JP3586274B2 - Apparatus and method for dynamic range compression processing of radiographic image - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dynamic range compression processing apparatus and method for a radiographic image, and more particularly, to a technique capable of displaying a processed image more appropriately.
[0002]
[Prior art]
Conventionally, as a method for compressing a density range (dynamic range) of a radiographic image while ensuring appropriate observation of a fine structure in a region, there is a method disclosed in Patent Document 1.
[0003]
According to the compression method disclosed in Patent Document 1, an unsharp mask signal (blurred mask signal) Sus is obtained by averaging an original image signal Sorg in a predetermined mask area including each pixel point corresponding to each pixel point. Assuming that f (Sus) is a function that monotonically decreases as the unsharp mask signal increases, the processed image signal SProc is calculated as Sproc = Sorg + f (Sus)
What you get as
[0004]
[Patent Document 1]
JP-A-3-222577
[Problems to be solved by the invention]
However, there is a problem in that if a person who is accustomed to viewing a radiation image that has not been subjected to the dynamic range compression processing is provided with the image that has been subjected to the dynamic range compression processing, the readability may be reduced.
[0006]
The present invention has been made in view of the above problems, and has an apparatus and method for dynamic range compression processing capable of performing display without deteriorating image interpretation even when an image subjected to dynamic range compression processing is unfamiliar. The purpose is to provide.
[0007]
[Means for Solving the Problems]
Therefore, in the dynamic range compression processing apparatus according to the first aspect, a display mode selection for selecting one of two display modes in which the original image and the processed image are displayed side by side and one display mode in which only the processed image is displayed Means, display means for displaying an image in accordance with the display form selection means, and compression degree changing means for changing the degree of compression of the dynamic range in accordance with the selection of the display form by the display form selection means. .
[0008]
In the dynamic range compression processing device according to the second aspect, the compression degree changing means is configured to increase the degree of compression in displaying two images as compared with displaying one image.
[0009]
In the dynamic range compression processing method according to the third aspect, the dynamic range compression processing method determines the dynamic range by selecting one of the two-image display in which the original image and the processed image are displayed side by side and the one-image display in which only the processed image is displayed. The compression degree is changed.
[0010]
In the dynamic range compression processing method according to the fourth aspect, the degree of compression in the two-image display is made larger than that in the one-image display.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 1 showing an embodiment shows a configuration example of a dynamic range compression processing apparatus for a radiographic image according to the present invention, and shows an example in which a chest radiography of a human body for medical use is performed.
[0012]
Here, the radiation source 1 is controlled by the radiation control device 2 to irradiate a radiation (generally, X-rays) to a subject (such as a human chest) M.
The recording and reading device 3 includes a conversion panel 4 on a surface facing the radiation source 1 with the subject M interposed therebetween. The conversion panel 4 has an energy according to a radiation transmittance distribution of the subject M with respect to an irradiation radiation amount from the radiation source 1. Is accumulated in the photostimulated layer, and a latent image of the subject M is formed thereon.
[0013]
The conversion panel 4 has a photostimulable layer provided on a support by vapor deposition of a photostimulable phosphor or application of a photostimulable phosphor paint, and the photostimulable layer blocks adverse effects and damage due to the environment. Is covered or covered by a protective member. As the stimulable phosphor material, for example, materials disclosed in JP-A-61-72091 or JP-A-59-75200 are used.
[0014]
A light beam generator (gas laser, solid-state laser, semiconductor laser, etc.) 5 generates a light beam whose emission intensity is controlled, and the light beam reaches a scanner 6 via various optical systems, where it is deflected. Then, the light path is further deflected by the reflecting mirror 7 and guided to the conversion panel 4 as stimulating excitation scanning light.
[0015]
The light collector 8 has a light collecting end, which is an optical fiber, positioned close to the conversion panel 4 on which the stimulating excitation light is scanned, and is proportional to the latent image energy from the conversion panel 4 scanned by the light beam. The photostimulable luminescence of the luminous intensity is received.
[0016]
Reference numeral 9 denotes a filter that passes only light in the stimulating emission wavelength region from the light introduced from the light collector 8, and the light that has passed through the filter 9 enters the photomultiplier 10 and corresponds to the incident light. It is photoelectrically converted into a current signal.
[0017]
The output current from the photomultiplier 10 is converted into a voltage signal by a current / voltage converter 11, amplified by an amplifier 12, and then converted into a radiation image signal composed of digital data for each pixel by an A / D converter 13. You.
[0018]
Then, the digital radiation image signal (original image signal Sorg) is sequentially output to the image processing device 14 having a built-in microcomputer.
Reference numeral 15 denotes an image memory (magnetic disk device) for storing image signals.
[0019]
Reference numeral 16 denotes an interface for transmitting a radiation image signal read directly from the image processing device 14 or from the image memory 15 to a printer 17 (display means).
[0020]
Reference numeral 18 denotes a reading gain adjustment circuit, which adjusts the light beam intensity of the light beam generating unit 5, adjusts the gain of the photomultiplier 10 by adjusting the power supply voltage of the high-voltage power supply 19 for the photomultiplier, and a current / voltage converter. The gain of the amplifier 11 and the amplifier 12 and the input dynamic range of the A / D converter 13 are adjusted, and the read gain of the radiation image signal is adjusted comprehensively.
[0021]
Further, a CRT device 20 (display means) is provided, and various kinds of processing information are sent from the image processing device 14 and displayed on the CRT device 20 in addition to the radiation image information.
[0022]
Reference numeral 21 denotes a man-machine interface such as a keyboard, a touch panel, and a mouse. Correction data for correcting the characteristics of image processing in the image processing device 14 is input via the man-machine interface 21. I can do it.
[0023]
Note that the method of obtaining the original radiation image signal Sorg to be output to the image processing device 14 is not limited to a method in which a stimulable phosphor is scanned with excitation light to emit light and the stimulable luminescence is photoelectrically changed. Instead, for example, a method of reading an image of a radiation film by photoelectric conversion or a method of irradiating a radiation transmitted through a subject to a fluorescent substance to convert the fluorescent light into fluorescent light, and photoelectrically converting the fluorescent light to read the fluorescent light may be used.
[0024]
The original radiation image signal Sorg may be in a form proportional to the intensity of the detected radiation or in a form proportional to the logarithm of the intensity of the detected radiation, the latter being preferred.
[0025]
Here, the image processing device 14 compresses the dynamic range of the original image signal Sorg input from the recording and reading device 3 and converts the processed image signal Sproc, which carries an image having a smaller dynamic range than the original image, into an image. A dynamic range compression function is provided, and image processing for such dynamic range compression processing is performed according to the following equation.
[0026]
Sproc = Sorg + f1 (Sus)
In the above equation, Sus is a non-sharp mask signal obtained by averaging the original image signal Sorg in a predetermined mask area including each pixel point corresponding to each pixel point.
[0027]
However, the method of obtaining the unsharp mask signal Sus is not limited to a method of obtaining it by averaging processing in a mask area, and may be configured based on, for example, a median value.
[0028]
F1 (Sus) added to the original image signal Sorg is a correction value obtained as a function of the unsharp mask signal Sus.
Note that the method of compressing the dynamic range is not limited to the method using the unsharp mask signal Sus.
[0029]
In addition, the contour of the subject is extracted based on the signal analysis of the original image signal Sorg. For example, in the chest front image, the region is divided into a lung field region, a blank region, and a subject region excluding the lung field, and each region is separated. Thus, it is possible to adopt a configuration in which the correction value f1 (Sus) of a different function type is applied.
[0030]
Here, in the above apparatus, as shown in FIG. 2, the processed image subjected to the dynamic range compression processing and the original image are displayed side by side (including a hard copy by the printer 17 and a soft copy by the CRT apparatus 20). ) And a mode in which only the processed image is displayed.
[0031]
In the single image display mode, if extreme compression is performed, information originally contained in the original image may be lost, a non-lesion may look like a lesion, or the information may be incorrect but may be misdiagnosed due to an optical illusion. Therefore, it is preferable that the compression degree is not so large.
[0032]
On the other hand, in the two-image display, the processed image is displayed side by side with the original image, so that even if the portion that was well visible in the original image becomes less visible due to the compression processing, the portion that was less visible in the original image is more visible. Therefore, setting of a relatively large compression degree is permitted.
[0033]
Therefore, the selection between the two-image display mode and the one-image display mode may be arbitrarily made by the operator via the man-machine interface 21. However, for example, the dynamic range of the subject is wider than a predetermined range and the If compression is desired, the two-image display can be automatically selected.
[0034]
When the operator arbitrarily selects a display mode via the man-machine interface 21, the man-machine interface 21 corresponds to a display mode selection unit. This corresponds to a display mode selection unit.
[0035]
The automatic selection of the display mode will be described below.
Here, it is assumed that a low-density portion of the chest front image is compressed.
The image processing device 14 automatically sets a region of interest including a lung field with respect to the original image, performs a histogram analysis of signals in the region, and obtains a maximum value Smax and a minimum value Smin of the signal in the region of interest. .
[0036]
The following equation is used as the correction function f1 (Sus), and the reference value Sus1 of the unsharp mask signal Sus for determining the correction area is determined as Sus1 = kSmax + (1-k) Smin. Shall be.
[0037]
f1 (Sus) = β (Sus1-Sus) ... Sus ≦ Sus1
f1 (Sus) = 0 ... Sus> Sus1
Then, to determine whether to select one-image display or two-image display, the subject dynamic range ΔS obtained as Smax−Smin = ΔS is compared with a predetermined value, and the dynamic range ΔS of the subject is determined to be larger than the predetermined value. When the dynamic range ΔS is smaller than a predetermined value, extreme compression is unnecessary, and when the dynamic range ΔS is smaller than a predetermined value, it is necessary and sufficient to display only one processed image. It is assumed that an excellent diagnostic performance can be obtained, and one-image display is selected.
[0038]
The setting of the degree of compression in accordance with the selection of the display mode is such that at least one of the coefficient β in the correction function f1 (Sus) and the coefficient k used in the calculation of the reference value Sus1 is changed according to the selection result of the display mode. This is done by:
[0039]
Specifically, coefficients β1 and k1 for the single-image display mode and coefficients β2 and k2 for the two-image display mode are set in advance, and which coefficient to use is determined according to the selection result.
[0040]
As the value of the coefficient, for example, β1 = 0.6, k1 = 0.5, β2 = 0.8, k2 = 0.6, and in the two-image display mode, the coefficient β is increased to set a larger correction value. In addition, the coefficient k is increased to widen the correction area.
[0041]
Therefore, in the present embodiment, the image processing device 14 corresponds to a compression degree changing unit.
By the way, in the above embodiment, the mask size or the frequency characteristic of the unsharp mask is an important parameter that affects the diagnostic performance of the image.
[0042]
In the dynamic range compression processing, only an ultra-low frequency component corresponding to a change in a rough structure of a subject (a smooth signal difference in a lung field, a mediastinum, etc.) is extracted as an unsharp mask signal Sus, and based on the Sus. By setting the correction value f1 (Sus), it is possible to compress the entire density range while maintaining fine changes in the structure (bones, blood vessels, etc.).
[0043]
When the mask size is small, the unsharp mask signal Sus includes not only an ultra-low frequency component corresponding to a rough change of a subject but also a frequency component corresponding to a change of a fine structure. By adding a correction value based on this, a change in a fine structure is canceled, and the contrast of bones, blood vessels, and the like is reduced.
[0044]
On the other hand, if the mask size is large, the edge sharpness of the unsharp image in a portion where the signal value changes abruptly becomes worse, and undesired compression is performed near the boundary between the region to be compressed and the region not to be compressed. .
[0045]
Further, if the mask size is further increased, even a frequency component corresponding to a rough change in the subject is lost (in an extreme case, a completely flat image is obtained). Therefore, a correction value based on the unsharp mask signal Sus is used. Does not provide a dynamic range compression effect.
[0046]
As a result of examination by the inventor from the above viewpoints, the size of the mask size is preferably 10 mm to 60 mm, more preferably 15 mm to 30 mm, and most preferably 20 mm to 30 mm in length on a life-size image. I found that.
[0047]
If the mask size is smaller than 10 mm, the frequency component corresponding to a change in a fine structure sharply increases. Therefore, when a correction value is set based on the unsharp mask signal Sus obtained with such a mask size, a remarkable diagnosis is performed. Performance will be reduced.
[0048]
In particular, in a chest image or an abdomen image, if the mask size is set to 15 mm or more, Sus has no frequency component corresponding to a thick blood vessel such as an aorta, and if the mask size is set to 20 mm or more, Sus becomes a rib or the like. Although the corresponding frequency is relatively low, it does not include a frequency component whose contrast is not desired to be reduced, so that an image with high diagnostic performance can be obtained.
[0049]
Here, the mask size indicates the average value of the length of the short side and the length of the long side in the case of a rectangle, the length of one side in the case of a square, the diameter in the case of a circle, and the average value of the major axis and the minor axis in the case of an ellipse.
In addition, when describing the frequency characteristics of the unsharp mask instead of the mask size, when the modulation transfer function of the unsharp mask is 0.01 cycle / mm or more, and when the modulation transfer function is 0.06 cycle / mm, 0.5 or more Or less, more preferably 0.5 or more at 0.02 cycles / mm and 0.5 or less at 0.04 cycles / mm, and even more preferably 0.5 at 0.02 cycles / mm. Above and 0.5 at 0.03 cycle / mm.
[0050]
Further, in the present invention, it is preferable that the maximum value of the absolute value of the correction value f1 (Sus), which is a function of the unsharp mask signal Sus, is １ ／ to の of the dynamic range of the region of interest of the subject.
[0051]
For example, when the dynamic range of the region of interest of the subject is two digits, the maximum value of the absolute value of the compression correction amount is preferably one-fourth to one digit.
When the correction value f1 (Sus) is represented by a linear function of the unsharp mask signal Su such as β (Sus1−Sus), the preferable range of β which is the slope and determines the degree of compression is 0.2. To 1.0, more preferably 0.4 to 0.8.
[0052]
If the correction amount is too small, the dynamic range compression effect does not appear. On the other hand, if the correction amount is too large, the magnitude relationship between the densities of the regions in the original image is reversed (for example, the average density of the mediastinum is lower than the average density of the lung field). (The density becomes higher), resulting in an image that cannot withstand diagnosis.
[0053]
For example, such a problem occurs when the slope β of the linear function is set to be larger than 1.
[0054]
【The invention's effect】
As described above, according to the present invention, it is possible to select one of a two-image display in which an original image and a processed image are displayed side by side and a one-image display of only a processed image. Is selected, greater compression is applied, so that it is possible to set a large degree of compression without deteriorating image interpretation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a radiation image reading processing apparatus to which the present invention is applied.
FIG. 2 is a diagram showing a display state in a two-image display mode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Radiation source 3 ... Recording / reading device 14 ... Image processing device 15 ... Image memory 16 ... Interface 17 ... Printer 20 ... CRT device 21 ... Man-machine interface

Claims (4)

A dynamic range compression processing apparatus for a radiographic image, comprising processing an original image signal representing an original image based on radiographic image information transmitted through a subject to obtain a processed image signal carrying an image having a smaller dynamic range than the original image. ,
A display mode selection unit that selects one of two displays for displaying the original image and the processed image side by side, and one display for displaying only the processed image,
Display means for displaying an image according to the display form selecting means;
Compression degree changing means for changing the compression degree of the dynamic range according to the selection of the display form by the display form selection means,
A dynamic range compression processing apparatus for a radiographic image, comprising: 3. The dynamic range compression processing apparatus for radiographic images according to claim 2, wherein the compression degree changing unit increases the compression degree in displaying two images as compared with displaying one image. A dynamic range compression processing method for a radiation image, wherein an original image signal representing an original image based on radiation image information transmitted through a subject is processed to obtain a processed image signal carrying an image having a smaller dynamic range than the original image. ,
The compression degree of the dynamic range is changed depending on whether to select the two-image display in which the original image and the processed image are displayed side by side or the one-image display in which only the processed image is displayed. Dynamic range compression processing method for a radiographic image to be compressed. 4. The dynamic range compression processing method for a radiographic image according to claim 3, wherein the degree of compression in the two-image display is made larger than that in the one-image display.

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