by the digital radiation image signal obtained from the imaging means. A radiation image signal processing device.