JP2824873B2 - Method for determining image points in subject image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining image points in a subject image based on image signals obtained from respective pixels on a recording sheet on which a radiation image including the subject image is recorded. is there.

[0002]

2. Description of the Related Art A recorded radiographic image is read to obtain an image signal, and the image signal is subjected to appropriate image processing.
Reproduction and recording of images are performed in various fields. For example, an X-ray image is recorded using an X-ray film having a low gamma value designed to be compatible with the subsequent image processing, and the X-ray image is read from the film on which the X-ray image is recorded, and is converted into an electric signal. After conversion, the electric signal (image signal) is subjected to image processing, and then reproduced as a visible image in a copy photograph or the like, a reproduced image with good image quality performance such as contrast, sharpness, and graininess can be obtained. A system has been developed (see Japanese Patent Publication No. 61-5193).

[0003] Further, the applicant of the present invention has proposed that radiation (X-ray, α
Radiation, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a portion of this radiation energy is accumulated, and then, when irradiated with excitation light, such as visible light, the accumulated light shows stimulated emission according to the accumulated energy. Using stimulable phosphor (stimulable phosphor)
A radiation image of a subject such as a human body is once photographed and recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light. A radiation image recording / reproducing system has been already proposed in which an exhaust signal is photoelectrically read to obtain an image signal, and a radiation image of a subject is output as a visible image to a recording material such as a photographic material or a CRT based on the image signal. (Japanese
55-12429, 56-11395, 55-163472, 56-104
Nos. 645 and 55-116340).

[0004] This system has the practical advantage of being able to record images over a very wide radiation exposure area compared to conventional radiographic systems using silver halide photography. That is, in the case of the stimulable phosphor, it has been recognized that the amount of emitted light that is stimulated by excitation after accumulation is proportional to the radiation exposure amount over an extremely wide range. Even if fluctuates considerably, the amount of the stimulating light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and converted into an electric signal. Recording materials such as photographic photosensitive materials using
By outputting a radiation image as a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by a change in radiation exposure.

[0005] In the above system, before the image signal is obtained by reading under the optimum reading conditions in accordance with the dose of the radiation applied to the stimulable phosphor sheet or the like, the stimulable phosphor sheet is previously irradiated with a low-level light beam. Perform a pre-read to scan and read the outline of the radiation image recorded on this sheet, analyze the pre-read image signal obtained by this pre-read,
After that, a system configured to perform a main reading by irradiating the sheet with a light beam having a higher level than the light beam at the time of the pre-reading and scanning the radiation image under the optimum reading conditions to obtain an image signal. Yes (JP-A-58-67240)
No. 58-67241, No. 58-67242).

Here, the reading condition is a general term for various conditions that affect the relationship between the amount of stimulated emission light in reading and the output of the reading device. It means the scale factor or the power of the excitation light in reading.

[0007] The high level / low level of the light beam means that the intensity of the light beam emitted per unit area of the sheet or the intensity of the stimulating light emitted from the sheet is, respectively. When it depends on the wavelength of the light beam (has a wavelength sensitivity distribution), the intensity of the light beam radiated per unit area of the sheet is weighted by the wavelength sensitivity, and the magnitude of the weighting intensity is determined as follows. As a method of changing the level of the light beam, a method of using a light beam of a different wavelength, a method of changing the intensity of the light beam emitted from a laser light source, etc.
Various known methods such as a method of changing the intensity of the light beam by inserting and removing a filter or the like, a method of changing the scanning density by changing the beam diameter of the light beam, and a method of changing the scanning speed can be used.

[0008] Regardless of whether the system performs the pre-reading or the system which does not perform the pre-reading, the obtained image signal (including the pre-reading image signal) is analyzed, and the optimum image when the image signal is subjected to the image processing is analyzed. In some systems, processing conditions are determined. The method for determining the optimum image processing conditions based on this image signal is not limited to the system using the stimulable phosphor sheet, but obtains the image signal from a radiation image recorded on a recording sheet such as a conventional X-ray film. It is also applied to the system.

Various methods have been proposed for analyzing the image signal (including the pre-read image signal) to obtain optimum reading conditions and image processing conditions. One of the methods is to create a histogram of the image signal. A method is known (for example, Japanese Patent Publication No. 3-22968). By obtaining the histogram of the image signal, it is possible to know, for example, the maximum value and the minimum value of the image signal, the value of the image signal at the point where the frequency is maximum, and the like, and from these values, the stimulable phosphor sheet, X The features of the radiation image recorded on the recording sheet such as a line film can be grasped. Therefore, by determining the optimal reading conditions and image processing conditions based on this histogram,
It is possible to reproduce and output a radiographic image with excellent observation suitability.

On the other hand, when a radiation image is photographed and recorded on a recording sheet, a portion unnecessary for observation of a subject is not irradiated with radiation, or a portion unnecessary for observation is irradiated with radiation. Because the scattered radiation enters the required area and the image quality performance deteriorates, use an irradiation field stop to limit the radiation irradiation area so that the radiation is irradiated only to the required part of the subject and a part of the recording sheet. I often shoot.

However, when the image signal is analyzed as described above to determine the reading condition and the image processing condition, the image signal used for the analysis is obtained by using the image signal obtained from the recording sheet photographed using the irradiation field diaphragm. In the case of, even if the image signal is analyzed ignoring the presence of this irradiation field, the captured and recorded radiographic image is not correctly grasped, and incorrect reading conditions and image processing conditions are required, and a radiographic image with excellent observation appropriateness is obtained. May not be reproduced and recorded.

In order to solve this, it is necessary to recognize the irradiation field and obtain the reading condition and the image processing condition based on the image signal in the irradiation field before obtaining the reading condition and the image processing condition.

Among the methods for recognizing an irradiation field, a versatile method for accurately recognizing the irradiation field even when the irradiation field has an irregular shape is, for example, included in the irradiation field. Based on image signals corresponding to each pixel along a plurality of radial directions from a predetermined point toward the sheet edge, a plurality of contour points considered to be on the contour of the irradiation field are obtained, and these contour points are determined. A method of recognizing an area surrounded by a line along the line as an irradiation field has already been proposed by the present applicant (JP-A-63-259538).

In this method, the predetermined point needs to be a point in the irradiation field, and more preferably a point in the subject image in the irradiation field. However, since the irradiation field diaphragm is used to photograph only a necessary part of the subject, in photographing using the irradiation field diaphragm, almost all image points in the irradiation field (especially at the approximate center of the irradiation field) are hardly formed. In the case of, the image point is within the subject image.

[0015]

As described above, first, an irradiation field is obtained, and then, by analyzing an image signal corresponding to the obtained irradiation field, appropriate reading conditions and image processing conditions are obtained. .

However, in order to recognize an irradiation field by the method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 63-259538, it is necessary to find an image point in the irradiation field (preferably in a subject image).

A method is also conceivable in which the center point of the recording sheet is set as an image point in the irradiation field (in the subject image). For example, FIG.
As shown in the figure, when the irradiation field 2 is at the center of the recording sheet 1, the center point C of the recording sheet 1 is an image point in the irradiation field 2, and as described above, in most cases, the image in the subject image 3 Points.

However, when the irradiation field is deviated from the center C of the recording sheet 1 as shown in FIG.
Image points in the irradiation field 2 cannot be determined. In the case where the photographing is performed without using the irradiation field diaphragm, as shown in FIG.
In this case, the irradiation field stop is not used, and the probability that the subject image 3 is not substantially at the center of the irradiation field 2 (in this case, the center is the same as the center C of the recording sheet 1) is shown in FIG. 8 is higher than the case where the photographing is performed using the irradiation field stop as shown in FIG. 8, and therefore the center point C of the recording sheet is often not an image point in the subject image.

The image point in the subject image is obtained by not only recognizing the irradiation field as described above, but also reproducing the radiographic image as a visible image by, for example, enlarging a part of the radiographic image. This is also effective in determining which part of the image to output as a visible image.

The present invention has been made in view of the above circumstances, and provides a method of obtaining an image point in a subject image of a radiation image including the subject image obtained by photographing with or without using an irradiation field diaphragm. It is intended for.

[0021]

According to the present invention, there is provided a method of determining an image point in a subject image, the method comprising the steps of: (a) determining an image point in a subject based on an image signal obtained from each pixel on a recording sheet on which a radiation image including the subject image is recorded; In a method for determining an image point in a subject image for determining an image point in an image, ◆ a histogram of the image signal is obtained, and a histogram analysis is performed from the histogram to obtain an approximate existence range of an image signal carrying the subject image. A center of gravity of the recording sheet is obtained by multiplying an image signal within the approximate existence range by a weighting coefficient, and the center of gravity is set as an image point in the subject image.

In a preferred aspect, in the above-described method of determining an image point in a subject image, the image signal in the approximate existence range is multiplied by a weighting coefficient that is large in the center of the existence range and small in the vicinity of the critical area. It is characterized in that the center of gravity of the recording sheet is obtained.

Here, the "image signal obtained from each pixel on the recording sheet" includes, for example, an image signal obtained by photoelectrically reading the stimulated emission light emitted from the stimulable phosphor sheet or a photograph. This includes, but is not necessarily limited to, image signals and the like obtained by photoelectrically reading light transmitted through or reflected from a photographic film.

[0024]

According to the method for determining an image point in a subject image according to the present invention, a histogram of image signals obtained from respective pixels on a recording sheet on which a radiation image is recorded is obtained, and an outline of the image signal carrying the subject image is obtained from the histogram. Is obtained by multiplying the image signal in this range by a weighting coefficient to obtain the center of gravity. Therefore, this center of gravity is obtained as an image point in the subject image with a sufficiently high probability for practical use.

Since it is better that the image point is located near the center of the subject image, the weighting coefficient is set large in the center of the approximate existence range of the image signal carrying the subject image, and reduced in the vicinity of the critical point. Is obtained, and the center of gravity is set as an image point, whereby the accuracy can be further improved.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of a radiation image reading / reproducing apparatus using an example of the method for determining an image point in a subject image according to the present invention. This radiation image reading and reproducing apparatus is an apparatus using the above-described stimulable phosphor sheet.

The stimulable phosphor sheet 11 on which the radiation image is recorded is set at a predetermined position of the reading means 100. The stimulable phosphor sheet 11 set at the predetermined position is conveyed in the direction of arrow Y (sub-scan) by sheet conveying means 15 such as an endless belt driven by a driving means (not shown).
Is done. On the other hand, the light beam emitted from the laser light source 16
The mirror 17 is reflected and deflected by a rotating polygon mirror 18 driven by a motor 24 and rotating at a high speed in the direction of the arrow. The main scanning is performed in an arrow X direction substantially perpendicular to the direction (arrow Y direction). From the portion of the sheet 11 irradiated with the light beam 17, a stimulating luminescent light 21 having an amount corresponding to the radiation image information stored and recorded is diverged, and the stimulating luminescent light 21 is guided by a light guide 22, Photoelectrically detected by a photomultiplier (photomultiplier tube) 23. The light guide 22 is formed by molding a light-guiding material such as an acrylic plate, and is arranged such that a linear incident end face 22a extends along a main scanning line on the stimulable phosphor sheet 11. The light receiving surface of the photomultiplier 23 is connected to the emission end face 22b formed in an annular shape. Incident end face 22
The stimulated emission light 21 that has entered the light guide 22 from a repeats the total reflection inside the light guide 22 and travels, and the emission end face 22b
The photomultiplier 23 converts the light quantity of the photostimulated light 21 representing the radiation image into an electric signal.

The analog output signal S output from the photomultiplier 23 is logarithmically amplified by the log amplifier 26.
The image is digitized by the A / D converter 27 and an image signal _SQ is obtained. The obtained image signal _SQ is temporarily stored in the storage means 28 and then read out by the image processing means 29.

The image processing means 29 obtains image points in the subject image, and converts the image points into image signals corresponding to pixels along a plurality of radial directions from the image points to the ends of the stimulable phosphor sheet 11. Based on this, a plurality of contour points considered to be on the contour of the irradiation field are obtained, and a region surrounded by a line along these contour points is recognized as the irradiation field. When the irradiation field is recognized, appropriate image processing is performed on the image signal S _Q corresponding to the irradiation field.

The image signals S _Q subjected to the image processing is sent to the playback unit 30, the reproduction unit 30 is a radiation image based on the image signal S _Q is reproduced recorded.

[0032] Here, performed by the image processing unit 29, further describes a method of determining based on an image point in an object image into an image signal S _Q.

The histogram of the image processing unit 29 in the image signal S _Q is determined, the existence range of the outline of the supported image signal S _Q is obtained a subject image from the histogram, the weighting coefficient to an image signal S _Q within this range And the center of gravity of the stimulable phosphor sheet 11 is obtained, and this center of gravity is used as an image point.

In order to perform this operation, first, the image signal S _Q
Seeking a histogram, then determine the existence range of the outline of the image signal S _Q carrying a subject image from the Hisudokuramu, determines the weighting factors. Then the weighting factor, weighted by multiplying the image signal S _Q within the existing range, determining the center of gravity of the stimulable phosphor sheet 11 from its weighted value.

FIG. 2 is a photograph taken using a field stop,
FIG. 6 is a diagram illustrating a state where radiation is applied only to a narrow area on the stimulable phosphor sheet 11.

The area outside the irradiation field 12 shown in FIG. 2, since the radiation is scarcely irradiated, the image signal S _Q obtained from each pixel of the region has a very small value. In the irradiation field 12 shown in FIG. 2, a region other than the subject image 13 is a region where the radiation is directly irradiated on the stimulable phosphor sheet 11 without passing (transmitting or reflecting) through the subject. image signals S _Q obtained from the pixels has a very large value. Image signals S _Q obtained from the pixels corresponding to the object image 13, since it corresponds to a region where the radiation after having passed through the subject is irradiated to the stimulable phosphor sheet, perforated intermediate values doing.

[0037] When a histogram A of the image signal S _Q corresponding to the order 2 is as shown in FIG. 3 (a).
Here between S _A -S _B histogram A in FIG. 3 (a), an image signal S _Q corresponding to the radiation field 12 outside the region, S _B
Inter -S _C is an image signal S _Q corresponding to the object image 13, S _C
Inter -S _D, out of the radiation field 12, represents an image signal S _Q corresponding to the region other than the object image 13, respectively.

When the histogram A corresponding to FIG. 2 is obtained, the weighting coefficient A 'is calculated based on the histogram A.
Is obtained, and a weighting table shown in FIG. 3 (b) is created. The weighting factor A ', as shown in FIG. 3, the histogram A, the radiation field 12 outside the region, an image signal S _Q corresponding to the region other than the object image 13 of the radiation field 12 is removed, the object for the presence range of outline of the image signals S _Q carrying the image 13, larger near the center of the existing range,
It is determined to be smaller at the critical point, that is, near S _B and S _C shown in FIG. Therefore, the weighting coefficient A 'has a maximum value of 1.0 near the center of the existence range and a minimum value of 0 near the critical point.

The multiplying above 'the weighting coefficients A' weighting factor A determined in the in the image signal S _Q corresponding to the existing range of, by weight, the stimulable phosphor sheet as shown in FIG. 4 By calculating the center of gravity G of 11, the center of gravity G is obtained as an image point in the irradiation field 12, and the irradiation field stop is used for photographing only a necessary portion of the subject as described above. Therefore, this center of gravity is obtained as an image point in the subject image 13 with sufficient accuracy for practical use.

[0040] Here, to obtain the center of gravity by weighting the values of the image signals S _Q weighting factor A 'described above, it refers to performing the calculation shown below.

As shown in FIG. 4, the coordinates of the pixels arranged in the x direction are represented by i (positive integer) and the coordinates of the pixels arranged in the y direction are represented by j (positive integer), and each pixel (i, j) carries Image signal S _Q
Is represented by P (i, j).
Also,

[0042]

(Equation 1)

[0043]

(Equation 2)

Where the centroids in the x and y directions are x _c ,
y _c

[0045]

(Equation 3)

[0046]

(Equation 4)

As a result, the coordinates (x _c , y _c ) of the center of gravity are obtained.

[0048] In the above calculation method, the weighting coefficient values of the image signals S _Q which each pixel carrying the radiation image A '
It converted to, 'is performed a calculation to determine the centroid of the transformed image by the weighting factor A' weighting coefficients A each pixel (i, j) is the value of the image signal S _Q to carry The center of gravity similar to the above method can be obtained even when the calculation is performed with weighting. That is, another method of calculating the center of gravity according to the embodiment of the present invention is as follows.
(i, j) the value of the image signal S _Q, which is carrying the q (i, j),

[0049]

(Equation 5)

[0050]

(Equation 6)

Where the centroids in the x and y directions are x _c ,
y _c

[0052]

(Equation 7)

[0053]

(Equation 8)

Thus, the coordinates (x _c , y _c ) of the center of gravity are obtained in the same manner as in the first calculation method described above. In this case, represented by a quadratic equation, as shown in FIG. 5 the product of the value P (i, j) of the value q of the image signals S _Q each pixel carries (i, j) and the weighting coefficient A ' The calculation for obtaining the center of gravity is performed by considering the weighting table.

In the present invention, the image processing means 29
In the calculation of the center of gravity in, either of the above-described two calculation methods may be used.

After the image points in the subject image are obtained as described above, as described above, each of the image points along the plurality of radial directions from the image points toward the end of the stimulable phosphor sheet 11 is obtained. Based on the image signal corresponding to the pixel, a plurality of contour points considered to be on the contour of the irradiation field are obtained, and a region surrounded by a line along these contour points is recognized as the irradiation field. appropriate image processing is performed on the image signal S _Q corresponding to.

In the above embodiment, the case where the obtained image points in the subject image are used for the recognition of the irradiation field has been described. However, obtaining the image points in the subject image is used only for the recognition of the irradiation field. is not. For example, when a visible image is obtained by the reproducing means 30 shown in FIG. 1, the image processing means 29 obtains an image point in the subject image as described above, and as shown in FIG. Even when the image is recorded on the edge of the sheet 11, a visible image in which the subject image is arranged at the center can be obtained.

In the above embodiment, a radiation image reading apparatus which does not perform prefetching has been described. However, prefetching is performed to obtain a prefetching image signal, and an irradiation field is obtained based on the prefetching image signal. It goes without saying that the method for determining an image point in a subject image according to the present invention can also be used in a system for obtaining a reading condition in main reading based on a corresponding preread image signal.

In the above embodiment, the weighting coefficient A 'is set to be large at the center of the area where the subject image 13 exists and to be small near the critical area. In this case, the image point can be obtained in the same manner as in the above embodiment even if the value is set to a constant value as shown in FIG.

Further, the present invention provides, in addition to an apparatus using a stimulable phosphor sheet, a light representing a radiation image obtained from a recording sheet on which a radiation image of a subject is recorded, such as an apparatus using a conventional X-ray film. The present invention can be applied to a general radiation image reading / reproducing apparatus that obtains an image signal by reading, and reproduces and outputs a radiation image based on the image signal.

[0061]

As described above in detail, the method for determining an image point in a subject image according to the present invention obtains an approximate existence range of an image signal carrying a subject image from a histogram of the image signal. The center of gravity of the recording sheet is obtained by multiplying the image signal by a weighting coefficient and weighting the image signal to determine the center of gravity as an image point in the subject image.

Further, in the above method, the weighting coefficient is increased at the center of the range where the image signal carrying the subject image is present, and is decreased near the critical area.
Image points in the subject image can be determined with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment of a radiation image reading and reproducing apparatus using an example of a method for determining an image point in a subject image according to the present invention.

FIG. 2 is a diagram showing a state where radiation is irradiated only to a narrow area on a stimulable phosphor sheet.

FIG. 3 is a diagram showing an example of a histogram of an image signal and a weighting table obtained from the histogram.

FIG. 4 is a diagram showing a stimulable phosphor sheet by coordinates and showing it together with a radiation image;

FIG. 5 is a diagram showing another example of a weighting table;

FIG. 6 is a diagram showing another example of the weighting table;

FIG. 7 is a diagram showing a radiation image having an irradiation field in the center of a recording sheet.

FIG. 8 is a diagram showing a radiation image in which an irradiation field is off the center of a recording sheet.

FIG. 9 is a diagram showing a radiation image in which the entire recording sheet is an irradiation field by photographing without using an irradiation field stop.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 recording sheet 2, 12 irradiation field 3, 13 subject image 11 stimulable phosphor sheet 12 stimulable emission light 23 photomultiplier 26 log amplifier 27 A / D converter 28 storage means 29 image processing means 30 reproduction means

Claims (2)

(57) [Claims] 1. A method of determining an image point in a subject image based on an image signal obtained from each pixel on a recording sheet on which a radiation image including the subject image is recorded, the method comprising: A histogram of the image signal is obtained, a histogram analysis is performed from the histogram to obtain an approximate existence range of the image signal carrying the subject image, and the image signal in the approximate existence range is multiplied by a weighting coefficient to calculate the recording sheet. A method for determining an image point in a subject image, wherein a center of gravity is determined and the center of gravity is used as an image point in the subject image. 2. The center of gravity of the recording sheet is obtained by multiplying an image signal in the approximate existence range by a weighting coefficient that is large in the center of the existence range and small in the vicinity of the critical area. 2. The method for determining an image point in a subject image according to item 1.