JPH01258079A - Radiological image reader - Google Patents

Abstract

PURPOSE:To prevent deterioration of the picture quality of read radiological image by providing an arithmetic mean processing means which calculates the arithmetic mean of the sampling outputs of the radiological image informa tion about plural picture elements in the scanning direction. CONSTITUTION:A sampling means 24 is formed of a sample and hold circuit 14 and A/D converter 15 and operates synchronously to clock signals sent from a CPU 25. The operating frequency of the means 24, namely, the sampling frequency of the radiological image information fetched through a logarithmic amplifier 13 is set at twice or more as high as the frequency of the grid imprinted on the film. An adder circuit 21 adds data in a buffer memory 22 and the data of the converter 15 to each other and the added result is again written in the memory 22. High-order number bits of the output bits of the memory 22 are inputted to a switch 2, meaning that division is performed on the data of the memory 22. In other words, the arithmetic means of the output of the converter 15 is taken by means of the adder 21 and memory 22. There fore, a read radiological image suitable for the diagnosis performed by reading the picture is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a radiographic image reading device that reads radiographic image information recorded on an image recording medium.

(Prior art) In the past, images stored on an image recording medium such as film, especially images from X-ray film, were placed on a Scherkasten or the like and diagnosed by direct visual observation, but in recent years, images stored on film have been After scanning with a narrowly focused laser beam and converting it into an electrical signal, it is subjected to various image processing such as spatial frequency processing and gradation processing to emphasize information useful for medical diagnosis, and then played back for diagnosis. It has become.

With this method, more diagnostic information can be obtained from a single X-ray examination, improving diagnostic performance. Furthermore,
It is also expected to improve the efficiency of storing and retrieving X-ray image information.

The system configuration diagram shown in FIG. 6 will be explained as follows.

The images stored on the film 1, which is an image recording medium, are
The film image reading device 2 scans the film surface with a laser beam to read the image.

This read information is sent to the data processing device 3 after being converted into a digital signal. The data processing device 3 performs data processing such as frequency emphasis and edge emphasis on the sent image information. This provides images with excellent diagnostic suitability. The display device 4 visualizes the data-processed image.

FIGS. 7(a) and 7(b) show a conventional film image reading device 2.
It is a conceptual diagram. 5 is a laser emitter that generates a laser beam, and 6 is a beam expander that expands the aperture of the incident laser beam to an arbitrary size to reduce the spread angle of the laser beam.

For example, the beam diameter of the laser beam can be set to 5 by the beam expander 6.
When magnified twice, the spread angle of the laser beam decreases to 115.

Reference numeral 7 denotes a high-speed angle changing mirror that reflects the incident laser beam at a constant angular velocity in the main scanning direction, and a galvanometer or a polygon is generally used.

Reference numeral 8 denotes an fθ lens, which serves to focus the laser beam on the same plane by keeping the linear velocity constant when the laser beam is incident at a constant angular velocity.

Reference numerals 9a and 9b are film feed rollers, which hold the film 10 on which image information is stored and run the film 10 at a predetermined speed in a direction perpendicular to the main scanning direction (sub-scanning direction).

The entire surface of the film 10 is scanned by the laser beam by the sub-scanning by the film feed rollers 9a and 9b and the main scanning by the high-speed angle change mirror 7.

11 is a laser beam that has passed through the film 10 and entered,
It is a condenser that guides the light to the detector 12 that converts it into an electric signal, and includes an optical system such as a bundled optical fiber and a lens.
A transparent acrylic resin or the like whose output end is processed so as to efficiently transmit incident light to the detector 12 is used.

An electronic circuit is connected after the detector 12, and in this electronic circuit, the light that has passed through the film 10 is correlated with the position information of each pixel and converted into a digital signal in time series.

The principle of film density measurement is as follows.

The reference amount of light incident on the detector 12 is Io, the distance between the lights incident on the detector 12 when there is no film and when there is a film is I1 and I2, respectively, and the density at that time is D1, respectively.
and D2, the relationship between density and light amount is Dt = -1
0gIt/Io.

D2 = -10012/Io.

At this time, if we calculate the density D3 which is the difference between 11 degrees D2 when there is a film and the density D1 when there is no film, we get D
3=D2-Dl=-IoOI2/It, which indicates the density of the film.

That is, if you measure and memorize the density D1 when there is no film in advance, then measure the density D2 when the film is placed, and calculate the difference between it and the previously memorized density, that value will be the same as that of the film. This indicates the density D3.

FIG. 8 shows the electronic circuit of the film image reading device 2. As shown in FIG. As described above, since IK has a log dimension, the signal converted into an electrical signal by the detector 12 is first converted into a log signal by the log amplifier 13.

The sample/hold circuit 14 holds the output signal of the log amplifier 13 in the previous stage in synchronization with a clock signal input from a controller (not shown) that manages electronic circuit hiatus, and is connected to the A/D converter. 15 converts the signal held by the sample/hold circuit 14 into a digital signal.

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

Calibration buffer 17 and line buffer 18
is a circuit that functions to store digital signals of the number of pixels for one line, and advances the storage address by a clock signal input from a controller (not shown) to associate pixel position information with stored information.

19 is a delivery calculation circuit, which is a line buffer 18 in the previous stage.
It has a function of outputting the difference between the density information of the film stored in the calibration buffer 17 and the density information stored in the calibration buffer 17 for each corresponding pixel in response to a signal input from a controller (not shown). This difference becomes the density of the film.

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 configuration, first, the density of one line when there is no film is measured, and this is stored in the calibration buffer 17. Next, the film feed roller ga
, gb moves the film 10 in the sub-scanning direction through the high-speed angle change mirror 7
As a result, the density of one line with the film is measured, and the measured value is stored in the line buffer 18.

By the action of a controller (not shown), the contents of the calibration buffer 17 and line buffer 18 are sent one after another to the difference calculation circuit 19, the difference, that is, the density of the film is calculated, and the result is sent to the interface 20. The data is sent to the data processing device 3 via.

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

Incidentally, one of the main causes of deteriorating the image quality of images stored on film is scattered radiation generated by the interaction between the subject and X-rays. This scattered radiation is recorded on the film and reduces the contrast of the image. Therefore, in order to reduce the number of scattered rays reaching the film, grids for removing scattered rays are widely used.

A typical grid has a density of 28 lines/cm to 40 lines/cm, and when this grid is left stationary during X-ray exposure, streaks appear on the film that are visible to the naked eye. So it affects the doctor's diagnosis. For this reason, a bucking device is used to move the grid back and forth during X-ray exposure to prevent the grid from being imprinted on the film.

However, recently, high-density grids with a density of 60 lines/cm have begun to be used. The fine grid stripes created by this high-density grid are almost invisible in a normal pattern. Therefore, with a high-density grid, even if the image is placed in a stationary state, a doctor's diagnosis will not be hindered in any way. Also, keeping the grid stationary has the advantage of reducing blur caused by movement. For this reason, there has been a trend to image high-density grids onto film.

(Problem to be Solved by the Invention) However, it is difficult to use a film with grids printed on it using the conventional
When measured with a reading device, a false image may occur on the read image. In addition, the image quality of the read image may be affected by the influence of noise that enters the detector, the fluctuation of the X-ray beam during X-ray radiation, or the fluctuation of the read data due to the graininess of blackened silver particles in the film. may deteriorate.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and its purpose is to provide a radiographic image reading system that reduces false images caused by grids and deterioration in image quality of read images caused by the above-mentioned noise, fluctuations, etc. The goal is to provide equipment.

[Structure of the Invention (Means for Solving the Problems)] The present invention scans an image recording medium on which radiographic image information is recorded with a laser beam and samples the radiographic image information, thereby obtaining data from the image recording medium. A radiographic image reading device that reads radiographic image information is provided with an averaging processing means that adds and averages sampling outputs of radiographic image information for a plurality of pixels in a scanning direction.

In addition to this, a four-noise sampling means is provided for sampling radiographic image information at a frequency that is at least twice as high as the frequency of the grid imaged on the image recording medium when recording the radiographic image information on the image recording medium. We are prepared.

(Function) First, the occurrence of false images caused by the grid will be explained.

When the grid frequency and the sampling frequency are different, a false image with a frequency that is the difference between them will always occur. For example, as shown in Figure 9, the original image of 5Hz is 4! When sampling at IZ, a false image of 111Z occurs. The sampling rate of radiation image reading devices is generally 50
Since it is between 100 lines/cm, the sampling theorem is not satisfied for a high resolution grid of 60 lines/cm. For this reason, a false image occurs.

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

By the way, the shape of the laser beam (laser beam output from the cylindrical device) is Gaussian (GauSSian) as shown in FIG. 2, and has an intensity distribution expressed by the following equation.

I (r) = Imax e-2r2' w2
(1) Here, I max is on the optical axis (r=o)
where r is the radial distance from the optical axis and W is the radius of the beam at Imax/e2.

Once the beam diameter is specified, the maximum and minimum density values of the film on which the grid is imaged can be calculated using equation (1) and the normal distribution table.

A normal grid is made up of a pair of lead foil and an interspacer made of aluminum, etc. When the grid is photographed on film, the lead foil part does not transmit X-rays, so this part appears white. The interspacer portion is exposed and becomes black according to the amount of transmitted X-rays. For a dense grid of 60 lines/cm, the lead foil thickness is 45 μm and the spacing is 167 μm.

When this grid is irradiated with a laser beam with a beam radius of 1 m, the maximum and minimum values of the concentration are as shown in FIGS. 3 and 4, respectively, when the center of the laser beam 26 is at the center of the interspacer 24 This occurs when the foil 25 is located at the center.

If the difference between the maximum and minimum density values is defined as the density difference, then 60 lines/
The calculated m of the film on which the crn grid is printed
The relationship between the degree difference and the beam diameter is shown in FIG. According to the figure, when the beam diameter is about 360 μm, the concentration difference is about 0.
02, which is approximately equal to the fluctuation in the degree of blackening of the X-ray film, and the artifacts generated by measuring the grid can be ignored.

However, increasing the beam diameter to this extent
This reduces the reading resolution and makes it impossible to read the details of the image stored on the film. In fact, since the beam diameter is fixed in the device, it is not possible to change it.

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

Therefore, in the present invention, the difference between the maximum density and the minimum density is reduced by averaging the sampling output of radiation image information for a plurality of pixels.
We are trying to reduce 4@. This averaging process also eliminates the effects of noise entering the detector, fluctuations in the X-ray minimum during X-ray transport, and fluctuations in the read data due to the graininess of blackened silver particles on the film. Image quality deterioration can be reduced.

Furthermore, 2 of the frequency of the grid imaged on the image recording medium
If the sampling theorem is satisfied by sampling radiographic image information at a frequency that is more than double the frequency, and the above-mentioned averaging process is performed on this sampling output,
False images caused by the grid will be significantly reduced,
Very good read images can be obtained in terms of interpretation and diagnosis.

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

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

In FIG. 1, parts having the same functions as those shown in FIG. 8 are given the same reference numerals, and detailed explanation thereof will be omitted.

The main difference between the device of this embodiment and the conventional device is the sample/hold circuit 14. The operating frequency of the A/D converter 15 is increased, and an adder circuit 21 is provided between the A/D converter 15 and the switch 16. This is because the buffer memory 22 is arranged.

The output of the sample/hold circuit 14 is sent to the A/D converter 15.
is converted into a digital signal by

The sample/hold circuit 14 and A/D converter 15 are
It is under the control of the microcomputer 25 and operates in synchronization with a clock signal sent from the microcomputer 25. This operating frequency, that is, log amplifier 1
The sampling frequency of the radiation image information taken in through the image recording medium 3 is set to be twice or more the frequency of the grid imaged on the film when recording the radiation image information on an image recording medium, for example, a film. Here, the sampling means 24 in the present invention is formed by a sample/hold circuit 14 and an A/D converter 15.

The addition circuit 21 performs addition processing between the data in the buffer 7 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 into the buffer memory 22 again. . buffer 7 memory 2
Of the two output bits, the lower several bits are discarded, and the upper several bits are input to the switch 16 disposed at the subsequent stage. This means division of the data in the buffer memory 22. In other words, adder 21 and buffer 7
The memory 22 performs averaging processing of the output of the A/D converter 15. Here, the averaging processing means 23 in the present invention is formed from an adding circuit 21 and a buffer memory 22.

The structure of the equipment in front of the detector 2 is shown in Fig. 7(a) and (b).
) can be applied as is.

In the above configuration, first, the sample/hold circuit 1
4 and the A/D converter 15 (sampling frequency) are made equal to those of the conventional device.

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

First, the contents of the buffer 7 memory 22 are cleared by the microcomputer. When the A/D converter 15 outputs the first data, the value enters the buffer memory 22,
It is 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 adds the data to the buffer memory 22.
Rewrite the contents of the memory 22.

When the third and fourth pieces of data are output from the A/D converter 15, the contents of the buffer 7 memory 22 are replaced with the added data in a similar operation. When the contents of the buffer 7 memory 22 become the value obtained by adding the fourth data, it must be divided by 4 to average it, but in this case, the last two digits of the output of the buffer 7 memory 22 are truncated. The value may be sent to the next stage switch 16. That is, if the quantization number of the A/D converter 15 is 10 bits, the buffer memory 22 is set to 12 bits, and the upper 10
Only the bits need to be sent to the subsequent stage. Incidentally, in order to add and average eight pieces of data, it is sufficient to set the buffer 7 memory 22 to 13 bits and discard the last three digits.

Since the process of this circuit is controlled by the microcomputer 25, it is easy to perform the above operations at optimal timing. The subsequent operations of each part are similar to those of the conventional device (see FIG. 8).

According to the test results of the inventors of this application, the difference in density (R maximum temperature and minimum density) when a film with 60 grids/cm is measured using a conventional device with a laser beam diameter of 200 μm and a sampling pitch of 200 μm. difference) is 0
．． The difference in density was 22, but the density difference could be reduced to 0.04 by performing an arithmetic average ffi calculation on four pieces of data under the same sampling pitch condition. In other words, by the averaging process described above, it is possible to reduce artifacts caused by the grid to the extent that they do not affect interpretation and diagnosis. Furthermore, by performing the above averaging process, noise that enters the detector 12, fluctuations in X-ray quanta during X-ray shadows (radiation image information recording on film), or blackened silver on the film can be eliminated. Image quality deterioration caused by fluctuations in read data due to the graininess of particles can also be reduced at the same time. Therefore, it is possible to obtain 1q of read images suitable for interpretation and diagnosis. Moreover, when compared with the conventional device, in terms of hardware, the addition circuit 21 and the buffer 7 memory 22 are
There is also the advantage that there is no need for a significant increase in cost, since only the following are added.

Next, the sample/hold circuit 14 and the A/D converter 1
The effect when the operating frequency of No. 5 is made higher than that of the conventional device will be explained.

For example, if the sampling pitch is 50 μm (the conventional sampling pitch is 200 μm, the sampling pitch will be 1/4, and the sampling frequency will be 4
), the sampling theorem is satisfied, and 60 pieces/c
No artifacts occur due to the m grid. However,
This sampling output (output of the A/D converter 15) is taken into the averaging processing means 23, where the averaging processing of the four pieces of data is performed, and the processing result is input to the switch 16. .

In this way, the (@ image) caused by the grid is further reduced compared to the case of only the averaging process described above, and furthermore, the image quality deterioration caused by noise etc. can be reduced by the averaging process described above. Because of this, extremely good read images can be obtained.Also, in the case of only the above-mentioned averaging process,
Since the sampling frequency remains the same as the conventional device, the time required for film measurement is four times that of the conventional device, but by increasing the sampling frequency four times, the measurement time becomes the same as that of the conventional device.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and that various modifications can be made.

For example, in the above embodiments, a film was used as the image recording medium, but the present invention can also be applied to a case where a medium other than a film, such as an imaging plate containing a stimulable phosphor, is used.

Furthermore, in the above embodiment, the case where a grid of 60 lines/cm was imaged was explained, but if a grid with a lower resolution, for example, a grid of 28 to 40 lines/ctn, is imaged, the Nyquist frequency will be Since it goes down, it becomes even more advantageous.

[Effects of the Invention] As detailed above, according to the present invention, false images caused by the grid, the influence of noise that enters the detector, and the fluctuation of the X-ray beam during X-ray tracing, etc. Accordingly, it is possible to provide a radiation image reading device that aims to reduce deterioration in image quality of read images caused by.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the main parts of a radiation image reading device that is an embodiment of the present invention, Fig. 2 is a diagram of the intensity characteristics of a laser beam, and Figs. 3 and 4 are explanations of the relationship between the grid and the laser beam. Figure 5 is a characteristic diagram showing the relationship between the calculated density difference and the laser beam diameter, Figure 6 is a block diagram of the system configuration of the image processing device, and Figures 7 (a) and (b) are the configurations of the conventional device. The explanatory diagram, FIG. 8, is a block diagram of the main parts of the conventional device, and FIG. 9 is a waveform diagram for explaining generation of false images caused by the grid. 10...Film (image recording medium), 23...Additional averaging processing means, 24...Sampling means. Figure 2 Figure 3 Figure 4 Figure 8 (4Hz): Figure 9

Claims (2)

[Claims] (1) In a radiation image reading device that reads radiation image information from an image recording medium by scanning an image recording medium on which radiation image information is recorded with a laser beam and sampling the radiation image information, multiple What is claimed is: 1. A radiographic image reading device comprising: an averaging processing means for averaging sampling outputs of radiographic image information for pixels. (2) Claim 1, further comprising sampling means for sampling radiographic image information at a frequency that is at least twice the frequency of a grid imaged on the image recording medium when recording the radiographic image information on the image recording medium. The radiation image reading device described above.