JP2001037745A - Radiation image processing system, system and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good medical image by subjecting a radiation image to deterioration restoration complying with a signal/noise ratio meeting a dose. SOLUTION: This radiation image processing method is an image processing method which inputs the image data indicating the radiation image and subjects the image data to space filter processing. A space filter coefficient used in the space filter processing is controlled in accordance with the image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to medical digital image processing (computer image processing).
In particular, suppress noise amplification and repair deterioration such as blurring
It relates to the restoration of X-ray images.

[0002]

2. Description of the Related Art An image obtained by an image capturing system includes deterioration such as blur due to various factors including a sensor, and further includes noise.
Various image restoration techniques have been considered to repair the blur.

[0003] Examples thereof include techniques such as an inverse filter, a Wiener filter, and a limited deconvolution (Rosenfeld, Kak, translated by Makoto Nagao: Digital Image Processing: Modern Science Co., Ltd.). Further, a method of directly creating a spatial filter for image restoration has been proposed by the present applicant.

[0004] An unsharp masking process is also known as a technique for enhancing an edge of an image. (Id.)

[0005]

In the technique used for image restoration, it is important to suppress the noise amplification to repair the deterioration. In this method, a model is used in which noise is added to the deteriorated image. Have been. In this model, it is premised that the noise is riding uniformly irrespective of the image (pixel value). However, in the X-ray image, there is a problem that the ratio of the signal to the noise changes depending on the pixel value. X received by the sensor in Fig. 7
As shown in the graph of the relationship between the dose of the line and the S / N ratio, the smaller the pixel value (dose), the worse the S / N ratio.

Therefore, if the image restoration method using a model with uniform noise is used as it is, the noise becomes conspicuous in a low dose range in the image (for example, the mediastinum in a chest image). In order to suppress this, a method with a low restoration level is used, and a high dose range (for example, lung field in chest image)
The degree of restoration is insufficient and blurring remains.

In order to solve such a problem, in the unsharp masking processing of the edge enhancement processing, a technique of changing the enhancement coefficient depending on a pixel value has been performed (for example, Japanese Patent Publication No. 62-62373).

However, what is performed here is only edge enhancement processing, and the purpose is to intentionally apply overshoot and undershoot to edges as shown in FIG. 8 and use the Mach effect of the human eye. It is a process to make it look clearer, and unlike the restoration process to restore the deterioration such as blurring, there is no theoretical requirement that the S / N ratio must be suppressed to just how much It just changes the degree of attachment. The frequency characteristic is also limited to a certain form as shown in FIG. 9, and the characteristic cannot be freely changed depending on the pixel value.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to restore a radiation image to a signal / noise ratio corresponding to a dose in a radiation image and obtain a good medical image. .

[0010]

Means for Solving the Problems In order to achieve the above object, the present invention is characterized by having the following constitution.

According to a first aspect of the present invention, there is provided an image processing method for inputting image data representing a radiation image and performing a spatial filtering process on the image data. And determining a spatial filter coefficient used in the spatial filtering based on the index of the dose.

The radiation image processing method according to a second aspect is characterized in that a low-frequency image is created from the radiation image, and the spatial filter coefficient is controlled based on the low-frequency image.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present embodiment will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing the overall configuration of an example of a radiation image processing system.

4. 3.X controlled by X-ray generator control unit
X-rays generated from the source are transmitted through the patient and detected by the X-ray sensor. The detected X-ray is input to the 5. image input unit as a digital X-ray image (radiation image). The input digital X-ray image is subjected to image processing such as X-ray sensor correction processing, gradation processing, dynamic range compression processing, and sharpening processing by the image processing unit. The processed digital X-ray image can be displayed on a diagnostic monitor, stored in an image storage unit, connected via a network, a printer, a diagnostic workstation,
4. Output to the image database. If the displayed and output images are not satisfactory, the image processing and display are repeated while changing the image processing parameters. The above operations are performed by the operation unit.

FIG. 2 shows a processing flow of an embodiment in which a spatial filtering process in which the frequency characteristic is changed depending on the dose in such a system. Fig. 3 shows this conceptual diagram.

First, an image serving as an index of the dose is created in S20. Basically, the pixel value output from the sensor is proportional to the X-ray dose incident on the sensor.
If it is converted, you need to restore it.) This pixel value may be used as it is, but as an index of the X-ray dose, the low-frequency image excluding the fine structure reflects the X-ray dose more. In the present embodiment, a low-frequency image is created by applying a low-pass filter to the original image, and this low-frequency image is used as an image serving as an index of the dose.

In the present embodiment, as shown in FIG.
A filter coefficient is extracted from the spatial filter table using the pixel value of the image serving as an index of the dose as an index, and the pixel value of the original image corresponding to the pixel value is filtered.

In step S21, a pixel value of an image serving as a dose index is extracted, and in step S22, a filter coefficient is extracted from the spatial filter table using the extracted pixel value as an index.

At S23, the filter coefficient extracted and S
A sum-of-product operation is performed on the pixel value of the original image corresponding to the pixel value of the image serving as an index of the dose extracted in 21 and the peripheral pixel values thereof.

The above processing of S21 to S23 is performed on all pixels of the original image.

For example, in the case of a 3 × 3 filter, the filtering is performed as shown in FIG.

[0023] (x, y) pixel value I _{'x, y} position of is calculated by the product-sum operation of the following equation.

[0024]

[Outside 1]

In this embodiment, this an _{, m} is extracted from the spatial filter table using the pixel value of the image as an index of the dose as an index.

Next, an embodiment of how to make this spatial filter table will be described.

As shown in FIG. 5, a frequency characteristic for each level is obtained based on a signal / noise ratio at a dose of an appropriately set level. As a method of obtaining the frequency characteristic, there are a method such as an inverse filter, a Wiener filter, a limited deconvolution, or a method using a multiple regression method. A spatial filter is created by performing a Fourier inverse transform on the frequency characteristics obtained using these techniques. Even if the frequency characteristics are not determined based on the signal / noise ratio for each dose level, the frequency characteristics can also be created by obtaining one reference frequency characteristic and multiplying it by a constant according to the level.

For example, it can be obtained by the following equation.

[0029] _{f 'n (α) = c} n × f (α) f' n (α): the frequency characteristic c _n Level n: level n constants f (alpha): a reference frequency characteristic

It is also possible to obtain a plurality of reference frequency characteristics and obtain a level therebetween by interpolation.

As a simpler example, there is a method of changing the coefficient of the spatial filter according to the dose level. Let the coefficients of the spatial filter be a _{i, j} (i = −N... N, j = −N ·
··· N) Let c _{n be} a constant of level n

[0032]

[Outside 2] Thus, a spatial filter coefficient a ′ _{i, j} for each level can be obtained.

The spatial filter created for each level in this manner defines the correspondence between the spatial filter and the pixel value of the image serving as a dose index as shown in FIG. The correspondence may be one-to-one, many-to-one, one-to-many, or many-to-many.

By using this table, a spatial filter can be derived using the pixel value of an image as an index of the dose as an index.

According to the present embodiment, the balance between the degree of restoration of degradation and the degree of suppression of noise can be controlled in accordance with the signal / noise ratio which differs depending on the dose, and a good output image can be obtained based on the X-ray image. Can be.

Further, by applying a spatial filter having different frequency characteristics according to an index indicating the dose at each pixel (for example, a pixel value of a low-frequency image), deterioration restoration suitable for the signal / noise ratio of each pixel is realized with high accuracy. can do.

(Other Embodiments) The functions of the above-described embodiments (for example, a computer connected to an apparatus or a system connected to the various devices so as to operate various devices so as to realize the functions of the above-described embodiments) 2) by supplying software program codes for realizing the functions realized by the flowchart of FIG. 2, and operating the various devices according to a stored program in a computer (CPU or MPU) of the system or the apparatus. Implementations are also included in the scope of the present invention.

In this case, the program code of the software implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to a computer, for example, the program code The storage medium storing the information constitutes the present invention.

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

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the functions of the above-described embodiment are realized in cooperation with other application software and the like. In this case, it goes without saying that an OS (Operating System) in which the program code runs on a computer, or such a program code is included in the embodiment of the present invention.

Further, the supplied program code is stored in a memory provided in a function expansion board of the computer or a function expansion unit connected to the computer, and then stored in the function expansion board or the function storage unit based on the instruction of the program code. It is needless to say that the present invention includes a case where a provided CPU or the like performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0042]

According to the present invention, it is possible to obtain a good medical image by performing deterioration restoration on a radiation image corresponding to a signal / noise ratio according to a dose.

[Brief description of the drawings]

FIG. 1 is a diagram of a system configuration example

FIG. 2 is a flowchart of a process.

FIG. 3 is a conceptual diagram of a filtering process using a spatial filter table.

FIG. 4 is a conceptual diagram showing spatial filtering.

FIG. 5 is a conceptual diagram showing frequency characteristics for each level.

FIG. 6 is a conceptual diagram showing a spatial filter table.

FIG. 7 is a graph showing a signal / noise ratio.

FIG. 8 is a conceptual diagram showing overshoot and undershoot.

FIG. 9 is a concept showing frequency characteristics of unsharp masking processing.

Claims (5)

[Claims] 1. An image processing method for inputting image data representing a radiation image and performing a spatial filtering process on the image data, wherein an index of a dose is obtained based on the image data. A radiation image processing method, wherein a spatial filter coefficient used in the spatial filter processing is controlled. 2. The radiation image processing method according to claim 1, further comprising: creating a low-frequency image from the radiation image; and controlling the spatial filter coefficient based on the low-frequency image. 3. The radiation image processing method according to claim 2, wherein the low frequency image is obtained by performing a low-pass filter process on the radiation image. 4. A radiation image processing system comprising: a radiation imaging apparatus; and an image processing apparatus that processes an image signal obtained by the imaging apparatus, wherein the imaging apparatus captures a medical image having system-specific deterioration. Input means for inputting image data indicating the medical image from the image capturing apparatus; spatial filter processing means for performing spatial filter processing on the image data; Control means for controlling a spatial filter coefficient used by said spatial filter processing means based on a dose index according to data. 5. A recording medium on which a program is recorded so as to be readable by a computer, the image processing method comprising: inputting image data indicating a radiation image; and performing a spatial filtering process on the image data. A recording medium storing a program for controlling a spatial filter coefficient used in the spatial filter processing based on an index of a dose corresponding to the image data.