JP2003319929A - Apparatus and method for dynamic range compressing processing of radiation picture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform displaying free from deteriorating radiogram interpretation properties even when a picture which is subjected to dynamic range compressing processing is unfamiliar to the eyes. <P>SOLUTION: In a constitution of processing an original picture signal expressing an original picture based on radiation picture information transmitted by a subject to obtain a processed picture signal carrying a picture of a narrower dynamic range, display of two pictures consisting of an original picture and a processed picture side by side or display of a single picture consisting of only the processed picture can be selected. The degree of compression of the dynamic range in display of two pictures is made to be larger than that in display of the single picture. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for dynamic range compression processing of a radiation image, and more specifically,
The present invention relates to a technique capable of displaying a processed image more appropriately.

[0002]

2. Description of the Related Art Conventionally, as a method for compressing a density range (dynamic range) in a radiographic image while ensuring proper observation of a fine structure in a region, there is a method disclosed in Patent Document 1.

The compression method disclosed in Patent Document 1 is
An unsharp mask signal (blurring mask signal) Sus is obtained by averaging the original image signal Sorg in a predetermined mask area including each pixel point corresponding to each pixel point, and monotonically increases as the unsharp mask signal increases. The decreasing function is f
(Sus), the processed image signal Sproc is changed to S
It is obtained as proc = Sorg + f (Sus).

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 3-222577

[0005]

However, if an image that has been subjected to the dynamic range compression processing is provided to a person who is familiar with radiographic images that have not been subjected to the dynamic range compression processing, the image interpretation will be rather degraded. There was a problem.

The present invention has been made in view of the above problems, and a dynamic range compression process capable of displaying without deteriorating the image interpretation even if the user is not familiar with an image subjected to the dynamic range compression process. It is an object to provide an apparatus and method.

[0007]

Therefore, in the dynamic range compression processing apparatus according to claim 1, a two-image display for displaying the original image and the processed image side by side and a one-image display for displaying only the processed image. Display form selecting means for selecting either one, display means for displaying an image according to the display form selecting means, and compression degree changing for changing the compression degree of the dynamic range according to the selection of the display form by the display form selecting means. And means.

According to another aspect of the dynamic range compression processing apparatus of the present invention, the compression degree changing means is configured to increase the compression degree in the two-image display as compared with the one-image display.

According to the dynamic range compression processing method of the third aspect, depending on which one of the two-image display for displaying the original image and the processed image side by side or the one-image display for displaying only the processed image is selected, The configuration is such that the degree of compression of the dynamic range is changed.

According to another aspect of the dynamic range compression processing method of the present invention, the degree of compression in the two-image display is larger than that in the one-image display.

[0011]

Embodiments of the present invention will be described below. FIG. 1, which shows an embodiment, shows a configuration example of a dynamic range compression processing device of a radiation image according to the present invention, and shows an example of performing chest radiography of a human body for medical use.

The radiation source 1 is controlled by the radiation control device 2 to irradiate the subject (human chest or the like) M with radiation (generally X-rays). The recording / reading device 3 is provided with a conversion panel 4 on a surface facing the radiation source 1 with the subject M interposed therebetween, and the conversion panel 4 has energy according to a radiation transmittance distribution of the subject M with respect to an irradiation radiation amount from the radiation source 1. Are accumulated in the photostimulation layer, and a latent image of the subject M is formed there.

The conversion panel 4 is provided with a stimulable layer on a support by vapor deposition of a stimulable phosphor or coating of a stimulable phosphor coating. The stimulable layer has a negative effect on the environment and It is shielded or covered by a protective member to block damage. Examples of the stimulable phosphor material include:
JP-A-61-72091 or JP-A-59-
A material as disclosed in Japanese Patent No. 75200 is used.

The 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 the scanner 6 via various optical systems. , Where it is deflected, and the reflector 7
The optical path is deflected by and is guided to the conversion panel 4 as stimulated excitation scanning light.

The condensing body 8 is located at the condensing end which is an optical fiber in the vicinity of the conversion panel 4 which is scanned by the stimulated excitation light, and the latent image energy from the conversion panel 4 which is scanned by the above light beam. The stimulated luminescence having a luminescence intensity proportional to is received.

Reference numeral 9 is a filter that allows only light in the stimulated emission wavelength range from the light introduced from the light collector 8 to pass through. The light that has passed through the filter 9 is incident on the photomultiplier 10,
It is photoelectrically converted into a current signal corresponding to the incident light.

An 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 a radiation image signal composed of digital data for each pixel by an A / D converter 13. Is converted to.

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 is an image memory (magnetic disk device) for storing image signals.

Reference numeral 16 is an interface for transmitting a radiation image signal read from the image processing device 14 directly or from the image memory 15 to a printer 17 (display means).

Reference numeral 18 is a read gain adjusting circuit. The read gain adjusting circuit 18 adjusts the light beam intensity of the light beam generating section 5, the gain of the photomultiplier 10 by adjusting the power supply voltage of the photomultiplier high-voltage power supply 19, and the current / current. The gain of the voltage converter 11 and the amplifier 12 is adjusted, and the input dynamic range of the A / D converter 13 is adjusted, so that the read gain of the radiation image signal is comprehensively adjusted.

Further, a CRT device 20 (display means) is provided, and in addition to the radiation image information, various processing information is sent from the image processing device 14 to be displayed on the CRT device 20.

Further, 21 is a keyboard, a touch panel,
It is a man-machine interface such as a mouse, and correction data for correcting the characteristics of the image processing in the image processing device 14 can be input through the man-machine interface 21.

The method of acquiring the original radiation image signal Sorg to be output to the image processing device 14 is limited to the method of photoelectrically converting the stimulated emission obtained by scanning the stimulable phosphor with excitation light to emit light. However, for example, a method of reading an image on a radiation film by photoelectric conversion, a method of irradiating a phosphor with radiation passing through an object to convert it into fluorescence, and photoelectrically converting the fluorescence to read good.

The original radiation image signal Sorg may be proportional to the intensity of the detected radiation or may be proportional to the logarithm of the intensity of the detected radiation, but the latter is preferable.

Here, the image processing device 14 compresses the dynamic range of the original image signal Sorg input from the recording / reading device 3 to process an image having a narrower dynamic range than the original image. A dynamic range compression processing function for obtaining the signal Sproc is provided, and image processing for such dynamic range compression processing is performed according to the following equation.

Sproc = Sorg + f1 (Sus) In the above equation, S
us 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.

However, the non-sharp mask signal Sus is not limited to the method of averaging in the mask area, and may be set based on, for example, a median value.

Further, f1 (Sus) added to the original image signal Sorg is a correction value obtained as a function of the unsharp mask signal Sus. The method of compressing the dynamic range is not limited to the method using the non-sharp mask signal Sus.

Further, the contour of the subject is extracted based on the signal analysis of the original image signal Sorg, and, for example, in the front chest image, the regions are divided into the lung field region, the blank region, and the subject region excluding the lung field, and the respective regions are divided. It is possible to adopt a configuration in which different functional correction values f1 (Sus) are applied to the regions.

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 on two sheets (a hard copy by the printer 17 and a soft copy by the CRT device 20). (Including and) and a mode in which only the processed image is displayed can be selected.

In the case of the single-image display mode, if extreme compression is performed, information originally contained in the original image is lost, non-lesion-like information looks like a lesion, or the information is correct but the Since the illusion may cause misdiagnosis, it is preferable that the compression degree is not too large.

On the other hand, in the two-image display, the processed image is displayed side by side with the original image. Therefore, even if the compression-processed portion makes it difficult to see the original image, the portion that was difficult to see in the original image is more Since it suffices to make it visible, setting of a relatively large compression degree is allowed.

Therefore, the operator can arbitrarily select the two-image display mode and the one-image display mode through the man-machine interface 21, but, for example, the dynamic range of the subject is wider than a predetermined range. If a large amount of compression is desired, the two-image display can be automatically selected.

When the operator arbitrarily selects the display mode through the man-machine interface 21,
In the case where the man-machine interface 21 corresponds to a display mode selecting means and is automatically set, an image processing device
14 corresponds to the display form selecting means.

The automatic selection of the display mode will be described below. Note that, here, the low density portion of the front chest image is compressed. The image processing device 14 automatically sets a region of interest including the lung field in the original image, analyzes the histogram of the signal in the region, and obtains the maximum value Smax and the minimum value Smin of the signal in the region of interest. .

As the correction function f1 (Sus), the one shown in the following formula is used, and the reference value Sus1 of the unsharp mask signal Sus for determining the correction area is Sus1 = k.multidot.Smax +
It shall be determined as (1-k) · Smin.

F1 (Sus) = β (Sus1−Sus) ... Sus ≦ Sus1 f1 (Sus) = 0 ... Sus> Sus1 Then, the judgment as to which of the one-image display and the two-image display is selected is performed. The dynamic range ΔS of the subject, which is obtained as Smax−Smin = ΔS, is compared with a predetermined value, and when the dynamic range ΔS of the subject is larger than the predetermined value,
If two images are selected for significant compression and the dynamic range ΔS is smaller than a predetermined value, extreme compression is not necessary and even a single image display of the processed image will provide the necessary and sufficient diagnostic performance. It is presumed that it is possible to select one display.

The setting of the compression degree according to the selection of the display mode is performed by the coefficient β in the correction function f1 (Sus).
And the coefficient k used to calculate the reference value Sus1 are changed according to the selection result of the display mode.

Specifically, the coefficient β for the single image display mode
1, k1 and coefficients β2, k2 for the two-image display mode are set in advance, and which coefficient to use is determined according to the selection result.

The value of the coefficient is, for example, β1 = 0.6,
When k1 = 0.5, β2 = 0.8, k2 = 0.6, the coefficient β is increased to set a larger correction value in the two-image display mode, and the coefficient k is increased to expand the correction area.

Therefore, in this embodiment, the image processing apparatus
14 corresponds to the compression degree changing means. By the way, in the above-mentioned embodiment, the mask size or frequency characteristic of the non-sharp mask is an important parameter that influences the diagnostic ability of the image.

In the dynamic range compression processing, only the ultra-low frequency component corresponding to the change in the rough structure of the subject (smooth signal difference in the lung field, the mediastinum, etc.) is extracted as the unsharp mask signal Sus, and Sus Correction value f1 (S
By setting us), it is possible to compress the entire concentration range while maintaining the changes of minute structures (bones, blood vessels, etc.).

When the mask size is small, the non-sharp mask signal Sus includes not only the ultra-low frequency component corresponding to the rough change of the object but also the frequency component corresponding to the change of the fine structure. By adding the correction value based on the signal Sus, the change of the fine structure is canceled and the contrast of the bone, the blood vessel, etc. is lowered.

On the other hand, if the mask size is large, the edge cut of the non-sharp image becomes worse in the portion where the signal value changes abruptly, and undesired compression is performed near the boundary between the region to be compressed and the region to be not compressed. Will be done.

If the mask size is made too large, even the frequency component corresponding to the rough change of the subject is lost (in an extreme case, the image becomes a flat image). The dynamic range compression effect cannot be obtained even if the correction value based on the above is added.

As a result of the inventor's examination from the above viewpoint, the size of the mask is 10 mm in the length on the life-size image.
To 60 mm are preferred, more preferably from 15 mm to 30 mm, most preferably from 20 mm to 30 mm.

If the mask size is smaller than 10 mm, the frequency component corresponding to the change of the fine structure sharply increases. Therefore, if the correction value is set based on the non-sharp mask signal Sus obtained by such a mask size. , The diagnostic performance is significantly reduced.

In particular, in the chest image and the abdominal image, if the mask size is 15 mm or more, Sus has no frequency component corresponding to a large blood vessel such as aorta, and if the mask size is 20 mm or more, Sus is Although it has a relatively low frequency corresponding to ribs and the like, it does not include a frequency component whose contrast is not desired to be lowered, so that an image with high diagnostic performance is obtained.

Here, the mask size refers to the average value of the length of the short side and the length of the long side for a rectangle, the length of one side for a square, the diameter for a circle, and the average value of the major axis and the minor axis for an ellipse. . If the frequency characteristics of the unsharp mask are used instead of the mask size, the modulation transfer function of the unsharp mask is 0.01
Cycle / mm is preferably 0.5 or more and 0.06 cycle / mm is preferably 0.5 or less, more preferably 0.02
Cycle / mm 0.5 or more and 0.04 cycle / mm 0.5 or less, more preferably 0.02 cycle / mm 0.
It is 0.5 or less when 5 or more and 0.03 cycles / mm.

Further, in the present invention, the non-sharp mask signal S
The maximum absolute value of the correction value f1 (Sus), which is a function of us, is 1/8 to 1 of the dynamic range of the region of interest of the subject.
It is preferably / 2.

For example, when the dynamic range of the region of interest of the subject is 2 digits, the maximum absolute value of the compression correction amount is preferably 1/4 digit to 1 digit. Further, when the correction value f1 (Sus) is represented by a linear function of the unsharp mask signal Sus like β (Sus1-Sus), the preferable range of β which is the slope and determines the compression degree is 0.2 to 1.0. And more preferably 0.4 to 0.8.

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 size relationship of the densities of the regions in the original image is reversed (for example, the median density of the lung field is higher than the median density). The average density of the area becomes higher), resulting in an image that cannot be diagnosed.

For example, such a problem occurs when the slope β of the linear function is set to be larger than 1.

[0054]

As described above, according to the present invention, it is possible to select either the two-image display in which the original image and the processed image are displayed side by side or the one-image display of only the processed image. Also, since the larger compression is applied when the two-image display is selected, there is an effect that a large compression degree can be set without deteriorating the image interpretation.

[Brief description of 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]

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

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Claims (4)

[Claims] 1. A dynamic range compression of a radiation image, wherein an original image signal representing an original image based on radiation image information transmitted through an object is processed to obtain a processed image signal carrying an image having a narrower dynamic range than the original image. A display device for selecting one of a two-image display in which the original image and the processed image are displayed side by side and a one-image display in which only the processed image is displayed; A display unit for displaying an image according to the display form selecting unit; and a compression degree changing unit for changing the compression degree of the dynamic range according to the selection of the display form by the display form selecting unit, Radiation image dynamic range compression processing device. 2. A dynamic range compression processing apparatus for a radiation image according to claim 2, wherein said compression degree changing means increases the compression degree in displaying two images as compared with the case of displaying one image. 3. A dynamic range compression of 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 narrower dynamic range than the original image. A method of processing, wherein the degree of compression of the dynamic range is determined by selecting either 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. A method for compressing a dynamic range of a radiation image, characterized by changing the method. 4. The method of compressing a dynamic range of a radiation 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.