JP2003111753A - Image capturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing device which properly corrects and removes density non-uniformity in a radiographic image, which occurs when a grid focal distance differs from a photographing distance in the case of radiography. SOLUTION: This image capturing device obtains information on the radiographic image which is photographed by the passage of radiation rays from a radiation generating device 30 through a subject M and a grid 28. The density non-uniformity in the radiographic image is corrected based on correction data concerning the photographing distance between the radiation generating device and the radiation input surface of a recording medium 4 in front of which the grid is disposed and which records the radiographic image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image acquisition device mainly used in the medical field for acquiring radiation image information.

[0002]

2. Description of the Related Art A radiation image reading apparatus is known in which a radiation generating apparatus irradiates a subject with radiation for diagnosing illness and the like, and a radiation image formed by the radiation transmitted through the subject is read. A grid is placed to prevent scattered rays. This grid generally has a structure in which a lead foil and an intermediate substance such as aluminum are arranged in a straight line so as to be alternately parallel to each other, and the lead foil has a constant pitch (for example, 40 to 60 pieces / cm). And has a thickness of about 2 to 5 mm and is formed in a rectangular plane shape as a whole. When such a grid is used and the focal length of the radiation generating apparatus is deviated, there is a case where a so-called “kicking” phenomenon occurs in which the left and right densities of the radiation image change and density unevenness occurs. This phenomenon will be described with reference to FIG.

That is, in FIG. 2, lead foils of the grid are arranged so as to extend in the direction perpendicular to the paper surface, and the grid has an appropriate focal length d for each grid, and the radiation generator is located at this focal length d. The focal point of the grid is d
If the shooting distance y is substantially the same as the shooting distance y, radiation is transmitted between the lead foils and no kicking phenomenon occurs, but the tube is located at a position far away from or close to the focal length position, and the shooting distance y. 2 changes, the radiation is blocked by the lead foil and does not pass through, causing a kicking phenomenon in the area D distant from the grid center c on the grid surface in FIG. 2, resulting in density unevenness due to a decrease in density. Also occurs on the opposite side of symmetry with respect to the grid center c of. For example, a stimulable phosphor sheet P (shown by a broken line in FIG. 2) of the radiation image reading device is arranged on the grid surface, and the radiation image recorded on the stimulable phosphor sheet P has the above-described density. The unevenness is formed.

[0004] When changing a region such as the chest and abdomen with a single radiation generator, it may be necessary to perform the photographing at a photographing position which does not match the grid focal length, but for the above reason. Due to the relationship of the lead foil pitch of the grid, a phenomenon occurs in which the right and left are averaged in the radiation image, and uneven density occurs. Doctors who look at radiographic images make corrections in their heads by taking into account the density unevenness due to the kicking phenomenon, and make a diagnosis, but because there are individual differences in the X-ray generator, reader, and grid, the device Diagnosis may be difficult unless the doctor is skilled in each image.

Further, in the case of a dedicated device or the like integrated with a photographing table, for example, the grid focal length is 150 cm, the abdomen is 120 cm, and the chest is 180 cm.
In the case of an apparatus in which normal imaging is performed on the abdomen, if calibration (uneven tube unevenness of the X-ray generator, uneven reading device, uneven grid, phototimer, etc.) for correcting uneven density is performed at 120 cm, 120 cm The kicked part during shooting is also corrected and removed. But in this case, 180
When the chest is imaged in cm, the correction value for the unevenness in kicking in 120 cm is double-processed in addition to the unevenness in 180 cm, and an unintended radiation image may be output.

[0006]

In view of the above-mentioned problems of the prior art, the present invention can appropriately correct and remove density unevenness in a radiographic image that occurs when the grid focal length and the radiographic distance are different during radiographic imaging. It is an object of the present invention to provide the image acquisition device.

[0007]

In order to achieve the above object, an image acquiring apparatus according to the present invention is an image for acquiring information of a radiation image captured by radiation from a radiation generating apparatus passing through a subject and a grid. An acquisition device, which corrects density unevenness in the radiation image based on correction data regarding an imaging distance between the radiation generation device and a radiation input surface of a recording medium in which the grid is placed and which records the radiation image. It is characterized by performing.

According to this image acquisition device, the density unevenness in the radiation image is corrected based on the correction data relating to the imaging distance between the radiation generator and the radiation input surface of the recording medium. It is possible to appropriately correct and remove density unevenness in a radiation image that occurs when the shooting distance is different.

In this case, the image acquisition device has a measuring means for measuring the shooting distance, and the correction can be performed by using the measured shooting distance information.

Further, it is possible to receive the information of the photographing distance obtained from the radiation generator by providing the same measuring means on the side of the radiation generator and to perform the correction by using the received photographing distance information. In this case, the image acquisition device can be configured to obtain the imaging distance information from the radiation generation device via the network.

Further, the information on the photographing distance can be inputted from an input means such as a keyboard, and the correction can be performed by using the inputted photographing distance information.

Another image acquisition apparatus according to the present invention is
An image acquisition device for acquiring information on a radiation image captured by radiation from a radiation generation device passing through a subject and a grid, wherein the radiation generation device and the grid are placed in front of the recording medium for recording the radiation image. The image pickup distance to the radiation input surface and the tube voltage of the radiation generator are used as correction data, and the uneven density in the radiation image is corrected based on the correction data.

According to this image acquisition device, the radiation transmissivity changes depending on the energy of the radiation even at the same grid focal length. However, in addition to the photographing distance, the transmissivity change due to the tube voltage of the radiation generator is also corrected. Since it is performed, more accurate correction can be performed.

Further, each correction value for a plurality of shooting distances centering on the focal length of the grid is stored as the correction data, and a correction value corresponding to the shooting distance at the time of shooting is selected from the correction data, The correction can be performed with this correction value. For example, the correction value for each shooting distance that is variously changed around the grid focal length is stored, the correction value is selected from the correction data according to the shooting distance at the time of actual shooting, and this selected correction value is set. For example, the correction can be performed by multiplying the signal value obtained by reading the radiation image in the image acquisition device.

Further, the correction may be performed by using a correction function based on the difference between the photographing distance and the grid focal length, and it is not necessary to perform the photographing for correction in advance.
The correction data can be easily obtained.

Further, the correction may be carried out by using the correction data of three points obtained for each of the shooting distance, the short shooting distance and the long shooting distance which are substantially the same as the grid focal length. The number of times decreases.

Further, the image acquisition device can be configured as an integrated imaging platform so that the grid and the recording medium are built in and the radiation image recorded on the recording medium is automatically read after imaging. Alternatively, the radiographic image may be read after the recording distance information is input and the recording medium on which the radiographic image is recorded is attached outside the image acquisition device. Since the shooting distance is determined by the shooting site,
Distance data is obtained according to the imaging condition key (processing condition of the device) (for example, 1.2 m imaging during abdominal imaging).

The correction may be performed when the information of the radiation image is read and a predetermined image processing is performed or after the image processing as a post-processing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a radiation image reading apparatus according to an embodiment of the present invention. The radiation image reading device 50 of FIG. 1 acquires information of the radiation image by reading the radiation image recorded on the stimulable phosphor sheet 4 as a recording medium, and as shown in the drawing, the reading device 50 3 and a controller 18.

When the reader 3 is irradiated with radiation, a part of this radiation energy is accumulated, and when it is subsequently irradiated with excitation light such as visible light or laser light, it emits stimulated luminescence according to the accumulated radiation energy. Using exhaustive phosphor,
On a stimulable phosphor sheet 4 in the form of a sheet in which a stimulable phosphor is laminated on a support, radiation image information of a subject M such as a human body due to the radiation emitted from the radiation generator 30 is temporarily stored and recorded. A laser beam is scanned to sequentially cause photostimulated luminescence, and the photostimulated luminescence light is sequentially photoelectrically read by the photoelectric reading unit 20 to obtain an image signal. Then, the reading device 3 irradiates the stimulable phosphor sheet after reading the image signal with erasing light to release the radiation energy remaining on the sheet, and prepares for the next imaging. The radiation generation device 30 includes a radiation irradiation unit 31 that irradiates the subject M with radiation from a tube and a control unit 32 that controls the radiation irradiation unit 31.

The reading device 3 is a laser light source including a stimulable phosphor sheet 4 for recording radiation image information of a subject and a laser diode for generating laser light as excitation light for the stimulable phosphor sheet 4. Section 6 and laser light source section 6
Laser drive circuit 5 for driving the
System 7 for scanning the laser beam from the stimulable phosphor sheet 4 onto the stimulable phosphor sheet 4, and a photoelectric reading unit 20 for collecting and photoelectrically converting the stimulated emission excited by the excitation laser beam to obtain an image signal. Have and.

Further, a distance meter 29 using ultrasonic waves or the like is provided on the front surface 3b of the device, which faces the radiation irradiating section 31 of the housing 3a containing the respective parts of the reading device 3, and the distance meter 29 is used.
Measures the imaging distance y (FIG. 2) between the radiation irradiation section 31 and the tube, and sends the measured distance information to the control section 17.
A grid 28 for preventing scattered rays is arranged on the front surface 3b of the device so as to cover the front surface (radiation input surface) of the stimulable phosphor sheet 4. The grid 28 has the above-described known structure and has a predetermined grid focal length d (FIG. 2).

The photoelectric reading section 20 includes a light collector 8 that collects stimulated emission emitted by the excitation laser light, and a photomultiplier (photoelectron multiplier) that photoelectrically converts the light collected by the light collector 8. Tube) 10, a high-voltage power supply 10a for applying a voltage to the photomultiplier 10, a current-voltage converter 11 for performing logarithmic-voltage conversion of the current signal from the photomultiplier (photomultiplier tube) 10, and this current-voltage converter A / D converter 12 for A / D converting the analog signal from 11
And a correction unit 13 that performs various corrections on the converted digital signal, and transmits the digital signal of the read radiation image data to the controller 3. Correction unit 1
Reference numeral 3 has a memory for storing correction data and the like, and it is possible to correct density unevenness caused by the grid 28 by using the correction data as one of various corrections.

The reading device 3 further includes a halogen lamp 14 for irradiating erasing light in order to release the radiation energy remaining on the stimulable phosphor sheet after the image signal is read,
It has a driver 15 for driving the halogen lamp 14. The reading device 3 also includes a control unit 17 that controls the laser drive circuit 5, the high-voltage power supply 10a, the current-voltage conversion unit 11, the A / D conversion unit 12, the correction unit 13, the driver 15, and the distance meter 29. Further, the laser light source unit 6, the optical system 7, the light collector 8, and the photomultiplier 10 of the reading device 3
The halogen lamp 14 integrally moves as a sub-scanning unit (not shown) by a ball screw mechanism in the sub-scanning direction perpendicular to the laser scanning direction. The sub-scanning unit moves to perform sub-scanning during image reading, and the halogen lamp 14 emits light during the backward movement to erase the radiation image information remaining on the stimulable phosphor sheet 4. In this way, the radiation image recorded on the stimulable phosphor sheet 4 is automatically read to obtain information, the afterimage after reading is erased, and the next radiation imaging can be performed.

The controller 18 is a personal computer body 25
, A keyboard 26, and a monitor display unit 27. The digital signal of the radiation image data received from the reading device 3 is temporarily stored in the memory, image processing is performed, and the keyboard 2
The display on the monitor display unit 27 and the image processing are controlled according to the operation input from 6, and the radiation image data subjected to the image processing is output to the outside.

Next, the reading unit 3 of the radiation image reading device 50.
The correction of the density unevenness caused by the grid 28 in the correction unit 13 will be described with reference to FIGS. 2 and 3.

In FIG. 2, the shooting distance y (the position of the tube) is variously changed around the grid focal length d (the position of the tube in FIG. 2) and a solid image of a predetermined density is displayed at a predetermined tube voltage (for example, 80 kV). Then, the density is measured in the horizontal direction x (position of the stimulable phosphor sheet) in the figure, and as shown in FIG. 3, when the shooting distance y0 is equal to the grid focal length d, a straight line i is obtained. And the position x of the stimulable phosphor sheet
Although the density is constant regardless of (hereinafter, referred to as a sheet position x), when the shooting distance y1 is larger than the grid focal length d (y1> d), the grid center c is centered like a curve j. It can be seen that the curve becomes a parabolic curve that is convex upward, and that the density decrease becomes remarkable as the sheet position x moves away from the grid center c to the left and right. When the shooting distance y2 is smaller than the grid focal length d (y2
In <d), a similar parabolic curve like the curve k is found, but it can be seen that the concentration decrease is more remarkable than the curve j. In general, when the distance is the same from the focusing distance,
The attenuation rate is larger in the proximal region (y2) than in the distal region (y1) with respect to the grid.

On curves j and k as shown in FIG. 3, the densities h1, h2, h3, h4 at the sheet positions x1, x2, ...
, Respectively, and each density and straight line i (shooting distance y0
= Ratio of grid focal length d) to the reference density h0 (h1 /
h0, h2 / h0, h3 / h0, h4 / h0, ...)
Ask for. Then, if the grid focal length is 150 cm, the shooting distance y is 120 cm, 130 cm,
Curves such as 140 cm, ..., 190 cm, 200 cm are changed for each 10 cm to obtain the curves shown in FIG.
Find a similar ratio. The correction values based on these ratios are stored as correction data in the memory of the correction unit 13 as a table corresponding to the sheet position x for each shooting distance.

In FIG. 1, the radiation irradiator 31 of the radiation generator 30 generates radiation at a predetermined tube voltage (for example, 80 kV), and the radiation passing through the object is grid 2
Radiographing is carried out so that the radiation image is recorded on the stimulable phosphor sheet 4 after passing through 8, and the radiation image is recorded by the photoelectric reading unit 20 from the stimulable phosphor sheet 4 on which the radiation image is recorded by the reading unit 3. read. Rangefinder 29 at the time of this radiography
The distance between the radiation irradiating section 31 and the tube is measured, and this distance information is sent to the correcting section 13 via the control section 17 and stored therein.

The current signal from the photomultiplier 10 based on the radiation image information read as described above is converted into a voltage signal by the current / voltage converter 11, and this voltage signal is A / D converted by the A / D converter 12. Then, a digital signal is obtained. With respect to this digital signal, the correction unit 13 selects the correction data corresponding to the measured shooting distance from the table in the memory, and the correction values corresponding to the sheet position x are multiplied to obtain the density caused by the grid 28 of the radiation image. Correct the decline. The digital signal of the radiation image data corrected in this way is sent to the controller 18 for image processing and then output to the outside, and the radiation image is visualized on, for example, a film.

When the actual shooting distance is different from the shooting distance stored in the table of the correction unit 13, the correction unit 1
In step 3, each correction value is interpolated by interpolation by mathematical processing or the like.

When the tube voltage is changed to 50 kV or 120 kV, data is separately obtained for each tube voltage in the same manner as in FIG. 3 and stored in the memory of the correction unit 13 for each tube voltage at the time of correction. Select Dable to. The reading unit 3 receives the information about the tube voltage from the radiation generator 30 via the network. The decrease in concentration due to the grid is due to the fact that the grid's lead foil and radiation are no longer parallel to each other.
This is because a part of the radiation energy is absorbed by the lead foil, and the radiation transmittance changes with the energy of the radiation even at the same grid focal length. The ratio can be increased), and the correction can be performed by taking into consideration the change in transmittance due to the tube voltage in addition to the shooting distance.

As described above, when radiography is performed using the grid, it is possible to correct the density reduction (due to the grid) that occurs when the grid focal length and the imaging distance are different, The difference in variations due to the radiation image reading device and the grid can be eliminated, and the diagnostic ability is improved. Since this correction is performed using the correction data based on the actual shooting distance, there is no possibility of overcorrection due to double processing as in the related art. Further, it is possible to correct the difference in the density reduction level due to the difference in the tube voltage, and to perform the correction with higher accuracy.

The rangefinder 29 shown in FIG. 1 may be provided on the side of the radiation generator 30, and the reading unit 3 can receive the measured photographing distance information from the radiation generator 30 via the network. The user may directly input the shooting distance information and the tube voltage information from the keyboard 26 of the controller 18.

Next, two examples of another method for correcting the density unevenness caused by the grid 28 in the correction unit 13 of FIG. 1 will be described.

One is a method using a correction function,
Shooting distance y, grid focal length d, grid lead foil 1
Radiation transmittance (unit%, transmittance 100% at center x = 0) as a function of position x (center is the origin) on the grid corresponding to the above-mentioned sheet position, where e is the number of lines per cm and grid ratio is f ) F (x) is expressed by the following equation (2). (However, all units related to distance are mm.)

Generally, the degree of attenuation (cutoff) G of the primary X-ray due to the deviation of the focusing distance is expressed by the following equation (1). G (%) = f × x {1 / y−1 / d} × 100 (1)

It is also represented by the following equation (2) such as tube voltage. f (x) = {1- | A * B * x | * e / 10} * 100 (2) B <1.0 (coefficient related to tube voltage determined by transmittance of tube voltage) A = 1- {y ( 1 · 10 / de) / (y · 10f / e)} (However, | x | <shooting size / 2)

A correction value is obtained by the correction function according to the above equation (2) and is multiplied by the linear signal value in the correction section 13 of FIG. 1 in the same manner as described above to reduce the density decrease due to the grid 28 of the radiation image. Can be corrected. By using this correction function, the number of grids, grid ratio,
By inputting each data of the grid focal length and the coefficient relating to the tube voltage, the correction can be performed freely and easily without taking a correction image as shown in FIG.

Next, there is a three-point correction method. As shown in FIGS. 2 and 3, the same shooting distance y with respect to the grid focal length d is used.
The correction data is obtained at three points obtained for 0, the short shooting distance y2, and the long shooting distance y1. For example, when the tube of the radiation irradiating section between the position of FIG. 2 (between the distances y1 and y2) is arranged, the tube position at the time of shooting (shooting distance y )
And a position (distance y2), a correction value obtained by multiplying the attenuation coefficient α (α (y) <1.0) based on the function of the distance difference (y−y2) is used, Correction unit 1
By multiplying the linear signal value by 3, it is possible to correct the density decrease due to the grid 28 of the radiation image.

Next, another radiation image reading apparatus as a modification of FIG. 1 will be described with reference to FIG. Figure 4 (a)
As described above, the radiation from the radiation irradiation unit 31 similar to that in FIG. 1 passes through the subject M and passes through the grid 38 to the cassette 40.
It reaches the stimulable phosphor sheet 39 inside and records a radiation image. Next, the radiation image reading device 51 of FIG. 4B is loaded with the cassette 40, and the stimulable phosphor sheet 39 taken out from the cassette 40 and conveyed is irradiated with laser light in the same manner as in FIG. The stimulated emission obtained by irradiation is condensed, photoelectrically converted by the photoelectric conversion unit 41, radiation image information is obtained by the reading unit 42 similar to that in FIG. 1, and the radiation image information is sent to the controller 43 for image processing to the outside. Output. In this case, the reading unit 42 performs the same correction as that shown in FIGS. 1 to 3, and it is possible to perform the correction of the density decrease that occurs when the shooting distance when shooting outside the apparatus 51 and the grid focal length are different. .

In this example, the information such as the grid focal length and the number of grids regarding the grid at the time of the radiography of FIG. 4A, the shooting distance information, the tube voltage information and the like are transmitted through the network to the radiographic image of FIG. 4B. Although it can be input to the reading device, it may be input from the keyboard of the controller 43 in FIG. 4B.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to these.
Various modifications are possible within the scope of the technical idea of the present invention. For example, the correction of the density decrease due to the grid in FIGS. 1 and 4B may be performed by the controllers 18 and 43 during image processing or afterward as post-processing.

Further, the radiation image reading apparatus of FIGS. 1 and 4 (b) uses a plate using a stimulable phosphor and collects photostimulable light generated by laser scanning to collect a PMT (photomultiplier). Although it is a system (CR type) that photoelectrically converts by a pliers) into an electric signal, it may be a system composed of an FPD (flat panel detector). That is, FPD is composed of CsI (cesium iodide) and rare earth (Gd ₂ O ₂ ).
In the case of the scintillator type of the joint conversion system using, etc., it can be composed of a scintillator (CsI etc.) and a semiconductor sensor (a-Si photodiode etc.).
It can consist of a D sensor. Alternatively, it may be a direct conversion type using Se. According to the FPD, the electric signal from the sensor is electrically processed in substantially the same manner as in FIG. 1 without using the photomultiplier 10 or the like shown in FIG.

[0045]

According to the image acquisition apparatus of the present invention, it is possible to appropriately correct and remove the density unevenness in the radiation image that occurs when the grid focal length and the photographing distance are different during radiation imaging.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a radiation image reading apparatus according to an embodiment of the present invention.

[Fig. 2] Position of tube (radiography distance) during radiography
It is a figure which shows the positional relationship of a grid focal length and a grid.

FIG. 3 is an explanatory diagram for obtaining correction data for correcting density unevenness in the radiation image reading apparatus of FIG. 1, and is a diagram showing a relationship between a position of a stimulable phosphor sheet and a measured density value. .

FIG. 4 is a diagram for explaining a modified example of the radiation image reading device according to the embodiment of the present invention, in the case of recording a radiation image on a stimulable phosphor sheet in a cassette outside the radiation image reading device. 2A is an explanatory view of FIG. 3B and a schematic view of a radiation image reading apparatus of FIG.

[Explanation of symbols]

Radiation image reading device (image acquisition device) 4,39 Photostimulable phosphor sheet (recording medium) 12 Correction unit 28,38 grid 29 rangefinder 30 Radiation generator

Claims (11)

[Claims] 1. An image acquisition device for acquiring information of a radiation image obtained by passing radiation from a radiation generation device through a subject and a grid, wherein the radiation generation device and the grid are placed in front of the radiation. An image acquisition apparatus, which corrects density unevenness in the radiation image based on correction data relating to an imaging distance from a radiation input surface of a recording medium for recording an image. 2. The image acquisition apparatus according to claim 1, further comprising a measuring unit that measures the shooting distance, and the correction is performed by using the measured shooting distance information. 3. The image acquisition device according to claim 1, wherein the information on the imaging distance is received from the radiation generation device, and the correction is performed by using the received imaging distance information. 4. The image acquisition according to claim 1, further comprising an input unit capable of inputting the information on the photographing distance, and performing the correction by using the inputted photographing distance information. apparatus. 5. An image acquisition device for acquiring information of a radiation image captured by radiation from a radiation generation device passing through a subject and a grid, wherein the radiation generation device and the grid are placed in front of the radiation image. The image pickup distance to the radiation input surface of the recording medium for recording the image data and the tube voltage of the radiation generator are used as correction data, and the uneven density in the radiation image is corrected based on the correction data. Image acquisition device. 6. The correction values for a plurality of shooting distances centered on the focal length of the grid are stored as the correction data, and a correction value corresponding to the shooting distance at the time of shooting is selected from the correction data, The image acquisition apparatus according to claim 1, wherein the correction is performed based on the correction value. 7. The image acquisition device according to claim 1, wherein the correction is performed using a correction function based on a difference between the shooting distance and the grid focal length. 8. The correction according to claim 1, wherein the correction is performed using correction data of three points respectively obtained for a shooting distance, a short shooting distance and a long shooting distance which are substantially the same as the grid focal length. The image acquisition device according to any one of items. 9. The grid and the recording medium are built-in, and the radiation image recorded on the recording medium is automatically read after imaging, according to any one of claims 1 to 8. Image acquisition device. 10. The radiographic image is read after the recording distance information is input and the recording medium on which the radiographic image is recorded is attached outside the image acquisition device. The image acquisition device according to any one of 8 above. 11. The image acquisition according to claim 1, wherein the correction is performed when the information of the radiation image is read and a predetermined image processing is performed or as a post-processing after the image processing. apparatus.