JPS6147537B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for reconstructing an X-ray tomographic image, and in particular to an apparatus for reconstructing an X-ray tomographic image by performing desired arithmetic processing.
The present invention relates to a device capable of reconstructing line tomographic images. In general, in the industrial and medical world, X-ray inspections are widely used to determine the internal structure of products and the human body.
Linear computerized tomography equipment (abbreviated as "CT") is being actively developed. By the way, in this type of conventional X-ray computerized tomography apparatus, first, as shown by the solid line in FIG. The X-ray projection distribution is measured by the X-ray detector c, and then, as shown by the chain line in FIG. 1, the X-ray generator a and the X-ray detector c are rotated by a predetermined angle α (for example, 1°). By irradiating the X-ray beam toward the X-ray inspection object b again from this position, the angle α is
After measuring the X-ray projection distribution when the distribution is moved by Arithmetic processing is performed using cloth, and then a tomographic image of the X-ray subject b is reconstructed based on the processing results. However, such a conventional X-ray computer tomography apparatus requires a large number of X-ray projection distributions in order to reconstruct a tomographic image of the subject b, which causes the following problems. (1) Since it takes a long time to collect data (several seconds to several minutes), for moving object b,
The tomographic image cannot be reconstructed. (2) Since the amount of X-ray exposure increases, if the subject b is a living body such as a human body, there is a risk of adverse effects on the living body. The present invention aims to solve these problems, and it is possible to obtain a highly accurate reconstructed image by simply using two X-ray projection distributions as data for reconstructing a tomographic image of a subject. An object of the present invention is to provide a multiple X-ray projection type tomographic image reconstruction device that can perform the following. For this reason, the multiple X-ray projection type tomographic image reconstruction apparatus of the present invention has a virtual tomographic plane S that includes the tomographic plane of the X-ray subject B and has m pixels vertically and n pixels horizontally. A multiple X-ray projection type tomographic image reconstruction device that obtains multiple X-ray projection distributions by irradiating unit X-ray beams from multiple directions, wherein the first unit X-ray beam is The above X should pass through at least one corner of the pixel.
A plurality of first unit X-ray beams are irradiated toward the object B to be inspected from a predetermined direction, and the X-ray The object B to be inspected is irradiated with a plurality of second unit X-ray beams from another predetermined direction, and the first and second units X are directed toward the object B to be inspected. X-rays for measuring a plurality of X-ray densities from one end to the other end of each of the first X-ray projection distribution D ₁ and the second X-ray projection distribution D ₂ obtained by irradiating a ray beam. A density measuring device is provided, and based on the X-ray density information from the X-ray density measuring device, the virtual tomographic plane S is divided into at least two
In order to calculate the X-ray absorption coefficient μ of each pixel constituting each virtual tomographic plane portion S ₁ , S ₂ , _the first basic pixel ₁ passes through only the first basic pixel 1. If the X-ray density obtained by one unit X-ray beam is the X-ray absorption coefficient μ of the first basic pixel ₁ , then the X-ray density _dkk for the pixels up to the kth (k is a natural number smaller than m and 2 or more) means for sequentially obtaining the X-ray absorption coefficient μ _k of the k-th pixel by subtracting the X-ray density d k _-1 from the second basic pixel m;
Let the X-ray density obtained by the second unit X-ray beam passing only through the second basic pixel m be the X-ray absorption coefficient μ _n of the second basic pixel m, and the X-ray density of the pixels up to the m-kth pixel d _n-k+1 A projective transformation device F is provided which has an arithmetic unit consisting of means for sequentially obtaining the X-ray absorption coefficient μ _rn-k of the m-kth pixel by subtracting the X-ray density d _nk from the projection transformation device F. In response to the signal from the conversion device F, the X
a reconstruction device H that reconstructs the tomographic image of the X-ray subject B by applying linear absorption coefficients μ ₁ to μ _no ; and a reconstruction device H that reconstructs the tomographic image of the X-ray subject B based on the output from the reconstruction device It is characterized by being provided with a display device J that displays tomographic images. Therefore, according to the small number of X-ray projection type tomographic image reconstruction apparatus of the present invention, the data acquisition time can be significantly shortened, so that a clear tomographic image can be reconstructed even for a moving X-ray object such as a heart. In addition, since the amount of X-ray exposure is very small, even if the subject to be examined by X-rays is a living body, there will be no adverse effect on it. Below, a small number of X-ray projection type tomographic image reconstruction apparatus as an embodiment of the present invention will be explained with reference to the drawings. FIG. 2 is a schematic diagram showing the measuring means of the X-ray projection distribution, and FIG. 3 is the system configuration. Figure, 4th and 5th
All figures are schematic diagrams for explaining the effects. As shown in FIG. 3 (a diagram corresponding to the claims), an X-ray inspection object B is positioned between an X-ray generation device A and an X-ray generation detector C. As shown by solid lines and chain lines in FIG. 2, X-rays can be irradiated from two predetermined directions to the
The first and second X-ray projection distributions D ₁ and D ₂ (see FIGS. 4 and 5) can be obtained by the X-rays that have passed through the X-rays. As shown in Fig. 5, this X-ray generator A has m units vertically (in the y-axis direction) within the x-y plane, which has an x-axis and a y-axis perpendicular to the x-axis within the same plane. X-ray inspection object B about a virtual tomographic plane S having n pixels horizontally (x-axis direction)
N/2 ( ₌ mn/2) first unit X-ray beams are irradiated from the direction of θ ₁ (=tan ^-1 m/2) with respect to the x-axis toward It irradiates N/2 second unit X-ray beams from the direction of = -tan ^-1 m/2), and the radiation quality (penetration power) is suitable for the X-ray inspection object B to be inspected. This apparatus A is equipped with a drive mechanism so that it can rotate around the X-ray subject B by a predetermined angle. Note that the first unit X-ray beam and the second unit X-ray beam are irradiated so as to pass through at least one corner of the pixel. In addition, the wavelength of the generated X-rays is proportional to the applied voltage, and the quality of the X-rays has come to be determined by the wavelength. When used, it is used in the range of 50,000 volts to 120,000 volts, and when used for non-destructive testing, it is used in the range of 100,000 volts to 300,000 volts. X-ray inspection object B refers to an object that is irradiated with X-rays and whose transmitted dose distribution (X-ray projection distribution) is measured to reconstruct an image in a desired tomographic plane. For example, in the case of medical diagnosis, it is a human body (generally a living body), and in the case of non-destructive testing, it is a so-called industrial product. Furthermore, as the X-ray detector C, an X-ray film, a scintillation detector, a semiconductor detector, a xenon gas detector, etc. are used. A drive mechanism is provided to allow rotation by a predetermined angle. By the way, the first X-ray projection distribution data _D1 obtained by the X-ray detector _C is determined by the X-ray projection distribution measuring means (X-ray density measuring device) E. From one end to the other, each value d _k (1) at mn/2 (=N/2) positions spaced at equal intervals w is measured,
By moving the X-ray generator A and the X-ray detector C from the above state, the second X-ray projection distribution data D ₂ obtained by this X-ray detector C can be obtained from the same X-ray projection distribution measurement. By means E, the second X
From one end of the line projection distribution D ₂ to the other, each value d _k (2) at mn/2 (=N/2) positions spaced at equal intervals w is measured. (See Figure 5). When the X-ray detector C is an X-ray film, the X-ray projection distribution measuring means E may be used to measure a plurality of X-ray density distributions (so-called X-ray photographs) obtained as darkening degrees on this film. A microdensitometer is used that can measure the value of . In the case of the present invention, since two X-ray density distributions are required, two X-ray films are required. In this way, the first and second X-ray projection distribution
From one end of D ₁ and D ₂ to the other, each value d _k (1) at a plurality of positions spaced at equal intervals w,
In addition to the above example, as a means of measuring d _k (2),
X-ray detector C transmits X-rays passing through X-ray inspection object B
In the case of a scintillation detector that receives radiation and outputs a signal corresponding to the X-ray concentration, one scintillation detector is connected to the first and second X-ray detectors.
It is possible to combine a mechanism that can move each of the ray projection distributions D ₁ and D ₂ from one end to the other, or to arrange a large number of scintillation detectors over the entire width of the X-ray projection distribution. It can be done. Furthermore, in the case where the X-ray detector C is a semiconductor detector that receives X-rays transmitted through the X-ray inspection object B and outputs a signal corresponding to the X-ray concentration, the above-mentioned scintillation detection can be used as the above-mentioned means. As in the case of detectors, one semiconductor detector and a mechanism for moving it may be combined, or a large number of semiconductor detectors may be arranged. Furthermore, when the X-ray detector C is a xenon gas detector, the above means includes one xenon gas detector and a mechanism for moving it, as in the case of the scintillation detector or semiconductor detector described above. Combinations and the arrangement of multiple xenon gas detectors may be used. In addition, if X-ray detector C is a combination of one scintillation detector, one semiconductor detector, or one xenon gas detector and a moving mechanism, each detector should be operated twice. scanning is performed,
If a large number of scintillation detectors, a large number of semiconductor detectors, or a large number of xenon gas detectors are provided, measurements are performed twice using these multiple detectors. The signals obtained in this way by the microdecintometer, scintillation detector, and semiconductor detector are analog signals, so in order to input them to a digital computer, this signal is converted to an analog-to-digital converter E' ( Below, “A/D
called a converter. ) is converted into a digital signal and then stored on a disk or the like. Next, data output d from this A/D converter
_k (1) and d _k (2) (digital signals) are respectively input to the projective transformation device F. This projective transformation device F divides the virtual tomographic plane S into at least two virtual tomographic plane parts S ₁ and S ₂ each consisting of a plurality of pixels based on the X-ray density information from the X-ray density measuring device, and Fault plane part S ₁ ,
In order to calculate the X-ray absorption coefficient μ of each pixel constituting S ₂ , the first unit X that passes only through the first basic pixel 1
Assuming that the X-ray density obtained by the ray beam is the X-ray absorption coefficient _μ of the first basic pixel 1, the X-ray density d _k to the means for sequentially obtaining the X-ray absorption coefficient μ _k of the pixel up to the k-th pixel by subtracting _k-1 ;
Let the X-ray density obtained by the unit X-ray beam be the X-ray absorption coefficient μ _n of the second basic pixel m, and the X-ray density d _n-k+1 to the X-ray density d _n for the pixels up to _{the nkth} pixel.
_-k to sequentially obtain the X-ray absorption coefficient μ _nk of the m-k pixels. Note that a specific example thereof is a digital computer containing a desired program. Here, mn/2 measured values d _k ( ₁ ) (one-dimensional data) on the first X-ray projection distribution D 1 and mn/2 measured values on the second X-ray projection distribution D ₂ d _k (2) (one-dimensional data), each X-ray absorption coefficient μ _k (two-dimensional We will explain the method for obtaining data). As shown in FIG. 5, with respect to the x-axis, the upper half plane is defined as one virtual tomographic plane half part S ₁ , and the lower half plane is defined as the other virtual tomographic plane half part S ₂ , in a predetermined direction relative to the x-axis. There are mn/2 first unit X-ray beams irradiated from θ ₁ (=tan ^-1 m/2), and also in another predetermined direction θ ₂ (=-tan ^-1 m/2) with respect to the x axis. Assume that there are mn/2 second unit X-ray beams irradiated from. Furthermore, the mn pixels that should constitute the virtual tomographic plane S are numbered sequentially starting from 1 as shown in Figure 5.
mn/2 first unit X-ray beams irradiated from θ ₁ direction, mn/2 pixels 1 to m/2, m+1 to 3/2 m, . . . (n-1)・
By determining the position of each of the above pixels so that they reach the X-ray detector C through the lower left corner of m+1 to mn-m/2, one virtual tomographic plane half _S1 is determined, and θ The mn/2 second unit X-ray beams irradiated from _two directions are applied to mn/2 pixels m to m/2, respectively.
The position of each pixel is determined so that it reaches the X-ray detector C through the upper left corner of +1,2m~3/2m+1,...,mn~(n-1)・m+m/2+1. Therefore, the other virtual tomographic plane half _S2 is determined. By determining each of the virtual tomographic plane halves S ₁ and S ₂ in this way, the virtual tomographic plane S is also determined. In this case, each unit X-ray beam is assumed to have the same mutual interval (sample point interval) w between the first and second unit X-ray beams. By the way, the first unit X-ray beam β
₁ is pixel 1 (this pixel 1 is called the first basic pixel)
Understand the relationship between the X-ray density d ₁ (1) obtained by this first unit X-ray beam β ₁ and the X-ray absorption coefficient μ ₁ of pixel 1. For example, this X-ray absorption coefficient μ ₁ can be uniquely determined. Furthermore, the second first unit X-ray beam β ₂
passes only through pixels 1 and 2, so the X obtained by this second first unit X-ray beam _β2
The linear density d ₂ (1) is the X-ray absorption coefficient μ ₁ of pixels 1 and 2,
As mentioned _above , since the X-ray absorption coefficient μ ₁ at pixel 1 is already known, the X-ray absorption coefficient μ ₂ at pixel 2 is also known. Thereafter, by repeating almost the same operations, the X-ray absorption coefficient μ〓 at the pixel m/2 is successively determined downward. In addition, since the first second unit X-ray beam β ₁ passes only through the pixel m (this pixel m is called the second basic pixel), the first second unit X-ray beam β ₁ ' The resulting X-ray density d ₁ (2) and pixel m
If we know the relationship between the X-ray absorption coefficient μ _n and
This X-ray absorption coefficient μ _n can be uniquely determined. Furthermore, a second second unit X-ray beam β
₂ ' passes only through pixels m, m-1, so the X-ray density d ₂ (2) obtained by this second second unit X-ray beam β ₂ ' passes through pixels m, m-1 However, as mentioned above, since the X _- ray absorption coefficient μ _n at pixel _m is already known, the X-ray absorption coefficient at pixel m-1 is The absorption coefficient μ _n-1 can also be determined. Thereafter, by repeating almost the same operations, the X-ray absorption coefficient μ〓 ₊₁ at the pixel m/2+1 is successively determined. In this way, the X-ray absorption coefficients μ ₁ to _{μ n} in pixels 1 to m constituting the leftmost column of the virtual tomographic plane S
is found, and then the pixels m+1 to composing the second column are determined.
To obtain the X-ray absorption coefficients μ _n+1 to μ _2n at 2 m, based on the already determined X-ray absorption coefficients μ ₁ to μ _n , calculate the first From the unit X-ray beam β〓 ₊₁ ~ β〓 _n, the X-ray absorption coefficient μ _{n +1} ~ μ〓 _n in the pixels m+1 ~ 3/2 m constituting the upper half of the second row is calculated from the above-mentioned upper half of the first row. The second unit X-ray beams from the _m /2 ₊ 1th to the 3/2mth unit The X-ray absorption coefficients μ _2n to μ〓 _{n+1 in 2 m to 3/2 m+1} are sequentially determined in substantially the same manner as in the case of the lower half of the first row described above. Hereinafter, for the X-ray absorption coefficients of the pixels composing the third column to the rightmost n columns, the upper half of the columns is determined, and the lower half is determined, based on the already determined X-ray absorption coefficients.
Next, the upper half and lower half of the column on the right are alternately calculated. If the values of the X-ray absorption coefficients of the mn pixels are known in this way, the tomographic image of the X-ray subject B can be immediately reconstructed. In this way, the tomographic image of the X-ray subject B can be reconstructed, but in addition to the qualitative explanation of the projective transformation described above, this projective transformation method will be described in detail quantitatively using mathematical formulas, etc. Then, it becomes as follows. First, as shown in FIG. 5, a virtual tomographic plane S (this virtual tomographic plane S consists of virtual tomographic plane halves S ₁ and S ₂ ) as a tomographic image reconstruction plane of the X-ray subject B is It is assumed that it consists of mn pixels divided into small sections, and the center of the plane S is taken as the origin of the xy coordinates. For convenience of explanation, m and n are assumed to be even numbers, and the size of one pixel is assumed to be a square of △×△. Also, the X-ray beam passing through the virtual plane S is θ ₁
2 that satisfies = tan ^-1 m/2 and θ ₂ = -tan ^-1 m/2
It is assumed that the beams are irradiated in parallel from all directions, and the diameter of each unit X-ray beam is sufficiently smaller than that of each pixel. Now, number each pixel in the order shown in Figure 5, express its absorption coefficient by μ _k , and irradiate it from _one direction θ, passing through the x-y coordinate point (x _j , y _i ). Let d _k (1) be the projected density obtained by the first unit X-ray beam. Here, x _j =(-2/2+j-1)・△, y _i =m/2-i)・△, (i=1,2,...,m/2; j=1,2,・, n), i represents the row and j represents the column, respectively. Further, if the projected density obtained by the second unit X-ray beam in the _θ2 direction is d _k (2), then the following equation is obtained. However, the X-ray beam in the _two directions of θ is at the point x _j = (-n/2+j-1)・△, y _i =(-m/2+i)・△, k=(j-1)・m+i, (i= 1, 2,..., m/2; j=1, 2,..., n). Lμ=D…(1) μ = (μ ₁ , μ ₂ , μ ₃ , ..., μ _no ) ^T D = (d ₁ (1), d ₂ (1), ..., d〓(1), d ₁ (2) ,d ₂ (2),...,d〓(2)) ^T /α
, and L is an mn×mn square matrix. Further, α is the length through which the X-ray beam in the θ ₁ and θ ₂ directions passes through one pixel, α=Δ√1+ ² ₁ =Δ√1+ ² ₂ , and the symbol T represents transposition. Now, as mentioned above, let mn=N. Solving equation (1), the tomographic two-dimensional data μ _k of the X-ray inspected object B becomes the X-ray concentration information and the unit X that passes through the pixel.
Based on the length information of the line beam, the projective transformation device F
Calculated by However, measurement errors are generally included. Therefore, in order to use mathematical programming, non-negative correction values γ ₁ , γ ₂ , γ ₃ , . . . γ _N are introduced. In addition, since the absorption coefficient of an X-ray beam transmitted through an object is generally non-negative and does not exceed a physically determined positive upper limit U, equation (1) can be modified as follows by adding these constraints. represent

_{[ Table} ^{] -2-2}
P _N = d ₁ (2)/α, P _N = d ₂ (2)/α,
^- ₂ ^{+1 -} ₂ ⁺²
......, p _N =d _N (2)/α.
^-2 _{_}
The objective function is calculated based on the constraint formula of equation (3). Using mathematical programming, we find a solution that minimizes
After a finite number of calculations, the optimal two-dimensional data μ _k is calculated. In the above example, the two tomographic images are calculated based on the objective function that minimizes the sum of the absolute values of the correction values in the constraint expression.
Although the dimensional data μ _k has been calculated, there is also a method of minimizing the objective function of Equation (6) based on the constraint expression of Equation (5) below.

[Table] By solving the above equation, the tomographic two-dimensional data μ _k of the X-ray inspected object B can be calculated under the condition that the maximum correction value of the absolute value in the constraint condition equation is the minimum. Furthermore, the objective function is It is also possible to carry out the method by minimizing the objective function F=γ ² (8) based on the constraint expression (5). By the way, as shown in FIG. 4, considering a virtual tomographic plane S including the X-ray subject B, θ(=
If mn unit X-ray beams irradiated from the tan ^-1 m) direction reach the X-ray detector C through the lower left corner of each pixel constituting this plane S, then
From a single X-ray projection distribution D (dashed line in Figure 4), the X of each pixel as two-dimensional data is calculated using the above theoretical formula.
Linear absorption coefficients can be determined, but in such a method based on a single X-ray projection distribution D, the sample point interval w' is determined by two X-ray projection distributions D ₁ ,
Sample interval w using means based on D ₂ (solid line in Figure 4)
becomes narrower. Therefore, as the number of pixels constituting a virtual plane increases, with a method based on a single X-ray projection distribution D, the sample interval w' becomes extremely small, and 1
The problem of resolution arises when measuring dimensional data. On the other hand, according to the apparatus of the present invention, since the sample interval w is wider than the sample interval w', the resolution in measuring one-dimensional data is greatly improved, and as a result, the reconstruction Image reproduction accuracy is also improved. The two-dimensional data μ _k obtained in this way is
Three-dimensional internal structure storage device G shown in FIG.
will be forwarded to. This three-dimensional internal structure storage device G stores in time series the two-dimensional data μ _k for tomographic image construction transferred from the projective transformation device F, and also stores the three-dimensional internal structure data of the X-ray inspection object B. This refers to the memory that calculates . By the way, the two-dimensional data μ _k sent for the first time from the projective transformation device F is about a certain cross section of the X-ray inspected object B, but it can be changed by changing the measurement location with the X-ray projection distribution measuring means E. Then, other X-ray projection distributions D ₁ ′ and D ₂ ′ are obtained, and from this, two-dimensional data μ _k ′ for other cross sections can be easily obtained.
Two-dimensional data μ for several different cross sections
By integrating _k , μ _k ′, μ _k ″...
Although it is possible to memorize the three-dimensional internal structure of the line-inspected object B, in order to construct a complete three-dimensional internal structure, interpolation between each cross-sectional data is required. This memory G is used as a memory device having a calculation function. An arbitrary tomographic image constructing device H is connected to this memory G, and this arbitrary tomographic image constructing device H uses the three-dimensional internal structure data of the X-ray inspected object B stored in the memory This is an apparatus that selectively extracts two-dimensional data regarding a specified arbitrary cross section of the object B to be inspected to construct a tomographic image. Note that the arbitrary cross section here refers to a cross section of the X-ray inspected object B in a horizontal, vertical, or diagonal direction. In this way, the two-dimensional data of any tomographic image obtained by this arbitrary tomographic image constructing device (reconstruction device) H is consistent based on the X-ray projection distribution obtained by the X-ray projection distribution measuring means E. Since it has been calculated mathematically without contradiction, it is sent to an arbitrary tomographic image display device J via an appropriate digital-to-analog converter F' (hereinafter referred to as "D/A converter"). Each of N pixels 1 constituting the virtual tomographic plane S
By applying and displaying the X-ray absorption coefficients μ ₁ to μ _no to the positions of ~mn, it is possible to display a tomographic image of the X-ray subject B from each two-dimensional data, but this image is free from noise and noise. Since it includes elements that degrade image quality such as blur, there is no guarantee that a suitable image will be obtained. Therefore, in order to correct the data from this optional tomographic image construction device H, this data is sent to the optional tomographic image quality improvement device I. This arbitrary tomographic image quality improvement device I improves image quality by removing noise, smoothing, and emphasizing sharpness of arbitrary tomographic image data sent from an arbitrary tomographic image construction device H. A digital filter is used for removing noise, a smoothing circuit is used for smoothing, and a differential circuit is used for emphasizing sharpness. The signal whose image quality has been improved in this way is D/A
It is sent to the arbitrary tomographic image display device J via the converter F'. This arbitrary tomographic image display device J receives a signal sent from the arbitrary tomographic image quality improvement device I and displays an arbitrary tomographic image of the X-ray subject B on a color or black and white cathode ray tube (braun tube) monitor. A device that displays images, and as mentioned above, cathode ray tubes are generally used. With the above configuration, in order to reconstruct a tomographic image of the X-ray inspection object B, first, X-ray detection is performed by irradiating X-rays from the X-ray generator A to the X-ray inspection object B from a predetermined direction θ ₁ . Regarding the first X-ray projection distribution D ₁ obtained with instrument C, using _the X-ray projection distribution measuring means E, mn/ By measuring each value d _k (1) at two positions until reaching the other end of the first X-ray projection distribution D ₁ , the first one-dimensional data d _k (1)
is obtained, and a second X-ray projection distribution _D 2 obtained by the X-ray detector C by irradiating X-rays from the X-ray generator A to the X-ray inspection object B from another predetermined direction θ ₂ Regarding, X-ray projection distribution measuring means E
Using , each value d _k (2) at mn/2 positions spaced at equal mutual intervals w from one end of the second X-ray projection distribution D ₂ is expressed as the second X-ray projection distribution D _{2 .} By measuring until the other end is reached, second one-dimensional data d _k (2) is obtained. Next, these one-dimensional data d _k (1), d _k (2) are appropriately analog-digital converted, and then converted into one and the other virtual tomographic plane halves using the above-mentioned method in the projective conversion device F. Each X-ray absorption coefficient μ _k (two-dimensional data) of mn pixels in the virtual tomographic plane S consisting of parts S ₁ and S ₂ is determined. Thereafter, these two-dimensional data μ _k are transmitted to an arbitrary tomographic image display device J via a memory G, an arbitrary tomographic image construction device H, an arbitrary tomographic image quality improvement device I, and a D/A converter F′. The line is reconstructed and displayed as a tomographic image of the object B to be inspected. FIG. 6 is a schematic diagram for explaining the operation of a multiple X-ray projection type tomographic image reconstruction apparatus as another embodiment of the present invention, and in FIG. 6, the same symbols as in FIGS. Similar parts are shown. In the case of other embodiments as well, a virtual tomographic plane S as a tomographic image reconstruction plane of the X-ray subject B is divided into mn pixels 1 divided into small sections as shown in FIG.
〜mn, and the center of the plane S is x−
The origin of the y coordinate is assumed, and for convenience of explanation, m and n are assumed to be even numbers, and the size of one pixel is assumed to be a square of △×△. Moreover, unlike the case of the above-mentioned embodiment, the X-ray beam passing through the virtual plane S is parallel to mn/2 from two directions satisfying θ ₃ =tan ⁻¹ m and θ ₄ =−tan ⁻¹ m. One book at a time shall be irradiated. Then, X-ray beams from these two directions (θ ₃ , θ ₄ ) are irradiated from the X-ray generator A. Note that the diameter of each unit X-ray beam is smaller than that of each pixel.
It shall be sufficiently small. In this way, the two predetermined directions in which X-rays are irradiated are set to θ
₃ and θ ₄ , the above equation (1) becomes the following equation. L′μ＝γD′…(9) μ=(μ ₁ , μ ₂ , μ ₃ ..., μ _no ) ^T D′=(d ₁ (3), d ₂ (3),..., d〓(3), d ₁ (4) , d ₂ (4), ..., d〓(4)) ^T / α'. Note that d _k (3) represents the measured value obtained by irradiating X-rays from θ ₃ directions, and d _k (4) represents the measured value obtained by irradiating X-rays from θ ₄ directions. ing. Also, α' is the length for the X-ray beam in the θ, ₃ , and _θ4 directions to pass through one pixel, α'=△√1+ _{2 3} = △√1− _{2 4} , and the symbol ^T represents transposition. ing. When this equation (9) is solved, the tomographic two-dimensional data μ
_h can be calculated, but since measurement errors are generally included, mathematical programming is used to minimize errors during reconstruction, as in the previous embodiment. The signal corresponding to the X-ray absorption coefficient μ _k as two-dimensional data obtained in this way is stored in the memory G,
It is reconstructed and displayed as a tomogram of the X-ray subject B on the arbitrary tomographic image display device J via the arbitrary tomographic image construction device H, the arbitrary tomographic image quality improvement device I, and the D/A converter F'. be. By the way, as shown in FIG.
If mn unit X-ray beams irradiated from the tan ^-1 m) direction reach the X-ray detector C through the lower left corner of each pixel constituting this plane S, then
As mentioned above, it is possible to obtain the X-ray absorption coefficient of each pixel as two-dimensional data from a single X-ray projection distribution D (dashed line in Figure 4). In the method based on the projection distribution D, the sample point interval w' is half of the sample interval w'' in the method based on the two X-ray projection distributions D ₃ and D ₄ (see FIG. 6) as in other embodiments. This is because, in the means of this other embodiment, the X-ray beam indicated by the solid line in FIG. Moreover, this is because the interval between unit X-ray beams is twice the interval between unit X-ray beams in a method based on a single X-ray projection distribution D. The beam direction is θ
₄ is -θ, and the irradiation interval is X shown by the solid line in the same figure.
Since it is the same as the irradiation interval of the line beam, this sixth
The same thing can be said about the X-ray beam indicated by the broken line in the figure. Therefore, in the case of this other embodiment, as in the case of the above-mentioned embodiment, the resolution in measuring one-dimensional data is greatly improved, and the reproduction accuracy of the reconstructed image is also improved. . As described in detail above, according to the multiple X-ray projection type tomographic image reconstruction apparatus of the present invention,
Since the tomographic image of the X-ray object B can be reconstructed from the two X-ray projection distributions D ₁ , D ₂ ; D ₃ , D ₄ obtained by irradiating the X-ray, the following effects can be achieved. or gain benefits. (1) Data collection time is very short;
Even for a moving X-ray subject B (for example, a heart), the tomographic image thereof can be clearly reconstructed with sufficient accuracy. (2) Since the amount of X-ray exposure is very small (several tenths to several hundredths of that of conventional means), there will be no adverse effects even if the X-ray subject B is a living body.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining a conventional X-ray tomographic image reconstruction means, and FIGS. 2 to 5 show a multiple X-ray projection type tomographic image reconstruction device as an embodiment of the present invention. Fig. 2 is a schematic diagram showing the means for measuring the X-ray projection distribution, Fig. 3 is a system configuration diagram, and Figs. 4 and 5 are schematic diagrams for explaining its operation. FIG. 6 is a schematic diagram for explaining the operation of a multiple X-ray projection type tomographic image reconstruction apparatus as another embodiment of the present invention. A...X-ray generator, B...X-ray inspection object, C...X
ray detector, _D1 to _D4 ...X-ray projection distribution, E...X-ray projection distribution measuring means (X-ray density measuring device), E'...A/
D converter, F... projective conversion device, F'... D/A converter, G... three-dimensional internal structure storage device as memory,
H...Arbitrary tomographic image construction device (reconstruction device), I...Arbitrary tomographic image quality improvement device, J...Arbitrary tomographic image display device, S...Virtual tomographic plane, _S1 ...One half of virtual tomographic plane, _S2 ... The other half of the virtual fault plane.

Claims (1)

[Scope of Claims] 1 A unit X-ray beam is irradiated from a plurality of directions on a virtual tomographic plane S that includes the tomographic plane of the X-ray inspected object B and has m pixels vertically and n pixels horizontally. The multiple X-ray projection type tomographic image reconstruction apparatus obtains a plurality of X-ray projection partial distributions by The X-ray beam is irradiated with a plurality of first unit X-ray beams from a predetermined direction toward the inspection object B, and the second unit X-ray beam passes through at least one corner of the pixel. A plurality of second unit X-ray beams are irradiated toward the inspection object B from another predetermined direction,
Regarding the first X-ray projection distribution D 1 and the second X-ray projection distribution _{D 2 obtained} by irradiating the first and second unit X-ray beams toward the X-ray inspection object B Each is equipped with an X-ray concentration measuring device that measures a plurality of X-ray concentrations from one end to the other, and based on the X-ray concentration information from the X-ray concentration measuring device, the virtual tomographic plane S is divided into a plurality of pixels. At least two virtual tomographic plane portions S ₁ consisting of
In order to calculate the X-ray absorption coefficient μ of each pixel constituting each virtual tomographic plane portion S ₁ , _{S 2} Let the X-ray density be the X-ray absorption coefficient μ of the first basic pixel ₁ and the kth (k is smaller than m and 2
X-ray density _dk for pixels up to
means for sequentially obtaining the X-ray absorption coefficient μ _k of the pixel up to the k-th pixel by subtracting the X-ray concentration d _k- 1 from Let the X-ray density be the X-ray absorption coefficient μ _n of the second basic pixel m, and the X-ray density d _n-k+1 to the X-ray density d _nk for the m-k pixels.
By subtracting X of the pixels up to _{the nkth}
A projective transformation device F having an arithmetic unit consisting of means for sequentially determining a linear absorption coefficient μ _nk is provided, and each of the N pixels constituting the virtual tomographic plane S receives a signal from the projective transformation device F. 1~
a reconstruction device H that reconstructs the tomographic image of the X-ray inspection object B by applying the X-ray absorption coefficients μ ₁ to μ _no to the positions of mn; A display device J for displaying a tomographic image of the object B to be inspected is provided. Multiple X-ray projection type tomographic image reconstruction device. 2. The X-ray concentration measuring device E includes a microdensitometer capable of measuring multiple X-ray concentration values on the X-ray concentration distribution obtained on the X-ray film, and an analogue from this microdensitometer. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting signals into digital signals. 3. The X-ray concentration measuring device E includes a scintillation detector with a moving mechanism that receives X-rays passing through the X-ray inspection object B and outputs a signal corresponding to the X-ray concentration, and scintillation detection of the same. 2. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting an analog signal from a device into a digital signal. 4 The X-ray concentration measuring device E includes a number of scintillation detectors that receive X-rays transmitted through the X-ray inspection object B and output signals corresponding to the X-ray concentration, and these scintillation detectors. 2. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting an analog signal from a device into a digital signal. 5 The X-ray concentration measuring device E includes a semiconductor detector with a moving mechanism that receives X-rays passing through the X-ray inspection object B and outputs a signal corresponding to the X-ray concentration, and a semiconductor detector from the semiconductor detector. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting an analog signal into a digital signal. 6 The X-ray concentration measuring device E includes a number of semiconductor detectors that receive incoming X-rays transmitted through the X-ray inspection object B and output signals corresponding to the X-ray concentration, and a plurality of semiconductor detectors that output signals corresponding to the X-ray concentration. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting an analog signal into a digital signal. 7 The X-ray concentration measuring device E includes a xenon gas detector with a moving mechanism that receives X-rays passing through the X-ray inspection object B and outputs a signal corresponding to the X-ray concentration, and a xenon gas detector. Claim 1 comprising an analog-to-digital converter capable of converting an analog signal from a device into a digital signal.
2. The multiple X-ray projection type tomographic image reconstruction device according to 2. 8 The X-ray concentration measuring device E includes a large number of xenon gas detectors that receive X-rays passing through the X-ray inspection object B and output signals corresponding to the X-ray concentration, and these xenon gas detectors. 2. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, comprising an analog-to-digital converter capable of converting an analog signal from a device into a digital signal. 9. Claims 1 to 9, wherein the projective transformation device F includes a digital computer that calculates and outputs a digital signal corresponding to the X-ray absorption coefficient of each pixel based on the data output. 9. The multiple X-ray projection type tomographic image reconstruction device according to any one of Item 8. 10 Between the projection conversion device F and the reconstruction device H, the projection conversion device Claim 1 in which a memory capable of storing the signal from the converting device F is interposed
The multiple X-ray projection type tomographic image reconstruction device according to any one of Items 1 to 9. 11 Claims 1 to 10, wherein a digital filter is interposed between the reconstruction device H and the display device J in order to improve the quality of the image displayed on the display device J. The multiple X-ray projection type tomographic image construction device according to any one of the above. 12 Claims 1 to 10, wherein a smoothing circuit is interposed between the reconstruction device H and the display device J in order to improve the quality of the image displayed on the display device J. The multiple X-ray projection type tomographic image reconstruction device according to any one of the items. 13 Claims 1 to 10, wherein a differentiation circuit is interposed between the reconstruction device H and the display device J in order to improve the quality of the image displayed on the display device J. The multiple X-ray projection type tomographic image reconstruction device according to any one of the above. 14 The irradiation direction of the first unit X-ray beam is
multiple X-ray projection type cross section according to claim 1, wherein tan ^-1 (m/2) and the irradiation direction of the second unit X-ray beam is -tan ^-1 (m/2). Image reconstruction device. 15 The irradiation direction of the first unit X-ray beam is
2. The multiple X-ray projection type tomographic image reconstruction apparatus according to claim 1, wherein tan ^-1 m and the irradiation direction of the second unit X-ray beam is -tan ^-1 m.