JPH05323479A - Radiation image conversion method - Google Patents

Abstract

PURPOSE:To reproduce the radiation images which are inconspicuous in joints and are easily visible at the time of sharing the reading of the radiation images by plural reading means in the radiation image conversion method for obtaining many pieces of picture element data corresponding to respective picture elements by reading the radiation images from a stimulable phosphor accumulated and recorded with the radiation images. CONSTITUTION:The stimulated luminous light beams emitted from respective scanning points are read when a stimulable phosphor panel 15 is repetitively scanned in an X direction by the stimulating light beams of the respective reading means while this panel is transported in a Y direction. As a result, the respective picture elements of a first region D1 and second region D2 are obtd. by the first and second reading means. Namely, the region held by lines L1 and L2 extending transversely is shared by the first reading means and the region held by the lines L3 and L4 is shared by the second reading means. The hatched part held by the lines L2 and L3 is read by both of the first and second reading means. The distance d1 of the picture element point(a) (m, n) from the line L3, the distance d2, from the line L2 and picture element data(x) (m, n) are computed in accordance with {d1.x1 (m, n)+d2.x2 (m, n)}/(d1+d2). The determined picture element is the fresh picture element data of the picture element point (a).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image conversion for reading a radiation image from a photostimulable phosphor in which a radiation image is stored and recorded to obtain a large number of pixel data corresponding to each pixel of the radiation image. Regarding the method.

[0002]

2. Description of the Related Art In recent years, a radiographic image is recorded on an X-ray film or the like, and the film on which the radiographic image is recorded is used as it is for observation and diagnosis. The stimulated phosphor panel (including the sheet) was irradiated with the radiation transmitted through the subject to accumulate and record the radiation image on the stimulated phosphor panel, and then the radiation image was photoelectrically read to obtain an image signal, A system has been used in which a reproduced image is obtained after subjecting the image signal to appropriate image processing. The basic method of the system using this stimulable phosphor panel is described in detail in US Pat. No. 3,859,527. Here, the stimulable phosphor means that when irradiated with radiation such as X-rays, α-rays, β-rays, and γ-rays, a part of the energy of the radiation is accumulated inside for a while, and infrared light, A phosphor that emits accumulated energy as stimulated emission light when irradiated with excitation light such as visible light or ultraviolet light. Depending on the type of the phosphor, the type of radiation that easily accumulates energy, stimulated emission light The wavelength of the excitation light that easily emits, the wavelength of the emitted stimulated emission light, and the like are different.

In a system using this stimulable phosphor panel, the energy of the radiation applied to this stimulable phosphor panel and the amount of the stimulated emission light emitted by the irradiation of the excitation light over a wide energy range. It is recognized that they are proportional to each other, and this ratio can be changed by the light amount of the excitation light, and therefore, a radiographic image that is not affected by fluctuations in the radiation exposure amount can be obtained. Further, in a system for obtaining an X-ray image of a human body, the exposure dose of the human body in X-ray photography can be reduced.

FIG. 1 is a diagram showing an example of the configuration of a system using a photostimulable phosphor panel. The system shown in FIG. 1 is an example in which a photographing device and a reading device are separately configured, and in the photographing device 10, an object 12 standing in front of a photographing table 14 is taken.
The X-rays 13 generated by the X-ray generator 11 are radiated on the illuminating phosphor panel 15, and the X-rays 13 transmitted through the subject 12 are radiated on the photostimulable phosphor panel 15 provided on the imaging table 14, thereby stimulating the photostimulable fluorescence. An X-ray image of the subject 12 is accumulated and recorded on the body panel 15.

After the photographing is performed in this manner, the photostimulable phosphor panel 15 is taken out from the photographing stand 14 and the reader 2
It is set in the panel insertion part 21 of 0. In this case, the stimulated phosphor panel 15 may be housed in a magazine or a cassette. If the photostimulable phosphor panel 15 set in the panel insertion portion 21 is stored in a magazine or cassette, it is taken out from the magazine or cassette and then conveyed along the conveyance path 22.
The reading unit 23 reads the X-ray image stored and recorded in the photostimulable phosphor panel 15 to generate an image signal. The configuration of the reading unit 23 will be described later. The image signal generated by the reading unit 23 is transmitted through the signal transmission path 24.
Is input to the image processing unit 25 via the image processing unit 25, appropriate image processing such as frequency enhancement processing is performed in the image processing unit 25, and further, via the signal transmission path 26, the image display unit 27.
X-ray image of the subject 12 is displayed on the CRT display screen, for example. An image recording device such as a laser printer (not shown) may be provided instead of or together with the image display unit 27 that displays an image, and an X-ray image may be reproduced and recorded on, for example, a silver salt film. You may make it obtain the X-ray image as a visible image by developing.

The photostimulable phosphor panel 15 read by the reading unit 23 is erased by the erasing unit 29 along the transport path 28.
Be transported to. In the erasing section 29, the stimulable phosphor panel 15 is irradiated with erasing light, so that the energy (afterimage) remaining in the stimulable phosphor panel 15 is erased. Photostimulated phosphor panel 1 from which this afterimage has been erased
The sheet 5 is conveyed to the panel take-out section 31 along the conveying path 30, taken out from the reader 20, set in the photographing device 10, and reused.

FIG. 2 is a diagram showing another system configuration example using the stimulated phosphor panel. In this figure,
The components corresponding to the components of the system shown in FIG. 1 are assigned the same numbers as the numbers given in FIG. 1, and only the differences will be described. The system shown in FIG. 2 is provided with a standing type image pickup device 40 in which the photographing stand 14 and the reader 20 of the photographing device 10 in the system shown in FIG. 1 are integrally configured, The photostimulable phosphor panel 15 includes a photographing unit 31.
Is imaged, is conveyed to the reading unit 23 along the conveyance route 22 for reading, is conveyed to the erasing unit 29 along the conveyance route 28 for erasing, and is further conveyed to the conveyance route 30. Along the line, it is set again in the photographing section 31 and reused for the next photographing.

FIG. 3 is a diagram showing an example of the configuration of the reading unit 23 shown as a block in FIGS. 1 and 2. The photostimulable phosphor panel 15 on which the X-ray image is accumulated and recorded is conveyed (sub-scan) in the reading section shown in FIG. Further, during this conveyance (sub scanning), the laser light source 101
A laser beam 102 as excitation light emitted from the laser beam is repeatedly reflected and deflected by a scanner 103 such as a galvanometer mirror or a rotary polygon mirror (polygon mirror).
After passing through a beam shape correction optical system 104 such as an fθ lens, the reflected stimulable phosphor panel 15 is irradiated with the laser beam 102 after being reflected by a reflection mirror 105. Repeated scanning (main scanning) is performed in the direction of arrow X. From each point of this scanning, stimulated emission light carrying the X-ray image accumulated and recorded in the stimulated phosphor panel 15 is emitted. This stimulated emission light
The light is condensed by the condenser 106 such as an optical fiber array,
It is guided to a photoelectric converter 108 such as a photomultiplier tube via an optical filter 107 that cuts the excitation light and transmits the stimulated emission light, and is converted into an electric signal. The stimulated emission light may be directly received without using the condenser 106, for example, by using a CCD photosensor or the like having an optical filter attached to the front surface for transmitting only the stimulated emission light.

The electric signal obtained by the photoelectric converter 108 is logarithmically amplified by the logarithmic amplifier 109 and then converted into a digital image signal S by the A / D converter 110. The sampling timing of the A / D converter 110 is controlled by the A / D conversion control unit 113, and a signal corresponding to each pixel forming the X-ray image (for example, “here Pixel data "
Called) is obtained. The digital image signal S is temporarily stored in the frame memory 111 or directly in the storage medium 112 such as a magnetic disk or an optical disk without passing through the frame memory 111. After that, the image signal stored in the storage medium 112 is read out and input to the image processing unit 25 shown in FIGS.

[0010]

When a point on a scanning line on the photostimulable phosphor panel 15 is irradiated with excitation light, stimulated emission light is emitted from that point. The light continues for a while even after the irradiation of the excitation light is completed. In the meantime, when irradiating excitation light to adjacent points on the same scanning line on the stimulated phosphor panel to receive the stimulated emission light emitted from that point, the stimulated emission light is still emitted from the previous point. Since it is emitted, the stimulated fluorescent light emitted from the point just before this is also received. That is,
When the stimulated emission light emitted from the adjacent point is read before the intensity of the stimulated emission light emitted from the immediately preceding point becomes sufficiently small, the image reproduced based on the image signal obtained by the reading The image quality of will deteriorate. Therefore, when the radiation image stored and recorded on the photostimulable phosphor panel is read, the reading time is limited by the lifetime of the stimulated emission of the photostimulable phosphor, and there is a limit that it cannot be shortened beyond a certain level.

In order to solve this problem, a scanning system for scanning the excitation light and a reading system for reading the radiation image by receiving the stimulated emission light (hereinafter, the scanning system and the reading system are collectively called reading means). ) Are provided, an image of a region obtained by equally dividing one photostimulable phosphor panel in the sub-scanning direction is read by each reading means, and data corresponding to the entire radiation image of the original is reconstructed from the obtained pixel data. A technique for doing so has been proposed (see Japanese Patent Laid-Open No. 3-265841).

FIG. 4 is a schematic configuration diagram of the reading unit when two reading means are provided. In this figure, the constituent elements corresponding to the constituent elements of the reading means in the reading section shown in FIG. 3 have the same numbers as those shown in FIG.
Are added and shown, and detailed description is omitted. By providing a plurality of reading means such as two as shown in FIG. 4, high-speed reading is possible even if the scanning speed of the excitation light and the transport speed of the stimulable phosphor panel 15 are the same.

Here, when a plurality of reading means are provided and the areas on one photostimulable phosphor panel 15 are shared by the plurality of reading means for reading, the areas read by different reading means are read. The problem is how to handle the joints. For example, although the radiation image is reproduced by simply joining the pixel data obtained by the reading by each reading unit, this method has a problem that the joints of the respective regions are too conspicuous.

It is an object of the present invention to provide a radiation image conversion method capable of reproducing an easy-to-see radiation image in which seams are not conspicuous when the reading is shared by a plurality of reading means.

[0015]

The present invention is directed to a scanning system in which a stimulable phosphor on which a radiation image is recorded is repeatedly scanned with excitation light in the main scanning direction, and the stimuli emitted from each scanning point by the excitation light. A plurality of reading means including a reading system for reading the radiation image by receiving emitted light to obtain a large number of pixel data respectively corresponding to a large number of pixels forming the radiation image are prepared. While relatively moving the photostimulable phosphor in the sub-scanning direction, the radiation images stored and recorded in the photostimulable phosphor by the plurality of reading means are arranged so that a partial area of the radiographic image overlaps. The present invention relates to a radiation image conversion method in which areas are shared and read.

To achieve the above object, the present invention provides, in the radiation image conversion method, pixel data corresponding to the partial areas obtained by the plurality of reading means for each pixel data corresponding to each other. It is characterized in that new pixel data corresponding to this partial area is obtained by weighted averaging. Here, as the weighted average, weighting considering the distance from the boundary line of each pixel in the partial area to the partial area and an area adjacent to the partial area and read in sharing. Is preferably performed.

It is also a preferable embodiment that the weighted average is weighted in consideration of a time difference between the partial areas that are read in duplicate. Further, as the weighted average, the partial area is excited by excitation light. It is also a preferable aspect to perform weighting in consideration of being scanned a plurality of times.

[0018]

According to the radiation image conversion method of the present invention, a plurality of reading means read a partial area of a radiation image in an overlapping manner.
Since the pixel data obtained by the plurality of reading units corresponding to the partial area is weighted and averaged for each pixel data corresponding to each other, new pixel data is obtained.
It is possible to obtain a high-quality reproduced image with no noticeable joint.

When this weighting means is performed, weighting is performed in consideration of the distance from the boundary line between the partial area and the area adjacent to the partial area and the area where the reading is performed. Then, the areas that have been read will be connected'smoothly '. Further, the photostimulable phosphor has a property of so-called latent image regression in which the amount of photostimulated luminescence light generated varies even if the same excitation light is irradiated, depending on the time until the reading is performed after the radiation image is accumulated and recorded. .. Therefore, when performing the weighted averaging, by performing weighting in consideration of the time difference between the areas that are read in duplicate, the joints can be more'smoothly 'connected and a high-quality reproduced image can be obtained. become.

Further, although the partial area is an area where the reading is performed a plurality of times, a part of the energy accumulated therein is released each time the reading is performed, and therefore the excitation under the same condition is performed in the next reading. The amount of stimulated emission light that is generated may vary even when irradiated with light. Therefore, when performing the weighted averaging, by performing weighting considering that the partial region is scanned a plurality of times by the excitation light,
The joints are connected more smoothly.

[0021]

EXAMPLES Examples of the present invention will be described below. Here, as shown in FIG. 4, a case where one photostimulable phosphor panel is read by two reading means will be described. Figure 5
FIG. 4 is a diagram schematically showing a stimulated phosphor panel and a radiation image accumulated and recorded therein.

The stimulated phosphor panel 15 is repeatedly scanned in the direction of arrow X by the excitation light of each reading means while being conveyed in the direction of arrow Y shown in the figure, and the stimulated emission light emitted from each scanning point is read. As a result, the pixel data of the first area D1 and the second area D2 surrounded by the dotted line are obtained by the first reading means and the second reading means of the two reading means. That is, the area sandwiched between the horizontally extending lines L1 and L2 is shared by the first reading means, and the area sandwiched between the lines L3 and L4 is read by the second reading means. Shared,
The shaded area between the lines L2 and L3 is read by both the first reading unit and the second reading unit.

Here, the first reading means starts reading from the side of the line L1 and reads between the line L3 and the second line.
Reading means starts reading from the line L2 side and reads from the line L4. Therefore, the area sandwiched between the line L2 and the line L3 is read by the second reading means after a certain time after being read by the first reading means.

Next, the weighting of the pixel data obtained by both the first reading means and the second reading means corresponding to the area sandwiched between the lines L2 and L3 will be described. The weighting of the pixel data corresponding to the pixel point a in this area will be described on behalf of the area. FIG. 6 is an explanatory diagram of weighting representing an area read by each reading unit and an ideal reproduced image based on pixel data obtained by each reading unit.

Pixel data obtained by the first reading means and the second reading means at the pixel point a sandwiched between the lines L2 and L3 are respectively x ₁ (m, n) and x _2.
(M, n). Here, (m, n) represents the coordinates of the pixel point a. Here, as shown in this figure, when the distance between the pixel point a and the line L3 is d ₁ , and the distance between the pixel point a and the line L2 is d ₂ , pixel data x (m, n)
Is calculated based on the equation x (m, n) = {d ₁ · x ₁ (m, n) + d ₂ · x ₂ (m, n)} / (d ₁ + d ₂ ) ... (1) The pixel data x (m, n) obtained by the above is set as new pixel data of the pixel point a.
In the calculation of the equation (1), as the pixel point a approaches the line L2, the pixel data x ₁ (m,
n), and means that the pixel data x ₂ (m, n) obtained by the second reading means is given more weight as the pixel point a gets closer to the line L3, and therefore the first reading means. An image of an area sandwiched between the line L1 and the line L2 shared by only the line L and the line L shared by only the second reading unit.
The image of the area sandwiched between 3 and the line L4 is smoothly continuous between the line L2 and the line L3, and thus a reproduced image with no conspicuous seam can be obtained.

By the way, the unevenness of the light collection efficiency of the light collector 106 (see FIG. 3) in the main scanning direction (the direction of the arrow X in FIG. 3) and the passage of time from the time when the photostimulable phosphor panel is irradiated with radiation. Due to the regress of the latent image recorded on the photostimulable phosphor panel, the pixel data obtained by the reading becomes uneven. Here, as shown in FIG. 7, the latent image regression means that the emission intensity of photostimulated luminescence light generated by irradiation of excitation light decreases with the lapse of time after X-ray irradiation. It is known that the change over time of the emission intensity of emitted light is exponential as shown in FIG.

All-pixel correction is known as a method for removing the unevenness of the X-ray image caused by both the unevenness of the light collector and the regression of the latent image. This is because the entire surface of the photostimulable phosphor panel is irradiated with X-rays in advance, and this is read to obtain pixel data that carries only unevenness. Based on this pixel data, the radiation image is stored and recorded. This is a method of correcting pixel data read from the phosphor panel.

This all-pixel correction is performed by the first reading means and the second reading means.
When both the reading means and the reading means are used, it is not necessary to consider the latent image regression in weighting, and a smooth continuous reproduced image can be obtained by the above equation (1). On the other hand, in the above-mentioned all-pixel correction, only the unevenness of the light collector may be corrected, and the unevenness due to the latent image regression may be removed by weighting. Next, a method of removing unevenness due to the latent image regression by weighting will be described.

As described above, it is known that the emission intensity of stimulated emission generated by irradiation with excitation light decreases exponentially. Therefore, the time from the time when the first reading means reads the pixel point a (see FIGS. 5 and 6) to the time when the second reading means reads it is Δ.
t, a constant representing the degree of latent image regression per unit time is μ
Then, the unevenness due to the latent image regression is expressed as x ₂ (m, n) = x ₁ (m, n) · exp (−μΔt) (2). Therefore, the pixel data x at the pixel point a
(M, n) are the distances d ₁ and d from the lines L2 and L3.
Considering _{2 as} well, x (m, n) = {d ₁ · x ₁ (m, n) + d ₂ · x ₂ (m, n) · exp (μΔt)} / (d ₁ + d ₂ ) (3) Given in. After that, for all pixels including the pixels obtained by only one of the first reading unit or the second reading unit without being read redundantly, the equation y (k, l) = x (k, l). By performing the correction based on exp (μt) (4), it is possible to obtain the pixel data y (k, l) in which the latent image regression is corrected over the entire screen. Where (k, l) is the coordinate of each pixel and x
(K, l) is the pixel data x ₁ obtained by the first reading means in the area between the line L1 and the line L2.
(K, l) and the pixel data x ₂ obtained by the second reading means in the area sandwiched between the line L3 and the line L4.
(K, l) and the pixel data x obtained by the above equation (3) in the area sandwiched between the line L2 and the line L3.
(M, n) is a general term, and t is from the reading start time until reading of each pixel (until the reading between the lines L2 and L3 is performed by the first reading means). ) Is the elapsed time.

When the latent image recorded at the same position on the photostimulable phosphor panel is read twice, even when the latent image is irradiated with the same excitation light, the second image is read more than the first image is read. This means that the amount of stimulated emission light is smaller and the obtained pixel data values are different. Therefore, it is preferable to correct this error as well. Here, for the same pixel point a, between the pixel value x ₁ (m, n) at the time of the first reading and the pixel value x ₂ (m, n) at the time of the second reading, the second reading is performed. As an error amount due to this, x ₂ (m, n) = α · x ₁ (m, n) (5) If α is a constant, the above-mentioned all pixel correction is performed. Instead of the above formula (1), x (m, n) = {d ₁ · x ₁ (m, n) + d ₂ · x ₂ (m, n) / α} / (d ₁ + d ₂ ) (6) ) Is used for correction.

If the unevenness caused by the latent image regression is not corrected by the all-pixel correction and the unevenness caused by the latent image regression cannot be ignored, x (m, n) = {d ₁ · x ₁ (m, n) + d ₂ · x ₂ (m, n) · exp (+ μΔt) / α} / (d ₁ + d ₂ ) ... (7)

[0032]

As described above, in the radiation image conversion method of the present invention, the radiation images accumulated and recorded in the photostimulable phosphor are divided into areas so that some areas of the radiation images overlap. While the reading is performed by the plurality of reading units, the pixel data corresponding to the partial areas obtained by the plurality of reading units are read for each pixel data corresponding to each other, for example, the distance from the boundary line and the overlapping reading. , The new pixel data corresponding to the partial area is obtained by performing weighted averaging in consideration of the time difference, multiple scans, etc., so that an easy-to-see reproduced image in which the joints are smoothly connected can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a system using a stimulated phosphor panel.

FIG. 2 is a diagram showing another system configuration example using a stimulated phosphor panel.

FIG. 3 is a diagram showing a configuration example of a reading unit indicated by blocks in FIGS. 1 and 2.

FIG. 4 is a schematic configuration diagram of a reading unit when two reading units are provided.

FIG. 5 is a diagram schematically showing a stimulated phosphor panel and a radiation image accumulated and recorded therein.

FIG. 6 is an explanatory diagram of weighting representing an area read by each reading unit and an ideal reproduced image based on pixel data obtained by each reading unit.

FIG. 7 is a graph showing latent image regression.

[Explanation of symbols]

 11 X-ray generator 12 Subject 15 Photostimulable phosphor panel 23 Reading means 102, 102A, 102B Laser light 106, 106A, 106B Condenser 108, 108A, 108B Photoelectric converter

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location // G06F 15/62 390 A 9287-5L (72) Inventor Kisuke Haraki 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Address within Fujitsu Limited (72) Hideyuki Hirano 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited (72) Kenji Ishiwata 1015 Kamedota, Nakahara-ku, Kawasaki, Kanagawa Within Fujitsu Limited

Claims (4)

[Claims] 1. A scanning system in which a stimulable phosphor on which a radiation image is recorded is repeatedly scanned with excitation light in the main scanning direction, and stimulated emission light emitted from each scanning point by the excitation light is received to obtain the stimulable phosphor. A plurality of reading means including a reading system for reading a radiation image and obtaining a large number of pixel data respectively corresponding to a large number of pixels forming the radiation image are prepared, and the plurality of reading means or the photostimulable phosphor are sub-scanned. While moving relatively in the direction, by these plural reading means,
In a radiation image conversion method of reading a radiation image accumulated and recorded in the photostimulable phosphor by sharing regions so that partial regions of the radiation image overlap, the radiation images obtained by the plurality of reading units A radiation image conversion method, wherein new pixel data corresponding to the partial area is obtained by weighting and averaging pixel data corresponding to the partial area for each pixel data corresponding to each other. 2. The weighted average takes into account the distance of each pixel in the partial region from the boundary line between the partial region and a region adjacent to the partial region and sharedly read. The radiation image conversion method according to claim 1, wherein the weighting is performed. 3. The radiation image conversion method according to claim 1, wherein the weighted average is weighted in consideration of a time difference between the partial areas which are read in an overlapping manner. 4. The radiation image conversion method according to claim 1, wherein the weighted average is weighted in consideration of the partial region being scanned a plurality of times by the excitation light.