JP5602014B2 - X-ray diagnostic equipment - Google Patents

Description

  The present invention relates to an X-ray diagnostic apparatus that displays an X-ray image based on a transmitted X-ray signal detected by irradiating a subject with X-rays, and in particular, to determine the exposure area dose of a subject without using a dosimeter. The present invention relates to an X-ray diagnostic apparatus used for indirect imaging that can be obtained with high accuracy.

  In an X-ray diagnostic apparatus used for medical diagnosis, since the subject is irradiated with X-rays, in recent years, the importance of managing the exposure dose of the subject has been recognized. Therefore, in order to confirm how much the subject has been exposed, the exposure area dose for each subject is managed.

  Conventionally, this measurement of the exposed area dose has been performed by mounting a dosimeter on an X-ray diagnostic apparatus. However, in actual radiography, there may be a blank area (direct line area) where no human body exists even within the X-ray irradiation image area, and the exposure area dose obtained by the dosimeter is used as it is. It may be inappropriate to use as. In view of this, a radiation imaging apparatus or the like has been proposed in which such problems are solved and the exposure area dose can be appropriately acquired (see, for example, Patent Document 1).

In this example, an area calculation means for calculating one of an area of an irradiation region, an area of the subject region, and an area of a blank region in a radiographic image obtained by radiographing the subject, and a radiation generator The subject is irradiated based on the acquisition means for acquiring the effective dose irradiated from the irradiation area, the area of the subject area, the area of the subject area or the area of the blank area, and the effective dose. A dose calculating means for calculating an exposed area dose as a radiation dose. An example using an exit dosimeter is described as the acquisition means. In this case, basically, based on the irradiation area dose acquired by the exit dosimeter, the exposure area dose corresponding to the area of the subject area obtained by subtracting the blank area area from the irradiation area area is obtained. ing. In addition, when there is no blank region, the irradiation area dose is equal to the exposure area dose.

JP 2004-69441 A

  When configured to acquire the effective dose emitted from the radiation generator using the exit dosimeter as in the above conventional example, the dosimeter is not only expensive, but the exit dosimeter is X-ray diagnosed. There is a problem that the device needs to be changed to be attached to the device. In particular, in a mobile X-ray diagnostic apparatus, the weight balance of the radiation generator may be disrupted by the weight of the dosimeter. Further, in the above conventional example, instead of the exit dosimeter, a predicted value of the irradiation area dose obtained based on the exposure conditions (tube current, tube voltage, exposure time, etc.) of the radiation generator may be used. Has been. However, in this case, since the exposure area dose to the human body is calculated based on the direct X-ray dose in the unexposed area, there is a problem that the exposed area dose cannot be obtained unless the unexposed area occurs. And even if there is a background area, even if the background area area is subtracted from the irradiation area area, the pixel value of the background area changes depending on the distance between the X-ray source and the X-ray detector, so in the first place, It is not possible to accurately recognize which pixel value region is an unclear region.

  The present invention has been made in view of such circumstances, and does not use a dosimeter, and regardless of whether a blank region (direct line region) occurs or not, a highly accurate exposure area dose can be obtained. An object is to provide an X-ray diagnostic apparatus that can be obtained.

In order to solve the above-mentioned problems, the present invention is an X-ray source that irradiates an X-ray that expands toward the subject, and is disposed opposite to the X-ray source, and detects transmitted X-rays of the subject. X-ray detector that outputs as image data, histogram creation means for creating a histogram of pixel values in the image data output from the X-ray detector, irradiation X-ray dose determined from X-ray irradiation conditions and the X-ray A direct X-ray dose calculating means for calculating a direct X-ray dose detected by the X-ray detector and a pixel value corresponding to the direct X-ray dose based on a distance from a source to the X-ray detector; and the histogram generating means In addition to calculating the subject image area in the image data based on the histogram created in step 1 and the pixel value calculated by the direct X-ray dose calculation means, the calculated subject based on the body thickness of the subject is also calculated. Test to correct specimen image area An area for calculating the exposure area dose of the subject based on the image area calculation means, the direct X-ray dose calculated by the direct X-ray dose calculation means, and the subject image area corrected by the subject image area calculation means A dose calculating means.

  The X-ray diagnostic apparatus of the present invention multiplies the direct X-ray dose on the surface of the X-ray detector obtained by taking into account the distance from the X-ray source to the X-ray detector by the area of the subject image region of the subject. It is possible to obtain a highly accurate exposure area dose without using a dosimeter and with or without a blank region (direct line region).

1 is a block diagram showing a configuration of an X-ray diagnostic apparatus according to Embodiment 1 of the present invention. It is explanatory drawing which shows one of the methods of calculating | requiring the body thickness by the same apparatus. It is a head photography image by the same device. It is a histogram of the same pixel value. FIG. 5 is a block diagram showing a configuration of an X-ray diagnostic apparatus according to Embodiment 2 of the present invention. It is a flowchart which shows an example of the calculation process of the exposure area dose. 12 is a flowchart showing an example of a process for calculating an exposed area dose according to a modification of Example 2. FIG. 4 is a schematic explanatory diagram illustrating a situation in which X-rays irradiated from an X-ray source pass through a subject and reach an X-ray detector.

  Hereinafter, an X-ray diagnostic apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. The meanings of the terms used in the description of the following examples are as follows.

SID: Distance from X-ray focus to X-ray detector.
FSD: Distance from the X-ray focus to the skin surface of the subject. It may simply be the distance from the X-ray focal point to the subject.
Body thickness: The thickness of the subject in the X-ray optical axis direction at the time of imaging.
Exposure area: Area of the subject surface irradiated with X.
Direct X-ray dose: The dose per unit area that reaches a predetermined distance from the X-ray focal point without passing through the subject.
Subject exposure area dose: (exposure area x FSD direct x-ray dose), almost the same as (subject image area x SID direct x-ray dose).
Subject image region: A region where X-rays pass through the subject and reach the X-ray detector. That is, the area occupied by the subject in the image data.
Subject image area: The area of the subject image region.
Direct ray region: A region where X-rays do not pass through the subject and reach the X-ray detector directly. That is, in the image data, an area within the irradiated image area and not the subject image area
Irradiation image area: An area in the image data that is not shielded by the X-ray diaphragm. That is, the sum of the subject image area and the direct line area.

  FIG. 1 is a block system diagram showing a basic configuration of an X-ray diagnostic apparatus. This X-ray diagnostic device is a mobile type X-ray diagnostic device for round trips, and its basic configuration is as follows: X-ray source 1, X-ray detector 2, histogram creation means 3, FSD and body thickness SID calculation means 4A, correction means 5, direct X-ray dose calculation means 6, subject image area calculation means 7, area dose calculation means 8, and display means 9 are provided.

  The X-ray source 1 includes an X-ray tube (not shown) that irradiates a subject with X-rays. In front of the X-ray tube, an X-ray diaphragm (not shown) for limiting irradiation of the X-ray irradiated from the X-ray tube to the subject is provided. The X-ray detector 2 is disposed facing the X-ray source 1 via a subject (not shown) and detects X-rays transmitted through the subject as image data. For example, an IP (imaging plate) or FPD (flat panel detector) of a pewted radiography apparatus can be used.

  The histogram creation means 3 creates a histogram of pixel values in the image data detected by the X-ray detector 2. Typically, a histogram indicating the relationship between the pixel value and its frequency is used as this histogram, but a cumulative histogram indicating the cumulative frequency of pixel values that are less than or equal to a certain pixel value may be used. Usually, since it is difficult to directly measure SID with a mobile round-trip X-ray diagnostic apparatus, FSD is measured by, for example, an ultrasonic distance meter.

  Therefore, the SID can be calculated by inputting the FSD to the SID calculation means 4A and adding the body thickness.

  The body thickness can be obtained by one of the following methods. In this example, actual measurement by a measure is selected.

(1) Measurement with a measure Measure the body thickness by applying a measure parallel to the X-ray optical axis on the side of the subject.

(2) Actual measurement and calculation of X-ray hypotenuse As shown in FIG. 2, the length of the hypotenuse Lx reaching the X-ray detector 2 from the X-ray source 1 through the contour of the subject P is measured with a measure. Here, SID = FSD + body thickness t and Lx ² = (FSD + t) ² + Ls ² . Therefore, the body thickness t can be obtained by calculating using the FSD obtained by the ultrasonic distance meter and Ls obtained from the image data. The position of the optical axis of the X-ray on the X-ray detector 2 is usually the intersection of diagonal lines of the irradiated image area.

(3) Calculation using histogram For a subject with different body thickness (or a simulated sample of the subject), the correlation between the feature value (for example, the average value) of the histogram of the pixel value in the image data and the body thickness is measured. The correlation calculation formula or table is prepared in the storage means. Then, a feature amount can be obtained from a histogram of actually captured image data, and a body thickness corresponding to the feature amount can be obtained with reference to the correlation. Examples of the feature quantity of the histogram correlated with the body thickness include an average value, a median value of the histogram, a mode value (mode), a maximum value, a minimum value, and the like.

  The correction means 5 is arranged on the back surface of the subject to absorb the absorbed X-ray dose of the grid that removes scattered rays and the absorbed X-ray dose of the additional filter that is mounted close to the X-ray source 1 and removes soft rays. Subtract (correct) the X-ray dose from 1.

  The direct X-ray dose calculation means 6 calculates the direct X-ray dose to reach the surface of the X-ray detector 2 based on the irradiation X-ray dose and SID obtained from the X-ray irradiation conditions (tube voltage and tube current time product) and its The pixel value corresponding to the direct X-ray dose is obtained. In other words, the irradiation X-ray dose at a unit distance and unit area is calculated from the X-ray irradiation conditions, and if the SID is known, the direct X-ray dose on the surface of the X-ray detector can be obtained by using this irradiation X-ray dose. Specifically, it is as follows.

DX = D * (L1 * L1) / (L2 * L2) -DF-DG (1)
Here, DX: Direct X-ray dose on the surface of X-ray detector 2
D: X-ray dose per unit area at unit distance from X-ray focus
L1: Unit distance for D
L2: SID
DF: Additional filter absorbed X-ray dose
DG: Absorbed X-ray dose of the grid The pixel value corresponding to the X-ray dose is obtained from the direct X-ray dose that should reach the surface of the X-ray detector 2 and the sensitivity of the pixels of the X-ray detector. Specifically, it is as follows.

C = DX * K (2)
Where C: Pixel value
K: Sensitivity to X-rays of the X-ray detector 2 The sensitivity K is expressed by COUNT / (μGy / Frame). Normally, the numerical value 1 is assigned to Frame and it is read as an image, so the sensitivity is COUNT / μGy. By multiplying this coefficient by DX, the pixel value C corresponding directly to the X-ray dose can be obtained.

  Next, the subject image area calculating unit 7 determines a threshold value for distinguishing the direct line region from the X-ray irradiation image region on the basis of the pixel value obtained by the direct X-ray dose calculating unit 6. This threshold value may be determined directly by the X-ray dose calculation means 6 instead of the subject image area calculation means 7.

  Then, the subject image area calculating unit 7 determines that the region having a pixel value equal to or greater than the threshold is a direct line region from the histogram created by the histogram creating unit 3, and determines the direct line region from the X-ray irradiation image region. The subject image area of the subject is obtained by subtraction. Alternatively, a region having a pixel value less than the threshold may be used as the subject image area.

  The area dose calculation means 8 calculates the exposure area dose of the subject based on the direct X dose calculated by the direct X dose calculation means 6 and the subject image area calculated by the subject image area calculation means 7. To do.

  An imaging mode of an apparatus using the FPD as the X-ray detector 2 in the above X-ray diagnostic apparatus will be described. FIG. 3 is a photographed image of the human head. In the figure, the white part 11 is the part where the X-ray is blocked by the X-ray aperture, the black part 12 is the part where the direct X-ray line is incident (direct line area), and the gray part 13 is the X-ray image that is transmitted through the head. (Subject image region). In this way, when the head or the like is photographed, X-rays are directly incident on the FPD without passing through the human body, and a black portion 12 is formed. When such a head image is subjected to histogram processing, a histogram as shown in FIG. 4 is obtained. In this histogram, the white portion 11 where the X-ray is blocked by the X-ray stop corresponds to a portion where the dose is 0 or close to 0 and the pixel value of the histogram is 0 or close to 0. The black portion 12 where X-rays are directly incident corresponds to a portion where the pixel value of the histogram is the maximum value or close to the maximum value. The black portion 12 is recognized as a direct line region based on the threshold value determined by the subject image area calculating unit 7 using a pixel value corresponding to the direct X-ray dose obtained by the direct X-ray calculating unit 6.

  In the histogram as described above, the subject image region corresponds to a portion between both broken lines 14 and 15. Therefore, in this histogram, the X-ray region can be directly recognized by applying the above-mentioned threshold value determined by the subject image area calculation means 7 to the upper threshold value (broken line 15). That is, the area of the direct line area obtained from the histogram and the upper threshold is subtracted from the area of the irradiated image area obtained from the open / closed state of the X-ray diaphragm (corresponding to the sum of the black portion 12 and the gray portion 13), and the subject image The area can be calculated. By multiplying the subject image area thus obtained by the X-ray dose directly in the SID, the exposure area dose can be calculated and displayed on the display means 9.

  The more accurate exposure area dose is obtained by the product of the exposure area of the subject and the direct X-ray dose in the FSD. In this embodiment, the exposure area is the product of the subject image area and the direct X-ray dose in the SID. Looking for dose. However, even in such a case, a considerably accurate exposure area dose can be obtained based on the subject image area excluding the direct line region accurately.

  Next, a stationary type X-ray diagnostic apparatus of the present invention will be described with reference to FIGS. In the following description, differences from the first embodiment will be mainly described. In this embodiment, as shown in FIG. 5, FSD calculation means 4B is provided instead of the SID calculation means 4A in the first embodiment. The FSD calculating means 4B first obtains information on the body thickness, and calculates the FSD by subtracting the body thickness from the SID. The method for obtaining the body thickness may be performed in the same manner as in the first embodiment. In this example, “(3) Calculation using histogram” is selected. Of course, the FSD may be measured with an ultrasonic distance meter. In addition, since the SID is a stationary type in this embodiment, the X-ray source and the X-ray detector are mechanically connected via a support mechanism that can be driven by the motor. X-ray diagnostic equipment can recognize from the number. In addition, in this embodiment, as an X-ray detector, a combination of I.I. (image intensifier) and a TV camera can be used in addition to IP and FPD. The functions of the direct X-ray dose calculation means 6 and the subject image area calculation means 7 are the same as those in the first embodiment. On the other hand, the area dose calculation means 8 calculates the exposure area dose of the subject based on the direct X-ray dose in the FSD and the subject image area calculated by the subject image area calculation means 7.

  Next, an example of a process for calculating the exposure area dose by the X-ray diagnostic apparatus will be described based on the flowchart shown in FIG. 6 with reference to FIG. First, image data obtained from the X-ray detector 2 is subjected to histogram processing by the histogram creation means 3 to create a histogram of pixel values (step S100), and the data is the subject image area calculation means 7 and the FSD calculation means 4B. Is output.

  Next, the X-ray absorption amount of the SID and the grid (additional filter) is directly input to the X-ray dose calculation means 6 (steps S101 and S102). Further, the irradiation X-ray dose obtained from the X-ray irradiation conditions (tube voltage and tube current time product) is directly input to the X-ray dose calculation means 6 (step S103). Further, the SID is also input to the FSD calculation means 4B. In the FSD calculation means 4B, the body thickness is acquired by “(3) calculation using the histogram”, and the FSD is obtained by subtracting the body thickness from the SID (step S104). The obtained FSD is input to the area dose calculation means 8.

  On the other hand, the direct X-ray calculation means 6 calculates a pixel value corresponding to the direct X-ray dose that should reach the surface of the FPD from the SID, the irradiation X-ray dose, and the X-ray absorption amount of the grid (additional filter) (step S105). ).

  Subsequently, a threshold value is determined based on the pixel value corresponding to the direct X-ray dose, and a pixel value equal to or greater than the threshold value is determined as a direct line region. Then, the subject image area calculating means 7 calculates the subject image area by subtracting the direct line region from the irradiation image region obtained from the open / closed state of the X-ray diaphragm (step S106).

  Next, the obtained subject image area is corrected in consideration of the body thickness, and the exposed area of the subject is obtained (step S107). That is, the exposure area of the subject corresponds to the distance LF in FIG. 2, and the SID and FSD and the subject image area (corresponding to the distance Ls in FIG. 2) are known, and Ls / SID = LF / FSD. The exposed area of the subject can be calculated. This correction may be performed by the subject image area calculation means 7.

  Further, the direct X-ray dose in the FSD is determined based on the irradiation X-ray dose determined based on the X-ray irradiation conditions and the FSD calculated by the FSD calculation means 4 (step S108). This calculation is performed by the area dose calculation means 8, but may be directly performed by the X dose calculation means 6 by causing the X dose calculation means 6 to directly recognize the FSD.

  Then, the area dose calculation means 8 calculates the exposure area dose by multiplying the exposure area of the subject and the direct X-ray dose in the FSD (step S109).

  According to the present embodiment, the exposure area dose can be obtained with higher accuracy by multiplying the exposure area of the subject, not the subject image area, by the direct X-ray dose in the FSD. In particular, it is not necessary to actually measure any of the SID, FSD, or body thickness by obtaining the body thickness by “(3) Calculation using a histogram”, and all distances are obtained by calculation processing in the X-ray diagnostic apparatus. Can do.

  As a modification of the present embodiment, as shown in FIG. 7, the FSD may be a value measured with an ultrasonic distance meter or a measure, and the body thickness may be a value measured with a measure or the like. In that case, the creation of the histogram (step S200) is the same as in FIG. 6, but the SID is not directly acquired by the X-ray dose calculation means 6, but the FSD and body thickness, and the X-ray absorption amount of the grid The irradiation X-ray dose is directly input to the X-ray dose calculation means 6 (steps S201, 202, 203, 204). Then, the SID is obtained by adding the body thickness to the FSD by the direct X-ray dose calculation means 6, and the direct X-ray dose at the SID is calculated from the X-ray absorption amount and irradiation X-ray dose of the SID and the grid (step S205). On the other hand, the direct X-ray dose in the FSD is calculated directly from the FSD and the irradiation X-ray dose by the X-ray calculation means 6 or the area dose calculation means 8 (step S206).

  Then, similarly to the case of FIG. 6, the subject image area and the subject exposure area are calculated (steps S207 and 208) to obtain the exposure area dose (step S209). According to this modification, the correlation between the feature value (for example, average value) of the histogram of pixel values in the image data and the body thickness may not be obtained in advance.

  Next, the X-ray diagnostic apparatus of the present invention using a method for correcting the exposure area dose according to the body thickness will be described with reference to FIG. The X-ray diagnostic apparatus of this embodiment may be either a mobile type or a stationary type. Also in this embodiment, the configuration of the X-ray diagnostic apparatus is basically common to Embodiments 1 and 2, and the following description will be focused on differences from Embodiments 1 and 2.

  FIG. 8 schematically shows a situation in which the X-rays irradiated from the X-ray source 1 pass through the subject P and reach the X-ray detector 2. As is clear from this figure, X-rays are not irradiated as parallel lines, but are irradiated onto the subject P as X-ray weights C that spread radially. Therefore, the subject image area calculated in the first and second embodiments is not the projection area SR corresponding to the actual body width of the subject P, but the projection indicated by the solid subject P and the X-ray weight C. The area SS. That is, the projection area SS> the projection area SR. Furthermore, as indicated by the broken subject P and the X-ray weight C, when the body thickness is large even if the body width is the same, the projected area SF is further increased. As a result, projection area SF> projection area SS> projection area SR.

  Therefore, for example, assuming that the projection area SR corresponding to the body width is an appropriate exposure area of the subject, it can be seen that the accurate exposure area can be obtained by correcting the subject image area according to the body thickness. For example, the subject image area (see Examples 1 and 2) calculated based on the image data of the X-ray detector may be multiplied by a coefficient so that the area after multiplication approaches the projection area SR. This coefficient is obtained in advance from the geometrical relationship between the body thickness and the X-ray weight corresponding to the SID, and the correlation between the projected area SR and the projected area SS, SR by the X-ray weight is obtained. What is necessary is just to set so that it may become a small value, so that a big subject is large. The multiplication of the coefficient may be performed by the subject image area calculation unit 7 or may be performed by the exposure area dose calculation unit 8.

  In the first embodiment, since the body thickness is not recognized by the X-ray diagnostic apparatus, in order to correct the subject image area, the X-ray diagnostic apparatus recognizes the body thickness by actually measuring the body thickness. Just keep it. In the second embodiment, the subject image area is corrected using Ls / SID = LF / FSD (see FIG. 2). However, the correction may be performed by the method shown in FIG.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, various methods can be obtained for SID, FSD, and body thickness. For example, there are the following methods. (1) SID is measured with a measure or the like, body thickness is calculated from the feature quantity of the histogram, and FSD is obtained by subtracting body thickness from SID. (2) SID and FSD are measured and body thickness is obtained by subtracting FSD from SID. (3) FSD and body thickness are measured, and SID is obtained by adding body thickness to FSD. (4) Measure SID, FSD, and body thickness.

  Further, although the mobile X-ray diagnostic apparatus for round trips is shown in the first embodiment, it may be a mobile X-ray diagnostic apparatus for surgery.

  The X-ray diagnostic apparatus of the present invention can be suitably used as an X-ray diagnostic apparatus used in the medical field regardless of whether it is a mobile type or a stationary type.

  1 X-ray source, 2 X-ray detector, 3 Histogram creation means, 4A SID calculation means, 4B FSD calculation means, 5 Correction means, 6 Direct X-ray dose calculation means, 7 Subject image area calculation means, 8 Area dose calculation means , 9 Display means, 11 White area, 12 Black area, 13 Gray area, 14, 15 Dashed line, CX weight, SR, SS, SF Projection area

Claims (3)

An X-ray source for irradiating X-rays having a spread toward the subject, is disposed opposite to the said X-ray source, the X-ray detector for detecting and outputting a transmission X-ray of the subject as image data An X-ray diagnostic apparatus comprising:
Histogram creation means for creating a histogram of pixel values in the image data output from the X-ray detector,
Based from the irradiation amount of X-rays obtained from X SenTeru morphism conditions as the X-ray source to the distance to the X-ray detector, corresponding to the direct X-ray dose and the direct X-rays that will be detected by the X-ray detector Direct X-ray dose calculation means for calculating pixel values;
Based on the pixel values calculated by the direct X-ray dose calculation means and the histogram created by said histogram creating means, the test and calculating the subject image area in the image data, based on the body thickness of the subject Based on the subject image area calculating means for correcting the calculated subject image area, the direct X-ray dose calculated by the direct X-ray dose calculating means, and the subject image area corrected by the subject image area calculating means And an area dose calculating means for calculating an exposed area dose of the subject,
X-ray diagnostic equipment characterized by A calculation unit that calculates the body thickness of the subject using the feature amount of the histogram generated by the histogram generation unit;
2. The X-ray diagnostic apparatus according to claim 1, wherein: A correction means for subtracting at least one of an absorbed X-ray dose of a grid arranged on the back surface of the subject or an absorbed X-ray dose of an additional filter mounted close to the X-ray source from the irradiated X-ray dose; about,
The X-ray diagnostic apparatus according to claim 1 or 2, wherein:

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