JPH10192265A - X-ray measurement unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically correct variation in characteristics of an X-ray generator or an X-ray detector, by calculating the quantity attenuated by a filter from an X-ray detection value in inserting a filter for correction and an X-ray detection value in not inserting the filter for correction and correcting the measurement result. SOLUTION: An X-ray generator 18 is equipped under a bed 16 and an X-ray detector 22 above the bed 16, and those are integrally driven by a scanner 24 in the horizontal direction. In a correction unit 20 equipped above the X-ray generator 18, when an arm is drawn into by a actuator 42, a filter plate 40 is moved in the horizontal direction and the X-ray beam 100 passes through a through hole 40A at the central part of the filter plate 40 in an ordinary measurement of a subject. On the other hand in a correction mode, the filter plate 40 is moved in the horizontal direction to pass the X-ray beam through the filter plate 40. Thus the measurement result is corrected by calculating the quantity of attenuation by the filter from the X-ray detection value with the correction filter inserted and the X-ray detection value without correction filter inserted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to correction in an X-ray measuring apparatus, particularly in a bone mineral density measuring apparatus.

[0002]

2. Description of the Related Art A bone mineral amount measuring device, which is a kind of X-ray measuring device, is a device for calculating the amount of bone mineral by transmitting X-rays through a subject, and is often used for diagnosing bone disease and preventing it. Used by medical institutions. As is well known, bones are composed of minerals (bone minerals) such as calcium which attenuate X-rays.
By calculating the amount of attenuation (attenuation rate) during line transmission,
The amount of bone mineral per unit area is calculated. Bone is covered with soft tissues such as muscle and fat, and X-ray attenuation is also caused in that part. In order to eliminate the influence of such soft tissue, a conventional bone mineral density measuring apparatus uses X-rays of two types of energy (DXA method). This specifies the attenuation of each of the bone portion and the soft tissue portion by solving simultaneous equations based on the attenuation calculated for each energy. Conventionally, in order to generate two types of X-rays, the voltage of the X-ray generator is varied or an attenuation filter is used.

[0003]

Incidentally, in the above-described bone mineral density measuring device, when the secular change (drift) of the operating characteristics of the X-ray generator and the X-ray detector occurs, the calculation is finally performed. The accuracy of estimating bone mineral density will be reduced. This also affects the accuracy of disease diagnosis. Also, in the case of regularly observing the bone mineral content of the same patient,
When the drift occurs, a problem occurs in reproducibility of each measurement. This problem is pointed out similarly in other X-ray measurement apparatuses.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an X-ray measurement system capable of automatically compensating for variations in the characteristics of an X-ray generator or an X-ray detector. It is to provide a device.

Another object of the present invention is to provide a bone mineral density measuring apparatus capable of performing a highly accurate bone mineral density calculation by reducing errors due to aging.

[0006]

To achieve the above object, the present invention provides an X-ray measuring apparatus for measuring an object by transmitting X-rays through the object, comprising: at least one correction filter; A filter insertion means for inserting the filter into the X-ray beam path in a state where the subject is not inserted into the X-ray beam path; and an X-ray detection value when the filter is inserted and an X-ray detection value when the filter is not inserted. It is characterized by including an attenuation amount calculating means for calculating the filter attenuation amount, and a correcting means for comparing the current filter attenuation amount with the reference attenuation amount and correcting the measurement result.

[0007] According to the above configuration, the X-ray detection value in a state in which the subject is not interposed in the X-ray beam path and the correction filter is inserted in the X-ray beam path, and a state in which the correction filter is not inserted. The amount of filter attenuation is calculated based on the X-ray detection value obtained in step (1), and the X-ray measurement result is corrected by comparing the amount of filter attenuation with the reference amount of attenuation. That is, when the drift occurs as described above, the effect appears on the measurement result of the subject, but similarly, the effect of the drift also appears on the filter attenuation, so that the current filter attenuation and the current filter attenuation are stored in advance. The drift amount is specified by comparison with the reference attenuation amount, and the measured value is corrected based on the drift amount.

According to the present invention, sensitivity adjustment and the like are automatically performed, so that maintenance of the apparatus can be simplified and high-precision measurement can be guaranteed. This correction is desirably performed periodically, for example, desirably for each measurement.
For example, X-ray irradiation for correction can be performed at the start of scanning of the X-ray beam or at the end of scanning. One or more correction filters are prepared. Further, the filters may be switched for each of the plurality of X-ray beam intensities.

In a preferred aspect of the present invention, the apparatus further comprises a reference attenuation storage means for storing a past filter attenuation as the reference attenuation. For example, by measuring the filter attenuation when the device is shipped from the factory or installed at the customer,
It can be stored as a reference attenuation. Further, it is also possible to measure the filter attenuation when the sensitivity adjustment is completed using a phantom or the like at the time of maintenance, and to store it as the reference attenuation. If the filter attenuation amount at each time point in the past is stored, the history of the device characteristics can be read. The above-mentioned filter is made of, for example, vinyl chloride, but other materials can be used.

In a preferred aspect of the present invention, the X-ray irradiation for the correction is performed within a scanning range of the X-ray beam and in an area other than the area where the subject exists. According to this configuration, X-ray irradiation for correction can be performed without moving the subject while the subject is placed on the mounting table.

In a preferred aspect of the present invention, the filter and the filter insertion means constitute a filter unit,
The filter unit is scanned together with the scanning of the X-ray beam, and the filter inserting means inserts the filter into the X-ray beam path at the X-ray irradiation point for the correction.

In a preferred aspect of the present invention, the filter has a through-hole through which an X-ray beam passes, and the filter inserting means shifts the X-ray beam from the through-hole by laterally moving the filter. It is characterized by the following.

In a preferred aspect of the present invention, the filter is fixedly arranged within an X-ray beam scanning range and in a region other than a region where the subject exists, and an X-ray beam scanning unit functions as the filter insertion unit. It is characterized by doing. According to such a configuration, there is an advantage that it is not necessary to separately provide a filter insertion unit.

In a preferred aspect of the present invention, the correction means compares the current filter attenuation amount with the reference attenuation amount to calculate a correction coefficient, and a bone calculating means using the correction coefficient. Correction operation means for performing an operation for correcting the amount of salt. Note that, in addition to the correction by the data processing described above, the correction can be performed by physical adjustment such as adjustment of the drive voltage of the X-ray generator or output adjustment of the X-ray detector. The configuration may be such that an alarm is automatically generated when drift occurs to the extent that correction is difficult.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of an X-ray measuring apparatus according to the present invention. FIG. 1 is a block diagram showing a bone mineral amount measuring apparatus as a kind of X-ray apparatus.

This bone mineral amount measuring device is a measuring device for measuring the bone mineral amount of an arm, a lumbar vertebra or the like, and a subject 10 is placed on a fixedly arranged bed 16. The subject 10 is a living body, and the bone 12 is covered with a soft tissue 14. In the present embodiment, an X-ray generator 18 is provided below the bed 16, and an X-ray detector 2 is provided above the bed 16.
2 are arranged. The X-ray generator 18 is a device that generates high-energy X-rays or low-energy X-rays as necessary, and the X-ray detector is an X-ray 10 that has passed through the subject 10.
This is a device that detects 0. The X-ray generation device 18 and the X-ray detection device 22 are driven integrally by the scanning device 24 in the horizontal direction.

A correction unit 20 is provided above the X-ray generator 18, and the correction unit 20 is scanned together with the X-ray generator 18. This correction unit 20
Is used for adjusting the sensitivity of the X-ray generation device 18 and the X-ray detection device 22, and its function will be described in detail later.

The control section 26 controls the operation of the present apparatus, and executes various calculations described later. Storage unit 3
0 stores various data, including a reference attenuation amount for sensitivity correction. The storage unit 30 stores, for example, EE
It is composed of a PROM or the like. The display unit 32 includes a control unit 26.
Is displayed.

In the embodiment shown in FIG.
And the X-ray detection device 22 is driven in the horizontal direction,
Of course, these may be fixedly arranged and the bed 16 may be driven in the horizontal direction. In this case, the bed 16 is driven by the scanning device 24, whereby the subject 10 itself is scanned.

FIG. 2 shows a specific example of the correction unit 20. In this embodiment, the correction unit 20
Is a filter plate 40 for attenuating X-rays and an actuator 4
2 and an arm 44. Actuator 4
When the arm 2 retracts the arm 44, the filter plate 40 moves in the horizontal direction. A through-hole 40A is formed in the center of the filter plate 40, and the X-ray beam 100 passes through the through-hole 40A during a normal measurement of an object. That is, the attenuation effect by the filter plate 40 is not performed. On the other hand, in the correction mode, the actuator 42
Is driven, the filter plate 40 moves in the horizontal direction with the retracting movement of the arm 44, and as a result, the X-ray beam passes through the filter plate 40. This is schematically indicated by reference numeral 102.

FIG. 3 shows another embodiment of the correction unit. In this embodiment, the bed 16 is composed of a frame 46 forming a frame thereof and a bed plate 48 made of resin or the like, and a correction filter plate 50 for attenuating X-rays is provided behind the bed plate 48. ing. In this embodiment, no equivalent to an actuator is provided, and the insertion of the filter plate 50 is achieved by scanning the X-ray beam 100 and transmitting the same through the filter plate 50. In other words, the filter plate 50 is located within the subject existence region 1
X-ray beam 1
By moving 00 to such a non-existent area, the X-ray beam can be positioned on the filter plate 50 as a result.

The above-described correction unit 20 and filter plate 5
Zero or the like is provided one or more. For example, a plurality of filter plates having different attenuation effects may be used.

In this embodiment, a 6 mm thick vinyl chloride plate is used as the filter plate 40 shown in FIG. Of course, for example, a thin aluminum plate can be used. Since the X-rays always pass through the bed 16 both when the subject exists and when the subject does not exist, the attenuation effect of the bet 16 does not matter.

Next, measurement of bone mineral content and sensitivity correction by the bone mineral content measuring device will be described. As shown in FIG. 1, when measuring the bone mineral content of the subject 10, the subject 10 is first placed on the bed 16, and then the scanning device 24
Thus, high-energy X-rays and low-energy X-rays are irradiated at predetermined intervals while scanning the X-ray generator 18 and the X-ray detector 22 in the horizontal direction.

FIG. 4 shows such scanning of the X-ray beam 100, and the subject 200 is composed of the soft tissue 204 and the bone 202, and the scanning of the X-ray beam 100 shown in FIG. An X-ray intensity pattern corresponding to the bone 202 is obtained as shown in FIG. In FIG. 4, CPS _H (x) is a count value of high energy at the x coordinate, and similarly CPS _L (x) is a count value of low energy X-ray at the x coordinate. After the data of each coordinate is thus obtained, the following equations (1) and (2) are calculated.

[0027]

(Equation 1) In the above equation, R _L (x) indicates the amount of attenuation of low energy X-rays at the x coordinate, and R _H (x) indicates the amount of attenuation of high energy X-rays at the x coordinate. In addition,
CPS _L (0) and CPS _H (0) are each subject 2
A count value at a position where 00 does not exist, specifically, at a coordinate of x = 0 is shown.

As described above, when the amount of attenuation by low energy X-rays and the amount of attenuation by high energy X-rays are obtained,
Based on them, the amount of bone mineral is calculated in the same manner as in the related art.

However, if the operating characteristics of the X-ray generator 18 and the X-ray detector 22 change due to aging, the count value may fluctuate from the true value. Therefore, in the present embodiment, the correction unit 20 is provided as described above, and a correction coefficient for sensitivity correction is calculated using the correction unit 20. Hereinafter, this will be described in detail.

In the present embodiment, the attenuation reference value is taken in at the time of factory shipment of the apparatus, at the time of installation at a customer, or at a predetermined time.
This is performed after adjusting the operating characteristics of the X-ray generator or the X-ray detector using an object with a known attenuation such as a phantom.

The acquisition of the reference attenuation will be described in detail with reference to FIG.

In step S101, it is confirmed that the subject does not exist and the filter plate is not inserted into the X-ray beam path. In step S102, low energy X-ray irradiation and high energy X-ray irradiation are performed. This allows X in the air
CPS _L-AIR and CPS _H-AIR, which are count values when the line is transmitted, are captured. Then, in S103, the actuator 42 operates as described above to insert the filter plate 40 on the X-ray beam. In S104, S10
2, the low energy and the high energy are sequentially irradiated, whereby the count values CPS _L and CPS _H are captured.

Next, when taking in the reference attenuation amount, that is, performing initial setting, an operation based on the following second equation is executed in S105.

[0034]

(Equation 2) Here, ATT _Lref is the reference attenuation of the filter when low energy X-rays are irradiated, and ATT _Href is the reference attenuation of the filter when high energy X-rays are irradiated. In S106, such two reference attenuations are stored in the storage unit 30 shown in FIG. The initial setting is completed by the above steps.

On the other hand, when correcting the bone mineral density measurement result of the subject, the respective steps of S101 to S104 shown in FIG. 5 are executed as described above. Then, this time, S107 is executed thereafter, and the following third equation is calculated.

[0036]

(Equation 3) Here ATT _L is the attenuation of the filter for the low energy X-rays, ATT _H is the attenuation of the filter for the high energy X-rays.

In step S108, the following formula is executed, and the attenuation of the subject calculated based on the above formulas (1) and (2) is corrected.

[0038]

(Equation 4) Here, R ′ _L (x) and R ′ _H (x) indicate the amounts of attenuation of the subject after correction, respectively. The amount of bone mineral is calculated in the same manner as in the prior art using these attenuation amounts.

As described above, according to the above-described embodiment, even if the characteristics of the apparatus change, the correction coefficient is determined by the ratio of the reference attenuation of the filter acquired in the past to the attenuation of the filter currently acquired. Then, the measurement result can be corrected by multiplying the obtained correction coefficient by the amount of attenuation of the subject. In the above embodiment, the attenuation amount is multiplied by the correction coefficient. However, the sensitivity may be adjusted by multiplying the count value by a correction coefficient for correcting the count value. In the above-described embodiment, the correction is performed by the data operation. However, for example, the voltage adjustment of the X-ray
It is also possible to adjust the sensitivity of the line detection device 22 and the like.

In the above embodiment, the amount of attenuation by the filter is obtained at the start of the X-ray beam scan. However, such an amount of attenuation is obtained not only at the start of the scan but also at the end of the scan, and the average value thereof is used. Then, the above-described correction calculation can be performed. According to such an embodiment, there is an advantage that drift during X-ray scanning can be further corrected.

[0041]

As described above, according to the present invention,
Even if the characteristics of the X-ray generator or the X-ray detector fluctuate, the fluctuation can be automatically corrected. In particular, according to the present invention, errors due to aging can be reduced to achieve high-precision measurement. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an entire configuration of a bone mineral density measuring device according to the present invention.

FIG. 2 is a diagram illustrating a specific configuration of a correction unit.

FIG. 3 is a diagram illustrating another embodiment of a correction unit.

FIG. 4 is a diagram showing acquisition of an X-ray intensity pattern by scanning with an X-ray beam.

FIG. 5 is a flowchart showing each process at the time of initial setting and at the time of performing correction.

[Explanation of symbols]

18 X-ray generation device, 20 correction unit, 22 X-ray detection device, 24 scanning device, 26 control unit, 30 storage unit, 40 filter plate, 42 actuator, 44
arm.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masaki Kobayashi 6-22-1, Mure, Mitaka-shi, Tokyo Aloka Co., Ltd.

Claims (7)

[Claims] 1. An X-ray measuring apparatus for measuring an object by transmitting the X-rays through the object, wherein the at least one correction filter and the filter are arranged in a state where the object is not inserted into the X-ray beam path. Insertion means for inserting the X-ray into the X-ray beam path; X-ray detection values when the filter is inserted;
X: an attenuation amount calculating means for calculating a filter attenuation amount from a line detection value; and a correcting means for comparing a current filter attenuation amount with a reference attenuation amount and correcting a measurement result. Line measuring device. 2. The X-ray measuring apparatus according to claim 1, further comprising a reference attenuation storage unit for storing a past filter attenuation as the reference attenuation. 3. The apparatus according to claim 1, wherein the X-ray irradiation for the correction is performed within a scanning range of the X-ray beam and in a region other than the region where the subject exists. measuring device. 4. The apparatus according to claim 1, wherein the filter and the filter inserting means constitute a filter unit, wherein the filter unit is scanned together with the scanning of the X-ray beam, and wherein the filter inserting means performs the correction. An X-ray measuring apparatus, wherein the filter is inserted into an X-ray beam path at one or more X-ray irradiation points. 5. The apparatus according to claim 4, wherein the filter has a through-hole through which an X-ray beam passes, and the filter insertion means moves the filter laterally to allow an X-ray beam to pass through the through-hole. An X-ray measuring device characterized by shifting. 6. The apparatus according to claim 1, wherein the filter is fixedly arranged in a scanning range of the X-ray beam and in a region other than a region where the subject exists, and the X-ray beam scanning unit includes the filter inserting unit. An X-ray measurement device characterized by functioning as a device. 7. The apparatus according to claim 1, wherein the correction means compares the current filter attenuation with the reference attenuation to calculate a correction coefficient, and uses the correction coefficient. An X-ray measuring apparatus, comprising: a correction calculating means for performing a calculation for correcting the amount of bone mineral.