JPH11338076A - Radiation image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image whose quality is improved by setting the value of the stimulating energy of stimulating light scanning a stimulable phosphor sheet to a specified value. SOLUTION: The stimulable phosphor sheet 50 where radiation image information is accumulated and recorded is carried (subscanned) in a direction shown by an arrow Y by endless belts 19a and 19b. A laser beam L emitted from a light source 11 is reflected and deflected by a rotary polygon mirror 13, converged on the surface of the sheet 50 by a scanning lens 14, and performs the main scanning of the surface of the sheet 50 in a direction shown by an arrow X. The whole surface of the sheet 50 is irradiated with the laser beam L whose stimulating energy is 10 J/m<2> . Stimulated luminescences M1 and M2 in accordance with the radiation image information accumulated and recorded are respectively emitted from the obverse and the reverse of the sheet 50. The stimulated luminescences M1 and M2 are guided to photomultipliers 16a and 16b by light guides 15a and 15b arranged proximately to the sheet 50 and photoelectrically detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image reading apparatus for reading image signals from both surfaces of a stimulable phosphor sheet on which a radiation image is stored and recorded, and more particularly to an excitation energy for exciting a stimulable phosphor. It is related to the improvement of.

[0002]

2. Description of the Related Art When radiation (X-ray, α-ray, β-ray, γ-ray, electron beam, ultraviolet ray, etc.) is irradiated, a part of this radiation energy is accumulated. Using a stimulable phosphor (stimulable phosphor) that emits stimulable light in response to the applied energy, radiation image information of a subject such as a human body is temporarily stored in a sheet-shaped stimulable phosphor (a stimulable phosphor sheet). ), The stimulable phosphor sheet is scanned with laser light or the like to generate stimulated emission light, and the obtained stimulated emission light is photoelectrically read to obtain an image signal. A radiation image recording / reproducing system for outputting a radiation image of a subject as a visible image on a recording medium such as a photographic photosensitive material or a display device such as a CRT is already known (Japanese Patent Application Laid-Open Nos. 55-12429 and 56-11395). No. 56-11397). This system has the practical advantage of being able to record images over a very large radiation exposure area compared to conventional radiographic systems using silver halide photography.

Further, as a method of photoelectrically reading the stimulated emission light described above, photoelectric reading means are separately provided on both sides of the stimulable phosphor sheet to excite only both sides or only one side of the stimulable phosphor sheet. There has been proposed a radiation image reading apparatus which scans light and reads the stimulated emission light emitted from both sides of the stimulable phosphor sheet by the scanning of the excitation light separately by each of the photoelectric reading means (for example, Japanese Patent Application Laid-Open No. H11-157572). Kaikai 55-879
No. 70). In such a radiation image reading apparatus, one radiation image is accumulated and recorded on the stimulable phosphor sheet, and photostimulable emission light is condensed by photoelectric reading means from both sides of the stimulable phosphor sheet, respectively. By adding the obtained signals in correspondence with the pixels, the light collection efficiency is improved and the noise components are averaged, so that the S / N ratio of the obtained radiation image can be improved.

[0004]

However, in the above-described radiation image reading apparatus of the type in which the stimulating light is read from both sides of the sheet, further improvement in image quality is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a double-sided reading type radiographic image reading apparatus capable of obtaining an image with improved image quality as compared with the related art. Things.

[0006]

According to the radiation image reading apparatus of the present invention, a stimulable phosphor sheet on which a radiation image is stored and recorded is scanned by excitation light, and stimulated emission light emitted from both sides of the sheet is emitted. A radiation image reading apparatus which photoelectrically detects the radiation image by means of photoelectric reading means provided separately on both surfaces to read two image signals representing the radiation image, wherein the excitation energy of the excitation light is 10 J / m ² or more. It is characterized by being.

If the excitation energy is 10 J / m ² or more,
Although it may be any value, depending on the type of the stimulable phosphor sheet used, an image quality (DQE value: Detective) against an increase in excitation energy near 20 J / m ^2.
Quantum Efficiency)
It is preferably around J / m ² .

Here, the DQE value is a value representing the image quality calculated by the following equation, and the image quality improves as the DQE value increases.

DQE (u) = ｛(log ₁₀ e) ² × γ ² × MT
F ² (u)｝ / {q × Φ _total (u)｝ (where Φ _total (u) indicates a Wiener spectrum and u indicates a spatial frequency.) Emit excitation light having an excitation energy of 10 J / m ² or more. As a light source, for example, an SH (semiconductor laser) pumped
A G (second harmonic generation) laser can be applied.

[0010] The stimulable phosphor sheet is not limited to a sheet having a stimulable phosphor layer on both sides thereof, but may have a stimulable phosphor layer only on one side. In this case, it is necessary that the photostimulable emission light be transmitted to the other surface. BaFBrI: Eu is suitable as the stimulable phosphor.

Further, the scanning of the excitation light may be performed only on one side of the sheet or may be performed by scanning both sides of the sheet separately. , Is more effective.

[0012]

According to the radiation image reading apparatus of the present invention,
By scanning the stimulable phosphor sheet with an excitation light having an excitation energy of 10 J / m ² or more, the stimulable phosphor of the sheet can be sufficiently excited, whereby the sheet has higher intensity than before. Strong stimulated emission light can be emitted.

As a result, the image quality (DQE value) of an image obtained based on the intensity of the stimulated emission light can be improved.

In a radiation image reading apparatus configured to scan excitation light only from one side of a sheet, the excitation light is incident on one side, passes through the inside of the sheet, and reaches the other side. Since the excitation light is attenuated by diffusion etc.
In order to improve the image quality by increasing the intensity of the stimulated emission light read on the other surface side, it is preferable that the excitation energy is large. From this viewpoint, the radiation image reading apparatus of the present invention is separately provided on both surfaces of the sheet. The radiation image reading apparatus having a configuration in which the excitation light is scanned only from one surface side is more effective than the radiation image reading apparatus in which the excitation light is irradiated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the radiation image reading apparatus of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the radiation image reading apparatus of the present invention. The radiation image reading apparatus shown in the figure has a stimulable phosphor sheet in which a stimulable phosphor layer (BaFBrI: Eu) is laminated on a base that transmits stimulated emission light, and a protective layer is further laminated on the stimulable phosphor layer. This is an apparatus for reading radiation image information recorded on the stimulable phosphor layer in one photographing operation from each side of the stimulable phosphor sheet 50. Hereinafter, the stimulable phosphor sheet
The surface on the 50 protective layer side is called the front surface, and the surface on the base side is called the back surface.

The illustrated radiation image reading apparatus has two endless belts rotated by a motor (not shown).
A stimulable phosphor sheet (hereinafter, referred to as a sheet) 50 is disposed on each of the sheets 19a and 19b. Above the sheet 50, a laser light source 11 for emitting a laser beam L for exciting the sheet 50, and the laser beam L are reflected and deflected. Rotating polygon mirror 13 and the rotating polygon mirror 13
And a scanning lens 14 for converging the laser beam L reflected and deflected by the rotary polygon mirror 13 on the sheet 50 and scanning at a constant speed. Specifically, the laser light L emitted from the light source 11 is an SHG laser having a wavelength of 657 nm, and has a rated maximum output of 300 mW. Also, the excitation power of the laser light L on the sheet 50 is adjusted to 167 mW, the irradiation spot of the laser light L on the surface of the sheet 50 is approximately 100 μm × 100 μm, and the irradiation time per one irradiation spot (pixel). Is adjusted to approximately 1.2 μsec. Therefore, the excitation energy of the laser beam L per unit area on the sheet 50 is approximately 20 J / m ² .

Immediately above the surface (upper side in the drawing) of the sheet 50 on which the laser light L is scanned, there is further provided a light guide 15a for condensing stimulated emission light M1 emitted from the surface of the sheet 50 by excitation by the laser light L. Are arranged in close proximity. The light guide 15a is connected to a photomultiplier (photomultiplier tube) 16a that photoelectrically detects the stimulated emission light M1 and converts it into an analog image signal y1.

A logarithmic amplifier 21a is connected to the photomultiplier 16a. The logarithmic amplifier 21a performs log conversion of the analog image signal y1 and outputs a logarithmic image signal q1. An analog / digital conversion circuit (hereinafter, referred to as an A / D conversion circuit) 22a is further connected to the logarithmic amplifier 21a.
The logarithmic image signal q1 is sampled at a predetermined sampling period T by the A / D conversion circuit 22a and converted into digital image data Q1.

On the other hand, also on the back side (the lower side in the drawing) of the surface of the sheet 50 on which the laser light L is scanned, a light guide for condensing stimulated emission light M2 emitted from the back surface of the sheet 50 by excitation by the laser light L. 15b are arranged in close proximity. Light guide 15
Connected to b is a photomultiplier (photomultiplier tube) 16b that photoelectrically detects the condensed photostimulated light M2 and converts it into an analog image signal y2.

A logarithmic amplifier 21b is connected to the photomultiplier 16b. The logarithmic amplifier 21b performs log conversion of the analog image signal y2 and outputs a logarithmic image signal q2. An analog / digital conversion circuit (hereinafter, referred to as an A / D conversion circuit) 22b is further connected to the logarithmic amplifier 21b.
The logarithmic image signal q2 is sampled at a predetermined sampling period T by the A / D conversion circuit 22b and converted into digital image data Q2.

Further, the A / D conversion circuits 22a and 22b are connected to the image processing unit 30. The image processing unit 30 includes a first digital image data Q1 input from the A / D conversion circuit 22a corresponding to the front side and a second digital image data Q1 input from the A / D conversion circuit 22b corresponding to the front side. Image data Q2
Are weighted and added at a preset addition ratio in correspondence with the pixels, and various signal processing is performed on the obtained one image signal Q for each pixel, and then output to an external image reproducing device or the like. To act. As the addition ratio between the front side and the back side, a ratio suitable for suppressing noise is used,
In the present embodiment, for simplicity, a ratio of 1: 1 is set, and Q
= 0.5Q1 + 0.5Q2.

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

Sheet 50 on which radiation image information is stored and recorded
Is set at a predetermined position on the endless belt 19a. The sheet 50 set at this predetermined position is conveyed (sub-scan) in the direction of arrow Y by the endless belts 19a and 19b.

On the other hand, the laser light L emitted from the light source 11
Is reflected and deflected by a rotary polygon mirror 13 driven by a motor 12 and rotated at a high speed in the direction of the arrow, and the deflected laser light L is converged on the surface of a sheet 50 by a scanning lens 14 and scanned at a constant speed. The main scanning of the surface of the sheet 50 is performed in the arrow X direction. By the main scanning of the laser beam L and the sub-scanning of the sheet 50, the sheet 50 is irradiated with the laser beam L having an excitation energy of about 20 J / m ² over the entire surface.

The laser beam L illuminating the sheet 50 is applied to the sheet
The 50 stimulable phosphors are excited, and from the surface of the sheet 50, the stimulating light M1 corresponding to the radiation image information stored and recorded.
Are emitted from the back surface of the sheet 50, and the stimulated emission light M2 corresponding to the radiation image information stored and recorded is emitted. Since the stimulated emission light M1 and M2 are excited by a large excitation energy (about 20 J / m ² ), the emission intensity is much higher than that of the conventional one.

Stimulated light M emitted from the surface of the sheet 50
1 is guided to the photomultiplier 16a by the light guide 15a arranged close to the upper surface of the sheet 50, and is photoelectrically detected by the photomultiplier 16a. Light guide
15a is made by molding a light-guiding material such as an acrylic plate, and the linear incident end face has a stimulable phosphor sheet.
The light receiving surface of the photomultiplier 16a is arranged to extend along the main scanning line on 50, and is coupled to an emission end surface formed in an annular shape. Light guide 15 from the entrance end face
The stimulated emission light M1 entering the light guide 15a repeats total reflection inside the light guide 15a, and is emitted from the exit end face, received by the photomultiplier 16a, and received by the photomultiplier 16a to represent radiation image information. Is the photomultiplier
The signal is converted into an analog image signal y1 by 16a.

The analog signal y1 output from the photomultiplier 16a is logarithmically amplified by the logarithmic amplifier 21a and converted to a logarithmic image signal q1.

The logarithmic-amplified image signal q1 thus log-amplified is input to an A / D conversion circuit 22a, and the A / D conversion circuit
The image data is converted into digital image data Q1 by 22a and input to the image processing unit 30.

On the other hand, the stimulated emission light M2 emitted from the back surface of the sheet 50 is a light guide arranged close to the lower surface of the sheet 50.
The photomultiplier 15b guides the photomultiplier 15b to the photomultiplier 16b and photoelectrically detects the photomultiplier 16b. The light guide 15b is also formed by molding a light-guiding material such as an acrylic plate, and is arranged so that a linear incident end face extends along a main scanning line on the stimulable phosphor sheet 50, The above-mentioned photomultiplier is attached to the emission end face formed in an annular shape.
The light receiving surface 16b is connected. The stimulated emission light M2 that has entered the light guide 15b from the incident end face is
b, the light is emitted from the output end face and received by the photomultiplier 16b, and the light quantity p 'of the photostimulated emission light M2 representing the radiation image information is converted into an analog image signal y2 by the photomultiplier 16b. Is converted.

The analog signal y2 output from the photomultiplier 16b is logarithmically amplified by the logarithmic amplifier 21b and converted into a logarithmic image signal q2.

The logarithmized image signal q2 thus logarithmically amplified is input to the A / D conversion circuit 22b, where it is input to the A / D conversion circuit 22b.
The image data is converted into digital image data Q2 by 22b and input to the image processing unit 30.

The image processing unit 30 performs an addition process on the two image data Q1 and Q2 in correspondence with the pixels, and performs a gradation process, a frequency process, etc. on the obtained image data Q (= 0.5Q1 + 0.5Q2). And outputs it to the outside.

As described above, according to the radiation image reading apparatus of the present embodiment, the sheet 50 is scanned by the laser beam L having the excitation energy of 10 J / m ² or more, so that the sheet is scanned.
50 of the stimulable phosphors can be sufficiently excited.
Can be emitted, and as a result, the image quality (DQE value) of the image obtained based on the intensity of the photostimulated light M can be improved.

FIG. 2 shows a stimulable phosphor sheet (BaFBrI: Eu) on which a predetermined radiation image is recorded, from one surface side, the images (surface and surface) obtained from each surface when the excitation energy is changed. The image quality (DQE) of the back side) and the added image (added as both sides in the figure) added at a predetermined addition ratio
Is the experimental data that recorded the change in value.

According to the experimental data, the excitation energy is
Image quality (DQE value) of added image at 10 J / m ² or more
Was found to have improved.

Further, when the excitation energy is around 20 J / m ² , it is recognized that the degree of improvement of the image quality (DQE value) with respect to the increase of the excitation energy is slowed down, and the excitation energy is about 20 J / m ^2. It was found to be favorable.

[Brief description of the drawings]

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

FIG. 2 shows image quality (DQE) when excitation energy is changed.
Value)

[Explanation of symbols]

 11 Laser light source 12 Motor 13 Rotating polygon mirror 14 Scanning lens 15a, 15b Light guide 16a, 16b Photomultiplier 19a, 19b Endless belt 21a, 21b Logarithmic amplifier 22a, 22b A / D conversion circuit 30 Image processing unit 50 Storage fluorescence Body sheet L Laser light M1, M2 Stimulated emission light y1, y2 Analog image signal q1, q2 Logarithmic image signal Q1, Q2 Digital image signal

Claims (1)

[Claims] 1. A stimulable phosphor sheet on which a radiation image is accumulated and recorded is scanned by excitation light, and stimulated emission light emitted from both sides of the sheet is read by photoelectric reading means provided separately on both sides. A radiation image reading apparatus for photoelectrically detecting two excitation light beams to read two image signals representing the radiation image, wherein the excitation energy of the excitation light is 10 J / m ² or more.