JPH0449950A - Image density adjustor - Google Patents

Abstract

PURPOSE:To enable the obtaining of a visible image of an appropriate density as a whole by a method wherein an image of a bone part is determined by an energy subtraction processing to obtain a deviation value of a density of the image from a specified density and the density of air original image is adjusted by a value equivalent to the deviation value to allow the reconstruction of a change as visible image. CONSTITUTION:First and second X-raw image signals S01 and S02 are read out of an image processor/display device 30 to perform a relative positioning of X-ray images 41 and 42 supported by the respective signals. Thereafter, a subtraction processing per pixel is performed to determine an image 43 of a bone part with a shade of the bone part alone extracted. To reduce noise components contained in the X-ray images 41 and 42, the images 41 and 42 are superimposed with pixels of the respective images corresponding to each other to obtain an image 44, which is used as original image. Then the bone part alone on the bone image is extracted based on a data of the bone image to determine a deviation value indicating a deviation from a reference value of the corresponding bone image data. The original image data obtained by a data conversion of the above original image data is further shifted by the deviation value. Thus, a visible image of an appropriate density is reconstructed and displayed on a display 32 based on the original image data finally converted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is based on image data representing a radiation image.
The present invention relates to an image density adjustment device that adjusts the density when the radiation image is reproduced and output as a visible image.

(Prior Art) It is practiced in various fields to obtain image data by reading a recorded radiation image, perform appropriate image processing on this image data, and then reproduce and record the image. for example,
X-ray images are recorded using an X-ray film with a low gamma value designed to be compatible with subsequent image processing, and the X-ray images are read from the film on which they are recorded and converted into electrical signals. By performing image processing on this electrical signal (image data) and then reproducing it as a visible image in a photocopy, etc., a system can obtain a reproduced image with good image quality performance such as contrast, sharpness, and graininess. has been developed (see Japanese Patent Publication No. 81-5193).

The applicant has also discovered that when radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, part of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, the energy is accumulated. Using a stimulable phosphor (stimulable phosphor) that emits stimulable luminescence light in an amount corresponding to the energy emitted, radiographic images of objects such as the human body are partially captured on a sheet of stimulable phosphor. The stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, the resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, A radiation recording and reproducing system has already been proposed in which a radiation image of a subject is output as a visible image to a recording material such as a photographic light-sensitive material, a CRT, etc.
No. 429, No. 5B-11395.

No. 55-11340, No. 5B-164645, No. 5
5-116340 etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposures than conventional radiographic systems using silver halide photography. In other words, it is recognized that the amount of stimulated luminescence light emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range, and therefore the amount of radiation exposure varies considerably depending on various imaging conditions. Even if the stimulable luminescent light is emitted from the stimulable phosphor sheet, the reading gain is set to an appropriate value, the photoelectric conversion means reads it and converts it into an electrical signal (image data), and this image data is used to create a photograph. By outputting a radiation image as a visible image to a display device such as a photosensitive material or a CRT, a radiation image that is not affected by fluctuations in radiation exposure can be obtained.

In systems using X-ray film, stimulable phosphor sheets, etc. as described above, in order to obtain a visible image in which the desired subject is reproduced at an appropriate density, a histogram of the image data is obtained, and from this histogram, the desired image is determined. An operation is being performed to extract image data corresponding to the subject.

FIG. 4 is a diagram showing an example of a histogram. The horizontal axis represents the image data S, and the vertical axis represents the frequency of appearance of multivalues in the image data S when each image data S corresponding to each pixel of the radiation image is counted as one piece.

This histogram can be roughly divided into two peaks A.

It is composed of B. Mountain A corresponds to image data of a desired subject, for example, the chest of a human body, and mountain B corresponds to image data of a desired subject, such as the chest of a human body, and mountain B corresponds to image data of a desired object, such as the chest of a human body, and mountain B corresponds to radiation that is directly irradiated onto a recording sheet such as a stimulable phosphor sheet or an X-ray film without passing through the subject. It corresponds to the image data of the direct radiology department. Here, in order to find the mountain A, a predetermined threshold value Th is used to search from the smaller value of the image data S (left side of the figure) to the larger value (right side of the figure), and the histogram and First crossing point a
Find the points that intersect with and then find these two points a and b
The image data is converted so that the corresponding image data Sa and Sb are converted into the minimum density 5iln and maximum density S■aX, respectively, within the appropriate density range on the visible image, that is, along the straight line G in Fig. 4. Standardized and standardized data are required. By reproducing the visible image based on this normalized data, it is possible to obtain a visible image in which the desired subject corresponding to the mountain A is reproduced at an appropriate density.

(Problem to be Solved by the Invention) However, when image data corresponding to a desired subject is extracted as described above, the result is a visible image in which changes in the desired subject (for example, progression of a disease) cannot be detected. There may be cases where this occurs.

For example, assume that the image data of mountain A in the histogram in FIG. 4 represents a chest X-ray image of a human body. At this time, cell infiltration, cell proliferation, fluid exudation, etc. within the lung field due to pneumonia, etc.
When filtration occurs, the air in the lung field is replaced by these, which means that the air content in the lung field decreases, and this causes the
The amount of line penetration decreases, and as shown in the mountain A' in Fig. 4, a mountain A' with a shape that lacks a large part of the image data S compared to the mountain A of normal lung field image data is formed. Become. This change in air content can be detected by the fact that the lung field appears whitish on a visible image compared to a normal case.

However, when the image data corresponding to mountain A' is extracted using the threshold value Th as described above, two points a and b are obtained.
' is calculated, and the image data Sa and Sb' corresponding to these two points a and b' are respectively the minimum density Sm1n within an appropriate density range on the visible image.

Straight line G so that each is converted to the maximum concentration S wax
Data conversion will be performed along .

In other words, on a visible image, an X-ray image of a normal lung and an X-ray image of a lung with a change in air content have almost the same average density, making it difficult to accurately understand changes in air content on a visible image. It becomes possible.

If we calculate mountain A in this way and perform data conversion so that the image corresponding to mountain A has an appropriate density, we will end up with a visible image in which no change in the subject can be detected. It is conceivable to reproduce a visible image with a certain density. For example, the maximum value SM of the image data S in FIG.
, and image data Sa' that is lowered by a predetermined value ΔS1 and image data Sb' that is lowered by a predetermined value ΔS2 from this maximum value SM.
is the minimum density 5 within the appropriate density range on the visible image, respectively.
Conversion is performed along the straight line G' so that the maximum density w1n and the maximum density S11ax are respectively converted.

When such conversion is performed, the subject corresponding to mountain A and mountain A
It is possible to obtain visible images with different average densities from the objects corresponding to . Therefore, it is possible to capture changes in the objects, such as changes in the air content, on the visible images.

However, for example, the thickness of the human chest varies depending on the person, and therefore the average transmittance of radiation differs even in a normal chest for different people. Therefore, when performing fixed data conversion as described above, For example, in the case of radiographic images with different average transmittances, such as mountain A', depending on the person, the image may have an overall high density or an overall low density image, and the visible image may not have the appropriate density. A problem arises in that the data may not be played back.

One possible method for capturing changes in the subject and obtaining a visible image with an appropriate density is to adjust the density of the entire visible image to match the density of the parts of the subject that do not change.

For example, in the above example, regarding X-ray images of the same person before and after a change in air content, even if the air content in the lung field changes, the amount of X-ray transmission does not change in areas other than the lung field, such as the shoulder bone. Density adjustment is performed to match the density of shadows. However, in this case, even though the desired subject is the lungs, it is necessary to take pictures that include the shoulders, but if the person is large, the shoulders may not be photographed, so the bones of the shoulders mentioned above may not be photographed. The method of matching the concentrations of is not necessarily an appropriate method. On the other hand, the ribs are always photographed, but since the shadows of the ribs overlap with the shadows of the lung field, when the air content changes, the density of the shadows of the ribs also changes, and the density of the visible image is adjusted using the density of this shadow. It cannot be done.

In view of the above-mentioned circumstances, the present invention is capable of reproducing a change in a visible image when a change such as a change in radiation transmittance occurs in the soft part in the case of a subject having a bone part and a soft part, and the entire body. An object of the present invention is to provide an image density adjustment device that adjusts the density so that a visible image with an appropriate density can be obtained.

(Means for Solving the Problems) An image density adjustment device according to the present invention provides for each of a plurality of radiation images obtained by irradiating at least two types of radiation having different energies to a subject composed of soft parts and bone parts. Based on a plurality of image data representing, bone image data in which mainly bone images of the subject are recorded, and an original image representing an original image in which both soft parts and bone parts of the subject are recorded. image calculation means for calculating the data, density variation calculation means for calculating the amount of deviation of the density of the bone part in the bone part image from a predetermined density based on the bone part image data, and based on the original image data. The image forming apparatus is characterized by comprising a density adjusting means for adjusting the density of the original image by an amount corresponding to the amount of deviation.

Here, the above-mentioned "original image" may be a radiation image photographed using any one of the above-mentioned "at least two types of radiation having different energies,"
It may be a radiation image obtained by superimposing a plurality of radiation images obtained by imaging using each of these plurality of types of radiation.

(Function) In the image density adjustment device according to the present invention, the density of the bone part changes on a radiographic image because the soft part and the bone part overlap, and the radiation transmittance of the bone part itself changes. Focusing on this fact, we extracted only the shadows of the bones using energy subtraction processing.

Here, energy subtraction processing refers to irradiating the same subject with radiation having different energies by utilizing the fact that specific parts of the subject have different radiation absorption rates for radiation having different energies. This refers to an operation in which a plurality of radiation images are obtained from each radiation having different energies, and a specific portion of the object is extracted by appropriately weighting the plurality of radiation images and calculating the difference.

The present applicant has also proposed energy subtraction using a stimulable phosphor sheet (Japanese Patent Laid-Open No. 59-83
(See Publication No. 488, Japanese Unexamined Patent Publication No. 80-225541)
have also proposed various methods for adjusting the density of bone images (Japanese Unexamined Patent Publication No. 80-208392).

(See 60-206393, 60-207642, and 80-227735).

The image density adjustment device of the present invention obtains a bone part image and an original image, calculates the amount of deviation in density of the bone part, and adjusts the density of the original image by an amount corresponding to this deviation amount. The density of the original image in which the shadows of both sides of the bone region overlap is adjusted correctly, and a visible image that correctly represents changes in the soft parts such as changes in air content is obtained based on the density-adjusted original image data. This means that you can do it.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Here, an example using the above-mentioned stimulable phosphor sheet will be described.

FIG. 1 is a schematic diagram of an X-ray imaging apparatus.

A subject (chest of a human body) 4 is irradiated with X-rays 3 emitted from an X-ray tube 2 of this X-ray imaging apparatus 1. The X-rays 3a that have passed through the subject 4 are irradiated onto the first stimulable phosphor sheet 5, and the relatively low-energy X-rays of the X-rays 3a are accumulated in the first stimulable phosphor sheet 5. , whereby the X-ray image of the subject 4 is accumulated and recorded on the sheet 5. The X-rays 3b that have passed through the sheet 5 further pass through a filter 6 that cuts low-energy X-rays, and the high-energy X-rays 3c that have passed through the filter 6 are irradiated onto the second stimulable phosphor sheet 7. As a result, the X-ray image of the subject 4 is also accumulated and recorded on the sheet 7.

Two marks 8 are attached to the subject 4, which serve as references for aligning two X-ray images when performing subtraction processing.

In addition, the above-mentioned X-ray imaging device can take two sheets 5,
7, X-ray images are stored and recorded, but one image may be taken at two temporally consecutive timings.

FIG. 2 is a perspective view of an image processing display device including an X-ray image reading device and an embodiment of the image density adjustment device of the present invention.

After imaging is performed with the X-ray imaging device 1 shown in FIG. 1, the first and second stimulable phosphor sheets 5°7 are
It is set at a predetermined position in the line image reading device 10. Here, the case of reading the first X-ray image accumulated and recorded on the first stimulable phosphor sheet 5 will be described.

The stimulable phosphor sheet 5 on which the first X-ray image has been accumulated and recorded is set at a predetermined position and is transported by a sheet conveying means 15 such as an endless belt driven by a driving means (not shown).
The paper is transported (sub-scanning) in the direction of arrow Y. On the other hand, the tip beam 17 emitted from the laser light source 1B is transferred to the motor 18.
Rotating polygon mirror 1 that is driven by and rotates at high speed in the direction of arrow Z
9 and is reflected and deflected by a focusing lens 2 such as an fθ lens.
After passing through point o, the optical path is changed by the mirror 21, and the light enters the stimulable phosphor sheet 14, and is main-scanned in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). The stimulable luminescent light 22 is emitted from the tube irradiated with the light beam 17 of the stimulable phosphor sheet 14, and the amount of stimulated luminescent light 22 corresponds to the accumulated and recorded X-ray image information. is light guide 23
and is photoelectrically detected by a photomultiplier (photomultiplier tube) 24. The light guide 23 is made by molding a light-guiding material such as an acrylic plate, and the linear entrance end surface 23a is formed from the stimulable phosphor sheet 1.
A photomultiplier 24 is disposed on an annular exit end surface 23b extending along the main scanning line on the top of the photomultiplier 24.
The light-receiving surfaces of the two are combined. The stimulated luminescent light 22 that has entered the light guide 23 from the incident end surface 23a is transmitted through the light guide 23.
The stimulated luminescent light 22 that travels through the interior of the camera through repeated total reflection, exits from the exit end face 23b and is received by the photomultiplier 24, and the stimulated luminescence light 22 representing a radiation image is sent to the photomultiplier 2.
4 into an electrical signal.

The analog signal S output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25, and then the A/D
The signal is input to the converter 2B and sampled to obtain a digital image signal SO. This image signal SO represents the first X-ray image accumulated and recorded on the first stimulable phosphor sheet 5, and is referred to as a first image signal S01.

This first image signal S01 is temporarily stored in an internal memory within the image processing display device 30.

This image processing display device 30 includes an embodiment of the image density adjustment device of the present invention, and includes a keyboard 31 for inputting various instructions, auxiliary information for instructions, and a visible image based on an image signal. CRT display 32,
A floppy disk drive unit 33 loaded with and driven a floppy disk as an auxiliary storage medium, and C
A main body section 34 is provided, which has a built-in PU and internal memory.

Next, in the same manner as above, a second image signal S02 representing the second X-ray image accumulated and recorded on the second stimulable phosphor sheet 7 is obtained, and this second image signal S02 is also subjected to image processing. It is temporarily stored in the internal memory within the display device 30.

FIG. 3 shows two image signals so! representing first and second X-ray images stored in internal memory within the image processing and display device 30. , so2, the image processing display device fif
FIG. 3 is a diagram showing the flow of processing performed in the computer 30.

The first and second X-ray image signals S01 and S02 stored in the internal memory of the image processing and display device 30 respectively correspond to the first X-ray image 41 and the second Xljl image 42 shown in FIG. This is the signal that it carries. The first X-ray image 41 is an image using relatively low-energy X-rays, and the second X-ray image 42 is an image using relatively high-energy X-rays, but the densities of soft parts and bone parts are different from each other. Both of these are original images in which both soft and bone parts are recorded.

These first and second X-ray image signals sol.

S02 is read from the internal memory in the image processing display device 30 shown in FIG. 2, and first these two image signals so1
．． Relative positioning of each X-ray image 41 and 42 carried by so2 is performed on the image signal (Japanese Patent Laid-open No. 5
8-183338). This alignment is performed by relatively linearly and rotationally moving the two X-ray images so that the two marks 8 shown in FIG. 1 overlap.

After this, subtraction processing is performed for each pixel according to the formula %, and a bone image 43 (see Figure 3) is obtained in which the shadows of the soft parts of the subject 4 are erased and only the shadows of the bones are extracted. It will be done. Here, Ka and Kb are parameters that determine the weighting of the two image signals sol and so2, and Kc is a parameter that determines the bias component.

Furthermore, both of the two X-ray images 41 and 42 are original images according to the present invention, but in this embodiment, these X-ray images LL,
In order to further reduce noise components included in the X-ray images 41 and 42, for each mutually corresponding pixel of these X-ray images 41 and 42,
A superimposed image 44 is obtained by performing calculations according to the formula (2), and this superimposed image 44 is used as the original image according to the present invention.

When the bone image 43 is obtained as described above, only the bone on the bone image is extracted by, for example, threshold processing based on the bone image data S1 representing the bone image 43, and A deviation amount ΔS is determined, which represents how much deviation the average value of the bone image data corresponding to the bone image data corresponds to the predetermined reference value.

Further, from the original image data obtained as described above, a predetermined fixed data conversion such as along the straight line G' in FIG. 4 is performed. The original image data converted in this way is further shifted by the shift amount ΔS. A visible image is reproduced and displayed on the CRT display 32 (see FIG. 2) based on the original image data finally converted in this way. Since this visible image is an image based on the original image data converted as described above, it is displayed at an appropriate density (including brightness when displayed on a CRT display), and the air content has changed. In this case, the image is reproduced as a visible image whose overall density changes according to the change in air content.

In the above embodiment, the visible image is displayed on the CRT display 32.
Although the visible image is reproduced and displayed, a hard copy of the visible image may be obtained using, for example, a laser printer or the like.

Furthermore, although the above embodiment describes an example in which the air content of the lung field changes in an X-ray image of the chest of a human body, the image density adjustment device of the present invention is limited to changes in the air content. Rather, it can be widely used to show changes in soft parts that are accompanied by changes in radiation transmittance in visible images.

Furthermore, although the above embodiments are examples in which a stimulable phosphor sheet is used, the present invention is not limited to those using a stimulable phosphor sheet. It can also be applied to those using

(Effects of the Invention) As described above in detail, the image density adjustment device of the present invention obtains a bone image by energy subtraction processing, calculates the deviation amount of the density of this bone image from a predetermined density, and Since the density of the original image is adjusted by the amount corresponding to the amount, a visible image with an appropriate density is reproduced and displayed based on the original image data, and if a change such as a change in the radiation transmittance occurs in the soft part. , the change will be reproduced on the visible image as well.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an X-ray imaging device; FIG. 2 is a perspective view of an X-ray image reading device and an image processing display device which is an embodiment of the image density adjustment device of the present invention; FIG. FIG. 4 is a diagram showing an example of a histogram of image data. 1... X-ray imaging device 2... X-ray tubes 3, 8
a, 8b, 8cm X-ray 4...Subject 5...
・First stimulable phosphor sheet 6... Filter 7... Second stimulable phosphor sheet 8... Mark 16... Laser light source 19... Rotating polygon mirror 22... Bright light Luminous light 23...Light guide 2
4... Photo multiplier 25... Log amplifier 26... A/D converter 30... Image processing display device 41. 42... Original image 43... Bone image 44... Overlapping Combined image (original image) '3c Figure Figure

Claims (1)

[Scope of Claims] Based on a plurality of image data representing each of a plurality of radiation images obtained by irradiating at least two types of radiation having different energies to a subject consisting of soft parts and bone parts, the subject is image calculation means for calculating bone image data in which mainly bone images are recorded, and original image data representing an original image in which both soft parts and bone parts in the subject are recorded; a density variation calculation means for calculating the amount of deviation of the density of the bone part in the bone part image from a predetermined density based on the amount of deviation from the density of the bone part in the bone part image; An image density adjustment device comprising a density adjustment means for adjusting density.