JPH10192267A - X-ray unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To distribute X-ray dose so as to increase S/N of the three dimensional image of the target area of a subject against the identical X-ray total sum, by controlling the radiation dose so as to obtain an X-ray image with a prescribed X-ray relative noise value based on an image intensity within a prescribed area of the X-ray image. SOLUTION: An X-ray controller 611 is connected to an image data collecting high speed imaging control circuit system 603 and an X-ray tube 612 and supplies X-ray tube supply voltage to the X-ray tube 312 based on a control signal from the image data collecting high speed imaging control circuit system 603. The image data collecting high speed imaging control circuit system 603 collects an X-ray image converted into digital signals, calculates the imaging condition, controls a rotation gantry 604, an optical system diaphragm 634, a TV camera 624, and an X-ray controller 611, and controls the irradiation dose so as to obtain an X-ray image with a prescribed X-ray relative noise value based on the image intensity within a prescribed area of the X-ray image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an X-ray apparatus,
In particular, the present invention relates to an X-ray apparatus capable of obtaining a high-quality X-ray image while suppressing an X-ray dose applied to a subject in imaging of a region (a region of interest) where the examiner is most interested. is there.

[0002]

2. Description of the Related Art Conventional X-ray devices include an X-ray tube and a two-dimensional X-ray tube.
2. Description of the Related Art There has been an X-ray fluoroscopic apparatus in which a two-dimensional X-ray image of a subject is seen through or continuously photographed from various directions with respect to the subject by using a pair of ray detectors. Further, there has been an X-ray rotary imaging apparatus that continuously captures a two-dimensional X-ray transmission image of a subject while rotating around the subject with an X-ray tube and a two-dimensional X-ray detector as a pair. In these X-ray apparatuses, it is possible to display an image obtained by imaging in real time or to continuously display the image after imaging.

Further, there has been a cone-beam CT apparatus having the above-mentioned X-ray rotary imaging apparatus as a measurement system and having a three-dimensional image reconstruction means as an image processing system. This apparatus can image the three-dimensional distribution of the X-ray absorption coefficient inside the subject from a series of two-dimensional X-ray transmission images taken.

In addition, an X-ray CT apparatus having a one-dimensional X-ray detector or a detector array comprising a plurality of one-dimensional detectors and measuring one or more X-ray tomographic images at a time. was there. However, in this X-ray CT apparatus, repetitive measurement was necessary to image the three-dimensional distribution of the X-ray absorption coefficient. On the other hand, a cone beam CT apparatus uses a two-dimensional X-ray for reconstructing a large number of X-ray tomographic images.
Since a line transmission image can be collected at a time, a three-dimensional image can be captured in a shorter time.

[0005] Such a cone beam CT apparatus includes, for example, JAMIT Frontier '95', 2
There has been a cone beam CT apparatus using a two-dimensional X-ray detector disclosed on pages 3-28 using a detector comprising an X-ray image intensifier, an optical lens system, and a television camera. In addition, a two-dimensional X-ray detector disclosed on page 109 of BME Vol. 33, Special Issue (34th Annual Meeting of the ME Society of Japan) includes a fluorescent plate, an optical lens system, and a television camera. There was a cone beam CT device used.

However, the dynamic range of the two-dimensional X-ray detector is smaller than that of the one-dimensional X-ray detector used in the X-ray CT apparatus. Cannot be detected. For this reason, the two-dimensional X-ray detector has lower density resolution of the measurement data than the one-dimensional X-ray detector. For this reason, the cone beam CT
The density resolution of a three-dimensional image obtained by the apparatus is inferior to that obtained by imaging using a CT apparatus having a one-dimensional X-ray detector. As a result, in the conventional cone-beam CT apparatus, imaging cannot be performed under the conditions of the subject where the amount of X-rays absorbed by the subject is large and the X-ray transmittance is small, and the maximum subject thickness that can be imaged is reduced. was there.

[0007] On the other hand, imaging conditions for performing rotational imaging using a two-dimensional X-ray detector could in principle be the same as those of a general X-ray CT apparatus. Moreover,
2. Description of the Related Art In rotational imaging using a two-dimensional detector, as a conventional technique for improving the density resolution of an object having a small X-ray transmittance and increasing the maximum thickness of an object that can be imaged, an X-ray dose is generally used in X-ray fluoroscopy. The diversion of the automatic exposure control means used for controlling the exposure has been considered. That is, when the X-ray absorption by the subject is large, the concept is to automatically increase the X-ray dose and increase the image level to compensate for the narrow dynamic range of the detector.

An X-ray apparatus using this automatic exposure means is described, for example, in Journal of the Japanese Society of Radiological Technology, Vol. 45, No. 8, No. 1014.
Page. In this X-ray apparatus, an optical sensor is installed inside an optical lens system that constitutes a two-dimensional X-ray detector, and the average luminance in an area of interest on an output phosphor screen of an X-ray image intensifier is measured by the optical sensor. Then, the X-ray tube voltage is controlled so that the output value of the optical sensor becomes constant.

When the concept of the automatic exposure means is applied to a rotary photographing apparatus or a cone beam CT apparatus, when the body thickness of the subject increases at a predetermined rotation angle and the X-ray absorptivity in the region of interest increases, the optical sensor Output value decreases. The level of the image is increased by increasing the amount of X-ray emitted from the X-ray tube by performing control to automatically increase the X-ray tube voltage to compensate for this. Therefore, the narrow dynamic range of the two-dimensional X-ray detector can be compensated.

Japanese Patent Application Laid-Open No. 53-126291 discloses a general X-ray CT apparatus which changes the X-ray dose for each imaging angle in order to reduce the X-ray dose applied to the subject. I have. In this X-ray CT apparatus, first,
X-ray imaging of the subject is performed as preliminary measurement. Next, this X
Based on the line image, information on the cross-sectional shape of the subject or X-ray absorption (X-ray absorption information) is created in advance. In this measurement, the X-ray dose incident on the detector was kept constant by controlling the application time of the voltage applied to the X-ray tube based on the cross-sectional shape or the X-ray absorption information.

[0011]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

In order to improve the S / N of a three-dimensional image of a region of interest with respect to the same sum of X-rays in a rotational imaging measurement system used in a cone beam CT apparatus, the distribution of X-rays and the image level must be adjusted. Should be adjusted. Here, the total X-ray dose refers to the total sum of X-ray doses used for imaging at all angles in a series of rotation imaging.

However, the rotary photographing apparatus and the cone beam CT apparatus provided with the automatic exposure means, and the X-ray CT apparatus described in Japanese Patent Application Laid-Open No. 53-126291 are not suitable for capturing one X-ray image. It has been intended to capture an X-ray image with as high an image quality as possible. That is, in the above-described conventional X-ray apparatus, the distribution of the X-ray dose is not adjusted so that the S / N of the three-dimensional image of the region of interest is appropriate for the same total X-ray dose. There is a problem that the density resolution of the reconstructed image cannot be further improved. Further, there is a problem that the X-ray dose applied to the subject cannot be further reduced.

In fluoroscopy and continuous radiography, in the automatic exposure of the logic for increasing or decreasing the X-ray dose in response to the time change of the characteristics of the subject, the X-ray tube voltage changes, and the image contrast of the same subject site is changed. Was changed.

In the measurement system of the X-ray apparatus, the X-ray dose is appropriately set for each imaging angle, and the image signal level is adjusted to maximize the dynamic range of the detector for the set X-ray dose. It should be. In order to adjust the image signal level, it is desirable to adjust the optical aperture in the optical system to adjust the camera incident light level.

A digital X-ray apparatus having a mechanism for adjusting the level of incident light on a camera is disclosed in Japanese Patent Laid-Open No. 4-33604.
No. 5 publication. In this digital X-ray imaging apparatus, the X-ray irradiation dose is controlled by the automatic exposure described above. On the other hand, the amount of light incident on the television camera is controlled by providing an optical diaphragm mechanism on the front of the television camera and controlling the optical diaphragm mechanism. A specific control method is to adjust the optical aperture based on the ratio between the maximum value of the video signal output from the television camera and the peak value of the video signal. However, in the digital X-ray imaging apparatus, the control of the X-ray dose applied to the subject and the control of the dose input to the television camera are performed separately.
Although the dynamic range of an AD converter that converts an X-ray image into a digital signal can be used to the utmost, the problem relating to automatic exposure control cannot be solved, so that the present invention is different from the present invention.

When the X-ray tube voltage is changed, the quality of X-rays, that is, the distribution of X-ray quantum energy changes. X
When the tube voltage increases, the average value of the X-ray quantum energy increases. As a result, the X-ray absorption coefficient of the target portion and the background portion of the subject generally decreases, and the X-ray absorption coefficient of the target portion and the background portion generally decreases. The ratio of the coefficients had changed. Therefore, the value of the absorption coefficient obtained by the three-dimensional reconstruction is inaccurate and varies depending on the position. As a result, there is a problem that the dispersion of the image is increased and the density resolution is reduced as compared with the case where the X-ray dose is controlled while the tube voltage is kept constant.

An object of the present invention is to provide a technique capable of realizing the distribution of X-rays such that the S / N of a three-dimensional image of a region of interest of a subject increases with respect to the same total X-rays. It is in.

Another object of the present invention is to provide an X-ray irradiating object.
An object of the present invention is to provide a technique capable of reducing a dose.

Another object of the present invention is to provide a measurement system having a two-dimensional X-ray detector having a limited dynamic range, in which the limited dynamic range of the detector is used to the maximum extent in imaging at each angle. It is an object of the present invention to provide a technique capable of simultaneously setting an X-ray dose and an image level.

Another object of the present invention is to provide an X-ray apparatus capable of improving the density resolution of an X-ray image.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0023]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

In the following description, the imaging means is X
This is a means for generating a line transmission image.

(1) In an X-ray apparatus for irradiating an X-ray to an object to obtain an X-ray image of the object, X-ray irradiating means for irradiating the object with X-rays, an X-ray image of the object And an irradiation dose control unit that controls the irradiation dose so as to obtain an X-ray image with a predetermined relative X-ray noise value based on the image intensity in a predetermined region of the X-ray image. .

(2) In an X-ray apparatus for irradiating an X-ray to an object to obtain an X-ray image of the object, X-ray irradiating means for irradiating the object with X-rays, an X-ray image of the object Imaging means for obtaining an X-ray image, irradiation dose control means for controlling an irradiation dose such that an X-ray image having a predetermined X-ray relative noise value is obtained based on the image intensity in a predetermined area of the X-ray image, Signal control means for controlling an incident dose and / or a signal amplification factor based on an image intensity in a predetermined area of the line image so that an analog signal before digitization in the image pickup means becomes a predetermined value or less. I do.

(3) In the X-ray apparatus according to the above (2), the signal control means calculates the X-ray relative noise value based on a maximum value of an image intensity in a predetermined area of the X-ray image. Set.

(4) In the X-ray apparatus according to any one of the above (1) to (3), the irradiation dose control means sets the minimum value of the image intensity in a predetermined area of the X-ray image. Based on this, the X-ray relative noise value is set.

(5) In the X-ray apparatus according to any one of the above (1) to (4), the X-ray image is one or more X-ray images taken immediately before.

(6) In the X-ray apparatus according to any one of the above (3) to (5), based on the X-ray image, a predicted X-ray image to be captured next is converted to a primary straight line or 2
X-ray image predicting means for generating using a curve equal to or more than the following, wherein the irradiation dose control means converts a minimum value of image intensity in a predetermined area of the predicted X-ray image into a predetermined reference condition. Is calculated, and the ratio of the second converted value obtained by converting the minimum value of the image intensity in the predetermined area of the X-ray image into the reference condition is calculated, and the product of the ratio and the X-ray dose under the reference condition is calculated. The irradiation dose is calculated from the calculation.

(7) In the X-ray apparatus according to any one of the above (3) to (5), the irradiation dose control means calculates a ratio between the second converted value and the reference value. Then, feedback control is performed to calculate the irradiation dose from a product operation of the ratio and the X-ray dose under the reference condition.

(8) In the X-ray apparatus according to the above (1) or (2), the X-ray relative noise value is set based on an X-ray image of the subject taken in advance.

(9) In the X-ray apparatus according to the above (1) or (2), the X-ray relative noise value is obtained in the past with information on the subject obtained by measurement other than X-ray imaging. The setting is made based on the irradiation dose of X-ray imaging.

(10) In the X-ray apparatus according to any one of the above (1) to (9), an irradiation dose value and an incident dose or an amplification factor which can be set in the X-ray apparatus; A settable range storing means for storing an irradiation dose value and an incident dose or an amplification factor when the set irradiation range is exceeded, wherein the calculated irradiation dose value and the incident dose or the amplification ratio exceed the settable range. In this case, the irradiation dose control means and the output value control means use a value stored in the settable range storage means as a calculated value.

(11) In the X-ray apparatus according to any one of the above (1) to (10), the irradiation dose control means controls an X-ray tube pulse width in the X-ray irradiation means.

(12) In the X-ray apparatus according to any one of the above (1) to (10), the irradiation control means controls an X-ray tube voltage value in the X-ray irradiation means.

(13) In the X-ray apparatus according to any one of the above (1) to (12), rotating means for rotating the X-ray irradiating means and the imaging means around a subject, Reconstructing means for reconstructing a tomographic image of the subject from the X-ray image.

(14) In the X-ray apparatus according to any one of the above (2) to (13), the signal control means is an optical aperture or an amplifier gain.

According to the above-mentioned means (1), (4) to (6) and (10), the image intensity in a predetermined area of the predicted X-ray image to be photographed next, which is generated by the X-ray image prediction means, The irradiation dose control means converts the minimum value of the image intensity within a predetermined area of the predicted X-ray image into a predetermined reference condition based on the first condition.
And the second value obtained by converting the minimum value of the image intensity in a predetermined region of one or more X-ray images captured immediately before to the above-described reference condition.
Is calculated from the product of the ratio and the X-ray dose under the reference condition, and the X-ray irradiating means irradiates the X-ray with the irradiation dose to the subject. X-ray distribution can be realized such that the S / N of the three-dimensional image of the region of interest increases with respect to the same total X-ray dose. Therefore, the X-ray dose applied to the subject can be reduced, and the density resolution of the captured X-ray image can be improved.

At this time, the calculated irradiation dose value is
If the irradiation dose value exceeds the settable range in the X-ray apparatus, the irradiation dose control unit sets the value stored in the settable range storage unit as the irradiation dose value. Even when the value falls outside the settable range of the X-ray apparatus, it is possible to minimize a decrease in the density resolution of the X-ray image.

On the other hand, the irradiation dose control means calculates a ratio between the first conversion value and the reference value, and performs feedback control for calculating the irradiation dose from a product operation of the ratio and the X-ray dose under the reference condition. However, almost the same effect as described above can be obtained.

The details of the above-described effects will be described later.

According to the above-mentioned means (2) to (6) and (10), based on the image intensity in a predetermined area of the predicted X-ray image to be photographed next generated by the X-ray image prediction means, A first conversion value obtained by the irradiation dose control unit converting the minimum value of the image intensity in a predetermined area of the predicted X-ray image into a predetermined reference condition; and a first conversion value in the predetermined area of one or more X-ray images taken immediately before The ratio of the minimum value of the image intensity to the second conversion value obtained by converting the minimum value into the above-described reference condition is calculated, and the irradiation dose is calculated from the product operation of the ratio and the X-ray dose under the reference condition. Since the subject is irradiated with the X-ray of the irradiation dose, the distribution of the X-ray dose can be realized such that the S / N of the three-dimensional image of the region of interest of the subject increases with respect to the same total X-ray dose.

Further, based on the maximum value of the image intensity in a predetermined region of the X-ray image, the output value control means controls the incident dose or the incident light so that the analog signal before digitization in the image pickup means becomes a predetermined value or less. And / or by controlling the signal amplification factor, the limited dynamic range of the detector can be maximally utilized in imaging at each angle.

Therefore, the setting of the X-ray dose and the image level can be performed simultaneously.

On the other hand, the irradiation dose control means calculates a ratio between the first converted value and the reference value, and feedback control for calculating the irradiation dose from a product operation of the ratio and the X-ray dose under the reference condition. However, almost the same effect as described above can be obtained.

According to the above-mentioned means (11), the change of the irradiation dose is controlled by the pulse width of the pulse voltage applied to the X-ray irradiation means. Can be prevented.

According to the above-mentioned means (13), in addition to the above-described effects, the density resolution of the captured X-ray image can be improved, so that a three-dimensional reconstructed image with high density resolution can be obtained. .

According to the above-mentioned means (14), the analog signal before digitization in the imaging means can be easily controlled, and the dynamic range of the detector can be used to the maximum.

(Principle) The calculation process of the three-dimensional image reconstruction, which is one form of the X-ray apparatus, will be described below. In the calculation process and the final image, the X-ray absorption characteristics of the subject in each imaging direction and each imaging direction are shown. The relationship between the X-ray dose and the variance of the data will be described, and the effectiveness (effect) of the present invention will be described.

In X-ray rotation imaging, X-ray absorption projection images are taken from various directions in order to determine the value of a three-dimensional image of the X-ray absorption coefficient. The number of X-ray absorption projection images to be taken is N
And FIG. 1 shows a model of shooting from the i direction. FIG.
For simplicity, the paper surface shows the rotation orbit plane of the X-ray tube,
The cross section of the two-dimensional model is displayed two-dimensionally.

In FIG. 1, reference numeral 201 denotes an object; 202, an X-ray source; 203, an X-ray detector;
05 is the direction of the X-ray source viewed from the rotation center, 206 is the image reconstruction point P of interest, 207 is the direction of the X-ray beam of interest from the X-ray source S to point P, and 208 is the X-ray beam of interest to the rotation center. The angle α, 209, which forms the X-ray beam heading, is a chord indicating the position where the focused X-ray beam passes through the subject 201, 21.
0 denotes an X-ray quantum number n _i (α) detected per channel by an X-ray beam from the i direction, and 211 denotes a raw projection data output signal I _i (α) in the i direction. Also, L in FIG.
_i (α) represents the length of the string 209, and μ represents the X-ray absorption coefficient of the subject.

The raw projection data I _i (α) (where i =
1,..., N) are expressed by the following equation 1 using the X-ray quantum number n _i (α).

[0054]

[Number 1] _{I i (α) = c 0} · n i (α) + ε ····· (1) However, c ₀ is a constant that controls the optical diaphragm, epsilon is the number of bits at the time of A / D converter This is circuit noise including noise due to restriction.

FIG. 2 is a diagram for explaining the flow of data processing from rotation X-ray imaging with a cone beam CT to calculation of values of a three-dimensional image and display of the three-dimensional image. Based on this, the flow of data processing will be described.

However, in FIG. 2, elements which are not directly related to the S / N ratio of the image, such as the positional relationship of the measurement system and the correction of the inherent distortion of the detector, which are problems of the present invention, are described in order to simplify the explanation. Omitted.

First, while rotating the X-ray source 202 and the detector 203 around the subject 201, the X-ray
A line image is captured (step 301).

Next, in step 302, the average value of the noise is separately measured, and the expected value E (ε) of the noise under the same conditions as when the raw data I _i (α) is measured is calculated. Correct by subtraction. The correction at this time can be calculated by the following equation (2).

[0059]

J _i (α) = I _i (α) −E (ε) (2) However, in the noise correction according to the expression (2), the number of bits at the time of A / D conversion is limited. Noise components cannot be corrected.

When the circuit noise correction data J _i (α) is based on the fact that the X-ray quantum number follows the Poisson distribution, the expected value E {J _i (α)} and the variance V {J _i (α)} are The following equations (3) and (4) are obtained, respectively.

[0061]

(Equation 3)

Where V (ε) in equation (4) is the variance of circuit noise.

Next, logarithmic conversion is performed (step 30).
3). The conversion at this time is represented by the following equation (5).

[0064]

P _i (α) = − c ₁ · ln (J _i (α)) (5) where P _i (α) indicates a projected image after logarithmic transformation.

Next, the non-uniformity of the beam intensity and the sensitivity of the detector is corrected for the projection image P _i (α) (step 3).
04). In this correction, a sensitivity image obtained by performing logarithmic conversion on an image obtained by performing noise correction on an image obtained without placing the subject separately from the main measurement is described above. This is performed by subtracting from P _i (α). However, it is obtained from the analysis result that the non-uniformity correction data Q _i (α) at this time is represented by the following equations (6) and (7).

[0066]

(Equation 5)

Next, a convolution operation is performed (step 305). This convolution operation is represented by the following equation (8).

[0068]

(Equation 6)

In the equation (8), w (k) is a convolution filter, and k is a sampling interval ts.
Indicates the distance in units of. This distance k is the value of Shepp & Logan as a typical convolution filter.
When the filter of (1) is used, the following equation (9) is obtained.

[0070]

(Equation 7)

The expected value and the variance of the convolution result are expressed by the following equations (10) and (11), respectively.

[0072]

(Equation 8)

Next, backprojection calculation is performed (step 30).
6). Generally, the number of projections used for image reconstruction is N, XY
A reconstructed image of a point (x, y, z) on the Z space is represented by Y (x,
y, z) and the corresponding convolution data is described as c ₁ · μ · S _i (x, y, z) for convenience, the reconstructed image Y (x, y, z) is given by the following equation (12). , X-ray doses do not depend on the distribution method.

[0074]

(Equation 9)

On the other hand, the variance V ｛Y (x, y,
z)｝ is given by the following equation (13).

[0076]

(Equation 10)

However, the first term of the equation (13) is a term not related to the circuit noise, and the second term is a term relating to the influence of the circuit noise.

On the other hand, the relative noise of the image is given by the following equation (1).
4) is defined on the left side, and its contents are on the right side.

[0079]

[Equation 11]

Here, the denominator of the equation (14) is a term that depends only on the X-ray absorption characteristics of the subject and the convolution filter, and is irrelevant to the measurement method. On the other hand, the numerator of the formula (14) is an X-ray quantum number n _i (x, y, z) (where n = 1,...) Measured by imaging from each direction.
, N) and a constant c ₀ depending on the circuit noise standard deviation σ _i (ε) and the circuit gain. Here, n _i (x, y, z) is given by the following equation (15).

[0081]

(Equation 12)

In the equation (15), n _0i is the X-ray quantum number at the position where the thickness of the subject is zero in the imaging from the i direction, and is proportional to the X-ray dose used for the imaging from the i direction. .

On the other hand, in the conventional cone-beam X-ray CT apparatus, since n _0i is not changed, the distribution is uniform and constant irrespective of i, and the following equation (16) is obtained.

[0084]

(Equation 13)

Here, n _T is the total X-ray dose.

On the other hand, in the present invention, the imaging dose is distributed according to the subject, and n _0i that makes equation (14) smaller is given under the condition of the following equation (17).

[0087]

[Equation 14]

[0088] Here, if the second term in the root of the molecule of formula (14) is negligible compared to the first term, i.e., the standard deviation of the circuit noise sigma (epsilon) is then compared to c _0, If it is negligibly small, n that minimizes equation (14)
_0i is analytically calculated from Schwartz's inequality by the following equation (1)
8).

[0089]

(Equation 15)

As is apparent from this equation, in order to optimize the S / N at a certain point of interest, instead of equation (16),
According to this equation (18), an X-ray dose that is inversely proportional to the square root of the X-ray transmittance may be allocated. However, the minimum value at this time is represented by the following equation (19).

[0091]

(Equation 16)

Therefore, the ratio between the minimum value of the equation (19) and the value σ _c according to the conventional method is given by the following equation (20).

[0093]

[Equation 17]

As is clear from the above description, by distributing the X-ray intensity which is inversely proportional to the square root of the X-ray transmittance to each imaging, the relative noise represented by the equation (14) is reduced, and the image noise is reduced to the ideal. The minimum value. However, the information on the X-ray transmittance at the position of interest is obtained from the ratio of a measurement image photographed (measured) with the subject arranged and a blank image photographed under the same X-ray conditions without the subject arranged. Can be.

On the other hand, the effect of the case where the second term cannot be ignored was confirmed by simulation.

FIGS. 3A and 3B are diagrams for explaining a simulation method. FIGS. 3A and 3B show X-rays passing through two kinds of target positions for a subject simulating a chest. The beam is shown.

The cross-sectional shape of the simulated subject shown in FIG. 3 has two circular regions 402 and 403 having an elliptical outer shape 401 and simulating a lung field and having no absorption therein, and a circular region simulating a spine. It has 404. However, it is assumed that the shape of the subject is symmetric with respect to the vertical axis. The focus position is the rotation center 405 in FIG. 3A, and the center position of one lung field in FIG. 3B. Lines 411 to 420 in FIG. 3A indicate the positions of the X-ray beam passing through the region of interest 405 at intervals of 10 degrees from 0 to 90 degrees of the rotation angle of the X-ray source.
On the other hand, straight lines 421 to 430 in FIG. 3B show the positions of the X-ray beam passing through the region of interest 406 at intervals of 10 degrees from 0 to 90 degrees of the rotation angle of the X-ray source.
The radius of rotation of the X-ray source is 72 cm.

A polygonal line 501 in FIG. 4A represents an X-ray dose simulating the subject shown in FIG. 3 by a rotating X-ray source at every 10 degrees shown in FIG. 3 and inversely proportional to the square root of the X-ray transmittance. The distribution result of the X-ray dose in the case of imaging is calculated, and the average value of the X-ray dose is normalized to 1 and displayed. In the data in this plane, a range of 6.85 degrees on both sides from the center of the visual field was set as the region of interest, and the X-ray transmittance used the minimum value in the region of interest. The standard deviation of the circuit noise was 1, the full scale of the image was 1023, and the number of X-ray quanta per pixel was used as a parameter. The simulation result shows that the X-ray intensity has a steep peak near 0 degree and a wide peak ranging from 60 to 120 degrees. Due to the symmetry of the subject, the data is approximately symmetric at multiples of 90 degrees.

A polygonal line 502 in FIG. 4A shows an example of the set value of the efficiency of the optical diaphragm (iris). The relative value indicates the result of setting the constant value so that the maximum value in the region of interest does not exceed the saturation level of the measurement system. It can be seen that the increase and decrease of the polygonal lines 501 and 502 are independent. This indicates that the optimum value can be independently determined for the increase / decrease of the X-ray dose and the efficiency of the optical diaphragm.

FIGS. 4B and 4C show the ratio between the image noise obtained by the above-described method and the noise of the conventional method, respectively, for the point of interest 405 in the center of the visual field and the point of interest 406 in the lung field. It is what I sought.

According to the present method, in radiography at a typical X-ray dose, there is almost no difference from the conventional method in the central part of the visual field, but the noise is significantly reduced in the lung field compared with the conventional method.

Thus, the circuit noise, that is, the equation (1)
It can be seen that even when the second term of 3) cannot be ignored, the effect of the X-ray distribution by the above-described method is very large.

Next, the number of images to be used and the characteristics at that time will be described below.

When only the immediately preceding image is used, only one image data is used, so that a control circuit is easily realized. When the angle pitch in the rotation imaging is small, it functions as a sufficiently accurate predicted image.

When using a total of two images, the immediately preceding image and the immediately preceding image, first, a predicted image is generated using the current average change rate information. Next, by predicting the feature amount, the accuracy of prediction of the next image is improved and the density resolution of the image is improved as compared with the case where only the immediately preceding image is used.

When a total of three images including the immediately preceding image, the immediately preceding image, and the two preceding images are used, a predicted image is generated by estimating a change in the rate of change in the future, and the characteristic Predict the amount. In this case, the accuracy of prediction is further improved as compared with the case where only two images are used, so that the density resolution of the image can be further improved. Also, it functions as a predicted image with sufficient accuracy even when the angle pitch in rotational imaging is large.

[0107]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) of the invention.

In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

(Embodiment 1) FIG. 5 is a view for explaining a schematic configuration of a rotary imaging apparatus which is an X-ray apparatus according to Embodiment 1 of the present invention. In particular, FIG. FIG. 5B is a diagram illustrating a schematic configuration of the apparatus, and FIG. 5B is a diagram illustrating a schematic configuration of an X-ray image measurement system.

In FIGS. 5A and 5B, 6
01 is an X-ray generator system (X-ray irradiation unit), 602 is an X-ray image measurement system (imaging unit), 603 is an image data collection / high-speed imaging control circuit system (irradiation dose control unit), and 604 is a rotating gantry ( 605, an X-ray controller, 612, an X-ray tube, 621
Is a scattered radiation shielding grid, 622 is an X-ray image intensifier (hereinafter referred to as X-ray II), 623 is an optical system, 624 is a television camera, 631a is a first primary lens, and 631b is a second lens. , 632 denotes a mirror, 634 denotes a secondary lens, and 634 denotes a secondary lens.

In FIG. 5A, the X-ray generator system 60
Reference numeral 1 denotes an X-ray control device 611 and an X-ray tube 612. The X-ray control device 611 is connected to the image data acquisition / high-speed imaging control circuit system 603 and the X-ray tube 612, and the image data acquisition / high-speed imaging control circuit system 60
An X-ray tube supply voltage is supplied to the X-ray tube 612 based on the control signal from the X-ray tube 3. The X-ray tube 612 is fixed to the rotating gantry 604.

The X-ray image measuring device system 602 includes a scattered radiation shielding grid 621 and an X-ray image intensifier 62.
2. It is composed of an optical system 623 and a television camera 624. The X-ray image measuring system 602 is fixed to the rotating gantry 604 so as to face the X-ray tube 612.

Image data collection / high-speed photographing control circuit system 60
Reference numeral 3 is connected to a television camera 624, and collects X-ray images converted into digital signals (digital information) by the television camera 624. The image data acquisition / high-speed imaging control circuit system 603 performs imaging condition calculation and controls the rotating gantry, optical system aperture, television camera, and X-ray generator. Image data collection / high-speed shooting control circuit 60
Reference numeral 3 has a configuration and a function unique to the present invention. The details will be described later.

The rotating gantry 604 rotates the X-ray tube 612 and the X-ray image measurement system 602 around the subject holding bed 605 by the power of a rotation driving device (not shown).

In FIG. 5B, a scattered radiation shielding grid 621 is a well-known radiation shielding grid.
I. 622 on the input surface.

X-ray I. I. 622 is a well-known X-ray I.O.
I. The image of the radiation incident from the input surface is converted into an optical image and output from the output surface.

The optical system 623 includes a first primary lens 631a and a second primary lens 63 that constitute a tandem lens system.
1b, a secondary lens 632, a mirror 633, and an optical stop 634. In the present optical system, the first primary lens 631a is an X-ray I.D. I. 622 is disposed on the side of the output surface, and an optical image emitted from the output surface enters. The optical system 623 is a known optical system.

The television camera 624 has a CCD as an image sensor.
This is a well-known television camera using an image sensor element, and is disposed on the secondary lens 632 side of the optical system 623.

Note that the photographing operation of the rotary photographing apparatus according to the first embodiment is performed by the image data collection / high-speed photographing control system 60.
3 in that it is performed based on the control signal.
Since the operation is the same as that of a well-known rotary imaging device, the description is omitted.

FIG. 6 is a block diagram for explaining a schematic configuration of an image data acquisition / high-speed photographing control circuit system according to the first embodiment. Reference numeral 101 denotes a control personal computer; 102, a camera synchronization signal control circuit; Is a camera interface, 104 is a frame memory for storing image data, 105
Denotes an inter-image operation unit (X-ray image prediction means), 106 denotes an operation area designation register, 107 denotes a photographing condition restriction condition setting register (settable range storage means), and 108 denotes a digital signal operation unit operation unit (DSP operation unit). , 109 are operation result registers, 110 is an external device control unit, and 115 is a personal computer interface.

In FIG. 6, a control personal computer 101 is a well-known information processing device, and controls a television camera 624, an X-ray control device 611, a rotary drive device (not shown) of the rotary gantry 604, and the like, and a captured image and three-dimensional image. A reconstructed image or the like is displayed.

The television camera synchronization signal control circuit 102
This is a well-known television camera synchronization signal control circuit, and controls a shooting mode, an optical aperture, and the like of the television camera 624 via the camera interface 103. However, in the present embodiment, the operation mode of the television camera 624 is 12 bits, 40 MHz, and 512 × 512 pixels.

The camera interface 103 is a well-known TV camera interface circuit for converting the signal format of the image data collection / high-speed shooting control system 603 into the signal format of the TV camera 624. Therefore, the camera interface 103 is connected to the personal computer interface 1
15, the image data storage frame memory 104, the arithmetic unit 105, the television camera synchronization signal control circuit 102, and the television camera 624.

Image data storage frame memory 104
Is, for example, a frame memory using a well-known semiconductor memory. In the present embodiment, 512 × 512
Pixels have a capacity to continuously collect 288 or more 12-bit images.

The inter-image calculation unit 105 is composed of a frame memory for calculating photographing conditions, and an inter-image weighting / subtraction unit for performing calculations on the images stored in the calculation frame memory. Ask. Therefore, the inter-image calculation unit 105 is connected to the camera interface 103, the frame memory 104 for storing image data, the calculation area designation register 106, and the DSP calculation unit 108.

The calculation region designation register 106 is a well-known register for storing, for example, a calculation region input from the control personal computer 101 by the examiner.
And connect to PC interface.

Restriction condition setting register 107 for photographing conditions
Is a register for storing an initial value, a current value, an upper limit value and a lower limit value regarding the X-ray pulse width, and an initial value, a current value, an upper limit value and a lower limit value regarding the optical aperture. I do. Therefore,
The shooting condition restriction condition setting register 107 is connected to the personal computer interface 115 and the DSP calculation unit 108.

The DSP operation unit 108 is an operation unit composed of a well-known digital signal processor. The DSP operation unit 108 calculates the maximum value of the pixel value indicating the image intensity in the operation area with respect to the current image and the image obtained by the inter-image operation unit. Calculate the minimum value. Therefore, the DSP operation unit 108 is connected to the inter-image operation unit 105, the photographing condition restriction condition setting register 107, and the operation result register 109. Note that the DSP
The details of the arithmetic unit 108 will be described later.

The operation result register 109 is, for example, a well-known semiconductor memory, and stores the X-ray pulse width for the next image photographing determined by the DSP operation unit 108 and the optical aperture for the next image photographing.

[0130] The external device control unit 110 includes the X-ray control device 6.
11 and the rotation control device of the driving device of the rotating gantry 604 is controlled. Therefore, the external device control unit 11
The X-ray generator control unit included in 0 outputs a TTL level pulse having the same pulse width as the X-ray pulse width. The output timing is controlled by a CPU (not shown). The pulse width in the case of continuous measurement is 0.3 ms to 5 ms.
It is. In addition, single-shot measurement is also possible. Moreover,
An optical diaphragm device control unit included in the external device control unit 110 outputs a DC voltage corresponding to an aperture value to the optical diaphragm device. The control voltage range at this time is 5.0 V to 1
0.0V. However, open at 5.5V or less (φ78
Above) and is reduced to φ10 or less at 10.0 V.

Next, FIG. 7 shows a flow for explaining the operation of the image data acquisition and high-speed photographing control circuit system according to the first embodiment. Hereinafter, based on FIG. 7, the present embodiment shown in FIG. The operation of the image data acquisition / high-speed shooting control circuit system according to the first embodiment will be described.

First, before the measurement is started, the external device control unit 110 of the image data collection / high-speed photographing condition control device system
Performs rotation control operation of the rotating gantry. That is, the rotating gantry in a stationary state starts a rotating operation, and starts rotating imaging from a state where the rotating gantry passes a predetermined position at a predetermined time. In a typical measurement, digital signal images (A _k (where k = 0,..., 277) of 288 512 × 512 pixel, 12-bit, 40 MHz CCD cameras)
Are collected continuously at a rate of 60 frames per second.

At this time, the arithmetic frame memory 104
Always overwrites and holds the current image, that is, the image taken immediately before, the image before one frame, and the image two frames before. The calculation frame memory 104
Always holds the image obtained by the above-described inter-image operation, that is, the predicted image.

On the other hand, the operation area designation register 106 designates an operation area for executing an operation described later by using four variables. FIG. 8 is a diagram for explaining parameters relating to the calculation area at this time.

Next, image processing is performed by the image data collection / high-speed imaging control circuit system. This processing is performed in real time when the i-th image A _i is measured, and the imaging conditions of the next image, that is, X-rays It is a calculation example when determining the pulse width α _{i + 1} and the optical stop (area) β _{i + 1} .

(1) First step: The current images A _i and 1 are stored in the photographing condition calculation frame memory of the calculation unit 105.
Two images A _i-1 before the frame are held (801).
This is for predicting the next image using these two images.

(2) Second step: The four coordinate parameters h, v, and
An operation area E (m, n) specified by x and y is determined (802). A typical example of this calculation area is 3 in the center of the image.
It is 84 pixels (horizontal) × 256 pixels (vertical). However, this calculation area is set so as to include a photographed part desired to have a good image quality and not to include, for example, a peripheral part such as a part where halation occurs.

(3) Third step: For the image A _{i in the} frame memory for calculating the photographing conditions, the maximum value ma in the calculation area is calculated.
xA _i and the minimum value minA _i are obtained (803).

(4) Fourth Step: Image A _i and Image A _i-1
Is used to obtain an image to be captured next, that is, a predicted image (predicted X-ray image) B _{i + 1} ^* (804).

The method of calculating the predicted image B _{i + 1} ^* is as follows.
Obtaining transformation coefficients f _i for obtaining an image, assuming the shooting in the initial condition (standard condition). This calculation method is
The following equation (21) is obtained.

[0141]

(Equation 18)

Here, α ₀ is the initial value of the X-ray pulse width, β ₀
Is the initial value of the optical aperture, α _i is the current X-ray pulse width, and β _i is the current optical aperture. Note that fi _-1 is calculated by the following equation (2)
It is assumed that the value is previously obtained by the calculation of 2).

[0143]

[Equation 19]

Here, α _i-1 indicates the X-ray pulse width one frame before, and β _i-1 indicates the optical stop one frame before.

Next, according to equation (23), an image to be taken, that is, the next image is extrapolated to a straight line by using two images, the image taken immediately before and the image taken one image before the image. Predict by The calculation formula at this time is as follows.

[0146]

(Equation 20)

Therefore, the above-described predicted image B _{i + 1} ^* can be calculated.

(5) Fifth step: The maximum value maxB _{i + 1} ^* and the minimum value minB of the predicted image B _{i + 1} ^* in the calculation area
_{i + 1} ^* is obtained (805).

(6) Sixth step: DSP operation unit 108
, A correction coefficient g _i for the initial X-ray pulse width is obtained by the following equation (24). Also, the following equation (2)
According to 5), the X-ray pulse width candidate α _{i + 1} ^* for the next imaging is obtained. Thereafter, the optical stop candidate β is calculated by the following equation (26).
Continue to find _{i + 1} ^* . However, Expression (24) is the first
3 shows the calculation of the ratio between the converted value of the second and the second converted value.

[0150]

(Equation 21)

The above-mentioned expression (26) means that the optical aperture is set so that the maximum value of the image does not change even when the X-ray transmittance and the X-ray dose of the subject change.

(7) Seventh step: DSP operation unit 108
At α _{i + 1} ^* and the photographing condition control condition setting register 1
07 relating to the X-ray pulse width stored in ma
xα and the lower and upper limit value minα, and β
_{i + 1} ^* , upper limit value maxβ, lower limit value min regarding optical aperture
β and the maximum change amount βv that can be changed in one frame time
Is determined. Specific determination conditions at this time are the following (a) to (h). Based on the results, the feasible X-ray pulse width α _{i + 1 of the} next imaging and the optical aperture β _{i + 1} And decide. FIG. 9 shows a state of the determination at this time. Note that the following (a) to (h) correspond to the regions (a) to (h) in FIG.

[0153]

(Equation 22)

(A) When γ _{i + 1} ^* ≧ maxα · β _{u, i + 1}

[0155]

(Equation 23)

(B) When γ _{i + 1} ^* ≦ minα · β _{l, i + 1}

[0157]

(Equation 24)

(C) minα ≦ α _{i + 1} ^* ≦ maxα and β
_{l, i + 1} ≤ β _{i + 1} ^* ≤ β _{u, i + 1}

[0159]

(Equation 25)

(D) The case other than the above, and β
_{When i + 1} ^* ≧ β _{u, i + 1}

[0161]

(Equation 26)

(H) In the case of the above (d), α _{i + 1} ^*
<Minα

[0163]

[Equation 27]

(F) In cases other than the above, ie, β _{i + 1} ^*
≤ β _{l, i + 1}

[0165]

[Equation 28]

(G) In the case of (f) described above, α
_{When i + 1} ^* > maxα

[0167]

(Equation 29)

On the other hand, the linear extrapolation by the equation (23) can be changed to the following equation (44) to make an extrapolation by a quadratic curve.

[0169]

[Equation 30]

At this time, setting values when the X-ray dose and the optical aperture are calculated beyond the limit values of the apparatus, for example,
The reason why (a) and (b) are set on the line where the product of the X-ray dose and the optical aperture is constant is that the deterioration of the image quality is minimized as compared with the case where other setting values are set. Because you can.

Next, FIGS. 10 and 11 show an example of a time sequence in the rotary photographing apparatus of the first embodiment. Hereinafter, the rotation of the first embodiment will be described with reference to FIGS. 10 and 11. The photographing operation of the photographing device will be described.

FIG. 10A is a diagram showing a timing sequence at the time of ultra-high-speed photographing. In this case, the external synchronization signal is 16.67 ms (16.67 ms in FIG. 10A).
7 ms) to the television camera 624 by the camera synchronization signal control circuit 102 (t0). The X-ray irradiation pulse (X-ray irradiation shown in the figure) is provided from the external device control unit 210 in synchronization with the external synchronization signal (t0).
At the same time, the external synchronization signal causes the TV camera 624 to
Image storage on the CD is performed (t0). The image accumulation time is set to be equal to or longer than the maximum X-ray pulse width in the main measurement based on an instruction from the control personal computer 101. CCD
When the accumulation operation is completed (t2), image reading from the CCD is started (t2). The CCD reading is performed, for example, from the top to the bottom of the screen. However, the shaded areas in the figure indicate image calculations (steps 801 to 805 in FIG. 7) performed simultaneously with image input (t3 to t4). The shooting condition calculation indicates the calculation by the DSP calculation unit 108 (steps 806 to 807 in FIG. 7) (t4 to t5). The movement of the optical diaphragm is executed when the photographing condition calculation ends (t
5) The movement is completed by the time of the external synchronization signal of the next frame (t6).

According to the above-described sequence of FIG. 10A, during the period between t4 and t6, the next frame (t6
Since the X-ray pulse width and the optical aperture for imaging in (t7) can be controlled, ultra-high-speed control is possible.

FIG. 10B is an example of a sequence in the case where the sequence of FIG. 10A is divided into two frames and executed. In this sequence, after completion of the imaging condition calculation (t1), the end of the next X-ray irradiation is waited (t3).
After the end of the X-ray irradiation, the optical stop is moved to realize a new optical stop condition (t4), and the movement ends by the next X-ray irradiation (t5).

As described above, in this sequence, control is performed with a delay of one frame time. Therefore, as compared with the sequence of FIG. 10A, the image storage time and the optical stop moving time are each set to about 2 times.
Can be twice as long. In this case, as the image prediction calculation in the DSP calculation unit 108, it is appropriate to predict the next frame, that is, the frame two frames ahead. For this purpose, the above-mentioned first-order extrapolation equation (23) is given by
The following equation (45) or equation (46) is used.

[0176]

(Equation 31)

The equation (44) for the quadratic extrapolation is given by the following equation (4)
Change to 7).

[0178]

(Equation 32)

FIG. 11A shows another example of a sequence in which the control is divided into two frame times and the control is executed with a delay of one frame time. In the control shown in FIG. 11A, the image reading and the image calculation proceed simultaneously with the X-ray irradiation of the next frame (t6 to t7).

Therefore, in this sequence, FIG.
Since there is no waiting time as in (b) and the time can be further used for image storage or image reading and calculation time of the calculation area, the X-ray irradiation dose range can be increased or
By expanding the region of interest, there is an effect that a higher quality image can be obtained.

The sequence shown in FIG. 11B is another example of a sequence in which the control is divided into two frame times and the control is executed with a delay of one frame time. In this sequence, only one group of the odd-numbered frame and the even-numbered frame is controlled, and the succeeding frame is shot under the same shooting conditions as the immediately preceding frame. For example, the first X
Using the data of the X-ray irradiation (t0 to t1), the next second X-ray irradiation (t3 to t4) has the same conditions as the first X-ray irradiation (t0 to t1) one frame before, and The conditions of X-ray irradiation (t5 to t6) of No. 3 are controlled. On the other hand, the optical diaphragm movement can be performed during X-ray irradiation. Therefore, even when the response time of the optical diaphragm is longer than one frame time, an X-ray apparatus to which the present invention is applied can be provided.

However, in this case, the primary extrapolation equation (2)
3) becomes the above-mentioned equation (46).

As described above, in the rotary photographing apparatus according to the first embodiment, the DSP computing section 108 firstly sets the maximum value maxA in the computing area E set by the examiner on the image A _i photographed immediately before. _i and the minimum value minA _i are determined. Next, from the two images A _i and A _i−1 taken immediately before, for example, by the DSP calculation unit 108, a predicted image B _{i + 1} ^* to be obtained in the next shooting is obtained. next,
The DSP calculation unit 108 calculates the maximum value maxB _{i + 1} ^* and the minimum value minB _{i + 1} ^* in the calculation area of the predicted image B _{i + 1} ^* , and obtains the maximum value maxB _{i + 1} ^* and the minimum value minB _{i + 1} ^* ,
And the above-mentioned maximum value maxA _i and minimum value min
An X-ray pulse width candidate α _{i + 1} ^* and an optical stop candidate β _{i + 1} ^* are obtained from A _i . Next, from the X-ray pulse width candidate α _{i + 1} ^* and the optical stop candidate β _{i + 1} ^* and the condition stored in the condition setting register, the feasible X-ray pulse width α _{i + 1} and the optical stop β _{i Find +1} . Next, the external device control unit 110
Based on this value, by controlling the irradiation X-ray dose of the X-ray tube 612 and the optical aperture 634, the next X-ray image is actually taken, so that the S / S of the image in the calculation region that is the region of interest of the subject is obtained. X so that N increases for the same total X-ray dose
A dose distribution can be realized.

In addition, the dynamic range is limited to 2
In a measurement system having a dimensional X-ray detector, it is possible to set an X-ray dose and an image level in a limited dynamic range of the detector in imaging at each angle.

Therefore, the density resolution of the X-ray image can be improved.

In this embodiment, the X-ray dose is controlled by controlling the X-ray pulse width. However, the present invention is not limited to this. It goes without saying that the configuration may be such that the X-ray dose is controlled by controlling the X-ray tube voltage value.

(Embodiment 2) FIG. 12 is a block diagram for explaining a schematic configuration of an image data acquisition / high-speed imaging control circuit system of a rotary imaging apparatus which is an X-ray apparatus according to Embodiment 2 of the present invention. Reference numeral 1101 denotes a control personal computer; 1102, a camera synchronization signal control circuit; 1103, a camera interface 1104; a frame memory for storing image data;
Reference numeral 110 denotes an external device control unit.

However, in the following description, only parts different from the rotary photographing apparatus according to the first embodiment will be described.

In FIG. 12, a representative example of the operation mode of the television camera 1111 is 12 bits, 40 MHz, 512 × 512 pixels as in the first embodiment.

The functions of the control personal computer 1101 and the camera synchronization signal control circuit 1102 control the camera 1111 through the camera interface 1103, and the digital images output from the camera are continuously collected in the storage frame memory 1104. Frame memory for storage 1
104 represents a 512 × 512 pixel, 12-bit image
It is possible to collect eight or more sheets continuously.

In the present embodiment, the value of the X-ray relative noise of the region of interest in the X-ray transmission image obtained by the main measurement is set to be substantially equal to the value of the preset X-ray relative noise. For this purpose, X-ray transmission images from a plurality of directions are preliminarily photographed with a small amount of X-rays. Here, the X-ray relative noise indicates a ratio of a noise component in a signal component of the X-ray image.

Under the conditions of the preliminary photographing, an X-ray dose that satisfies the preset condition of the relative X-ray noise is calculated from the image of the preliminary photographing and used. In addition, for the condition in which the preliminary photographing is not performed, the condition is obtained by interpolation from the condition obtained from the preliminary photographing. Using the obtained measurement conditions, for example, a series of photographing is performed under program control set in the control personal computer 1101.

Next, the operation of the image data collection / high-speed photographing condition control system according to the second embodiment will be described with reference to FIG.

In the image data collection / high-speed shooting condition control system according to the second embodiment, both the preliminary shooting and the main shooting are rotated by the external device control unit 1110 of the image data collection / high-speed shooting condition control system before starting the measurement. Performs gantry rotation control operation. That is, the rotating gantry in a stationary state starts a rotating operation, and starts rotating imaging from a state where the rotating gantry passes a predetermined position at a predetermined time. In a typical example of the actual photographing, a digital signal image (A) of 288 512 × 512 pixels, 12 bits, 40 MHz CCD camera is used.
_k (where k = 0,..., 277)) are continuously collected at a rate of 60 frames per second.

Before or after the preliminary photographing, an X-ray noise relative value, an upper limit value and a lower limit value regarding the X-ray pulse width, and an upper limit value and a lower limit value regarding the optical aperture in the pixel region of interest in the main photographing are set. However, in the preliminary imaging, imaging is performed from a plurality of directions under the conditions of a fixed X-ray dose, an optical aperture, and an amplifier gain.

The control personal computer 1101 calculates both the maximum value and the minimum value in the calculation area of interest for the image obtained by the preliminary photographing. Next, from these values, the imaging X-ray dose, and the specification of the X-ray relative noise in the region of interest,
The X-ray condition and the optical aperture condition of the main imaging under the same subject condition (imaging angle) as the preliminary imaging are calculated. Next, the condition for which the preliminary photographing was not performed is obtained by interpolation based on the condition obtained from the preliminary photographing.

Next, for all the imaging angle conditions for performing the main measurement, the values that can be realized from the upper and lower limits of the X-ray pulse width and the upper and lower limits of the optical aperture are determined by the main measurement. The X-ray pulse width and the optical aperture are determined.

Using the measurement conditions obtained in the above-described procedure, a series of photographing is performed by, for example, program control. The measurement conditions at this time are sent to the external device control unit 1110 through the interface of the personal computer, and the X-ray controller 6
11 and the optical stop 634 are controlled.

Next, FIG. 13 shows a flow for explaining the operation of the image data acquisition / high-speed photographing control circuit system according to the second embodiment. Hereinafter, based on FIG. 7, the present embodiment shown in FIG. The detailed operation of the image data acquisition / high-speed shooting control circuit system according to the first embodiment will be described.

However, FIG. 13 shows the photographing condition of the main image, that is, the X-ray pulse when the measurement of the i-th preliminary measurement image D _0i is performed with the X-ray pulse width α ₀ and the optical aperture β _0. 9 shows an example of an operation of an algorithm for determining a width α _i and an optical stop (area) β _i .

The target specification of the relative X-ray noise in the region of interest of the main measurement image is R _i . Conditions for realizing the relative noise are obtained in advance by experiments. An example of a measurement condition to realize this relative noise, X-rays pulse width alpha _r, optical diaphragm beta _r, X-rays relative noise under this condition the image level when the R _r and D _r.

(1) First step: A calculation area E (m, m) specified by four coordinate parameters h, v, x, y
n) is determined (1201).

(2) Second step: For the preliminary measurement image D _0i , the maximum value maxD _0i and the minimum value minD in the calculation area
_0i is obtained (1202).

(3) Third step: An X-ray pulse width candidate α _i ^* is obtained by the following equation (48), and an optical stop candidate β _i ^* is obtained by the following equation (49) (1203).

[0205]

[Equation 33]

Here, h is the maximum value of the digital image.

(4) Fourth step: For the condition where the preliminary photographing was not performed, the condition is obtained by interpolation from the condition obtained from the preliminary photographing.

The above-described second to fourth steps are repeated for all the predicted images.

(5) Fifth step: Upper limit value maxα and lower limit value min for all α _i and X-ray pulse width
It is possible to determine the magnitude relationship between α and all optical stops β _i and the upper limit value maxβ, the lower limit value minβ, and the maximum change amount β _v that can be changed in one frame time with respect to the optical stops β _i. The X-ray pulse width α _i and the optical stop β _i for the next imaging are determined. This determination method is the same as in the above-described embodiment.

Next, the external device control unit 1110 controls the X-ray pulse width of the X-ray tube 612 to be α _i, and controls the optical diaphragm 634 to be β _i .
The X-ray dose can be distributed so that the S / N ratio of the image of the calculation region, which is the region of interest of the subject, increases with respect to the same total X-ray dose.

[0211] The dynamic range is limited 2
In a measurement system having a dimensional X-ray detector, it is possible to set an X-ray dose and an image level in a limited dynamic range of the detector in imaging at each angle.

Therefore, the density resolution of the X-ray image can be improved.

Next, FIG. 14 shows an example of a time sequence of control of the rotary photographing apparatus according to the second embodiment.
4, the operation of the rotary photographing apparatus according to the second embodiment will be described.

The external synchronizing signal is provided by the external camera synchronizing signal control circuit 1102 every 16.67 ms as in the first embodiment (t0). The X-ray irradiation pulse is output from the external device control unit in synchronization with the external synchronization signal (t0 to t1). At the same time, the external synchronization signal
The television camera 1111 stores images in the CCD (t0 to t2). The image storage time is set by the control personal computer 1101 to be equal to or longer than the maximum X-ray pulse width in the main measurement. When the CCD accumulation operation is completed (t2), C
Image reading from the CD is started (t2). Reading from the CCD is performed, for example, from the top to the bottom of the screen. The movement of the optical diaphragm is executed when the image reading is started (t2), and the movement is completed by the time of the external synchronization signal of the next frame (t3).

As described above, in the control sequence shown in FIG. 14, since the X-ray and the optical stop of the next frame can be controlled, ultra-high-speed control is possible.

(Embodiment 3) FIG. 15 is a view showing a schematic configuration of an X-ray detector of a rotary X-ray apparatus according to Embodiment 3.
The rotary imaging apparatus according to the third embodiment is different from the rotary imaging apparatus according to the first embodiment in that the X-ray detector has no optical diaphragm.

1501 is a scintillator, 1502 is a photodiode, 1503 is a first amplifier, 1504 is a changeover switch, 1505 is a second amplifier, and 1506 is an AD.
3 shows a converter.

FIG. 15 is a diagram showing one row of the two-dimensional detector taken out. The actual X-ray detector includes a scintillator 1501, a photodiode 1502,
A plurality of changeover switches 1503, a first amplifier 1504, a second amplifier 1505, and an AD converter 1506 are arranged in order.

In FIG. 15, a scintillator 1501 is a well-known scintillator, and a photodiode 150 for detecting light emitted from the scintillator is provided on one side.
2 are arranged.

The photodiode 1502 is a known photodiode, and its output is connected to the first amplifier 1503.

The first amplifier 1503 is a first-stage amplifier that converts a change in the resistance of the photodiode 1502 into a change in the output voltage, and the output is connected to a changeover switch. The first amplifier 1503 is connected to the photodiode 1
502 and one-to-one.

The changeover switch 1504 is connected to the first amplifier 15
03 is switched in order and the second amplifier 1505
This is a well-known changeover switch for connecting to the input of the switch.

The second amplifier 1505 is a well-known amplifier that amplifies the output of the first amplifier 1503 connected via the changeover switch, and the output is connected to the AD converter 1506. Further, the second amplifier 1505 can change the amplification factor based on the calculation result.

[0224] The AD converter 1506 is a well-known AD converter, and converts the voltage output from the second amplifier 1505 into a digital signal.

Next, the operation of the rotary imaging apparatus using the X-ray detector shown in FIG. 15 will be described only for the parts different from the rotary imaging apparatus of the first embodiment.

In the rotary imaging apparatus according to the third embodiment, since the X-ray detector has no optical stop,
Instead of changing the optical aperture, the gain (amplifier gain) of the second amplifier 1505 is controlled. Therefore, AD
Since the limited dynamic range of the converter 1505 can be used effectively, X-rays with a wide dynamic range can be imaged.

In the third embodiment, the amplification factor of the second amplifier 1505 is controlled. However, the present invention is not limited to this.
03 or first and second amplifiers 1503 and 150
It goes without saying that the gain of 5 may be controlled.

In addition to the first to third embodiments, the width of the subject and the thickness of the subject in the depth direction are determined in advance.
The main items that determine the X-ray transmittance are obtained by measurements other than X-ray imaging, and the program control of the X-ray dose value under similar conditions in the past can be applied as it is, or some programs can be modified. In addition, it can be applied.

Further, as for the setting of the calculation area E (m, n), for example, an image of a target is set on a three-dimensional image, and the target is photographed at any coordinate position in each projected image of the rotation photographing. It is needless to say that the coordinate position may be calculated, and the coordinate position may be set as the imaging part desired to obtain a good image quality.

In the present embodiment, the image used as the reference for obtaining the X-ray pulse width candidate α _{i + 1} ^* and the optical stop candidate β _{i + 1} ^* by the DSP calculation unit 108 is referred to as the predicted image B
_{i + 1} ^* , but is not limited to this. For example, the immediately preceding image A _i or the immediately preceding image A _i and the preceding image A _i-1 may be used as a reference. In this case, for example, the maximum value and the minimum value of the image A _i taken immediately before only, or image A _i taken immediately before
A so-called feedback control for calculating an X-ray pulse width candidate α _{i + 1} ^* and an optical stop candidate β _{i + 1} ^* from a value obtained by averaging the maximum value and the minimum value of the image A _i-1 and the preceding image A _i−1 Do.

Another method is based on measurement information obtained by directly measuring information relating to the X-ray transmittance such as the body thickness and the width of the subject, and the transmittance obtained from an X-ray image taken in the past. It goes without saying that the X-ray pulse width candidate α _{i + 1} ^* and the optical stop candidate β _{i + 1} ^* may be obtained.

In the present embodiment, a case has been described in which the present invention is applied to a typical X-ray rotary imaging apparatus. However, the present invention is not limited to this. The present invention is also applicable to a fluoroscopic apparatus and an X-ray CT apparatus. For example, when the present invention is applied to an X-ray fluoroscopy apparatus, the effects described in the above-described first to third embodiments can be obtained by setting the region of interest at the center of the body axis of the subject. Further, when the present invention is applied to an X-ray CT apparatus, a well-known reconstructing means for reading a transmission image around the subject from the image data storage frame memory 104 and reconstructing the transmission image is provided. , C of the subject
A T image, that is, a tomographic image, can be reconstructed. At this time, the X-ray CT image of the subject can be reconstructed under the imaging conditions described in the above embodiment.

In the X-ray rotation imaging according to the present invention, not only an imaging apparatus in which an X-ray tube and an X-ray image measurement system are paired and rotated around the subject, but also the subject is arranged on a rotary table. The X-ray tube and the X-ray image measurement system are opposed to each other with the rotary table interposed therebetween. At the time of measurement, the X-ray tube and the X-ray image measurement system remain stationary while the rotary table on which the subject is mounted rotates. Alternatively, the present invention is also applicable to a system that measures while repeating rotation and stationary in a step-like manner. Such a rotary table type device has an advantage that it can be easily manufactured at a low cost because the rotating portion is small. In addition, since the stationary state can be set at the time of measurement, there is an advantage that high-resolution imaging can be performed on an object that does not move or deform over time without any influence of the imaging system or the movement of the object.

As described above, the invention made by the present inventors is described below.
Although specifically described based on the embodiments of the present invention, the present invention is not limited to the embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the gist of the present invention. .

[0235]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) S of the three-dimensional image of the region of interest of the subject
X doses can be distributed such that / N increases for the same total X dose.

(2) The X-ray dose applied to the subject can be reduced.

(3) Dynamic range limited 2
In a measurement system having a two-dimensional X-ray detector, the setting of the X-ray dose and the image level can be made compatible so that the limited dynamic range of the detector is used to the maximum in imaging at each angle. .

(4) The density resolution of an X-ray image can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an imaging model when an object is imaged from a predetermined direction.

FIG. 2 is a diagram for explaining a flow of data processing from rotation X-ray imaging to calculation of a value of a three-dimensional image and display of the three-dimensional image in the cone beam CT apparatus.

FIG. 3 is a diagram for explaining a method of performing a simulation assuming the shape of a subject when a second term cannot be ignored;

FIG. 4 is a diagram for explaining the effect of the present invention when the second term cannot be ignored.

FIG. 5 is a diagram for explaining a schematic configuration of a rotary imaging apparatus which is the X-ray apparatus according to the first embodiment of the present invention.

FIG. 6 is a block diagram illustrating a schematic configuration of an image data acquisition / high-speed imaging control circuit system according to the first embodiment;

FIG. 7 is a flowchart for explaining the operation of the image data acquisition / high-speed imaging control circuit system according to the first embodiment;

FIG. 8 is a diagram for explaining parameters related to a calculation area specified by a variable of a calculation area specification register;

FIG. 9 is a diagram for explaining specific determination conditions in a DSP calculation unit.

FIG. 10 is a diagram illustrating an example of a time sequence in the rotary imaging device according to the first embodiment.

FIG. 11 is a diagram showing an example of a time sequence in the rotary imaging device of the first embodiment.

FIG. 12 is a block diagram for explaining a schematic configuration of an image data acquisition / high-speed imaging control circuit system of the rotary imaging apparatus which is the X-ray apparatus according to the second embodiment of the present invention.

FIG. 13 is a flowchart for explaining the operation of the image data acquisition / high-speed imaging control circuit system according to the second embodiment;

FIG. 14 is a diagram illustrating an example of a time sequence of control of the rotary imaging device according to the second embodiment.

FIG. 15 is a diagram illustrating a schematic configuration of an X-ray detector of the rotary imaging apparatus according to the third embodiment of the present invention.

[Explanation of symbols]

101, 1101 ... Control personal computer, 102, 1102
... camera synchronization signal control circuit, 103, 1103 ... camera interface, 104, 1104 ... frame memory for storing image data, 105 ... inter-image calculation unit, 106 ... calculation area designation register, 107 ... restriction condition setting register for shooting condition, 108 ... Digital signal operation unit operation unit
P operation unit), 109 ... operation result register, 110, 11
10: External device control unit, 115: PC interface, 201: Subject, 202: X-ray source, 203: Detector, 601: X-ray generator system, 602: X-ray image measurement system, 603: Image data collection・ High-speed shooting control circuit,
604: rotating gantry, 605: subject holding bed, 611: X-ray controller, 612: X-ray tube, 621
Scattered ray shielding grid, 622: X-ray image intensifier (hereinafter referred to as X-ray II), 623: optical system, 624: TV camera, 631a: first primary lens, 631b: second Primary lens, 632 ... optical aperture,
633: mirror, 634: secondary lens.

Claims (14)

[Claims] An X-ray apparatus for irradiating a subject with X-rays to obtain an X-ray image of the subject, comprising: an X-ray irradiating unit configured to irradiate the subject with X-rays;
Imaging means for obtaining a line image, and irradiation dose control means for controlling the irradiation dose so as to obtain an X-ray image having a predetermined X-ray relative noise value based on the image intensity in a predetermined area of the X-ray image. An X-ray apparatus, comprising: 2. An X-ray apparatus for irradiating an object with X-rays to obtain an X-ray image of the object, comprising: an X-ray irradiator for irradiating the object with X-rays;
Imaging means for obtaining a line image, and irradiation dose control means for controlling an irradiation dose so as to obtain an X-ray image having a predetermined X-ray relative noise value based on an image intensity in a predetermined region of the X-ray image, Signal control means for controlling an incident dose and / or an amplification factor of a signal based on an image intensity in a predetermined area of the X-ray image so that an analog signal before digitization in the image pickup means becomes a predetermined value or less. An X-ray apparatus comprising: 3. The X-ray apparatus according to claim 2, wherein the signal control unit sets the X-ray relative noise value based on a maximum value of an image intensity in a predetermined area of the X-ray image. An X-ray apparatus characterized by the above-mentioned. 4. The X-ray apparatus according to claim 1, wherein the irradiation dose control unit is configured to perform a control based on a minimum value of an image intensity in a predetermined area of the X-ray image. An X-ray apparatus, wherein the X-ray relative noise value is set. 5. The X-ray apparatus according to claim 1, wherein the X-ray image is one or more X-ray images taken immediately before. apparatus. 6. The X-ray apparatus according to claim 3, wherein a predicted X-ray image to be photographed next is set to one based on the X-ray image.
X-ray image predicting means for generating using a quadratic line or a quadratic or higher-order curve, wherein the irradiation dose control means
A first conversion value obtained by converting the minimum value of the image intensity in a predetermined region of the line image into a predetermined reference condition, and a first conversion value obtained by converting the minimum value of the image intensity in a predetermined region of the X-ray image into the reference condition. 2
An X-ray apparatus comprising: calculating a ratio of the irradiation value to the converted value; and calculating the irradiation dose from a product operation of the ratio and the X-ray dose under the reference condition. 7. The X-ray apparatus according to claim 3, wherein the irradiation dose control means calculates a ratio between the second converted value and the reference value, and Ratio and X in the reference condition
An X-ray apparatus, wherein feedback control is performed to calculate the irradiation dose from a product operation with the dose. 8. The X-ray apparatus according to claim 1, wherein the relative X-ray noise value is set based on an X-ray image of the subject captured in advance. 9. The X-ray apparatus according to claim 1, wherein the X-ray relative noise value is information on a subject obtained by measurement other than X-ray imaging and irradiation of X-ray imaging performed in the past. An X-ray apparatus characterized by setting based on a dose. 10. The X-ray apparatus according to claim 1, wherein an irradiation dose value and an incident dose or an amplification factor that can be set in the X-ray apparatus, and a settable range. A settable range storing means for storing an irradiation dose value and an incident dose or an amplification factor in the case where the calculated irradiation dose value and the incident dose or the amplification factor exceed the settable range. An X-ray apparatus, wherein a value stored in the settable range storage means is a calculated value. 11. The method according to claim 1, wherein
The X-ray apparatus according to any one of the preceding claims, wherein the irradiation dose control unit is configured to control X-rays in the X-ray irradiation unit.
An X-ray apparatus for controlling a line pulse width. 12. One of claims 1 to 10.
13. The X-ray apparatus according to claim 1, wherein the irradiation control unit controls an X-ray tube voltage value in the X-ray irradiation unit. 13. One of claims 1 to 12
The X-ray apparatus according to Item, wherein a rotating unit configured to rotate the X-ray irradiation unit and the imaging unit around the subject, and a reconstructing unit configured to reconstruct a tomographic image of the subject from the X-ray image An X-ray apparatus, comprising: 14. A method according to claim 2, wherein
The X-ray apparatus according to claim 1, wherein the signal control means is an optical diaphragm or an amplifier gain.