JP2005261487A - Method and apparatus for reading radiograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographs free from distortions due to errors in precision of a scan optical system without making a structure complicated in both a method and an apparatus for reading radiographs which scan or emit excitation light to an accumulative phosphor sheet through the scan optical system and read radiographs by detecting photostimulable light emitted from an irradiation part photoelectrically. <P>SOLUTION: The distortions are corrected by image processing through a software without using a hard means. In other words, the correspondence of positions of each pixel on the read radiograph to positions of sampling points on the sheet corresponding to each pixel is acquired from fluctuation characteristics of the scanning speed of the excitation light obtained in advance. The coordinate transformation for each pixel is so performed that the position of each pixel on the image relatively corresponds to the positions of the sampling points on the corresponding sheet from the correspondence. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiographic image reading method and apparatus, and more specifically, scans a stimulable phosphor sheet on which radiographic image information is accumulated and recorded with excitation light through a scanning optical system, and generates a brightness corresponding to the radiographic image information. The present invention relates to a radiographic image reading method and apparatus for generating read-out light and performing reading by a reading unit that photoelectrically detects the emitted light and obtains an image signal.

  Conventionally, when radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, a part of the radiation energy is accumulated, and when irradiated with excitation light such as visible light, the accumulated energy is Using a stimulable phosphor (stimulable phosphor) that emits a corresponding amount of stimulated luminescence, a radiation image of a subject such as a human body is temporarily stored with a sheet-like stimulable phosphor. Photographed and recorded on a sheet (hereinafter also referred to simply as a sheet), this stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light, and the resulting stimulated emission light is photomultiplier, etc. A radiation recording / reproducing system has been proposed in which an image signal is obtained photoelectrically by a detector, and a radiographic image of a subject is output as a visible image to a recording material such as a photographic material, a CRT or the like based on the image signal. (E.g. special Documents 1 to 5, etc.).

  By the way, a stimulable phosphor sheet used for such a radiation recording / reproducing system, in which radiation image information is accumulated and recorded, is scanned with excitation light to generate stimulated emission light, and the obtained stimulated emission light is detected. As a radiographic image reading device that photoelectrically reads an image signal representing a radiographic image by an optical device, an optical deflector such as a galvanometer mirror or a polygon mirror is applied to a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, fθ A scanning optical system consisting of a lens, a plane reflecting mirror, etc., scans a beam of excitation light such as laser light at a constant speed, and samples a signal from a detector at a clock frequency synchronized with a predetermined timing of the beam scanning. (For example, a reading and scanning device described in Patent Document 6).

  In the case of such an apparatus, if the scanning optical system is an ideal system having no optical accuracy error, the temporal change of the position on the stimulable phosphor sheet irradiated with the beam is shown in FIG. ), The signal is linear. Therefore, if the signal from the detector is sampled at a constant time interval, that is, a constant frequency, an image signal having a uniform pixel pitch (interval between reading positions on the sheet) can be obtained. .

  However, in reality, there may be an optical accuracy error in the scanning optical system. In such a case, the beam scanning speed varies depending on the irradiation position due to the accuracy error. There is. When the scanning speed of the beam fluctuates, the temporal change in the position where the beam on the stimulable phosphor sheet is irradiated becomes non-linear, for example, as shown in FIG. When sampling is performed, an image signal with an uneven pixel pitch is obtained, and in the radiographic image represented by this image signal, image distortion corresponding to the variation in the scanning speed occurs.

Therefore, the scanning speed of the excitation light is detected, the sampling clock frequency is adjusted so that the actual scanning speed and the sampling frequency correspond appropriately, and the pixel pitch is kept constant to prevent image distortion. A radiation image reading apparatus configured as described above has been proposed (for example, an image reading apparatus described in Patent Document 7).
JP-A-55-12429 JP-A-56-11395 JP 55-163472 A JP 56-164645 A JP 55-116340 A Japanese Patent Publication No.5-20027 JP-A 64-86130

  However, in the radiation image reading apparatus that detects the scanning speed of the excitation light and adjusts the sampling clock frequency as described above, a means for detecting the scanning speed, a means for adjusting the clock frequency, and the like are required. There is a problem that the structure becomes complicated and the manufacturing cost increases.

  In view of the above circumstances, the present invention provides a radiological image reading method and apparatus capable of obtaining a radiographic image from which image distortion caused by an optical accuracy error of a scanning optical system is removed without complicating the structure. It is intended to provide.

  In the radiation image reading method of the present invention, the stimulable phosphor sheet on which radiation image information is accumulated and recorded is scanned with excitation light via a scanning optical system to generate stimulated emission light according to the radiation image information. In the radiation image reading method in which reading is performed by reading means that photoelectrically detects the stimulated emission light and obtains an image signal, based on the characteristics of fluctuations in the scanning speed of the excitation light due to the characteristics of the scanning optical system, Image distortion correction data for performing image distortion correction for removing image distortion due to fluctuations in the scanning speed in the radiation image read by the reading unit is calculated, and the radiographic image of the subject read by the reading unit is calculated. Thus, the image distortion correction is performed based on the image distortion correction data.

  In the radiological image reading method of the present invention, after the calculation of the image distortion correction data, image distortion correction is performed based on the image distortion correction data for a radiographic image without a subject read by the reading unit. To obtain an image without a subject after image distortion correction, calculate density correction data for performing density correction to remove density unevenness in the image based on the image without a subject after image distortion correction, and After the image distortion correction, the density correction may be performed on the radiographic image of the subject after the image distortion correction based on the density correction data.

  The radiographic image reading apparatus of the present invention scans the stimulable phosphor sheet on which radiographic image information is accumulated and recorded by scanning excitation light via a scanning optical system, and emits the stimulated emission light according to the radiographic image information. In the radiation image reading apparatus that generates and outputs the image signal by photoelectrically detecting the stimulated emission light, based on characteristics of fluctuations in the scanning speed of the excitation light due to characteristics of the scanning optical system Correction data calculated in the above-described manner, and image distortion correction data for storing image distortion correction data for performing image distortion correction for removing image distortion caused by fluctuations in the scanning speed in the radiographic image read by the reading unit The image processing apparatus includes: a storage unit; and an image distortion correction unit that performs image distortion correction based on the image distortion correction data with respect to a radiographic image of the subject read by the reading unit. A.

  In the radiological image reading apparatus of the present invention, an image without a subject after image distortion correction is obtained by performing image distortion correction based on the image distortion correction data for a radiographic image without an object read by the reading unit, Density correction data calculating means for calculating density correction data for performing density correction for removing density unevenness in the image based on the image without subject after image distortion correction, and a radiation image of the subject after image distortion correction On the other hand, it is possible to further include density correction means for performing density correction based on the density correction data.

  Here, the “scanning optical system” is an optical system configured to scan excitation light at a constant speed on the stimulable phosphor sheet. For example, an optical deflector such as a galvanometer mirror or a polygon mirror, or an fθ lens. An optical system composed of a plane reflecting mirror or the like is conceivable.

  “Characteristics of fluctuations in the scanning speed of the excitation light due to the characteristics of the scanning optical system” are theoretically obtained from information indicating optical characteristics of lenses and mirrors constituting the scanning optical system, information on arrangement design, and the like. Alternatively, it may be obtained by experimentally measuring the scanning speed of the beam of excitation light.

  As the “image distortion correction”, for example, the position of each pixel on the read radiation image and the sheet corresponding to each pixel on the basis of the fluctuation characteristics of the scanning speed of the excitation light grasped in advance. A correspondence relationship with the position of the sampling point is obtained, and based on the correspondence relationship, coordinate conversion of each pixel is performed so that the position of each pixel relatively matches the position of the corresponding sampling point. Can do. In this case, since the intervals between the pixel points after the coordinate conversion are non-uniform, for example, each pixel is divided into each region at an actual pixel interval on the coordinate axis, and the coordinate-converted pixels existing in the region for each region. A method is conceivable in which the values of the points are averaged to calculate a new pixel value, and that value is used as the pixel value corresponding to the region. If no pixel point exists in the region, interpolation may be performed based on the values of neighboring pixels.

  When “image distortion correction” is coordinate conversion of the pixel as described above, the “image distortion correction data” includes an equation for the coordinate conversion or a table indicating the correspondence between coordinates before and after the coordinate conversion. can do.

  The “radiation image without a subject” is a radiation image obtained by reading a storage phosphor sheet obtained by radiography in the absence of a subject with a reading unit.

  “Density unevenness” refers to brightness caused by unevenness in the irradiation time of excitation light caused by variations in reading sensitivity due to the reading means system and fluctuations in the scanning speed of excitation light at each reading position on the stimulable phosphor sheet. It means a variation in density on a radiographic image caused by a variation in the amount of exhausted light.

  “Density correction” refers to so-called shading correction. As “density correction”, for example, a pixel that converts a density distribution including the above-described density variation, that is, a distribution of pixel values into a uniform distribution of pixel values. It can be a value conversion.

  When the “density correction” is the pixel value conversion as described above, the “density correction data” can be a pixel value conversion arithmetic expression or a weighting coefficient by which the pixel value for each pixel is multiplied.

  According to the radiation image reading method and apparatus of the present invention, the correction data calculated based on the characteristics of the fluctuation in the scanning speed of the excitation light due to the characteristics of the scanning optical system of the reading means, the radiation read by the reading means Based on the image distortion correction data for performing image distortion correction for removing the image distortion caused by the fluctuation in the scanning speed in the image, the image distortion correction is performed on the radiographic image of the subject read by the reading unit, and the image is corrected. Since distortion is removed, image distortion is removed by software image distortion correction, which is image processing, without using hardware means such as means for detecting the scanning speed of the excitation light or means for adjusting the sampling clock frequency. Therefore, it is possible to obtain a radiation image from which image distortion caused by an optical accuracy error of the scanning optical system is removed without complicating the structure.

  Hereinafter, embodiments of the radiation image reading apparatus of the present invention will be described.

  FIG. 1 is a schematic block diagram showing a configuration of a radiographic image reading apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing a configuration of reading means 20 provided in the radiographic image reading apparatus shown in FIG. is there.

  The radiographic image reading apparatus shown in FIG. 1 scans the stimulable phosphor sheet on which radiographic image information is accumulated and recorded by scanning the excitation light L via a scanning optical system 12 described later, and performs the excitation according to the radiographic image information. Readout means 20 that generates emission light, photoelectrically detects the stimulated emission light and obtains an image signal, and correction data calculated based on fluctuations in the scanning speed of excitation light due to the characteristics of the scanning optical system 12 An image distortion correction data storage unit 31 for storing image distortion correction data D for performing image distortion correction for removing image distortion caused by the fluctuation of the scanning speed in the radiographic image read by the reading unit 20, and an image Based on the distortion correction data D, image distortion correction is performed on the image P0 without the subject read by the reading unit 20 to obtain an image P0 'without the subject after image distortion correction, and an image P0' without the subject after image distortion correction. Based on Then, the density correction data calculation means 32 for calculating density correction data H for performing density correction for removing density unevenness in the image P0 ′, and the subject read by the reading means 20 based on the image distortion correction data D Image distortion correction means 33 for performing image distortion correction on the radiation image P1 of the subject to obtain a radiation image P1 ′ of the object after image distortion correction, and the radiation image of the object after image distortion correction based on the density correction data H Density correction means for obtaining a corrected radiation image P1 ″ of the subject by performing density correction on P1 ′.

  The reading unit 20 includes an excitation light source 1 that emits excitation light L, a beam expander 2 that adjusts the beam diameter of the excitation light L, and a galvanometer mirror that deflects the excitation light L that has passed through the beam expander 2. And a light deflector 3 such as a polygon mirror, a plane reflecting mirror 4 that reflects the light deflected by the light deflector 3 toward the stimulable phosphor sheet 11, and an excitation light L reflected by the plane reflecting mirror 4 Excitation on the sheet 11 and the fθ lens 5 disposed between the optical deflector 3 and the flat reflector 4 so that the stimulable phosphor sheet 11 is scanned at a constant speed with a uniform beam diameter. A condensing guide 6 for condensing the stimulated emission light emitted from the portion irradiated with the light L, a photomultiplier for detecting the stimulated emission light collected by the condensing guide 6 and converting it into an electrical signal, etc. Photodetector 7 and light detection Based on the digital signal converted by the A / D converter 9, the amplifier 8 that amplifies the electrical signal converted by the amplifier 7, the A / D converter 9 that converts the electrical signal output from the amplifier 8 into a digital signal, and the like. And a signal processing unit 10 for obtaining an image signal. The optical deflector 3, the plane reflecting mirror 4, and the fθ lens 5 constitute a scanning optical system 12.

  Next, the operation of the radiation image reading apparatus according to the present embodiment will be described.

  First, the operation of the reading unit 20 will be described.

  The excitation light L emitted from the excitation light source 1 is adjusted in the beam diameter strictly by the beam expander 2 and is incident on the scanning optical system 12. In the scanning optical system 12, the incident excitation light L is deflected by the optical deflector 3, and the radiation image information is accumulated and recorded on the stimulable phosphor sheet 11 via the fθ lens 5 and the plane reflecting mirror 4. The incident light is deflected. At this time, the excitation light L has a uniform beam diameter on the sheet 11 and is scanned at a constant speed in the direction of arrow C by the function of the fθ lens 5. The sheet 11 is transferred in the direction of the arrow A and subjected to sub-scanning. As a result, the excitation light L is irradiated over the entire surface of the sheet 11. When the excitation light L is irradiated in this way, the sheet 11 emits the stimulated emission light whose amount is proportional to the radiation energy stored and recorded, and this emission light is emitted to the light collection guide (light guide sheet) 6. Incident light travels through the light collecting guide 6 while being totally reflected, and is received by the photodetector 7. The stimulated emission light detected by the photodetector 7 is converted into an electrical signal, and this electrical signal is sent to the signal processing unit 10 via the amplifier 8 and the A / D converter 9. The signal processing unit 10 receives a detection signal indicating the timing from a timing detection unit (not shown) that detects the timing at which scanning of the excitation light L in the main scanning direction C is started, and based on the detection signal, the excitation light A signal is sampled at a constant frequency in synchronization with the start of L main scanning, and this sampling is continuously performed on the sub-scanning of the excitation light L to obtain an image signal representing a radiation image.

  Next, the operation of the entire radiation image reading apparatus will be described.

  FIG. 3 is a block diagram showing a processing flow in the present embodiment.

  First, as a preparatory stage, a radiographic image read by the reading unit 20 based on characteristics of fluctuations in the beam scanning speed of excitation light due to characteristics (such as optical accuracy errors) of the scanning optical system 12 obtained in advance. In step S1, image distortion correction data D for performing image distortion correction for removing image distortion due to fluctuations in scanning speed is calculated.

  Specifically, the image distortion correction can be performed by performing coordinate conversion on each pixel of the image in the radiographic image read by the reading unit 20. For example, the scanning speed of the excitation light L is an S-shaped variation in the main scanning direction C as shown in FIG. 6B, that is, a variation in which a region Rs having a low scanning speed and a region Rf having a high scanning speed appear. In some cases, when a signal is sampled at a constant frequency as described above, in the radiographic image (original image) read by the reading unit 20, as shown in FIG. 4, there is a portion corresponding to the region Rs where the scanning speed is low. The image is stretched in the main scanning direction C, and the portion corresponding to the region Rf having a high scanning speed is contracted in the main scanning direction C to cause image distortion. When the characteristics of the fluctuation of the scanning speed of the excitation light L are known in advance from the characteristics of the scanning optical system 12, the image distortion is corrected by performing coordinate conversion for each pixel in the obtained radiation image. be able to. That is, the correspondence between the position of each pixel on the read radiographic image and the position of the sampling point on the sheet corresponding to each pixel based on the fluctuation characteristics of the scanning speed of the excitation light grasped in advance Based on the correspondence relationship, coordinate conversion of each pixel is performed so that the position of each pixel relatively matches the position of the corresponding sampling point. In this case, since the intervals between the pixel points after the coordinate conversion are not uniform, for example, the pixels that are coordinate-converted exist in each region by dividing each region at the actual pixel interval on the coordinate axis. A method is conceivable in which the values of the points are averaged to calculate a new pixel value, and that value is used as the pixel value corresponding to the region. If no pixel point exists in the region, interpolation may be performed based on the values of neighboring pixels.

  Accordingly, the image distortion correction data D can be such a coordinate conversion arithmetic expression or a table indicating the correspondence before and after the coordinate conversion. The image distortion correction data D may be obtained theoretically or experimentally.

  When the image distortion correction data D is calculated, it is input and stored in the image distortion correction data storage means 31 (step S2).

  On the other hand, a stimulable phosphor sheet obtained by radiography in the absence of a subject is prepared, and this sheet is read by the reading means 20 to obtain a no-subject image P0 (step S3). This object-free image P0 has image distortion due to fluctuations in the scanning speed of the excitation light L, density unevenness due to fluctuations in the scanning speed of the excitation light L, and the scanning optical system 12 of the reading means 20 and the light collection. Density unevenness due to variations in the read sensitivity of the system signal including the guide 6 and the like appears.

  When the subjectless image P0 is obtained by the reading unit 20, the density correction data calculating unit 32 is based on the image distortion correction data D stored in the image distortion correction data storage unit 31 with respect to the objectless image P0. Image distortion correction (coordinate conversion) is performed to obtain an image P0 ′ having no subject after image distortion correction (step S4). In this image P0 ′, the image distortion due to the fluctuation of the scanning speed of the excitation light L included in the image P0 is corrected, but the density unevenness still remains while changing its position.

  Further, the density correction condition calculation unit 32 is based on the non-subjected image P0 ′ after image distortion correction, and the density unevenness K due to the fluctuation in the scanning speed of the excitation light L in the image P0 ′ and the reading unit 20 system. The density correction data H for performing density correction to make the density unevenness K + J uniform density, which is synthesized with the density unevenness J by the above, is calculated. FIG. 5 is a diagram showing the concept of density correction in which density unevenness K + J, which is a combination of density unevenness K and density unevenness J, is corrected to a uniform density. Note that K0 in FIG. 5 indicates a flat density when there is no variation in the scanning speed.

  Specifically, the density correction can be performed by pixel value conversion for converting a density distribution including density variations, that is, a distribution of pixel values into a uniform distribution of pixel values.

  Therefore, the density correction data H can be an arithmetic expression for pixel value conversion or a weighting coefficient by which the pixel value for each pixel is multiplied.

  When the image distortion correction data D and the density correction data H are obtained, the stimulable phosphor sheet obtained by radiographing the subject is read by the reading means 20 to obtain a radiation image P1 of the subject (step S6).

  Then, the image distortion correction means 33 performs image distortion correction on the radiographic image P1 of the subject based on the image distortion correction data D to obtain a radiographic image P1 ′ of the subject after image distortion correction (step S7). The density correction unit 34 performs density correction on the radiographic image P1 ′ of the subject after image distortion correction based on the density correction data H, and the corrected radiographic image P1 of the object subjected to image distortion correction and density correction. ″ Is obtained (step S8).

  As described above, according to the radiological image reading apparatus according to the above-described embodiment of the present invention, reading is performed by the reading unit 20 which is calculated based on the characteristics of the fluctuation in the scanning speed of the excitation light L by the scanning optical system 12 of the reading unit 20. Based on the image distortion correction data D for performing image distortion correction for removing the image distortion caused by the fluctuation of the scanning speed in the obtained radiographic image, the image is applied to the radiation image P1 of the subject read by the reading unit 20. Since distortion correction is performed and image distortion is removed, software image processing that is image processing can be performed without using hardware means such as a means for detecting the scanning speed of the excitation light L or a means for adjusting the sampling clock frequency. Image distortion can be removed by distortion correction, and a radiation image P1 ′ of a subject from which image distortion caused by an optical accuracy error of the scanning optical system 12 is removed without complicating the structure is obtained. Door can be.

  Further, in the present radiation image reading apparatus, after calculating the image distortion correction data D, image distortion correction is performed based on the image distortion correction data D on the radiation image P0 without the subject read by the reading unit 20. By doing this, an image P0 ′ without subject after image distortion correction is obtained, and density correction data H for performing density correction for removing density unevenness in the image P0 ′ is calculated based on the image P0 ′ without subject after image distortion correction. After the image distortion correction for the radiographic image P1 of the subject, the density correction is performed on the radiographic image P1 ′ of the subject after the image distortion correction based on the density correction data H. It is also possible to correct density unevenness due to fluctuations in scanning speed and density unevenness due to the system of the reading means 20, and obtain a radiation image of a subject that is more useful for observation, image processing, and the like. It can be.

The figure which showed the structure of the radiographic image reading apparatus by one Embodiment of this invention. The figure which showed the structure of the reading means of the radiographic image reading apparatus by this embodiment The figure which showed the processing flow in the radiographic image reading apparatus by this embodiment. Diagram showing the correspondence between the sampling position on the sheet and the pixel position on the radiation image Diagram showing the concept of density correction in radiographic images The figure which showed the temporal change of the position of the excitation light beam on the sheet

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Excitation light source 2 Beam expander 3 Optical deflector 4 Plane reflecting mirror 5 f (theta) lens 6 Condensing guide 7 Photodetector 8 Amplifier 9 A / D converter 10 Signal processing part 11 Storage phosphor sheet 12 Scanning optical system 20 Reading means 31 Image distortion correction data storage means 32 Density correction data calculation means 33 Image distortion correction means 34 Density correction means

Claims (4)

The stimulable phosphor sheet on which the radiation image information is accumulated and recorded is scanned with excitation light through a scanning optical system to generate stimulated emission light according to the radiation image information. In the radiation image reading method of reading by the reading means for detecting the image signal to obtain
Based on the characteristics of fluctuations in the scanning speed of the excitation light due to the characteristics of the scanning optical system, image distortion correction for removing image distortion due to fluctuations in the scanning speed in the radiation image read by the reading means is performed. Calculate image distortion correction data,
A radiation image reading method, wherein image distortion correction is performed on a radiation image of a subject read by the reading unit based on the image distortion correction data. After calculating the image distortion correction data,
An image without a subject after image distortion correction is obtained by performing image distortion correction based on the image distortion correction data with respect to a radiation image without an object read by the reading unit,
Based on the image without subject after image distortion correction, density correction data for performing density correction for removing density unevenness in the image is calculated,
After the image distortion correction for the radiographic image of the subject,
The radiographic image reading method according to claim 1, wherein density correction is performed on the radiographic image of the subject after the image distortion correction based on the density correction data. The stimulable phosphor sheet on which the radiation image information is accumulated and recorded is scanned with excitation light through a scanning optical system to generate stimulated emission light according to the radiation image information. In a radiographic image reading apparatus that performs reading by a reading means that detects an image signal and
Correction data calculated based on characteristics of fluctuations in the scanning speed of the excitation light due to characteristics of the scanning optical system, and removing image distortion due to fluctuations in the scanning speed in a radiographic image read by the reading unit Image distortion correction data storage means for storing image distortion correction data for performing image distortion correction;
A radiation image reading apparatus, comprising: an image distortion correction unit configured to perform image distortion correction based on the image distortion correction data with respect to a radiographic image of a subject read by the reading unit. An image without a subject after image distortion correction is obtained by performing image distortion correction based on the image distortion correction data with respect to a radiation image without an object read by the reading unit,
Density correction data calculating means for calculating density correction data for performing density correction for removing density unevenness in the image based on the image without subject after image distortion correction;
4. The radiographic image reading apparatus according to claim 3, further comprising density correction means for performing density correction on the radiographic image of the subject after the image distortion correction based on the density correction data.

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