JP2877876B2 - Digital X-ray equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a digital X-ray apparatus that performs X-ray imaging on a stimulable phosphor and scans the stimulable phosphor with an excitation light to obtain an X-ray image. It is intended to be able to obtain a normal image even when reading the phosphor, and to make it possible to reduce the cost by enabling a polygon mirror by enabling high-speed scanning, An X-ray imaging unit, excitation light irradiation means, fluorescence detection means,
A digital X-ray apparatus having a data processing unit;
The photometric point P _i at time T _i, and metering the metering point P _i-1 of the previous time T _i-1, the time T _i-1 intervals time T _i and time Δt from the photometric point P _{i -1,} the photometric quantity of _{P i s i-1, s} i, the time emitted light of the accelerated phosphorescence fluorescent material is 1 / e (e is the base of natural logarithm) tau
And then, the true light emission amount K _i of the photometric point _{P i, K i = S i} -S i-1 ex
A correction means for outputting as p (−Δt / τ) is provided.

[Industrial applications]

The present invention relates to a digital X-ray apparatus, and more particularly to a digital X-ray apparatus that performs X-ray photography on a stimulable phosphor and scans the stimulable phosphor with excitation light to obtain an X-ray image.

In general, when obtaining information inside a living body by X-rays for diagnosing a disease, the fluorescent screen is irradiated with X-rays transmitted through the subject, thereby generating visible light, and exposing the silver halide film with the visible light, A so-called radiograph for observing a silver halide film as a development fixation is used.

By the way, instead of using the above-described silver halide film as a high sensitivity and high resolution X-ray imaging system in recent years,
After irradiating the stimulable phosphor (accumulative phosphor) with X-rays transmitted through the subject, the stimulable phosphor is scanned and irradiated with excitation light, and the stimulable phosphor emits energy accumulated by the X-rays. A digital X-ray apparatus that converts the optical signal into a digital signal and processes the optical signal is used.

The stimulated fluorescence used in such a digital X-ray apparatus is composed of components such as BaFBr: Eu ²⁺ , BaClBr: Eu ²⁺ , BaBr ₂ : Eu ²⁺ , and the energy of radiation such as X-rays is used. Upon receipt, they store some of that energy. This state is relatively stable, and is maintained for a while or for a long time in this state. When the stimulable phosphor is irradiated with the first light as the excitation light, the stored energy is emitted as the second light. At this time, a wide range of electromagnetic waves from infrared to ultraviolet as well as visible light is used as the first light.

Further, the second light emitted at this time also outputs electromagnetic waves of various wavelengths from infrared to ultraviolet due to the components of the stimulable phosphor.

[Conventional technology]

FIG. 7 shows an example of the digital X-ray imaging apparatus described above. In the figure, 11 is an X-ray generator for irradiating an object with X-rays, 12 is a stimulable phosphor, 13 is a stimulable phosphor transport mechanism, 14 is an optical system for reading an image of the stimulable phosphor, and 15 is an image. The input circuit system 16 indicates an image processing device, and the image information processed by the image processing device is hard-copied on an X-ray film as needed, displayed on a CRT,
It is stored on the optical disc 17.

The stimulable phosphor transport mechanism 13 erases the stimulable phosphor 12 from the erasing unit 13a,
It moves to the imaging unit 13b and the reading unit 13c, and the reading unit 13c emits light to the entire stimulable phosphor 12 to release the accumulated energy. In the imaging unit 13b, the stimulable phosphor 12 is irradiated with X-rays emitted from the X-ray generator 11 and transmitted through the subject 18. Then, in the reading section 13c, the laser light from the laser source 20 is scanned and irradiated on the stimulable phosphor 12 photographed by the scanning means such as the galvanometer mirror 21 and the light generated by the stimulable phosphor 12 The light is input to a photomultiplier tube 24 (photomultiplier) through a filter 23 that collects the laser light and collects the laser light, and amplifies the signal.

[Problems to be solved by the invention]

Incidentally, the above-mentioned digital X-ray apparatus has a problem that it takes a long time to read. This is because, as shown in FIG. 8, even if the excitation light is applied to the pixel region of the photostimulable phosphor and the excitation light is stopped momentarily after the photostimulated emission light is detected, the excitation light is stopped. This is because the emitted light continues to be emitted while being logarithmically attenuated even after the excitation light is stopped. Further, since the condensed light receiving system of the stimulated emission light is arranged on the scanning line of the excitation light, when the next pixel is irradiated with the excitation light, the stimulated emission light of the previous pixel and the pixel described above are irradiated. And the stimulable light of the next pixel is detected at the same time, and accurate image information of the pixel cannot be obtained. Therefore, the stimulable light of the previous pixel attenuates below the noise level of the device. This is because irradiation must be waited.

That is, the excitation light is radiated to a place where the stimulable phosphor is present, and the moment when the excitation light is radiated is t = 0, and the amount of the stimulable luminescence is K at that time. The light emission amount k (t) at t is represented as: k (t) = Kexp (−t / τ).

The time required for the stimulated emission light to decay to the first 1 / e (e is the base of the natural number) is τ, this time is, for example, 0.8 μs, and the noise level is 1/1000 of the maximum detection amount, ie, −. 60
If dB, the reading time t of one pixel is t = −2.303 log (1/1000) × 0.8 μs = 5.5 μs.

Here, assuming that the arrangement of pixels to be read on the stimulable phosphor is 2048 pixels per line, 2048 lines, and the excitation light scanning efficiency is 0.7, the total reading time T of the stimulable phosphor is T = 5.5 μ × ( 2048 × 2048) /0.7=30s. Ie
Reading 2000 lines in 30 seconds means 67 scans per second.

By the way, a polygon mirror used as a laser beam scanning means in a laser beam printer or the like is excellent in optical accuracy and easy to adjust, and is supplied at low cost because of its high productivity. However, when the rotation speed is low, for example,
If it is less than 2000 rpm, the jitter increases and it cannot be used. In general, since the polygon mirror has a pentagonal to decagonal shape, the number of scans per second when the polygon mirror is used is 330 to 670 times. At such a scanning speed, the polygon mirror cannot be used for the above-described reason. Therefore, scanning is performed using a galvanometer mirror as the scanning means. However, the galvanometer mirror must be adjusted according to the difference in surface accuracy when mounting the mirror on the shaft and the difference in vibration characteristics. There is a problem that the later adjustment is troublesome and the cost increases.

Therefore, the present invention assumes that a normal image can be obtained even when scanning the stimulable phosphor by scanning at a high speed, and by enabling high-speed scanning, a polygon mirror can be used to reduce costs. It is an object of the present invention to provide a digital X-ray apparatus capable of performing such operations.

[Means for solving the problem]

In the present invention, means for solving the above-described problem is, as shown in FIG. 1, an X-ray for performing X-ray imaging on a stimulable phosphor that absorbs and accumulates energy of X-rays transmitted through a subject.
An X-ray imaging unit 1, an excitation light irradiating unit 2 that scans and irradiates the stimulable phosphor imaged by the X-ray imaging unit 1 with an excitation light by using a polygon mirror, and detects emitted stimulable emission light. In a digital X-ray apparatus having a fluorescence detecting means 3 for outputting a photometric signal and a data processing unit 4 for processing the photometric signal and outputting image information, a photometric point P _i is set at a time T _i , the metering is metering point P _i-1 to the time T _i-1, the time from the time T _i-1
The interval T _i and time Delta] t, photometric s of each of the photometry points P _i-1, P _i
a _i-1, s _i, the time emitted light of the accelerated phosphorescence fluorescent material is 1 / e (e is the base of natural logarithms) and tau, the true light emission amount K _i of the photometric point P _i , K _i = S _i −S _i−1 exp (−Δt / τ).

[Action]

According to the present invention, the correction means, the photometric point P _i Time
To T _i, and photometric photometric point P _i-1 of the previous time T _i-1, time T
from _i-1 and the interval of time Δt of time T _i, each of the photometry point P _i-1, P _i
A photometric quantity s _i-1, s _i, emitted light of the accelerated phosphorescence fluorescent body 1
/ e (e is the base of natural logarithms) and tau the time satisfying the true luminescence amount K _i of the photometric point _{P i, K i = S i} -S i-1 exp (-Δt / τ)
As a result, it is possible to obtain a value in which the influence of the stimulating light at the photometry point before the photometry point to be read is corrected, and the scanning speed can be increased. Therefore, an image can be read at high speed, so that an inexpensive and easily adjustable polygon mirror can be used, and the cost of the digital X-ray apparatus can be reduced as a whole.

According to the experiment of the inventor of the present invention, even when there is continuous excitation light irradiation, the stimulating light emission amount is sampled at time t = t, and t and t + α are obtained regardless of the time α until the next sampling. It was found that it was possible to obtain only the information that was emitted during the time between.

That is, if the excitation light irradiation is suddenly stopped while the stimulated emission amount is measured in the continuous excitation scanning, any change in the amount of excitation light emission before that will always result from the moment the excitation light irradiation stops. It has been experimentally confirmed that there is a tailing of the amount of excitation light emission according to the above equation. From this, since the time constant of the temporal tailing of the excitation light emission at all locations is the same at all locations, the sum of photostimulated luminescence at all locations at a certain time t, that is, measured The sum proportional to the amount of stimulated light emission is affected by the temporal tailing of light emission at all locations that have emitted light in the past, and the temporal trailing of the sum at times after t also emits light in the past. Since the emitted light at all the places where the light is emitted is extracted and attenuated with the same time constant and shows a temporal tail, the information of the place scanned by the excitation light between t and time α after t is t + α
It can be obtained by subtracting the amount of temporal trailing of the light amount measured at t from the measured light amount of.

Therefore, if the amount of stimulated emission is sampled at certain time intervals (t ₁ , t ₂ ) and the measured light amounts are S ₁ S ₂ , and the information only between t ₁ and t ₂ is K _t1-t2 , K _t1−t2 = S ₁ −S ₂ exp [−τ (t ₁ −t ₂ )].

Here, S ₁ and S ₂ are measured values, and τ and (t ₁ −t ₂ ) are known values, so that K _t1−t2 can be obtained. Also, (t ₁ −
Whatever the value of t ₂ ), ie, no matter how short, the formula holds.

Therefore, if the above-described correction is performed, the influence of the previous pixel can be corrected no matter how short the sampling interval is.

〔Example〕

An embodiment of a digital X-ray apparatus according to the present invention will be described below with reference to the drawings.

FIG. 2 and FIG. 4 show a first embodiment of the digital X-ray apparatus according to the present invention. In this embodiment,
As in the prior art, the X-ray generator stimulable phosphor transport mechanism is the same as that shown in the prior art. In the present embodiment, a polygon mirror is used as a scanning unit in the optical system, and high-speed scanning is realized. In this embodiment, the signal from the photomultiplier is processed by each device shown in FIG. In FIG. 2, 31 is a photomultiplier tube, 32 is a preamplifier, 33 is a correction unit for performing the above-described correction processing, 34 log amplifier, 35 is an analog-to-digital converter, 36 is a frame memory, 37 is an image processing unit, and 38 is 4 shows an image display unit.

The metering in the present embodiment, the photometry value of the fourth in one pixel as shown in FIG assumed performed in 6 positions each preceding sampling _{point, K i = S i -S i} -1 exp (- Δt / τ), and the image processing is performed with the average value or the total value as the pixel information of the pixel.

Therefore, according to the present embodiment, as shown in FIG. 3A, the photostimulated light is converted into a signal by the optical converter (ST1, ST1).
2) After amplification by the preamplifier (ST3), the above-mentioned correction by the pre-metering point is performed (ST4), log processing is performed by the log amplifier (ST5), and the signal digitized by the A / D converter is framed. The image data is stored in the memory (ST6, ST7), image processing is performed, and the image data is displayed as an image (ST8, ST9).

Therefore, according to the present embodiment, the correction is performed so that the scanning can be performed at a high speed, so that the polygon mirror can be used as the scanning means, and the cost can be reduced. In addition to obtaining an image with a good noise-to-noise ratio, the image data of each photometric point is stored, so that when creating an enlarged image, the image data of each point is used. be able to.

Next, a second embodiment of the digital X-ray apparatus according to the present invention will be described. In this embodiment, the arrangement of each processing unit of the apparatus is the same as that shown in the first embodiment, but the procedure of the processing is changed. That is, in the present embodiment, as shown in FIG. 5, it is assumed that the photometry of each pixel is performed at one location in one scan, and the control system in the sub-scanning direction is adjusted to move the photostimulable phosphor 41 (sub-scan). (Scanning) is controlled to scan one pixel 42 a plurality of times, correction is performed by adjacent pixels, a plurality of photometric values are obtained for one pixel, and the average or the sum of the photometric values of each pixel is used as pixel information. Things.

By combining this embodiment and the first embodiment, photometry is performed at a plurality of locations in both the main scanning direction and the sub-scanning direction of one pixel, and the photometry data is corrected.
The average value or the sum thereof can be used as the image data of the pixel.

FIG. 6 shows a third embodiment of the digital X-ray apparatus according to the present invention.

In this embodiment, photometry is performed at a plurality of locations of the same pixel as in the first and second embodiments described above.
Using the average or the sum of the photometric values at these locations, correction of adjacent pixels is performed. At this time 1
The scanning time from the center point of a pixel to the center of the next pixel is Δt
Is to be corrected.

Although this method is not strictly accurate, according to experiments performed by the inventor, the effect of each stage can be obtained as compared with the case where no correction is performed. This can be considered to be because the variation in photometric data within one pixel is relatively small.

In addition, when there is a variation in the light collection efficiency in the light collection system, it is theoretically correct to perform the above correction after correcting the light collection efficiency, but it actually depends on the degree of the variation in the light collection efficiency. However, even if the light-collecting efficiency is corrected after performing the above-described correction, there is a sufficient effect of the correction.

In each of the above embodiments, the correction is performed before performing the log conversion. However, the correction according to the present invention can be performed in any process after sampling. For example, correction may be performed after converting the photometric data between ST11 to ST19 shown in FIG. 3 (2) into a digital signal (ST14) (ST15), or FIG. 3 (3) The correction may be performed after the data is stored in the frame memory (ST25) between the series of processes ST21 to ST29 shown in (2) (ST2).
6).

〔The invention's effect〕

As described above, according to the present invention, the digital X
In the line device, the photometry point P _i is set at time T _i , and the photometry point
The metering is P _i-1 at time T _i-1, the time T _i-1 and interval time Δt of time T _i from the photometric quantity s _i-1, s _i of each of the photometry points P _i-1, P _i age,
The time stimulated emission of the accelerated phosphorescence fluorescent material is 1 / e (e is the base of natural logarithms) and tau, the true light emission amount K _i of the photometric point P _i
Is output as K _i = S _i −S _i−1 exp (−Δt / τ), so that the effect of photostimulated light at the photometry point before the photometry point to be read is corrected. Value can be obtained, and the scanning speed can be increased. Therefore, an image can be read at high speed, so that a polygon mirror which is inexpensive and easy to adjust can be used, and the cost of the digital X-ray apparatus can be reduced as a whole.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a block diagram showing an embodiment of a digital X-ray apparatus according to the present invention, and FIG.
FIG. 4 is a flow chart showing the signal processing state of the digital X-ray apparatus shown in the figure and the signal processing state of another embodiment. FIG. 4 is a diagram showing the photometric state of the digital X-ray apparatus shown in FIG. FIG. 6 is a diagram showing a photometric state of a digital X-ray apparatus according to a second embodiment of the present invention. FIG. 6 is a diagram showing a photometric state of a third embodiment of the digital X-ray apparatus according to the present invention. FIG. 1 is a block diagram showing a configuration of a digital X-ray apparatus to which the present invention is applied, and FIG. 8 is a diagram showing a state of stimulated emission. DESCRIPTION OF SYMBOLS 1 ... X-ray imaging part 2 ... Excitation light irradiation means 3 ... Fluorescence detection means 4 ... Data processing part 5 ... Correction means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03B 42/02 H04N 5/32

Claims (4)

(57) [Claims] An X-ray imaging unit for performing X-ray imaging on a stimulable phosphor that absorbs and accumulates energy of X-rays transmitted through a subject, and a stimulable fluorescent image captured by the X-ray imaging unit. An excitation light irradiating means (2) for irradiating the body with excitation light by scanning using a polygon mirror; a fluorescence detecting means (3) for detecting emitted stimulating light and outputting a photometric signal; In a digital X-ray apparatus having a data processing unit (4) for processing a signal and outputting image information, a photometric point P _i is set to a time _Ti , and a previous photometric point P _i-1 is set to a time T _i-1. , The interval from time T _i-1 to time T _i is defined as time Δt, and the photometric light amounts s _i-1 and s _i at the respective photometry points P _i-1 and P _i are determined. The time when the emitted light becomes 1 / e (e is the base of natural logarithm) is τ
Digital to and to the true light emission amount K _i of the photometric point P _i, and _{K i = S i -S i-} 1 exp characterized in that a correcting means (5) for outputting as an (-.DELTA.t / tau) X-ray equipment. 2. A digital X-ray as claimed in claim 1, wherein photometry is performed a plurality of times during scanning of the range of one pixel, and a value based on the corrected value is averaged to obtain pixel information of the pixel. apparatus. 3. The digital X-ray apparatus according to claim 1, wherein one pixel is scanned a plurality of times, and values based on the corrected values are averaged to obtain pixel information of the pixel. 4. The digital X-ray apparatus according to claim 1, wherein a plurality of photometric operations are performed in one pixel, and a value based on the photometric value is corrected with a value based on the photometric value of the previous pixel to obtain pixel information. .