JPH05111481A - Reference for quantitative analysis of bone-salt and quantitative analysis of bone-salt - Google Patents

Abstract

PURPOSE:To provide the reference for the quantitative analysis of the bone-salt which can make automatic detection and the method for the quantitative analysis of the bone-salt using this reference. CONSTITUTION:Markers 2A, 2B are provided on the reference 1 for the quantitative analysis of the bone-salt arrayed with sections 1a, 1b to 1f stepwise simulating the contents of the bone-salt (CaCO3).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference for quantitative analysis of bone mineral used for quantitative analysis of bone mineral in human body and a method for quantitative analysis of bone mineral using this reference and energy subtraction technique. Is.

[0002]

2. Description of the Related Art Bone mineral quantification, that is, quantitative measurement of the amount of calcium in bone is necessary for preventing fractures. That is, knowing the minute changes in calcium in the bone enables early detection of osteoporosis and is effective in preventing fractures.

Therefore, various methods for quantifying bone mineral have been proposed and implemented in the past, as listed below.

I) MD method (Microdensitometry): This is an X-ray image of the middle phalanx with an aluminum step wedge (stepped pattern), and the density is measured by a densitometer.
The amount of X-ray absorption is converted corresponding to the aluminum step wedge, and the value is corrected by the bone width to quantify bone mineral. The device configuration is simple, but there is a problem in quantitative accuracy. In addition, there is a drawback in that the vertebra, which most commonly represents osteoporosis, cannot be measured.

Ii) SPA method (Single Photon Absorptiome
try): This is 15 cm after low-energy gamma rays penetrate the bone
It is detected by a scintillation detector that is far away, and the weight per unit length of bone is calculated from the analog calculation by the change in the count number of γ rays, which is more accurate than the MD method. Also, it has the drawback that it cannot measure the vertebrae, and it requires special management due to the use of radioisotopes, and has the drawback that the radiation source must be replaced because it has a half-life period.

Iii) DPA method (Dual Photon Absorptiome)
try): This uses ¹⁵³ Gl, which is a nuclide having two energy peaks of 44 KeV and 100 KeV, as a radiation source.
The amount of bone mineral is measured by the difference in the amount of bone penetration of the energy rays of the species. The amount of bone mineral in the lumbar spine and femoral neck is measured.
Moreover, there is an advantage that the bone mineral content and fat mass of the whole body can be measured with high accuracy, but this also has a difficulty associated with the use of a radioisotope. In addition, since the irradiation of radiation is a scanning method, there is a problem that it takes 10 to several minutes for the lumbar spine and 30 to 40 minutes for the whole body.

Iv) QDR method (Quantitative Digited Radi
(ography): (aka DPX method) This is almost the same as the DPA method,
Two types of energy are obtained by combining a pulsed X-ray with a filter instead of a radioisotope, which gives good reproducibility and shortens inspection time (about 1/3 of DPA).
) Has the effect. Although it is the method most expected in terms of simplicity and performance, even though the examination time is shortened, it takes about 6 minutes to image the lumbar spine, and further shortening is desired.

V) QCT method (Quantitative Computer Tom)
(ography): This is a method for quantitatively determining the bone mineral content of the third lumbar vertebra mainly by CT number using X-ray CT, and it is possible to quantify by cross-section, but the problem is that the device becomes large-scale. There is.

Vi) DQCT method (Dual energy Quantitativ)
e Computer Tomography): This is to quantify bone mineral by performing energy subtraction using two kinds of energy in the QCT method, and it is possible to quantify bone mineral without the influence of fat in bone tissue. However, this also has a problem that the device becomes large-scale.

As enumerated above, the conventional methods for quantifying bone mineral have the problems that a simple method has low accuracy, and a high accuracy method has a large apparatus and a long inspection time.

Therefore, the applicant of the present invention has proposed a bone mineral quantitative analysis method using energy subtraction (see Japanese Patent Application No. 2-114611). The method using the energy subtraction means that two or more stimulable phosphor sheets are irradiated with radiation having different energies transmitted through a subject including soft tissue and bone tissue, respectively. Is stored and recorded, these sheets are scanned with excitation light to photoelectrically read the radiation image and converted into a digital image signal, and the digital image signal is subtracted between corresponding pixels of each image to obtain a radiation image. In the energy subtraction for obtaining the difference signal forming only the image of the bone tissue, the bone mineral reference simulating a human bone in which the bone mineral content is changed stepwise is obtained at the same time when the radiation image of the subject is obtained. By comparing the density of the shadow of the bone tissue with the density of the bone mineral reference on the image of the bone tissue alone (bone image). A method of quantifying bone mineral density.

[0012]

However, in the above-mentioned energy subtraction method, the operator must manually specify the area where the bone mineral reference exists and obtain the concentration calibration curve from this area. It was a very time-consuming task for me. In addition, since the area where the reference exists is manually specified, it may not be possible to grasp the exact position of the bone mineral reference due to an input error, and it may not be possible to obtain a calibration curve with an appropriate concentration.

In view of the above circumstances, it is an object of the present invention to provide a reference for quantitative analysis of bone mineral which can be automatically detected, and a method for quantitative analysis of bone mineral using the reference for quantitative analysis of bone mineral.

[0014]

In the reference for quantitative analysis of bone mineral according to the present invention, two or more stimulable phosphor sheets have different energies transmitted through a subject including soft tissue and bone tissue. Radiation is applied to store and record the radiation image of the subject on each of the stimulable phosphor sheets, and the sheet is scanned with excitation light to convert the radiation image into stimulated emission light, and the stimulated emission light is emitted. A difference signal for photoelectrically reading the light emission amount and converting it into a digital image signal, and performing weighted subtraction between the corresponding pixels of each image to form an image of only the bone tissue of the radiographic image. And a portion equivalent to the soft tissue and the radiation absorption coefficient, which is stored and recorded together with the subject as a reference subject when quantitatively analyzing bone mineral in the bone tissue based on the difference signal. A reference for quantitative analysis of bone mineral having a portion simulating the amount of bone mineral in a stepwise manner, and to provide a reference point to the stimulable phosphor sheet when the subject and the radiation image of the reference are accumulated and recorded. It is characterized by having various markers.

Further, the method for quantitatively analyzing bone mineral according to the present invention comprises:
Each of the two or more stimulable phosphor sheets is irradiated with radiation having different energy transmitted through a subject including soft tissue and bone tissue, and a radiation image of the subject is displayed on each of the stimulable phosphor sheets. When performing cumulative recording, the above-mentioned reference for quantitative analysis of bone mineral is cumulatively recorded simultaneously with the subject at a position fixed with respect to the radiographic image, and is excited in each stimulable phosphor sheet in which the radiographic image is cumulatively recorded. Scan the light to convert the radiation image into stimulated emission light, photoelectrically read the emission amount of the stimulated emission light to convert into a digital image signal, from the image signal of the reference for quantitative analysis of bone mineral The position of the reference point provided by the marker is detected, and the position between the respective radiographic images from the respective reference points corresponding to the respective radiographic images read out from the respective stimulable phosphor sheets is detected. Calculate the deviation, correct the position deviation on the digital image signal of each radiation image according to the position deviation, detect the position of the reference based on the position of the reference point, the detected Obtaining a weighting coefficient when subtracting the digital image signal from a portion where the radiation absorption coefficient is equivalent to the soft tissue of the reference, and weighting subtraction of the digital image signal between corresponding pixels of each radiation image based on the weighting coefficient And obtaining a difference signal forming an image of only the reference with the bone tissue, and quantitatively analyzing bone mineral in the bone tissue with reference to the image of the reference from the difference signal. It is a thing.

[0016]

The reference for quantitative analysis of bone mineral according to the present invention is
Reference for quantitative analysis of bone mineral, which is stored and recorded in a stimulable phosphor sheet together with the subject when performing bone mineral quantitative analysis, and has a portion having an equivalent radiation absorption coefficient to soft tissue and a portion simulating the amount of bone mineral in stages A marker is provided to provide a reference point to the stimulable phosphor sheet when recording a radiation image. Further, the method for quantitative analysis of bone mineral according to the present invention is to perform quantitative analysis of bone mineral using the reference for quantitative analysis of bone mineral according to the invention,
The position of the reference is automatically detected by detecting the position of this marker. Therefore, it is possible to save the operator's trouble of manually inputting the reference position and prevent an input error. Further, the bone mineral quantitative analysis method according to the present invention automatically corrects the positional deviation generated between the radiographic images stored and recorded on two or more stimulable phosphor sheets by using this marker. Further, it is possible to obtain a subtraction image having a high spatial resolution and excellent in observation and interpretation suitability without a false image, and it becomes possible to perform a bone mineral quantitative analysis with high accuracy.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings.

FIG. 1 is a schematic perspective view showing an embodiment of the reference for quantitative analysis of bone mineral according to the present invention.

As shown in FIG. 1, the reference 1 for quantitative analysis of bone mineral according to the present invention is the amount of bone mineral, that is, CaCO ₃
Sections 1a, 1b with stepwise different contents (wt%) of
The structure has 1f arranged, and the content of CaCO ₃ is known in advance. In the embodiment according to the present invention, the section 1f is set so that the soft tissue of the subject and the radiation absorption coefficient are equivalent. Furthermore, in the vicinity of the corner of the reference 1, two circular marker forming members 2A, 2 made of a radiation shielding material are formed.
B is provided.

Reference 1 for quantitative analysis of bone mineral
Also, the same subject having soft tissue and bone is irradiated with X-rays to capture an X-ray image.

FIG. 2A shows two stimulable phosphor sheets A,
B shows a state in which X-rays 4 that have passed through the same subject 3 having soft tissues and bones and the reference 1 are irradiated with different energies. That is, the X-ray transmission images of the subject 3 and the reference 1 are accumulated and recorded on the first stimulable phosphor sheet A, and then the stimulable phosphor sheet A,
At the same time as B is quickly replaced, the tube voltage of the X-ray source 5 is changed, and the X-ray images of the subject 3 and the reference 1 having different transmission X-ray energies are accumulated and recorded in the stimulable phosphor sheet B. At this time, the positional relationship between the subject 3 and the reference 1 in the stimulable phosphor sheets A and B is the same.

Further, FIG. 2 (b) shows that two stimulable phosphor sheets A and B are overlapped with each other, and a filter F which partially absorbs radiation energy is interposed therebetween and the object 3 and the reference 1 are inserted.
This shows a state of irradiating the X-ray 4 that has passed through and the radiation of different energy levels to the stimulable phosphor sheets A and B at the same time (so-called one-shot energy subtraction). Regarding one-shot energy subtraction, Japanese Patent Laid-Open No. 59-8
Details are disclosed in 3486.

Two radiation images are accumulated and recorded on the two stimulable phosphor sheets A and B by using either the method shown in FIG. 2 (a) or the method shown in FIG. 2 (b). Next, an X-ray image is read from these two stimulable phosphor sheets A and B by an image reading means as shown in FIG. 3 to obtain a digital image signal representing the image. First, while moving the stimulable phosphor sheet A in the direction of arrow Y for sub-scanning, the laser light 11 from the laser light source 10 is main-scanned in the X direction by the scanning mirror 12, and the phosphor sheet A is accumulated X. The linear energy is increased according to the accumulated and recorded X-ray image.
Diverge as. The stimulated emission light 13 is emitted from one end of a light guide 14 formed by molding a transparent acrylic plate.
The light enters the inside of 14 and repeats total internal reflection, and the photo
At 15, the emission amount of the stimulated emission light 13 is output as the image signal S. The output image signal S is supplied to the amplifier and A / D.
It is converted into a digital image signal log S _A logarithmic values (log S) by logarithmic converter 16 including a transducer. This digital image signal logS _A is stored in a storage medium 17 such as a magnetic disk. Next, in the same manner, the recorded image of the other stimulable phosphor sheets B is read, the digital image signal log S _B are stored similarly in the storage medium 17.

If the reference 1 and the subject 3 are accumulated and recorded on the stimulable phosphor sheets A and B by the method shown in FIG. 2 (a) or 2 (b), the markers 2A and 2B and the subject 3 will be recorded. The relative positional relationship of does not change. Therefore, at the time of photographing, when the stimulable phosphor sheet is carried into the photographing table, the subject 3 which is generated due to the mechanical accuracy is generated.
Absolute positional relationship of the storable phosphor sheets A and B,
Further, even if the absolute positional relationship of the scanning light with respect to the subject 3 that is generated during reading is changed, the relative positional relationship of the subject 3 with respect to the markers 2A and 2B does not change.

That is, the positions of the markers recorded on the stimulable phosphor sheets A and B are detected, and the positional deviation between the images is corrected based on the positions of the markers on the read digital image signal, and the subtraction is performed. By performing the processing, a good energy subtraction image can be obtained. As a method for correcting this positional deviation, Japanese Patent Laid-Open No.
As disclosed in detail in Japanese Patent Laid-Open No. 58-163338, there is a method of detecting the center coordinates of the marker by detecting the coordinates of the edge portion of the marker based on the set position of the marker and correcting the positional deviation. Be done.

As described above, the subtraction process is performed using the optimum energy subtraction parameters based on the digital image signals logS _A and logS _B in which the positional deviation has been corrected. The parameters used for this subtraction process are determined as follows.

As described above, since the center positions of the markers 2A and 2B are detected and the positional deviation is corrected,
The position where the reference 1 exists is automatically detected from the center position of each of the markers 2A and 2B. When the position of the reference 1 is detected, first, only the digital image signal of the reference 1 image is extracted and calculated. The method for quantitative analysis of bone mineral using the reference 1 for quantitative analysis of bone mineral according to the present invention requires the energy subtraction image in which the soft tissue is erased. Therefore, the radiation absorption coefficient of the soft tissue of Reference 1 is equivalent to the section 1f.
In order to match the density B _H in the high-voltage image (image of the stimulable phosphor sheet A) with the density in the low-voltage image B _L (image of the stimulable phosphor sheet B), the two images are weighted. Then, the density of the section 1f having the same radiation absorption coefficient as that of the soft tissue is made equal to the density _{BL of the} low-voltage image, and then the image signal is subtracted between the corresponding pixels of both images.

[0028] That _{is, Ssub = B L logS A -B} H · logS B + C ... (1) (C is a bias component such that substantially constant concentration) by subtraction of the image signal energy subtraction image Ssub To get In this image, the soft tissue is deleted, and an image in which only the bone part is extracted is obtained. That is, the irradiation parameter B _H / B _L is determined based on the density difference (ratio) between the high-voltage image and the low-voltage image of the section 1f having the same radiation absorption coefficient as that of the soft tissue.

FIG. 4 is a schematic diagram showing the subtraction process described above. The image 18 is an image carried by the image signal logS _{A and} is an image obtained by taking a tube voltage of the X-ray source 5 at a high voltage (for example, 120 kV) at the time of shooting. The image 19 is an image obtained by photographing with the tube voltage of the X-ray source 5 at a low voltage (60 kV). These two images
The shadows 18a and 19 of the bones of the lower back of the human body are included in 18 and 19, respectively.
a, soft tissue shadows 18b, 19b, reference 1 shadow
18c and 19c are imprinted, and the bone part image 20 in which the shadows 18b and 19b of the soft tissue are erased is obtained by performing the arithmetic processing shown in Expression (1).

Since the subtraction image thus obtained has the image 20c of the reference 1 in addition to the image 20 of the bone part of the subject 3, the operator refers to the reference image 20c and the bone part of the subject 3 is referred to. You can see the image. Here, it is possible to select the portion of the stepwise pattern of the reference image 20c that is the same as or close to the density of the portion of the bone image for which the bone mineral is to be quantified, and to know the amount of bone mineral corresponding to the density.

For this purpose, the CaCO ₃ content of each section 1a, 1b, ...
A calibration curve 24 (see FIG. 5) is created in association with the density on the bone image 20, which is the subtraction image, and the point on the calibration curve 24 corresponding to the measured value is associated with the true value to obtain the true value. Know the value (salt amount). At this time, if the density on the subtraction image 20 is, for example, an intermediate value d ₁ between the densities Pb and Pc of two adjacent sections of the pattern of the reference image 20c, the corresponding true value v ₁ obtained from the calibration curve 24 is obtained. This is the amount of bone mineral to be sought.

The amount of salt obtained as described above may be displayed and recorded by various known display devices and recording devices. For that purpose, the value read from the calibration curve 24 may be manually input, displayed, and recorded, but the calibration curve is stored in a table memory and the bone image of the bone image designated on the display device such as a CRT is displayed. The concentration at the position may be converted into the amount of salt by this calibration curve and automatically displayed and recorded.

In the above-mentioned embodiment, a circular marker is provided near the corner of the reference for quantitative analysis of bone mineral, but the marker may be provided at any position as long as the reference position can be detected. However, the shape is not limited to the circular shape.

Further, in the above-mentioned embodiment, only the section 1f of the reference for quantitative analysis of bone mineral is set so that the radiation absorption coefficient is equal to that of the soft tissue of the subject, but the thickness varies depending on the site of the soft tissue. Since the radiation transmittance may be different, the two sections of the reference may be set to be equal to the radiation absorption coefficient of each of the thick and thin portions of soft tissue.

[0035]

As described in detail above, the reference for quantitative analysis of bone mineral according to the present invention is provided with a marker for providing a reference point to the stimulable phosphor sheet at the time of recording a radiation image. .. The method for quantitative analysis of bone mineral according to the present invention uses this reference, and the position of the reference is automatically detected by the marker. Therefore, it is possible to save the operator's trouble of manually inputting the reference position and prevent an input error.

Furthermore, the method for quantitative analysis of bone mineral according to the present invention can correct the positional deviation generated between the radiographic images accumulated and recorded on two or more stimulable phosphor sheets by this marker, and therefore, it is suitable for observation and interpretation. An excellent subtraction image can be obtained, and the bone mineral quantitative analysis can be accurately performed.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a reference for quantitative analysis of bone mineral according to the present invention.

FIG. 2 is a diagram showing imaging steps in an embodiment of the method for quantitative analysis of bone mineral according to the present invention.

FIG. 3 is a diagram showing a reading step in the embodiment of the present invention.

FIG. 4 is a diagram schematically showing a subtraction process in the embodiment of the present invention.

FIG. 5 is a diagram showing a calibration curve of concentration obtained by an example of the present invention.

[Explanation of symbols]

 1 Reference 2A, 2B Marker 3 Subject 4 X-ray 5 X-ray source 10 Laser light source 12 Scanning mirror 13 Photostimulated emission light 15 Photomul 20 Bone image

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G01N 33/50 7055-2J G21K 4/00 L 8805-2G

Claims (2)

[Claims] 1. The two or more stimulable phosphor sheets are irradiated with radiations having different energies which have passed through a subject including soft tissue and bone tissue, and the stimulable phosphor sheets are subjected to the irradiation. A radiation image of a subject is stored and recorded, each sheet is scanned with excitation light to convert the radiation image into stimulated emission light, and the emission amount of the stimulated emission light is photoelectrically read out and converted into a digital image signal. Then, a weighted subtraction of the digital image signal is performed between corresponding pixels of each image to obtain a difference signal forming only an image of the bone tissue of the radiation image, and the bone in the bone tissue is based on the difference signal. For quantitative analysis of bone salt, which has a portion equivalent to the soft tissue and the radiation absorption coefficient and a portion simulating the bone mineral content stepwise, which is accumulated and recorded as a reference photograph object together with the medical object when quantitatively analyzing salt. Les A reference for quantitative analysis of bone mineral, comprising a marker for providing a reference point to the stimulable phosphor sheet when accumulating and recording a radiation image of the subject and the reference. 2. Two or more stimulable phosphor sheets are irradiated with radiations having different energies that have passed through a subject including soft tissue and bone tissue, and each stimulable phosphor sheet is exposed to the radiation. When accumulating and recording a radiation image of a subject, the reference for quantitative analysis of bone mineral according to claim 1 is simultaneously accumulated and recorded at a position fixed with respect to the radiation image, and the radiation image is accumulated and recorded. Each stimulable phosphor sheet is scanned with excitation light to convert the radiation image into stimulated emission light, and the emission amount of the stimulated emission light is photoelectrically read out to be converted into a digital image signal. The position of the reference point provided by the marker of the reference for quantitative analysis of bone mineral is detected, and from each reference point corresponding to each radiographic image read from each stimulable phosphor sheet. The position shift between the radiographic images is calculated, the position shift on the digital image signal of the radiographic images is corrected according to the position shift, and the position of the reference is determined based on the position of the reference point. Detecting, the weighting coefficient when subtracting the digital image signal from the portion where the radiation absorption coefficient is equivalent to the soft tissue of the detected reference is obtained, and between the corresponding pixels of each radiation image based on the weighting coefficient A weighted subtraction of the digital image signal is performed to obtain a difference signal forming an image of only the reference with the bone tissue, and the bone mineral in the bone tissue is quantified by referring to the image of the reference from the difference signal. A method for quantitatively analyzing bone mineral, characterized by analyzing.