JP2005176974A - X-ray image processing method and apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute the image processing not for an image after the logarithmic transformation but for an image before the logarithmic transformation, equivalent to the sensor output to be primarily processed. <P>SOLUTION: In the X-ray image processing method, a gain-corrected image after the logarithmic transformation is returned to the image before the logarithmic transformation by executing the exponential transformation, which is the inverse transformation to the logarithmic transformation, and after necessary image processing, the image is logarithmically transformed again. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention belongs to the field of digital image processing (computer image processing).

  In particular, the present invention relates to an image processing method for improving the image quality of an X-ray (X-ray) image and an apparatus using the image processing method.

  The analog X-ray (X-ray) image before digitization is converted into light received by a phosphor (screen) as shown in FIG. 4, and the film is exposed to the converted light. To make an image.

The light emitted by the phosphor is proportional to the amount of X-rays received. Therefore, the density of the film when it becomes an image is determined by the physical characteristics of the film as shown in FIG. This physical property is usually expressed as the relationship of concentration to the logarithm (log) of the incident X-ray dose, and has an S-shape. In recent years, an analog image such as this film has been shifted to a digital image. Examples of digital image apparatuses include an apparatus using a stimulable phosphor and an apparatus using a solid sensor instead of a film. Even in such a digital image device, it is a doctor who finally makes a diagnosis by looking at the image. Doctors have been educated to make diagnoses by looking at X-ray film images and have actually made diagnoses. Therefore, in a digital image apparatus, image processing is performed so that the image is similar to an X-ray film image, and the processed digital image is often output to film. The flow of image processing for a digital image is shown in FIG. Sensor correction processing is performed on image data input from a stimulable phosphor or a solid sensor. The sensor correction processing includes offset correction for removing dark current, defect correction for correcting defective pixels, gain correction, and the like. (In FIG. 3, the gain correction is separated from the sensor correction process for the sake of explanation.) The gain correction is a process for correcting the variation for each pixel of the sensor and is an image in which no subject is placed (usually called a white image) ). Since the variation for each pixel in the white image represents the variation for each pixel of the sensor, as shown in FIG. 6, a certain fixed value (for example, an average value of all pixel values) f _n and each pixel value f _{1 of the} white image. If the correction coefficient is applied to each pixel of an image taken with the ratio f _n / f ₁ as the correction coefficient of the image, the pixel-to-pixel variation can be corrected. If the operation for applying the correction coefficient is performed with logarithmically converted data, the multiplication can be replaced with the addition to speed up the processing. Since this and the physical characteristics of the gradation processing film are defined logarithmically, the image data is converted to logarithmic data in this gain correction. Therefore, even for processing other than gradation processing, processing such as sharpening processing and dynamic range compression, which are processing performed after gain correction of sensor correction processing as shown in FIG. 3, has been performed on logarithmic data. . In addition, the sharpening process is basically a process for enhancing high-frequency components, and noise is also amplified. Since the magnitude of this noise varies depending on the X-ray dose in the X-ray image, the pixel value itself or the pixel value of the smoothed image is used as an index of the dose. That is, sharpening processing is performed in which the intensity of emphasizing high-frequency components is controlled by this pixel value to suppress noise amplification. Logarithmic data is also used for this pixel value.

  Image processing should be performed on the image itself output from the sensor, and if it is performed on the logarithmically converted image, its meaning will also change. In particular, the spatial filter is a product-sum operation, and the product before logarithmic conversion corresponds to the sum after logarithmic conversion. Therefore, the processing contents differ between applying a spatial filter to an image before logarithmic transformation and applying a spatial filter to an image after logarithmic transformation.

  In addition, the noise control in the sharpening process is proportional to the X-ray dose if it is the output value of the sensor, but the logarithmically transformed value is not proportional.

  According to the present invention, even after an image having undergone logarithmic transformation, necessary image processing is performed after performing exponential transformation that is inverse transformation of logarithmic transformation to restore the image before logarithmic transformation, and logarithmic transformation is performed again. Thus, the original image processing function can be realized.

  By performing sharpening processing and dynamic range compression processing on an image equivalent to the sensor output by inverse log conversion, these original functions can be achieved. In addition, the sharpening process can also be performed with appropriate noise suppression. As a result, an image with higher diagnostic ability can be created.

  Embodiments of the present invention 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 according to the present invention.

  4. The X-ray generated from the X-ray source controlled by the X-ray generator control unit 2. The patient passes through the patient and is detected by the 1. X-ray sensor. The detected X-ray is input to the image input unit as a digital X-ray image. The input digital X-ray image is subjected to image processing such as X-ray sensor correction processing, gradation processing, and spatial filtering processing by the image processing unit. The digital X-ray image that has been processed is displayed on the diagnostic monitor, stored in the image storage unit, the printer, the diagnostic workstation, and the image database via the network. Or If the displayed or output image is not satisfactory, the image processing and display are repeated while changing the image processing parameters. The above operations are performed by the 10. operation unit.

  An embodiment in which logarithmic conversion is performed again after performing image processing after returning to an image before logarithmic conversion in such a system will be described according to the processing flow of FIG.

  The X-ray image input from the X-ray sensor is first subjected to sensor correction processing such as offset correction for correcting dark current and defect correction for correcting defective pixels. At the end of the sensor correction process, white correction is performed. In order to perform this white correction, log conversion is performed in advance. After the white correction is completed, a sharpening process and a dynamic range compression process, which are image quality improvement processes for diagnosis, are performed. Here, in order to perform the original functions of the sharpening process and the dynamic range compression process, inverse log conversion is performed before these processes. Since the reverse log conversion results in an image equivalent to the original sensor output before log conversion, sharpening processing and dynamic range compression processing can perform their original functions. In sharpening processing, if the intensity of high-frequency component enhancement is controlled using pixel values of an image equivalent to the original sensor output before log conversion or an image obtained by smoothing this, there is a proportional relationship with the dose. Because of this, it is possible to perform sharpening while appropriately suppressing noise amplification. When these processes are completed, the log conversion is performed again, and then the gradation process is performed. Gradation processing can perform its original function because the input image is defined by a log conversion image.

Figure of system configuration example Process flow Conventional process flow Illustration explaining X-ray film photography Diagram showing physical properties of X-ray film Conceptual diagram explaining gain correction

Explanation of symbols

1 X-ray sensor
2 patients
3 X-ray source
4 X-ray generator control unit
5 Image input section
6 X-ray imaging system controller
7 Image input section
8 Image storage
9 Diagnostic monitor
10 Operation unit
11 network
12 Printer
13 Diagnostic workstation
14 Image database

Claims (6)

Step 1-White correction is performed on the logarithmically converted image.
Step 2-Perform inverse logarithmic transformation (exponential transformation).
Step 3-Perform various image processing.
Step 4-Perform the conversion.
An X-ray digital image processing method including the above steps.   The method of claim 3, comprising pixel value dependent processing.   A method comprising a spatial filter in step 3 of claim 1. Step 1-White correction is performed on the logarithmically converted image.
Step 2-Perform inverse logarithmic transformation (exponential transformation).
Step 3-Perform various image processing.
Step 4-Perform logarithmic conversion.
A radiation image processing apparatus comprising image processing according to the above steps.   5. The radiation image processing apparatus including pixel value dependent processing in step 3 of claim 4.   5. The radiation image processing apparatus including a spatial filter in step 3 of claim 4.

Images