JP3312280B2 - X-ray image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image processing apparatus. The present invention relates to a technique for correcting density data.

[0002]

2. Description of the Related Art In the medical field, diagnosis based on radiation images has conventionally been important. In particular, in an intensive care unit or the like, an X-ray photograph is taken periodically to grasp the condition of the patient, and a copy of the X-ray photograph is immediately made, and is simultaneously read by a treating physician and a radiologist. May be done.

Conventionally, a copy of the X-ray photograph has been made by closely exposing an X-ray photograph as an original to a duplication film and developing the film. In this method, variations in the photosensitive material, the development processing, and the exposure apparatus are large. Therefore, in order to obtain the same density as that of the X-ray photograph of the original, it is necessary to repeat the trial and error to set the exposure conditions. Obtaining a duplicate image requires a great deal of time and effort.

[0004] Further, since the gradation characteristics of the duplication film are not linear, even if the same density as that of the original image can be obtained partially, the density may be different in other portions and the same contrast and gradation may be obtained. Was difficult to get. Also, regarding the image quality, information necessary for diagnosis may be lost due to a decrease in sharpness or an increase in noise. In order to solve such a problem, an X-ray photograph is photoelectrically read using a high-quality film digitizer that has been recently developed, and digital image data obtained by the reading is read using a high-quality hard copy device. There has been proposed an apparatus that creates a copy of image quality having no problem in diagnosis by printing on a film.

By using such an apparatus, the tone characteristics of the image input / output device can be corrected by digital image processing technology even in reproducing the same density gradation as that of the original in a duplicate photograph. Almost the same density gradation can be easily obtained.

[0006]

As an aggressive use of the digital image processing technology of such an apparatus, an improper density of an X-ray photograph due to overexposure or shortage caused by a failure in setting conditions at the time of photographing. Correction is conceivable. However, since the gradation characteristics of an X-ray film are non-linear and complicated, the change in density on an X-ray photograph when the exposure amount is changed is not a simple shift in density but a change in density distribution. It is accompanied by change.

For example, in chest X-ray photography, when an image is taken with overexposure, the density increases in the lung field but the contrast decreases, and conversely, the contrast increases in the mediastinum. Therefore, if tone correction is performed by relatively simple image processing such as enhancement of contrast or addition and subtraction of a constant, some densities can be corrected to densities equivalent to proper exposure, but other densities can be corrected. In some parts the concentration is different,
Or, the overall contrast becomes inappropriate,
It is often difficult to correct to the optimum density gradation required for diagnosis.

Therefore, in order to correct image data of an X-ray photograph taken by overexposure and underexposure to a gradation equivalent to that of a properly exposed X-ray photograph, in addition to the input / output characteristics of the image data, A complicated process of correcting the density gradation using a non-linear gradation conversion characteristic taking into account the characteristic curve of the X-ray film (density characteristic with respect to the relative X-ray dose) is required. To perform such a density correction, a technician must determine the exposure conditions for each X-ray photograph and specify how much correction should be performed. could not. Alternatively, only those that need correction (X-ray photographs underexposed or underexposed) are selected, and those that are normal (X-rays with proper exposure) are selected.
In order to automate only the X-ray photograph, it is necessary to select whether or not the density gradation is normal (X-ray photograph with proper exposure).

In such a density determination of an X-ray photograph (judgment of exposure conditions), a technician who is skilled in X-ray photography and has abundant knowledge and experience can check the degree of excessive or insufficient exposure by looking at the X-ray photograph. Although it is possible to judge to a certain extent, it is difficult for those who do not to make the above judgment accurately, and in practice, using such a system requires considerable skill,
It has been difficult to use these functions effectively.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of an inappropriate density (excessive or insufficient exposure) due to failure of photographing conditions in gradation correction of X-ray image data obtained by reading an X-ray photograph. It is an object of the present invention to make it possible to accurately and easily perform the correction of the above in consideration of the non-linear gradation characteristics of the X-ray film.

[0011]

Therefore, an X-ray image processing apparatus according to the present invention comprises: means for reading an X-ray photograph and converting it into X-ray image data; Means for detecting at least one of density representative data among data representative of a high density part, data representative of a low density part, and data representative of an average density;
The concentration representative based on a characteristic function indicating the relationship with X-ray dose
The relative X-ray dose obtained by converting the data is represented by the characteristic function
Is obtained by converting the optimum value of the concentration representative data based on
The image data is converted into a relative X-ray dose based on
Means for setting a gradation conversion function for converting data, and means for converting and outputting the X-ray image data according to the set gradation conversion function.

Here, when data representative of a high density portion is detected as the density representative data, a density of 1.5 to 2.
It is preferable to set a gradation conversion function as a predetermined density included in the range of 5 as an optimum density corresponding to the high density portion. When data representing a low density portion is detected, it is preferable to set a predetermined density in the range of 0.1 to 0.5 as the corresponding optimum density.

Further, when data representing an average density is detected, the corresponding optimum density is 0.5
It is preferable to set a predetermined density within the range of 1.5 to 1.5. Further, when the X-ray photograph is a chest X-ray photograph, a rectangular region including a lung field is preferably set, and this rectangular region may be used as a main subject region. Further, it is also possible to use different X-ray film characteristic functions for the conversion from the density data to the relative X-ray dose and the conversion from the relative X-ray dose to the density data.

The read X-ray image data is X-ray image data.
When the density exceeds the set density range in the characteristic function of the line film, the characteristic function may be corrected and used. Further, when the degree of conversion of the X-ray image data according to the gradation conversion function is within a preset range, the conversion of the X-ray image data may be prohibited. In setting the gradation conversion function, a plurality of characteristic functions of the X-ray film may be stored, and a characteristic function to be used may be selected from the plurality of characteristic functions in accordance with an imaging region.

The imaging region can be estimated by analyzing the shape pattern of the main subject in the X-ray image data. Further, the characteristic function may be selected according to the film size of the X-ray photograph instead of the imaging region.
Further, when information indicating the type of X-ray film is recorded on the X-ray photograph, the information may be recognized, and the characteristic function may be selected according to the type of X-ray film.

[0016]

According to the X-ray image processing apparatus having such a configuration, an X-ray photograph is read and converted into X-ray image data, and density representative data (high-level data) representative of the density characteristics of the main subject detected from the X-ray image data. At least one of data representing a density portion, data representing a low density portion, and data representing an average density) is converted into optimum density data on an X-ray photograph. Here, the gradation conversion function used for the conversion uses a characteristic function indicating the relationship between the relative X-ray dose and the density in the X-ray film, and the relative X-ray dose corresponding to the density representative data corresponds to the optimum density data. It is set to be converted into a relative X-ray dose.

Therefore, according to the X-ray image processing apparatus of the present invention, the correction characteristic taking into account the non-linear gradation characteristics of the X-ray film is set according to the density characteristic of each X-ray photograph, and the X-ray image to be read is set. It is possible to accurately correct the density level improperness due to the radiographing conditions. In general radiographs, the concentration distribution is almost constant,
As density representative data, at least one of data representative of a high density part, data representative of a low density part, and data representative of an average density is detected as described above, and the density representative is detected. By converting the data to the optimum density data, the density gradation can be corrected to substantially the same as that of a properly exposed X-ray photograph.

The optimum density ranges corresponding to the data representative of the high density part, the data representative of the low density part, and the data representative of the average density detected as the density representative data are 1.5 to 2.5, respectively. 0.1 to 0.5, 0.5 to 1.
5. By setting a function so that the actual density data is converted to a predetermined density included in these ranges, the density can be converted to density data corresponding to the optimal exposure.

In a chest radiograph, a rectangular area including a lung field is set, and this area is regarded as X-ray image data corresponding to a main subject, and density representative data is detected in this area. For example, it is possible to accurately obtain data representing the density characteristics of the main subject portion. In addition, as a characteristic function of the X-ray film used in the gradation conversion function, a characteristic function for converting the density data into a relative X-ray and a characteristic function for converting the relative X-ray into the density data are separately used. If, for example, when imaging using an X-ray film that is not optimal for the imaging region, while the density representative data is converted to a relative X-ray dose by a characteristic curve corresponding to the X-ray film actually used for the imaging, By converting the converted relative X-ray dose into a density according to a characteristic curve corresponding to an X-ray film that is optimal for a target imaging region, imaging is performed with an X-ray film suitable for the imaging region with optimal exposure. It becomes possible to convert the data into the density data when it is performed.

Further, when the X-ray image data exceeds the set density range in the characteristic function of the X-ray film, the characteristic function is corrected so as to conform to the density range of the X-ray image data. Can respond. Further, if the conversion is prohibited when the conversion degree of the X-ray image data by the gradation conversion function is within a predetermined range, the gradation data of the X-ray photograph taken by the substantially appropriate exposure is unnecessary. Can be avoided.

When the X-ray film is properly used according to the imaging region, a characteristic function for each X-ray film expected to be used is stored, and the characteristic function selected according to the imaging region is used. . Further, since the film size may be limited for each shooting type, it may be appropriate to select a characteristic function from the film size.

Further, when the type of the X-ray film is recorded in the X-ray photograph, a characteristic function of the X-ray film used for gradation correction is selected based on the recording information on the X-ray photograph. can do.

[0023]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a system configuration of an X-ray image processing apparatus according to the present invention, and is an X-ray photograph (developed X-ray film).
Is read and converted into digital image data, the image data is subjected to gradation correction, and then hard-copyed using a printer to create a copy of the X-ray photograph.

In FIG. 1, an X-ray photograph reader 1 (X-ray photograph reader) photoelectrically reads an X-ray photograph and converts it into X-ray image data (digital image signal). The X-ray image data obtained by the X-ray photograph reading device 1 is temporarily stored in an image data storage device 2.

In the image gradation analysis device 3, the X-ray image data stored in the image data storage device 2 and the X-ray film characteristic curve (characteristic function) storage device 4 (characteristic function storage means) are stored in advance. Using a characteristic curve (characteristic function) indicating the relationship between the relative X-ray dose and the concentration for each X-ray film,
A gradation conversion function for correcting the X-ray image data to an optimal density (a density on an X-ray photograph when photographed with proper exposure) is set.

In the present embodiment, the image data storage device 2, the image gradation analysis device 3, and the X-ray film characteristic curve storage device 4 constitute a gradation conversion function setting means and a density representative data detection means. . Then, the image data conversion device 5 (conversion means) uses the gradation conversion function set by the image gradation analysis device 3 to store the image data in the image data storage device 2.
The X-ray image data stored in is converted.

The X-ray image data converted (gradation corrected) by the image data conversion device 5 is output to the hard copy device 6, where the X-ray image set in the X-ray image reading device 1 is output. Is created. Next, the details of the X-ray image processing apparatus of the present embodiment will be described with reference to the processing procedure shown in the flowchart of FIG.

In this embodiment, a laser digitizer for X-ray photography is used as the X-ray photography reader 1 for reading X-ray photographs. This device scans a set X-ray photograph (S1) with a laser beam and photoelectrically converts transmitted light, and converts an electric signal obtained by the photoelectric conversion into an A / A signal.
D converted and output as digital image data (S
2).

In this embodiment, image data is sampled at a sampling pitch of 175 μm, and the densities 0 to 4 are digitized into 12 bits (4096 gradations). For example, 35cm
In the case of a four-sided radiograph, the sampling pitch is approximately
The number of pixels is 2000 × 2000. In X-rays such as the chest,
Image data having a sharpness equivalent to that of a substantially original image can be obtained with such an accuracy. Also, the noise hardly increases in the physical measurement with respect to the original image.

As described above, an image quality equivalent to that of an original X-ray photograph can be obtained. However, in some cases, a finer sampling pitch, for example, 87 μm, is sampled, and image data of 4000 × 4000 pixels is obtained in a 35 cm square X-ray photograph. It can also be. When a small film is used, digitization can be performed at a finer sampling pitch.

Regarding the gradation, in the case of a normal X-ray photograph,
12 bits (4096 tones) is sufficient, and if the density is not particularly high, the necessary and sufficient tones can be obtained even if the density 0 to 3 is quantized by 10 bits (1024 tones). . In the laser digitizer for X-ray photography used in this embodiment, since the density range described above is quantized at equal intervals, the pixel data is 1000 times the density value. Is easy to reproduce. However, if the relationship between density and pixel data is known,
The density and the pixel data need not be particularly proportional.For example, the number of gradations can be obtained by finely quantizing a low-density part where the contrast resolution of the human eye is high and coarsely quantizing a high-density part with little effect. It is possible to obtain a sufficient density resolution even when the density is small.

Further, since a bar code reader can be incorporated in the digitizer, a bar code sticker on which various data are written is attached to an X-ray photograph serving as a manuscript, and an image is read on the X-ray photograph at the same time. Can also be configured to read the barcode of (1) and control image processing described later. The image data read by the digitizer (X-ray photograph reading device) is transferred to a general-purpose computer, and is temporarily stored in an image data storage device 2 (for example, a hard disk device) attached to the general-purpose computer. The image data on the device 2 is analyzed, and a representative density (density representative data) of the main subject portion is obtained (S3). This part corresponds to the density representative data detecting means.

Here, for example, in the case of a chest front photograph,
As shown in FIG. 3, for example, a rectangular area surrounding the lung field is set based on profile information and the like, and this is used as the area of the main subject, and the maximum density Dmax and the minimum density in the X-ray image data in this area are set. Dmin (density representative data representing the density characteristics of the lung field) is obtained. In the case of the lung side surface, a rectangular area may be set in the same manner, and the maximum density Dmax and the minimum density Dmin may be obtained in this area.

Further, in the case of a chest X-ray, it is considered good that the density of the lung field is within a certain range, and the lung field area is extracted by extracting the contour of the lung field using image recognition technology. , The average value in the area can be used as the representative density data. When there is no characteristic shape pattern such as a lung field as in the case of photographing an abdomen or a lumbar spine, a rectangular region of interest that does not include a part other than the human body (such as a background) is set. As a simple but effective method, as shown in FIG.
It can be substituted by setting a rectangular area having a length of two. This method can also be applied to the front and side of the chest.

In the measurement of the maximum density Dmax (data representative of a high density part) and the minimum density Dmin (data representative of a low density part), a histogram in the set oblique photographic subject area is determined and considered as a noise component. Detected as the maximum and minimum values of the part excluding the unique maximum and minimum densities. As a method for removing noise having such specific maximum and minimum values, in addition to the method using a histogram as described above, the maximum value of image data processed using an average filter or a median filter is used. , The minimum value may be obtained.

The maximum density Dmax and the minimum density Dmin
It is not necessary to use all the pixels in the set main subject area in order to obtain, and the calculation time can be reduced by appropriately thinning out. As shown in FIG. 4, the shape of the histogram of the read image data is different from the characteristic curve of the X-ray film used for the imaging or the reading device (image input), even if the exposure is different at the time of X-ray imaging, even for the same subject. Device). For this reason, in order to correct the difference in the exposure amount at the time of imaging, it is necessary to convert the value of the image data into a relative X-ray dose.

The setting of the gradation conversion function using the conversion to the relative X-ray dose (S4) will be described with reference to FIG. still,
Step S4 in FIG. 2 corresponds to a gradation conversion function setting unit. The determined maximum density Dmax and minimum density Dmin are a function D indicating a characteristic curve of the X-ray film (a curve indicating the relationship between the relative X-ray dose and the density) stored in the X-ray film characteristic curve storage device 4 in advance. = F ₁ (E) using the inverse function E = f ₁ ^-1 (D), the relative X-ray dose Emax, Em
in.

Next, using the same characteristic curve, typical maximum density Dcmax and minimum density Dcmin (optimum density data) on an X-ray photograph when a predetermined proper exposure is performed are similarly calculated. The relative X-ray doses are converted into Ecmax and Ecmin, respectively. Note that the maximum density Dcmax and the minimum density Dcmin indicate the density levels in the main subject portion obtained when the same imaging site is imaged under the optimal exposure condition using the X-ray film to be read.

The values of these four relative X-ray doses Emax, E
The conversion formula for converting the relative X-ray dose corresponding to the read image data into the relative X-ray dose corresponding to the optimum concentration from min, Ecmax, and Ecmin is the following primary expression in the dimension of the relative X-ray dose. Can be obtained as a conversion equation f ₂ (E).

[0040]

(Equation 1)

Here, when the above-mentioned function f ₁ (E) of the characteristic curve of the X-ray film and its inverse function f ₁ ^-1 (D) are combined with the above-mentioned conversion formula of the relative X-ray dose, the function in the density dimension is obtained. The function F (D) (tone conversion function) for tone correction is as follows. F (D) = f ₁ (f ₂ (f ₁ ^-1 (D)) By converting the X-ray image data using this function (gradation conversion function) (S5), the non-linear characteristics of the X-ray film are considered. Thus, it is possible to perform the density correction of the image underexposed or underexposed.

In an X-ray photograph in which the exposure was excessive or insufficient due to failure of the exposure condition at the time of photographing and did not reach an appropriate density, not only a simple density shift but also a partial change in contrast occurs. Since this occurs because the characteristic curve of the X-ray film is not linear, there is no difference in the contrast of the X-ray dose applied to each part with respect to the X-ray dose applied to the X-ray film during imaging. Therefore, X
By converting the input X-ray image data into numerical values in units of relative X-ray dose using the characteristic curve of the X-ray film used to create the radiograph, correction of exposure errors can be converted by a linear function or simply. It can be performed by addition and subtraction of various constants.

For this reason, in this embodiment, density representative data (maximum density D) is obtained by using a characteristic curve of an X-ray film.
max, the minimum density Dmin or the average value) is converted into a relative X-ray dose, and the representative density (maximum density Dcmax, minimum density Dcmin) at the time of proper exposure is similarly calculated as the relative X-ray dose.
Convert to dose. Then, a first-order function is calculated in which the difference is obtained and the difference is added to the value of the relative X-ray amount in a range where the image data can be taken. Then, replace this with the previous X
After re-creating a function for the density value which is a unit of the image data using the characteristic curve of the line film, the image data is converted to correct the density.

By such gradation correction, even with an X-ray photograph taken under inappropriate exposure conditions, it is possible to obtain the same density, gradation, and contrast as those of an appropriately exposed X-ray photograph. When performing tone correction as described above,
It is necessary to accurately obtain data indicating the density of the main subject portion of the X-ray photograph. The density distribution of an X-ray photograph varies greatly from photograph to photograph due to individual differences in the human body as a subject and changes in photographing conditions. In particular, the area of the high-density portion of the background greatly differs depending on the size of the subject, and greatly affects the shape of the histogram of the X-ray image.

However, in a chest front photograph, which accounts for a large proportion of X-ray photography, empirically, the density distribution of lung shadows is substantially constant, and typical density values are also distributed in a fairly narrow range. It is known. Therefore, even for an X-ray photograph having an inappropriate density gradation due to overexposure and underexposure, a representative density value of the lung shadow is detected and converted to a density in the proper exposure, thereby obtaining an equivalent to the proper exposure. Can be converted into image data of the density gradation of.

It is preferable to use the maximum density and the minimum density as the density representative data as described above, but it is also possible to use only one of the maximum density value, the minimum density value, and the average value. Here, when only one density representative data is used, it is particularly preferable to use the substantial (excluding noise component) maximum density in the lung shadow, because the detection is easy and the difference between the subjects is different. Is also less effective.

The substantial maximum density in the lung shadow is distributed in a range of about 1.8 to 2.1 at the time of proper exposure (maximum density Dcmax = 1.8 to 2.1). Therefore, an X-ray photograph obtained by inappropriate exposure is photographed with appropriate exposure by using a function that converts the maximum density of the lung shadow into a value (optimal density data) within the preset density range. It is possible to obtain an image having the same density gradation as that obtained by the above method.

If the lung field area can be accurately grasped as described above, it is possible to use the average value of the image data in that area. In this case, the average value is obtained under the optimum exposure condition. The concentration range that can be obtained is about 0.8 to 1.2,
A value within this range may be used as the optimum density data. Furthermore,
When the minimum density in the X-ray image data corresponding to the main subject is density representative data, the range of the minimum density at the time of proper exposure is the noise component of the mediastinum in front chest imaging. Excluding, it is about 0.2 to 0.4.

The above-described gradation conversion is not limited to the above-described chest front photograph, and can be applied to other parts such as the chest side, abdomen, and lumbar spine as it is. The range expands, with the maximum concentration in the range of about 1.5 to 2.5, the average concentration in the range of about 0.5 to 1.5,
The minimum concentration is in the range of about 0.1 to 0.5. However, the variation among the parts is small and falls within a range of about 0.2 in density difference.

In X-ray photography, X-rays are scattered by a human body, and the grid is usually used to remove the scattered radiation in order to lower the contrast of the X-ray photograph. However, due to improper placement of the grid, the effect is reduced and scattered radiation cannot be removed. As a result,
The contrast of the X-ray photograph may be reduced. In such a case, even if the maximum density is detected as the density representative data and the correction for converting the maximum density into the optimum density is performed, the density of the low density portion is increased due to the influence of the scattered radiation. Is required. Similarly, for such a photograph, in order to automatically perform the density correction, in addition to the maximum density, a value representing a low density portion of a main subject is detected, and the maximum density and the minimum density are used as described above. It is preferable to obtain a first-order gradation conversion function.

Further, in this embodiment, at the same time as obtaining the gradation correction function, the density correction coefficient (conversion degree) is also determined, and if the value is within a range of the substantially proper exposure, no conversion is performed. That is, density correction is effective for X-ray photographs that are overexposed and deficient, but slight correction of typical density data is performed for those that have been properly exposed due to slight variations in typical density data. Become. This effect is unsuitable when a plurality of X-rays are taken for the same person under the same exposure conditions to check a change in density. Therefore, the above-described problem can be solved by not performing correction on a photograph determined to be appropriate exposure within a certain range even if it is determined that slight correction is necessary. Note that such a function corresponds to a conversion prohibiting unit in the present embodiment.

Further, the coefficient of the density correction may be displayed on the user's terminal to confirm whether or not to perform the correction under this condition. In this case, if the user determines that the correction condition of the gradation conversion is inappropriate, it is preferable that the user can manually set the conversion characteristics. However, these operations are
When a large amount of X-ray photographs are automatically processed, the processing is complicated, so that the processing can be omitted.

In the above embodiment, in the function F (D), the same characteristic curve is used when converting the density data into the relative X-ray dose and when converting the relative X-ray dose into the density data. It is also possible to use characteristic curves of different films as characteristics of the inverse function. By performing such processing, it is possible to correct inappropriate gradation when a film that is not optimal for a part is used at the time of photographing.

That is, while the density data is converted into the relative X-ray dose using the characteristic curve of the X-ray film actually used for the radiography, the conversion of the relative X-ray dose into the density is performed by using the X-ray which matches the radiographed part. What is necessary is just to use the characteristic curve of a film. Specifically, for example, the maximum density Dmax,
When the minimum density Dmin is used as the representative density data, the characteristic function D corresponding to the X-ray film actually used for the photographing is used.
= F ₁ (E), the maximum density Dmax and the minimum density Dmin are converted into relative X-ray doses, respectively, while the characteristic function D =
Using f ₁ ′ (E), the optimum maximum density Dcmax and the optimum minimum density Dcmin are converted into a relative X-ray dose, and the value of the relative X-ray dose obtained in this way is converted in the dimension of the relative X-ray dose according to the above equation (1). Equation f ₂ (E) is set.

Then, the conversion equation F in the density data dimension
(D) is F (D) = f₁'(F_Two(f₁ ^-1(D))
Is set. The density characteristics of X-ray photography
Fluctuates depending on the lot and development conditions.
The minimum or maximum concentration of
Concentration range may be exceeded. In such a case,
With the above method, conversion from concentration to relative X-ray dose is not possible.
Concentration range. Such an inconvenience
The minimum and maximum values on the image that include areas other than the scenery and illumination area
And adjust the characteristic curve to fit the range
(Characteristic curve shift and rotation correction)
Can be avoided.

In general, X-ray films having different characteristics are used for each radiographic part, and their characteristic curves are also different. Five or six types are used for ordinary radiography. Further, although it slightly changes depending on the combination with the screen and the developing process, it does not affect the density correction described later. For this reason, in the present embodiment, a plurality of representative characteristic curves are stored in the X-ray film characteristic curve storage device 4, and a menu of imaging parts for chest, abdomen, bone, and the like is displayed. The user can select each film. It is also possible to automate these selections, and it is possible to determine the imaged region by pattern analysis by a computer and incorporate a function of estimating the used film from the imaged region determination.
The above-described function corresponds to a characteristic function selecting unit based on an imaging part, and when the computer estimates the imaging part by pattern analysis, the computer corresponds to the imaging part estimating unit.

Further, information on the type of film can be written in the bar code attached to the X-ray photograph, and the characteristic curve can be automatically selected. Alternatively, in the case of a photographing apparatus that imprints a label at the time of photographing, a pattern indicating film type information is provided on the label, and the film type is determined by recognizing the pattern of the label portion of the read image data. You can also. The function described above corresponds to the characteristic curve selection unit based on the film type in the present embodiment, and the barcode reader or the X-ray photograph reader 1 corresponds to the type information recognition unit.

In some facilities, the film size may be limited for each type of photographing.
The characteristic curve can be selected according to the size of the film (X-ray photograph) identified at the time of reading the photograph. Such a function corresponds to a characteristic curve selecting means based on the film size. Note that one characteristic curve cannot be specified depending on the film size, and a plurality of characteristic curve candidates may be raised for the same film size.
For example, when selecting a characteristic curve based on a film type, candidates may be narrowed down using film size information, thereby simplifying the processing.

By the above means, the image data subjected to the density correction processing is again stored in the storage device, and after being subjected to various image processing, is printed on the film by the hard copy device 6 (S6). A copy of the X-ray photograph read by the X-ray photograph reader 1 is completed (S
7). In the image processing, it is also possible to perform an edge enhancement process or the like that makes the characteristics of the patient stand out.
Further, a scaling process for adjusting the size of the output image can be performed. In this case, since the size of the document differs from the size of the copy, it is preferable to draw the scale indicating the length on the document around the screen so that the size of the shadow can be easily obtained.

In the case of reduction, a plurality of image data are arranged in a memory and printed at the same time,
A copy in which a plurality of X-ray images are arranged in a single photograph can be made. In this way, the cost of duplication can be reduced, and there are other advantages such as simultaneous observation of many photographs of the same patient. In addition, when a patient (region of interest) other than the patient (region of interest) that is desired to be viewed is photographed in a large size, an important part can be enlarged and printed as a single photograph, so that the fine structure can be interpreted. Becomes

Further, the host computer is equipped with software for detecting abnormal shadows, etc., automatically extracts abnormal shadow candidates from the read image data, and overwrites the results as graphics on a hard copy image. It can also be used as an aid in interpretation. In this case, two images can be printed on one copy, graphics can be overwritten on one side, and the original image can be printed on the other side as it is.

In this embodiment, a laser printer that scans a film with a laser beam and prints a digital image is used as an apparatus for creating such a hard copy. This prints an image of 4000 × 5000 pixels on a 14 × 17 inch film at 1296 bits at 4096 gradations, and can make a copy almost the same size and scale as the original. This printer includes a conversion table for tone correction, and can correct tone characteristics due to fluctuations in the printer main body and the developing machine.

The setting of the conversion table can be automatically performed by measuring the density of the step wedge using a densitometer attached to the printer, or can be performed by transferring data from a host computer. For this reason, by writing the above-mentioned density correction function of an overexposed / underexposed photograph as data of a conversion table into a hard copy device, the X-ray image data read by the X-ray photograph reading device 1 can be directly transferred and printed. Thus, it is possible to obtain a copy which has been subjected to density correction processing corresponding to overexposure and underexposure.

In this printer, since character information can be printed around an image, character information input by a user, conditions for density correction, and the like may be printed. When the bar code includes a patient number or the like, patient information can be read from a radiation information system or the like based on the patient number and printed on the peripheral portion.

As an image output (hard copy) means,
In addition, an apparatus used for creating a hard copy of a CT image can be used. In this case, if the hard copy device for CT images has a digital interface, the digital image can be transferred as it is. If the hard copy device does not have the interface, the digital image can be transferred as a video signal or the original image can be transferred. If the image is a video signal, it can be printed as it is.

In some cases, the copy need not be a film, and in this case, a hard copy device for printing on photographic paper or thermal paper can be used. It is also possible to divert an ink jet printer or an electrophotographic printer for plain paper. In any case, the relationship between the X-ray image data value and the corresponding density value on the output hard copy has a one-to-one correspondence,
All that is required is that the relationship be known.

In the present embodiment, a system is used in which an X-ray photograph is read and converted into image data, and a duplicate hard copy of the X-ray photograph is created using this image data.
Since the present invention is characterized by the gradation conversion technology of X-ray image data read from an X-ray photograph, it is not limited to a system for creating a hard copy, but is not limited to a system for creating a hard copy. If the correspondence with the data is known, a system that displays an X-ray image on a display device such as a CRT using an appropriate conversion table may be used.
Of course, the configuration may be such that the X-ray image data subjected to the gradation conversion is stored in a database, and the read-out X-ray image data is transferred to a hard copy device or a display device as needed.

[0068]

As described above, X according to the present invention is
According to the X-ray image processing apparatus, image data (density data) of an X-ray photograph taken at an inappropriate density due to failure of imaging conditions (excessive or insufficient exposure) is taken into consideration in consideration of the non-linear gradation characteristics of the X-ray film. By performing the conversion, the density can be converted into a density equivalent to that obtained when the image is captured under the optimal imaging condition (appropriate exposure) in a well-balanced manner.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a system configuration according to an embodiment.

FIG. 2 is a flowchart illustrating a flow of image processing according to the embodiment.

FIG. 3 is a view showing the setting of a main subject area in a front chest photo.

FIG. 4 is a diagram showing a state in which a histogram of image data is deformed due to excessive or insufficient exposure.

FIG. 5 is a diagram showing how a gradation conversion function is set in the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 X-ray photograph reading device 2 Image data storage device 3 Image gradation analysis device 4 X-ray film characteristic curve storage device 5 Image data conversion device 6 Hard copy device

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI H04N 7/18 G06F 15/68 310 (58) Investigated field (Int.Cl. ⁷ , DB name) G03B 42/02 A61B 6 / 00 G06T 1/00 G06T 5/00 H04N 5/243 H04N 7/18

Claims (12)

(57) [Claims] An X-ray photograph reading means for reading an X-ray photograph and converting the X-ray image data into X-ray image data; data representing a high density portion in a main subject, data representing a low density portion, Density representative data detecting means for detecting at least one density representative data among the data representative of the average density ; a density and a relative X-ray dose in a predetermined X-ray film
The concentration representative data is based on a characteristic function indicating the relationship with
The relative X-ray dose obtained by the conversion is calculated based on the characteristic function.
Relative X obtained by converting the optimum value of the density representative data
The image data is converted based on a conversion formula for converting into dose.
Gradation conversion function setting means for setting a gradation conversion function to be converted
When, X-ray image processing apparatus characterized by being configured to include a converting means for converting the X-ray image data as the gradation conversion function that has been set by the conversion function setting means. 2. The density representative data detecting means detects at least data representative of a high density part, and the gradation conversion function setting means sets a predetermined density included in a density range of 1.5 to 2.5 to a high density part. 2. The X-ray image processing apparatus according to claim 1, wherein a gradation conversion function is set as a corresponding optimum density. 3. The density representative data detecting means detects at least data representative of a low density part, and the gradation conversion function setting means converts a predetermined density included in a density range of 0.1 to 0.5 into a low density part. 2. The X-ray image processing apparatus according to claim 1, wherein a gradation conversion function is set as a corresponding optimum density. 4. The density representative data detecting means detects at least data representative of an average density, and the gradation conversion function setting means converts a predetermined density included in a density range of 0.5 to 1.5 to an average density. 2. The X-ray image processing apparatus according to claim 1, wherein a gradation conversion function is set as an optimum value of the density data. 5. The radiographic apparatus according to claim 1, wherein the radiograph is a chest radiograph, and the density representative data detecting means sets a rectangular area including a lung field and uses the rectangular area as a main subject area. The X-ray image processing apparatus according to any one of claims 1, 2, 3, and 4. 6. A gradation conversion function set by said gradation conversion function setting means, wherein the conversion of density data into relative X-rays and the conversion of relative X-rays into density data are different for X-ray films. The X-ray image processing apparatus according to claim 1, wherein a characteristic function is used. 7. The gradation conversion function setting means, wherein when the read X-ray image data exceeds a set density range in a characteristic function of an X-ray film, the characteristic function is corrected and used. Claims 1, 2, 3, 4, 5
Or the X-ray image processing apparatus according to any one of 6. 8. When the conversion degree of the X-ray image data according to the gradation conversion function by the conversion means is within a preset range, the conversion of the X-ray image data by the conversion means is prohibited. The X-ray image processing apparatus according to any one of claims 1, 2, 3, 4, 5, 6, and 7, further comprising a conversion prohibiting unit that performs conversion. 9. A characteristic function storage means for storing a plurality of characteristic functions of an X-ray film, a characteristic function storage means for storing a plurality of characteristic functions of the X-ray film, 3. A function selecting means, comprising:
The X-ray image processing apparatus according to any one of 3, 4, 5, 6, 7, and 8. 10. The image processing apparatus according to claim 1, wherein the gradation conversion function setting means includes an imaging part estimating means for analyzing a shape pattern of a main subject in the X-ray image data to estimate an imaging part. 10. The X-ray image processing apparatus according to 9. 11. A method according to claim 1, wherein said gradation conversion function setting means comprises: a characteristic function storage means for storing a plurality of characteristic functions of the X-ray film; and a film size of the X-ray photograph read by said X-ray photograph reading means. 3. A characteristic function selecting means based on a film size for selecting a characteristic function from a plurality of characteristic functions.
The X-ray image processing apparatus according to any one of 3, 4, 5, 6, 7, and 8. 12. A method according to claim 1, wherein said gradation conversion function setting means stores a plurality of characteristic functions of the X-ray film, and an X-ray film recorded on the X-ray photograph read by said X-ray photograph reading means. Type information recognizing means for recognizing information indicating the type of the film, and characteristic function selecting means for selecting a characteristic function from the plurality of characteristic functions according to the type of the X-ray film recognized by the type information recognizing means. 3. The method according to claim 1, further comprising:
The X-ray image processing apparatus according to any one of 3, 4, 5, 6, 7, and 8.