JPS6215800A - X-ray diagnostic apparatus - Google Patents

Abstract

PURPOSE:To make it possible to photograph a fine picture image easily by automatically setting a condition attainable of highest density resolution from a constraint condition constituted of the density value of a fluoroscopic image and tube voltage, tube current, gain of optical diaphragm diameter and X-ray dose. CONSTITUTION:An X-ray tube 1 being operated by an X-ray controller 9, X-ray transmitted through an objective 2 being converted into an optical image, video signal obtained through an optical system 7 with an optical diaphragm and an image pickup tube 5 is A/D converted and put in a processor 10. And the maximum and minimum value of the image density being detected by a discriminating means 10B, their values and values of, tube voltage and current from the X-ray controller 9, gain of otpical diaphragm and X-ray dose are computed by a computing element 10D and then the condition providing the highest density resolution is discriminated by a discriminating means 10G and given to the controller 9. Therefore, the condition for obtaining picture image in with high resolution can be automatically set and operability can be greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention belongs to the technical field of X-ray diagnostic devices such as xwA television imaging devices.

[Technical background of the invention and its problems]

In conventional X-ray diagnostic equipment, such as X-ray television imaging equipment, the setting of the optical aperture that determines the tube voltage, tube current, and gain of the X'a tube is such that the output current level of the image pickup tube falls within a predetermined range. It is determined according to the experience of line technicians.

However, even if we focus on the output current level of the image pickup tube,
Since there are countless combinations of tube voltage, tube current, and optical aperture diameter, it is unclear whether the set values of the three, which have been determined based on experience, will give an image with optimal concentration resolution. .

Additionally, in order to keep the output current level of the image pickup tube within an acceptable range, a pink-up tube that measures the amount of light passing through the optical diaphragm is placed in the optical system immediately after the optical diaphragm. Since the pickup tube monitors only the vicinity of the center within the aperture diameter of the umbrella, halation may occur at the periphery of the obtained image, or a shadow of the pickup tube may appear in the image.

The problem with X-ray I shadows is always the issue of X-ray exposure dose.

In order to capture images with good image quality, it is generally better to give a higher dose of X-rays, but simply increasing the dose may end up giving the subject unnecessary exposure that has no effect on improving image quality. There is.

In this way, appropriate countermeasures are desired for imaging with an appropriate exposure dose that contributes to the effect of improving image quality, and for imaging that requires careful handling of the exposure dose, such as when imaging children. This is where I am.

[Object of the Invention] The present invention has been made in view of the above circumstances, and in addition to the constraint conditions for X-ray photography that the output level of the image pickup tube does not saturate and that the load of the X-ray tube is within the rated range. , the tube voltage and tube current that can achieve the highest density resolution within the allowable or set exposure dose based on the fluoroscopic image obtained in advance, taking into account the allowable or set value of the X-ray exposure dose. Another object of the present invention is to provide an X-ray diagnostic apparatus that enables automatic setting of an optical aperture diameter.

[Summary of the invention]

The outline of the present invention for achieving the above object is to provide an X-ray tube that emits X-rays using a tube voltage and a tube current controlled by an X-ray controller, and an X-ray tube that emits X-rays that are transmitted through an object. an optical system having an image intensifier that converts the image into an optical image, an optical aperture that changes the amount of light of the optical image output from the image intensifier, and an optical system that converts the optical image obtained through the optical system into a video signal. Image pickup tube and A that converts the video signal output from the image pickup tube from A/D.
/D converter, detects the maximum density value and minimum density value in the displayed image based on the digital video signal, and then detects the maximum density value and the minimum density value, the tube voltage, tube current, and optical A processor that determines the tube voltage, tube current, and gain of the optical aperture diameter to maximize the S/N ratio of the image from the gain of the aperture diameter and the allowable value or set value of the X-ray dose, and provides high-resolution images. The present invention is characterized in that the tube voltage, tube current, and gain of the optical aperture diameter can be automatically set to obtain the desired results.

[Embodiments of the invention]

A detailed explanation of this invention will be given first.

As shown in FIG. 1, the concentration resolution of an XvA diagnostic device, for example, an X-ray television imaging device, is based on the X-rays (number of photons φI) emitted from an X-ray tube 1 and transmitted through a subject 2, and the region to be identified within the subject 2. The X-rays (photon number φ2) that pass through image 1. It is converted by the image pickup tube 5 via the intensifier 4 and determined by N,, N,. That is, unless the difference between the signal 1 and the signal I2 is observed as a significant difference without being obstructed by noise, the region to be identified 3 cannot be observed in the image. In other words, the first
Indices P, I (Performance
The thicker the index), the more the identification target part 3
This allows for more reliable observations. The indicators P and I are equal to the S/N ratio.

P, I=(12I"/(Nl"+NZ") -
(1) On the other hand, signals II and I2 are output current values of the image pickup tube 5, respectively, and are expressed by the following equations 2 and 3.

I, =φ,・E・α...(
2) h = φ2・E・α...
(3) However, E is photon 1 after passing through object 2
α is the average energy (KeV) possessed by the individual, and α is the total gain of the image intensifier and image pickup tube.

Also, the noise effective value N4. N2 is noise due to photon fluctuation [φ1 ・E・α (mA)), shot noise generated in the beam generation process of the image pickup tube (V' I
・C+ (m^)] and noise generated in the amplification process of the signal current in the image pickup tube (CZ (mA)) are the main components, and noise components caused by other causes can be ignored), and each of the above noise components is Each is independent. Therefore, Nl''=NZ'' can be expressed by the fourth equation.

Nl”: Nzz-(II + ・B2・α2+11 ・
CI"+CZ"...(41 Therefore, the first
The equation can be rewritten as the fifth equation.

P, I-α2・B2・(φ2-φ,)2/(α2・B2
・φ1+α・B・φ1・CI”+CzJ...(5) By the way, the output current of the image pickup tube 5 can be controlled externally by determining the tube voltage, tube current, and gain of the X-ray tube. It is an optical aperture.

Moreover, the target cannot be controlled arbitrarily, but must be controlled under the constraint that the X-ray tube's rating is not exceeded and that the output current level of the image pickup tube is within an allowable range. Follow me.

↑Focus on the constraint conditions for the most image tube.

The thickness of the subject 2 is generally not uniform.

Therefore, as shown in FIG. 2, depending on the shape of the subject 2, a thinner part of the subject 2 may fall within the X-ray irradiation field, and the signal I0 for the thinner part is determined by the second equation and the third equation. It can be expressed as the sixth equation in the same way as the equation.

■. =φ.・E・α (6) In order to keep the output current level of the image pickup tube 5 within the permissible range, the seventh equation must be satisfied.

Io≦Imax−
(7) From the form of the fifth equation, it is clear that the indices P and I become maximum when the equality sign holds in the seventh equation. Therefore, from the sixth and seventh equations, α (gain) when the indices P and I are maximized can be expressed by the eighth equation.

E・φ.

Therefore, by substituting the eighth equation into the fifth equation, the ninth equation is obtained.

P, I= I”max(ψ2−φ+)”/(Imaxφ
. φ1C1'0C2'φo"+12maxφ, )
・(91 Photon number φ., φ, φ2 are proportional to the tube current.

As explained above, if the tube voltage is fixed at a certain predetermined value, the maximum tube current can be determined from the rating of the X-ray tube, and this maximum tube current provides the maximum index at the predetermined tube voltage. P, I can be calculated, and therefore the combination of tube voltage and tube current that gives the maximum index P, I among the many indexes p, r obtained under various tube voltage values gives the optimal state. . The optical diaphragm diameter at that time is determined by Equation 8.

In order to calculate the indices P and I using the ninth equation, φ. .

φ3. It is necessary to find quantities such as φl+E. φ. ,φ1
Since the quantities such as ゜φ2rE change depending on the thickness of the subject 2, in order to obtain the above-mentioned capacity, ゛the minimum thickness ρ when expressed by an equivalent water phantom as shown in Fig. 3, and when the identification target part 3 is Thickness of the existing part (maximum thickness 11
) must be estimated first.

The minimum thickness 10 and the maximum thickness 11 can be determined from data obtained by perspective photography to determine the position of the subject 2. In other words, the average signal voltage 'al
Fo and the average signal current IF+ for the portion specified by the ROI etc. in the image are respectively expressed as the tube voltage VPF (KVP "J", tube current IPF
(mA) and the optical aperture α that determines the gain, as shown in Equations 10 and 11.

T (VPF, io) corresponding to 11 combinations
, T (VFF, l, ) through simulation. , β1 can be determined.

■,. -IFF・α,・T (VPF, lo)
...(10) IFI=IFF・α,・T (VPF
, 7! + ) ... (11) However, T (VPF, (l o) = (1) (VPF)
・e −/′(vpr, 4)j@・H(VPF,
la ) ... (12) T (Vry+ 1 +
) = (1) (VPF) ・e−μ(Vpyj't
)”1・H(VPF, l, )...(1
3) In addition, in the 12th and 13th equations, φ(VP
F) is the number of tube output photons per unit time when the tube voltage VPF and tube current are 1 mA, and μ(VPF,
l-o), μ(VPF, !!+) is the tube voltage VPF
and the average absorption coefficient of water when the ice thickness is 10 or 1, and these can be determined in advance by simulation.

1o and β1 are determined, the 10th
From the equation and comparison with the first equation, φ. .

φ8. φ2 can be expressed by Equation 14, and φ(VP
), p can be obtained by simulation, and ■ and are set values, so they can be easily calculated.

Note that Δμ(vp+xz) represents the absolute value of the difference between the average absorption coefficient of the object to be identified and the average absorption of water with the same thickness of 7!2.

To summarize the above, depending on the conditions during fluoroscopic photography, when the subject is an equivalent water phantom, the minimum thickness is 1°, the maximum thickness is a,
is determined based on data obtained through simulation, and then the minimum thickness l is determined. , at the maximum thickness of 7!1, find the indices P and I at various tube voltages, and find the index P and I that have the maximum value among the many indices P and I.
The values of tube voltage, tube current, and optical aperture when giving .

The basic principle has been described above, and among the constraint conditions, the condition of the X-ray tube load capacity (rating of the X-ray tube) will be explained below.

The capacity of an X-ray tube is determined by the amount of heat generated in the X-ray tube, and since the heat generation is due to Joule heat at the anode of the X-ray tube, the tube voltage ■2 is determined by the tube current! , can be treated as a variable. That is, H= VP - I P
-(15)L=C,・H...(
16) However, C3 is a constant determined by the X-ray radiation mode (continuous, intermittent radiation, etc.), the type of power supply, etc.

x! The constraint condition for vI tube load capacity is the condition for determining the maximum tube current ■, which can be passed when the tube voltage ■, is given by the relationship of equations (15) and (16) as the rating of the X-ray tube. Can be used.

This X-ray tube load capacity constraint condition is
In addition to using it as the maximum capacity of the tube, it is possible to freely determine and use any setting value.

For example, it can be determined according to the purpose of imaging, or the accumulated heat of the X-ray tube can be monitored and the setting value can be determined for each imaging based on the remaining allowable heat capacity. It is possible to do this.

The present invention further adds constraint conditions regarding X-ray dose, for example, exposure dose, in order to reduce the exposure dose and realize efficient imaging from the exposed surface.

The principle in this case will be explained below.

Among the X-ray doses of the X-ray tube, the exposure ray NRo has a relationship with the imaging conditions of tube voltage VP, tube current 1p, and exposure time T as shown in the following equation.

However, C4 is a constant related to the shooting mode, etc., D Fon is the distance between the X-ray focal point and the subject, CF (E) is the X-ray photon energy dose function, E is the X-ray photon energy, φ (E)
is the X-ray tube output.

Further, the X-ray dose, that is, the exposure dose (absorbed dose) R3 at the maximum thickness 11 of the subject can be expressed as in the following equation.

...(20) However, DFDD is the distance between the X-ray focal point and the image intensifier (1, I), and μ(E) is the absorption coefficient of water.

The exposure dose R, and the exposure dose (absorbed dose) R3 are each 1
Since it can be expressed by equations 7 and 19, the shooting mode,
After the shooting distance is determined (C,,,T,.

After DFOII + Drno is determined, R1
(VF, ), R2 (V,, l I) for various tube voltages V
P, maximum Jix+ must be determined in advance or stored in ROM.
(By recording the read-only memo in January, the combination of tube voltage Vp and tube current I can be given.

When the exposure dose is a constraint condition, the exposure dose R8
The imaging conditions can be determined by setting a permissible value for the radiation exposure line MR1, and when the exposure L5ui (absorbed dose) is a constraint condition, a permissible value is similarly set for the radiation exposure line MR1.

When the exposure dose RII and the exposure dose R3 are given as allowable values, the tube current ■ is determined for various tube voltages ■, and the previously mentioned indices P and f are determined, and this becomes the maximum value. You can give the shooting conditions at the time. The imaging conditions given in this way are the maximum S/N at the allowable dose.
It will be the best one that gives the ratio.

Next, an embodiment of the present invention based on the above principle will be described.

As shown in FIG. 4, XwA which is an embodiment of the present invention
The diagnostic apparatus places a subject 2 (an X-ray tube 1 placed above a bed 6, an image intensifier (1, I) 4 placed opposite the X-ray tube 1 with the bed 6 in between, ．．
An optical system 7, for example, a tandem lens system, adjusts the optical image output from the optical diaphragm 14 to a predetermined amount of light with an optical diaphragm (not shown) and guides it to the input surface of the image pickup tube 5. An image tube 5 that captures an image, converts it into an electrical signal, and outputs it; an A/D converter 8 that converts an analog video signal output from the image pickup tube 5 into digital; and an X-ray tube 1. An X-ray controller 9 that controls the voltage and tube current, the diameter of the optical aperture in the optical system 7, and the timing of X-ray exposure
Based on the data obtained from X-ray fluoroscopy, the tube voltage and tube current of the X'Ia tube, the optical aperture diameter in the optical system 7, and the The apparatus includes at least a processor 10 that automatically sets the permissible value or the optimal value of the set value of the X-ray exposure dose.

The processor 10 calculates the density of a fluoroscopic image from a first memory IOA that stores a video signal obtained by XvA fluoroscopy output from the A/D converter 8 and a video signal read from the memory IOA. Determine the maximum value and minimum value of and ■ in the 10th and 11th equations. Discrimination means 10B for determining +IFl and maximum thickness in various equal immersion water phantoms! , and minimum thickness 1
0 and various tube voltages 2, the 12th formula to the 1st formula
T (VP,
.

io),'r(VPF, 11) as a table, a second memory IOC that stores the following as a table, the tube voltage vFF+tube current IFF which is the X-ray fluoroscopy condition output from the X-ray controller 9, and the optical Gain α1 that determines the aperture diameter, I output from the discriminating means 10B
FO+IF and data T (Vpy, No) corresponding to the tube voltage VPF and tube current IFF output from the first memory IOC.

Maximum thickness 11 and minimum thickness 10 that satisfy equations 10 and 11 by inputting T (VPF, l, )
a thickness determining means 10D for calculating the thickness determining means 1;
For various tube voltages vP at the maximum thickness 10 and minimum thickness 11 determined at 0D, for each tube voltage V, the tube current IP, the gain α and φ that determine the optical aperture diameter. ,φ
P, I calculation means 10E which calculates various indices P, 'l by calculating 1φ2, and the P, I calculation means 1
A third memory IOF stores the indices P and I calculated at 0E, the tube voltage VP, tube current 2, and gain α that give these indices, and the data in the third memory IOF is read out to determine the maximum index P. , I, and give this maximum index P, I. Tube voltage ■1, tube current I, and gain α are expressed as X&1
Maximum P and I determining means 10G for outputting to the controller 9, timing control means 10H for controlling the operation timing of each of the memories and means, and the P and I calculation means 1
It is configured to have a fourth memory lOI as a ROM table that stores the indexes P and I calculated in 0E and also stores various values of the function Ih (Vp, 1 + ) revealed by the above equation 20 in advance. ing.

Next, the operation of the above configuration will be described.

First, X-ray fluoroscopic imaging of the subject 2 is performed. This X-ray fluoroscopic imaging is normally performed to position the subject 2.

As shown in FIG. 5, the operation console (not shown) sets the tube voltage VPF (KVP), the tube current Ipp (mA), and the gain α determined by the optical aperture as the X-ray irradiation conditions. input to the line controller 9.

X-rays are irradiated from the X-ray tube 1 to the subject 2 using the tube voltage VPF and tube current IPF controlled by the X-ray controller 9. The X-rays transmitted through the subject 2 are converted into an optical image by 1.17, and then the optical image is captured by the imaging tube 5 via the optical system 7, and the imaging tube 5 outputs a video signal. The video signal is digitized by the A/D converter 8 and then stored in the first memory IOA. Next, the video signal stored in the first memory IOA is read out by the discriminating means 10B, and as shown in FIG. and determine the minimum value, and determine IFO and IFI, which are the left sides of the 10th and 11th equations,
The IFQ and rr+ are output to the thickness determining means 10D. The thickness determining means 10D receives the X from the X-ray controller 9.
The values of the tube voltage ■2, tube current ■2, and Cain α, which are the line fluoroscopic imaging conditions, are also input, and the thickness l of the equi-immersed water phantom is set to °0, and the tube is set as IV, o=0. By outputting voltage V, to the second memory IOC, T corresponding to No-0 and tube voltage ■, is output from the second memory.
(VPF, i, ) and read T(
V.P.F.

x), tube current r output from the X-ray controller 9
Calculate the right side of Equation 10 using pr and gain α,
Compare the calculation result with the TPO output from the determining means 10B, and if they do not match, set the thickness l to 1° + △
l is determined, and β+Δl and tube voltage VP are stored in the second memory I.
Output to OC, read T (VFF, 1 o) corresponding to the above l + △l and tube voltage ■, calculate the right side of Equation 10 in the same way as last time, and compare the calculation result with IFO. . The calculation result of the right side of Equation 10 and 1. . Repeat the same operation until the calculation result and I,
. β when and match. This is set as the minimum thickness of the equi-immersed water phantom and is output to the P, I calculation means 10E.

The maximum value A of the thickness of the equi-immersed water phantom is also determined in the same manner as the minimum value 10, and is output to the P, I calculation means 10E. As shown in FIG. 6, the P, I calculation means 10B calculates the maximum thickness X and the minimum thickness l.

In this case, an arbitrary tube voltage, for example, the tube voltage vP during X-ray fluoroscopic imaging, is fixed, and the tube current IP at this tube voltage (2) is
is determined from the tube rating, and furthermore, the tube voltage Va and the maximum thickness II are sent to the fourth memory 101, and from this fourth memory IOI, the tube voltage vP and the maximum thickness value! , read the value of R2 (VP, 1 +) corresponding to , and calculate this Rz
Calculation based on formula 19 is performed using the value of (Vp, l,) and the exposure time T9 sent from the X-ray controller 9, and the tube current 1. Find r.

Then, the values of the tube current I and the tube currents H and l are compared, and the smaller one is determined as the actual tube current (2).

φ according to Equation 14. , φ1 and φ2, and the obtained tube currents IF, φ. Then, the gain α is calculated according to Equation 8 based on E determined in advance, and the obtained φ is further calculated. , φ1 and φ2, C8 and C2 obtained in advance, and the tube current I, calculate the indexes p and r according to No. 9, and calculate the indexes P and I and the tube voltage Vp and tube current I that give the indexes P and I. , and gain α
is output to the third memory IOF. Next, the P, I calculating means 10E changes the tube voltage V, which was the basis of the previous calculation, to the tube voltage V, +△VP, thereby making the tube voltage VP+△V.

Indices P, I are calculated in the same manner as last time, and the obtained indices P, I and the tube voltages that give these indices P, I are calculated.
△Vp, tube current IP and gain α are stored in the third memory IO
Output to F. The P, I calculation means 10E calculates the tube voltage VP+
The same calculation as the previous one is repeated until ΔV reaches the maximum value in the rating of the X-ray tube, and the obtained data is output to the third memory IOF. After the calculation by the P, I calculating means 10E is completed, the maximum P, I determining means 10G reads out a large number of indices P, I stored in the third memo IJ 10F and the data giving them, By comparing the indices P and I, the maximum indices P and I are determined. Then, the values of the tube voltage VP, tube current {circle around (2)}, and gain α that gave the maximum index P, I are outputted to the X-ray controller 9 from the maximum P, 1 determining means 10G. In this way, the tube voltage 2, the tube current 2, and the gain α for determining the optical aperture diameter are determined by the processor 10 as the X-ray irradiation conditions that give the maximum resolution, and the X-ray controller 9 determines the X-ray tube 1. And the optimum state of the optical system 7 is realized.

Therefore, in the image obtained by injecting a contrast medium into the subject 2 and performing X-ray photography under the conditions determined above, there is a contrast between the image of the identification target region 3, for example, the blood vessel where the contrast medium is present, and the image of other parts. This results in a high resolution X-ray image being displayed.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and can be implemented with appropriate modifications within the scope of the gist of the invention. Needless to say.

For example, in the above-mentioned embodiment, a case was explained in which the exposure dose R3 itself is used as a constraint condition regarding the exposure dose to control the imaging conditions.
By adding a ROM table of R1(vP) and performing Equations (15) and (16) with the value of R1(vP), it is possible to control the imaging conditions using the exposure dose R9.

〔Effect of the invention〕

According to the present invention described in detail above, based on a fluoroscopic image obtained by photographing in advance, the density value of the fluoroscopic image, the tube voltage at the time of image capture, the tube current, the gain of the optical aperture diameter, and the X-ray dose are determined. It is possible to automatically set the tube voltage, tube current, and gain that provides the optical aperture diameter that achieves the highest concentration resolution under constraint conditions, and outputs a clear X-ray image that shows the area to be identified with good contrast against other areas. An X-ray diagnostic apparatus can be provided.

[Brief explanation of the drawing]

1 to 3 are principle explanatory diagrams showing the principle of this invention, FIG. 4 is a block diagram showing an embodiment of this invention, and FIG.
6 and 6 are flowcharts showing the operating procedure of the embodiment, respectively. 1... X-ray tube, 2... Subject, 4... Image intensifier, 5... Image pickup tube, 7... Optical system,
9... X-ray controller, 10... processor. I+wN+ Figure 6

Claims (1)

[Claims] An X-ray tube that emits X-rays using tube voltage and tube current controlled by an X-ray controller, an image intensifier that converts the X-rays emitted from the X-ray tube and transmitted through the subject into an optical image, and an image An optical system having an optical aperture that changes the amount of light of the optical image output from the intensifier, an image pickup tube that converts the optical image obtained through the optical system into a video signal, and a video signal output from the image pickup tube. A/D
An A/D converter to perform the conversion, detects the maximum density value and minimum density value in the displayed image based on the digital video signal, and then detects the maximum density value and the minimum density value, the tube voltage at the time of image capture, and the tube voltage. and a processor that determines the tube voltage, tube current, and gain of the optical aperture diameter to maximize the S/N ratio of the image from the current, the gain of the optical aperture diameter, and the allowable value or set value of the X-ray dose. An X-ray diagnostic device characterized in that the tube voltage, tube current, and gain of the optical aperture diameter can be automatically set to obtain high-resolution images.