JPH083845B2 - Radiation image reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a radiation image reading device for reading radiation image information recorded on an image recording medium.

(Prior Art) Conventionally, an image stored in an image recording medium, for example, a film, particularly an image formed by an X-ray film was placed on a Schaukasten or the like to be directly visually diagnosed. After scanning with a narrowly squeezed laser beam and converting it to an electrical signal, various image processing such as spatial frequency processing and gradation processing is performed to emphasize information effective for medical diagnosis, and then reproduced and diagnosed. It's coming.

With this method, more diagnostic information can be obtained from one X-ray imaging, and the diagnostic performance is improved. Furthermore, it is also expected to improve the efficiency of storage and retrieval of X-ray image information.

It will be as follows when it explains with the system block diagram of FIG.

The image stored in the film 1 as an image recording medium is read by scanning the film 1 with a laser beam in the film image reading device 2. This read information is
After being converted into a digital signal, it is sent to the data processing device 3. The data processing device 3 subjects the sent image information to data processing such as frequency enhancement and edge enhancement. As a result, an image with excellent diagnostic suitability can be obtained. Display device 4
Visualizes the data-processed image.

FIGS. 7A and 7B are conceptual views of the conventional film image reading device 2. Reference numeral 5 is a laser oscillator for generating a laser beam, and 6 is a beam expander for expanding the diameter of the incident laser beam to an arbitrary size to reduce the divergence angle of the laser beam. For example, if the beam diameter of the laser light is expanded five times with the beam expander 6, the divergence angle of the laser light is reduced to 1/5.

A high-speed angle changing mirror 7 reflects the incident laser light with a constant angular velocity in the main scanning direction, and a galvanometer or a polygon is generally applied. Reference numeral 8 denotes an fθ lens, which plays a role of focusing a laser beam on the same plane with a constant linear velocity by incidence of a laser beam having a constant angular velocity.

Film feed rollers 9a and 9b hold the film 10 in which the image information is stored and run the film 10 in a direction (sub-scanning direction) perpendicular to the main scanning direction at a predetermined speed. The sub-scanning by the film feed rollers 9a and 9b and the main scanning by the high-speed angle changing mirror 7 scan the entire surface of the film 10 with laser light.

Reference numeral 11 is a condenser for guiding the laser light that has passed through the film 10 and is incident to a detector 12 that converts it into an electric signal,
An optical system such as a bundled optical fiber or lens, a transparent acrylic resin having an output end processed so as to efficiently transmit incident light to the detector 12, and the like are used.

An electronic circuit is connected to the subsequent stage of the detector 12, and in this electronic circuit, the light passing through the film 10 is converted into a digital signal in time series in association with the positional information of each pixel.

The principle of film density measurement is as follows. The reference light amount incident on the detector 12 is I _0, and the light amounts incident on the detector 12 with and without the film are I ₁ and I ₂ , respectively, and the densities at that time are D ₁ and D ₂ , respectively. Then, the relationship between the density and the light amount is D ₁ = −logI ₁ / I ₀ , D ₂ = −
It becomes logI ₂ / I ₀ .

At this time, the concentration D ₂ when there is a film, when obtaining the concentration D ₃ of the difference between the concentration D ₁ of the case where the film is not, D ₃ = D ₂ -D
₁ = −logI ₂ / I ₁ , which indicates the density of the film.

That is, the density D ₁ when there is no film is measured and stored in advance, the density D ₂ when the film is placed is measured, and the difference from the previously stored density is calculated. It will indicate the density D ₃ of the film.

FIG. 8 shows an electronic circuit of the film image reading device 2. Since the density has a log dimension as described above, the signal converted into the electric signal by the detector 12 is first log-converted by the log amplifier 13.

The sample / hold circuit 14 holds the output signal of the log amplifier 13 at the preceding stage in synchronization with a clock signal input from a controller (not shown) that controls the entire electronic circuit, and the A / D converter 15 Sample / hold answer 14
It converts the analog signal for one scanning line held by the digital signal into a digital signal and outputs it.

The above controller divides continuous image information into pixels by generating a clock signal corresponding to the speed of main scanning. The switching unit 16 sends the signal output from the A / D converter 15 to the calibration buffer 17 or the line buffer 18 according to the signal instructed by the controller. That is, the density information when the film 10 is not placed in FIG. 7 is sent to the calibration buffer 17,
The switch 16 operates so that the density information when 10 is placed is sent to the line buffer 18.

The calibration buffer 17 and the line buffer 18 are circuits that function to store a digital signal of the number of pixels for one line, and advance the memory address by a clock signal input from a controller (not shown) to obtain pixel position information and memory information. Are associated with.

Reference numeral 19 denotes a difference calculation circuit, which calculates the difference between the density information of the film stored in the line buffer 18 in the preceding stage and the density information stored in the calibration buffer 17 by a signal input from a controller (not shown). It has a function to calculate each. This difference is the film density.

Reference numeral 20 denotes an interface, which functions to send the output signal of the difference calculation circuit 19 to the data processing device 3.

In the above structure, first, when there is no film,
The density of the line is measured and stored in the calibration buffer 17. Next, film feed rollers 9a, 9
b moves the film 10 in the sub-scanning direction to the main scanning line by the high-speed angle changing mirror 7, whereby the density of one line with the film is measured, and the measured value is stored in the line buffer 18.

After that, by the operation of the controller (not shown), the contents of the calibration buffer 17 and the line buffer 18 are sequentially sent to the difference calculation circuit 19, the difference, that is, the density of the film is calculated, and the calculation result is passed through the interface 20. It is sent to the data processing device 3.

After the data for one line is transferred to the data processing device 3, the film feed rollers 9a and 9b move the film 10 in the sub-scanning direction by a predetermined distance, and the measurement of the next line is performed. Such an operation is performed one after another, and the entire surface of the film 10 is measured.

By the way, one of the main causes of degrading the image quality of the image stored in the film is scattered radiation generated by the interaction between the subject and the X-ray. This scattered radiation is stored on the film and reduces the contrast of the image. Therefore,
Scattering-removing grids are widely used to reduce the amount of scattered radiation that reaches the film.

A normal grid has a density of 28 lines / cm to 40 lines / cm, and when this grid is left stationary during X-ray exposure, a visually noticeable streak appears on the film. So
Affect doctor's diagnosis. For this reason, a buki device is used to reciprocate the grid during X-ray exposure so that the grid is not exposed on the film.

However, recently, high density grids with a density of 60 lines / cm have begun to be used. The fine grid stripes due to this high-density grid can hardly be seen in normal photography. Therefore, in the high-density grid, even if the image is taken in a stationary state, the doctor's diagnosis will not be hindered.
Also, keeping the grid stationary has the advantage of reducing motion blur. For this reason, when using a high density grid, it has tended to be imprinted on the film.

(Problems to be Solved by the Invention) However, when a film having a grid image is measured by a conventional pixel reading device, a false image may occur on the read image. Also, the quality of the read image deteriorates due to the influence of noise that jumps into the detector, the fluctuation of the X-ray quantum at the time of X-ray photography, or the fluctuation of the read data due to the granularity of blackened silver particles on the film. There is a case.

Therefore, the present invention eliminates the above-mentioned drawbacks, and an object of the present invention is to improve the image quality of a read image due to a false image due to the grid and the above noise and fluctuations without increasing the reading time. It is an object of the present invention to provide a radiation image reading apparatus that reduces deterioration.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention scans a radiation image information with a laser beam on an image recording medium on which radiation image information is recorded together with a grid. In a radiation image reading apparatus that reads radiation image information from the image recording medium by sampling, a frequency corresponding to the pitch of a grid projected on the image recording medium when recording the radiation image information on the image recording medium. It is characterized in that a sampling means for sampling the radiation image information at a frequency more than twice the frequency and a averaging processing means for sequentially averaging the radiation image information sampled by the sampling means are provided.

(Operation) First, generation of a false image due to the grid will be described.

When the frequency of the grid and the frequency of the sampling are different, a false image having the frequency of the difference is surely generated.
For example, as shown in FIG. 9, when a 5 Hz original image is sampled at 4 Hz, a 1 Hz false image occurs. The sampling rate of the radiation image reading device is generally 50 to 100 lines / cm.
Therefore, the sampling theorem is not satisfied for the high resolution grid of 60 lines / cm. Therefore, a false image is generated.

However, the false image can be ignored if the difference between the maximum density and the minimum density when measuring the image recording medium on which the grid is imprinted, such as a film, is sufficiently small.

By the way, the shape of the laser beam output from the laser oscillator is Gaussian as shown in FIG. 2, and has the intensity distribution represented by the following equation.

I (r) = Imax e ^−2r2 / w ² (1) where Imax is the intensity on the optical axis (r = 0), and r
Is the distance from the optical axis in the radial direction, and w is the radius of the beam that gives Imax / e ² .

When the beam diameter is specified, the maximum value and the minimum value of the density of the film on which the grid is imprinted can be calculated by using the equation (1) and the normal distribution table.

A normal grid is composed of a pair of lead foil and an inter-spacer made of aluminum or the like. In the film on which the grid is photographed, the lead foil portion does not transmit X-rays, so this portion is transparent. Therefore, the inter-spacer portion is exposed and blackened according to the transmitted X-ray dose. With a high density grid of 60 pieces / cm, the lead foil thickness is 45
μm and the spacing is 167 μm.

When this grid is irradiated with a laser beam having a beam radius of w μm, the maximum and minimum values of the concentration are the third and third, respectively.
This occurs when the center of the laser beam 26 is located at the center of the inter spacer 24 and the center of the lead foil 25 as shown in FIGS.

If the difference between the maximum and minimum density is the density difference, 60 lines / c
The relationship between the calculated density difference and the beam diameter of a film on which an m grid is imprinted is as shown in FIG. According to the figure, the density difference when the beam diameter is about 360 μm is about 0.02, which is almost equal to the fluctuation of the blackening degree of the X-ray film, and the false image generated by measuring the grid. Can be ignored.

However, increasing the beam diameter to this extent lowers the reading resolution and makes it impossible to read the details of the image stored on the film. In fact, it is impossible to change this because the beam diameter is fixed in the device.

If the density of the grid is constant at 60 lines / cm, the density of the laser beam to be measured will change greatly depending on the center position of the beam diameter because the shape of the laser beam is Gaussian.

Therefore, in the present invention, by sampling the radiation image information at a frequency twice or more the frequency corresponding to the pitch of the grid projected on the image recording medium, the sampling theorem is satisfied, and the false image caused by the grid is eliminated. This is significantly reduced, and a very good read image can be obtained for diagnosis. Also, since the averaging process is performed on this sampling output, the difference between the maximum density and the minimum density is reduced, thereby reducing false images and noise that jumps into the detector. It is possible to reduce the deterioration of image quality due to the influence of the above, fluctuation of X-ray quantum at the time of X-ray photographing, fluctuation of read data due to graininess of blackened silver particles of the film, and the like.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples.

FIG. 1 shows the configuration of an electric circuit in a radiation image reading apparatus as an embodiment of the present invention.

In FIG. 1, those having the same functions as those shown in FIG. 8 are designated by the same reference numerals, and detailed description thereof will be omitted.

The device of the present embodiment is largely different from the conventional device in that the operating frequencies of the sample / hold circuit 14 and the A / D converter 15 are increased, and the addition between the A / D converter 15 and the switch 16 is added. Circuit 2
1, the buffer memory 22 is arranged.

The output of the sample / hold circuit 14 is converted into a digital signal by the A / D converter 15. The sample / hold circuit 14 and the A / D converter 15 are under the control of the microcomputer 25 and operate in synchronization with the clock signal sent from the microcomputer 25. This operating frequency, that is, the sampling frequency of the radiation image information captured via the log amplifier 13 is more than twice the frequency of the grid imaged on the image recording medium, for example, the film when recording the radiation image information on the film. Is set to.
Here, the sampling means 24 in the present invention is formed by the sample / hold circuit 14 and the A / D converter 15.

The adder circuit 21 performs addition processing of the data in the buffer memory 22 and the output data of the A / D converter 15 under the control of the microcomputer 25, and the addition result is written in the buffer memory 22 again. Of the output bits of the buffer memory 22, the lower several bits are truncated and the upper several bits are input to the switch 16 arranged in the subsequent stage. This means division of the data in the buffer memory 22. That is, by the adder 21 and the buffer memory 22,
That is, the averaging process of the output of the A / D converter 15 is performed. Here, the averaging processing means 23 in the present invention is composed of an adding circuit 21 and a buffer memory 22.

The device configuration in the front stage of the detector 2 is as shown in FIG.
What is shown in (b) can be applied as it is.

In the above configuration, first, the sample / hold circuit
The operation when the operating frequency (sampling frequency) of 14 and the A / D converter 15 is made equal to that of the conventional device will be described.

Assuming that the arithmetic mean processing means 23 performs arithmetic mean processing of four pieces of data, the processing in this case is performed as follows.

First, the contents of the buffer memory 22 are cleared by the microcomputer. When the A / D converter 15 outputs the first data, the value is stored in the buffer memory 22 and transmitted to the adder circuit 21. When the second data is output from the A / D converter 15, the adder circuit 21 adds the first data and the second data output from the buffer memory 22, and the adder 21 stores the data in the buffer memory 22. Rewrite the contents.

When the third and fourth data are output from the A / D converter 15, the contents of the buffer memory 22 are replaced with the added data by the same operation. Buffer memory 22
When the contents of the above becomes a value obtained by adding the 4th data, it has to be divided by 4 for averaging. In this case, the value obtained by truncating the lower 2 digits of the output of the buffer memory 22 is given to the next stage. It may be sent to the switch 16. That is, if the quantization number of the A / D converter 15 is 10 bits, the buffer memory
22 should be 12 bits, and only the upper 10 bits should be sent to the subsequent stage. In order to add and average eight pieces of data, the buffer memory 22 may be set to 13 bits and the last three digits may be discarded.

Since the process of this circuit is controlled by the microcomputer 25, it is easy to perform the above operation at the optimum timing. The operation of each unit thereafter is similar to that of the conventional device (see FIG. 8).

According to the test results of the inventors of the present application, the difference in density (when the maximum density and the minimum density are different from each other when the film in which the grid of 60 lines / cm is imaged is measured in the conventional apparatus at the laser beam diameter of 200 μm and the sampling pitch of 200 μm Although the difference) was 0.22, the density difference could be reduced to 0.04 by performing the averaging process of the four data under the same sampling pitch condition. In other words, the above-mentioned addition and averaging process can reduce the false image caused by the grid to the extent that it does not affect the reading diagnosis. Furthermore,
By performing the above-mentioned averaging process, noise that jumps into the detector 12, fluctuations of X-ray quanta during X-ray photography (recording radiation image information on the film), or graininess of blackened silver particles of the film It is also possible to reduce image quality deterioration due to fluctuations in read data and the like at the same time. Therefore,
It is possible to obtain a read image suitable for image interpretation diagnosis. Moreover, as compared with the conventional device, only the addition circuit 21 and the buffer memory 22 are added in terms of hardware, so that there is an advantage that a large increase in cost can be avoided.

Next, the operation when the operating frequencies of the sample / hold circuit 14 and the A / D converter 15 are made higher than those of the conventional device will be described.

For example, if the sampling pitch is 50 μm (since the conventional sampling pitch is 200 μm, the sampling pitch is 1/4 and the sampling frequency is 4 times), the sampling theorem is satisfied, and it results from the grid of 60 lines / cm. False images do not occur. Then, this sampling output (output of the A / D converter 15) is added and averaged by the averaging means 23.
Is taken in, and the arithmetic mean processing of the four data is performed here, and the processing result is input to the switch 16.

By doing so, the false image caused by the grid is further reduced as compared with the case of only the averaging process described above, and further, the averaging process can reduce the image quality change caused by noise or the like. Therefore, a very good read image can be obtained. In the case of only the above averaging process,
Since the sampling frequency is the same as that of the conventional apparatus, the time required for film measurement is four times as long as that of the conventional apparatus. However, by increasing the sampling frequency four times, the measurement time is the same as that of the conventional apparatus.

The present invention is not limited to the above embodiment,
It goes without saying that various modifications can be made.

For example, in the above-mentioned embodiments, the image recording medium is a film. However, the present invention can be applied to the case of using a medium other than the film, for example, an imaging plate containing a stimulable phosphor.

Further, in the above-mentioned embodiment, the case where a grid of 60 lines / cm is imaged has been described, but when a grid with a lower resolution than this, for example, a grid of 28 to 40 lines / cm is imaged, the Nyquist frequency is Since it lowers, it is even more advantageous.

[Advantages of the Invention] As described in detail above, according to the present invention, the influence of false images caused by the grid and the noise rushing into the detector and X-rays.
It is possible to provide a radiographic image reading apparatus that reduces deterioration in the image quality of a read image due to fluctuations in X-ray quanta during radiography.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a main part of a radiographic image reading apparatus according to an embodiment of the present invention, FIG. 2 is an intensity characteristic diagram of laser light, and FIGS. 3 and 4 are explanations of a relation between a grid and a laser beam. 5 and 5 are characteristic diagrams showing the relationship between the calculated density difference and the laser beam diameter, FIG. 6 is a block diagram of the system configuration of the image processing apparatus, and FIGS. 7A and 7B are the configuration of the conventional apparatus. FIG. 8 is a configuration block diagram of a main part in the conventional apparatus, and FIG. 9 is a waveform diagram for explaining false image generation due to the grid. 10: film (image recording medium), 23: arithmetic mean processing means, 24: sampling means.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location 7517-2J A61B 6/00 350 A

Claims (1)

[Claims] 1. A radiation image reading apparatus for reading radiation image information from the image recording medium by scanning the image recording medium on which the radiation image information is recorded together with a grid with a laser beam and sampling the radiation image information,
Sampling means for sampling the radiation image information at a frequency that is at least twice the frequency corresponding to the pitch of the grid projected on the image recording medium when recording the radiation image information on the image recording medium, and this sampling means. And an averaging processing unit for sequentially averaging the radiation image information sampled in 1. are provided.