JP3256667B2 - X-ray measurement device - Google Patents

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]

In order to achieve the above-mentioned object, the present invention provides a low-energy X-ray as an X-ray beam.
An X-ray generator that generates high-energy X-rays at a predetermined cycle ;
And the X-ray detection unit, wherein provided between the X-ray generator and said X-ray detector comprising a bed on which a patient, the low energy X-rays and high energy X generated by the X-ray generator
The line by transmitting to the subject, wherein each of the transmitted X-rays X
In an X-ray measuring apparatus that measures an object by detecting the object with a X-ray beam path, the X-ray measurement apparatus includes at least one correction filter and the filter that is not inserted into the X-ray beam path. A filter unit provided in the X-ray generation unit, and an X-ray generation unit and the X-ray detection unit provided with the filter unit, which are integrally scanned in a horizontal direction. A scanning unit, and the low energy X-rays and the high energy
For each energy X-ray , attenuation calculating means for calculating a filter attenuation from an X-ray detection value when a filter is inserted and an X-ray detection value when a filter is not inserted;
For each high energy X-ray, the current filter attenuation and the reference attenuation are compared, and the X-ray generator and the X-ray detector are compared.
And correcting means for correcting the measurement result by specifying the drift amount of the operation characteristic of (1 ).

[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.

[0011]

[0012] In a preferred embodiment of the invention, the through hole for passing the X-ray beam is formed on the filter, the filter insertion means causes the lateral movement of the filter in the horizontal direction
When the filter is inserted, the X-ray beam is shifted from the through hole so that the X beam is
Filter, and when the filter is not inserted,
The X-beam is passed through the hole .

[0013]

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.

[0020]

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 a reference example of the correction unit. In this reference example , 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 the actuator is provided.
By scanning the line beam 100 and transmitting it through the filter plate 50, the insertion of the filter plate 50 is achieved as a result. In other words, the filter plate 50 is provided in a non-existing area other than the subject existing area 106 in the X-ray beam scannable area 104, and by moving the X-ray beam 100 to such a non-existing area, The X-ray beam can be positioned on the filter plate 50.

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 a reference example 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.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaki Kobayashi 6-22-1, Mure, Mitaka-shi, Tokyo Aloka Co., Ltd. (56) References JP-A-3-185344 (JP, A) JP-A-6 -179 (JP, A) JP-A-62-161348 (JP, A) JP-A-60-237349 (JP, A) JP-A-4-11473 (JP, A) (58) Fields investigated (Int. . ^7, DB name) A61B 6/00 - 6/14 H05G 1/00 - 1/70 G01N 23/00 - 23/18 G01T 1/00 - 1/40

Claims (5)

(57) [Claims] 1. X-rays having low energy and high energy
An X-ray generation unit that generates energy X-rays at a predetermined cycle, an X-ray detection unit, and a bed provided between the X-ray generation unit and the X-ray detection unit and on which a subject is placed, An X-ray measurement apparatus that transmits a low-energy X-ray and a high-energy X-ray generated in a generation unit to a subject and detects the transmitted X-rays by the X-ray detection unit to measure the subject, One correction filter, and 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; A scanning unit that integrally scans the X-ray generation unit and the X-ray detection unit provided with the filter unit in the horizontal direction, and the low-energy X-rays and the high-energy X-rays.
To the attenuation amount calculation means for X-ray detection value when the filter insert and from the X-ray detection value when the filter is not inserted calculates the filter attenuation, each of the low energy X-ray and the high energy X-ray
Before comparing the current filter attenuation with the reference attenuation.
Drift of operating characteristics of the X-ray generator and the X-ray detector
An X-ray measuring apparatus, comprising: correcting means for correcting a measurement result by specifying an amount . 2. The apparatus according to claim 1, wherein each of the low energy X-rays and the high energy X-rays
A, X, which comprises a reference attenuation value memory to store a past filter attenuation as the reference attenuation
Line measuring device. 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 of claim 1, wherein said through hole for passing the X-ray beam is formed on the filter, the filter insertion device is capable to traverse the filter in the horizontal direction, When the filter is inserted, the X-ray beam is shifted from the through hole to transmit the X beam through the filter, and when the filter is not inserted, the X beam passes through the through hole.
Line measuring device. 5. The apparatus according to claim 1, wherein the correction unit is configured to output the low energy X-rays and the high energy X-rays separately.
A, a coefficient calculating means for calculating a correction coefficient by comparing the current of the filter attenuation and the reference attenuation, each of the low energy X-ray and the high energy X-ray
To the correction arithmetic means for performing an operation to correct the bone mineral content by using a correction factor, X-rays measurement apparatus which comprises a.