JPH05183817A - Breast energy subtraction method and photographing device - Google Patents

Abstract

PURPOSE:To improve the diagnostic efficiency of a tumor within a breast in a breast energy subtraction method and photographing device. CONSTITUTION:A breast 7 is irradiated with radiation 12 through a strontium filter 9 and the high energy radiograph information of the breast 7 is stored and recorded in a stimulable phosphor sheet 11A. Then, the low energy radiograph information of the breast 7 is stored and recorded in a stimulable phosphor sheet 11B by using a molybdenum filter 10. From the stimulable phosphor sheets 11A, 11B, two picture signals are obtained, a weighing calculation is performed and the energy subtraction picture of the breast 7 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording and reproducing an energy subtraction image of a breast, and an image capturing apparatus, and more particularly, to two radiation image information of the breast by radiation having different radiation qualities on two stimulable phosphors. After accumulating and recording, and then irradiating it with excitation light, the light stimulatingly emitted according to the accumulated and recorded image information is detected, and the image information is read and converted into an electric signal. The present invention relates to a breast energy subtraction method for obtaining a subtraction image by subtracting an electric signal, and a breast energy subtraction imaging apparatus.

[0002]

2. Description of the Related Art Radiation (X rays, α rays,
When irradiated with β rays, γ rays, ultraviolet rays, electron beams, etc.), a part of the energy of this radiation is accumulated in the phosphor, and then, when the phosphor is irradiated with excitation light such as visible light, it is accumulated. The phosphor emits stimulated emission depending on energy. A phosphor having such properties is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, radiation image information of a subject such as a human body is once recorded on a stimulable phosphor sheet (hereinafter referred to as a stimulable phosphor sheet) and scanned with excitation light. Then, a method of obtaining a radiation image of a subject having a good diagnostic suitability by processing the image signal by photoelectrically reading the stimulated emission light, photoelectrically reading the stimulated emission light, and processing the image signal has been proposed (for example, Japanese Patent Laid-Open No. 2004-242242). 55-12429, 55-116340,
55-163472, 56-11395, 56-104645, etc.).
This final image can be played as a hard copy or on a CRT. In any case, in such a radiation image information recording / reproducing method, the stimulable phosphor sheet does not finally record image information, but temporarily stores image information in order to give an image to the final recording medium as described above. Therefore, the stimulable phosphor sheet may be used repeatedly, and if it is used repeatedly, it is extremely economical.

In order to reuse the stimulable phosphor sheet as described above, the radiation energy remaining in the stimulable phosphor sheet after the stimulated emission light is read is determined by, for example, JP-A-56.
No. 11392 and No. 56-12599, the sheet is irradiated with light or heat to be released to erase the residual radiation image, and the stimulable phosphor sheet may be used again for recording a radiation image. .

On the other hand, subtraction processing of radiation images has been conventionally known. This subtraction of the radiation image means that two radiation images captured under different conditions are photoelectrically read to obtain a digital image signal,
It is a method of performing arithmetic processing on these digital image signals by associating each pixel of both images with each other to obtain a difference signal for extracting a specific structure in the radiographic image, and using the difference signal thus obtained, It is possible to reproduce the radiation image in which only the specific structure is extracted.

There are basically the following two methods for this subtraction processing. That is, the so-called time for extracting a specific structure by subtracting (subtracting) the image signal of the radiation image in which the contrast agent is not injected from the image signal of the radiation image in which the specific structure is emphasized by the injection of the contrast agent. Subtraction processing and irradiation of radiation having different energy distributions to the same subject, or irradiation of radiation after passing through the subject with different energy distribution states, is applied to the two radiation detection means, whereby a specific structure is obtained. Images different from each other are present between the two radiation images, and then the image signals of the two radiation images are appropriately weighted and then subtracted (subtract) to extract an image of a specific structure. Energy subtraction processing.

Since this subtraction processing is an extremely effective method especially for medical diagnosis, it has received a great deal of attention in recent years, and its research and development have been actively promoted by making full use of radiation physics / digital image processing technology.

In the radiation image information recording / reproducing system using the above-mentioned stimulable phosphor sheet, the radiation image information recorded on the sheet is directly read in the form of an electric image signal, so that this system is used. According to this, it becomes possible to easily perform the subtraction processing as described above. In order to perform energy subtraction processing using this stimulable phosphor sheet, image recording (photographing) should be performed on the two stimulable phosphor sheets such that the image information of the portions corresponding to specific structures are different. Well, specifically, 1) two images with different energy distributions are used for imaging, 2) a metal that absorbs low energy components of radiation between two stimulable phosphor sheets. There is known a method in which two stimulable phosphor sheets are simultaneously irradiated with the radiation that has passed through the subject by interposing a filter such as the above.

By the way, conventionally, in the examination of breast cancer and the like, a radiation image of the breast is obtained by mammography,
Diagnosis was made by observing this image. However, in the normal compression mammography, the normal mammary gland tissue in the breast, other soft tissues, the tumor, etc. are depicted in an overlapping manner. Therefore, in mammography diagnosis, the separation of the tumor from normal mammary gland and other soft tissues was unclear, and it was difficult to recognize the presence of the tumor and the extent of infiltration.

Therefore, there is a method in which a radiation image of the breast is subjected to energy subtraction processing to remove normal mammary glands and other soft tissue, which are obstacles when recognizing a tumor, on the image to clarify the existence and the tumor infiltration range. Reported as a clinical case (Maga et al. 6: Dual-Energy Subt of breast)
raction Radiography, Japanese Journal, 84th issue No.6, P931〜
935, June 1, 1988, Maga et al., 6 people: Examination of extent of breast cancer progression by dual-energy subtraction of mammography, Breast Cancer Clinical Volume 6, No. 1, May 1991, P. 65.
~ 71). According to this report, by performing energy subtraction processing on the radiographic image of the breast, the diagnosis efficiency of breast cancer is improved, and the extent of breast cancer progression (systematic spread from the main cancer lesion, multiple lesions, daughter nodules) is accurately determined. Can be grasped.

[0011]

The radiographic image obtained by the energy subtraction processing for the breast described above can improve the diagnostic rate as compared with the conventional mammography, but in the report of the clinical cases mentioned above, the ac
Curacy is 75.5% and specificity is 63.1%, which is not enough. This is because normal mammary gland tissue is not completely erased in the energy subtraction process,
The image of the normal mammary gland remains in the energy subtraction image, and the S / N ratio decreases.

The residual shadow of the normal mammary gland is caused by the fact that the radiation energy applied when the breast is imaged is not completely separated. That is, in the energy subtraction process, so-called low-energy radiation and high-energy radiation are used to image the breast, but since the low-energy radiation and the high-energy radiation are not completely separated during imaging. It occurs in. For example, when a low energy image of the breast is taken, the tube voltage of the radiation source is set to 30 keV and a molybdenum filter is used to use radiation having a spectrum as shown in FIG. The radiation source has a tube voltage of 40 keV and an aluminum filter is used to use radiation having a spectrum as shown in FIG. 5, but the spectra of both are overlapped at a portion of energy of about 17 keV. Therefore, the low energy component and the high energy component of the radiation cannot be completely separated, and the image of the normal mammary gland remains in the energy subtraction image.

In view of the above circumstances, it is an object of the present invention to provide an energy subtraction method for a breast and an imaging apparatus which improve the separation of low energy radiation and high energy radiation during the energy subtraction processing of the breast. It is a thing.

[0014]

A first method for energy subtraction for a breast according to the present invention is to irradiate the breast with radiation through a strontium filter, and to transmit the radiation transmitted through the breast through the strontium filter,
Irradiating the first stimulable phosphor sheet to accumulate and record high-energy radiation image information of the breast on the first stimulable phosphor sheet, and to the breast, energy of radiation transmitted through the strontium filter. The radiation that has passed through the breast through the low energy transmission filter is different from that of the first stimulable phosphor sheet. Irradiating a second stimulable phosphor sheet to store and record low-energy radiation image information of the breast on the second stimulable phosphor sheet, and then to the first and second stimulable phosphor sheets. The excitation light is irradiated onto the substrate to emit stimulated emission light, and the stimulated emission light is photoelectrically read to obtain first and second image signals, respectively, and the first and second image signals are obtained. Performing operation between the signal for the corresponding pixels with respect to an image signal, it is characterized in that to obtain an energy subtraction image of the breast.

Here, the strontium filter is not limited to a filter using only strontium alone,
It means a filter using a material containing strontium, such as a strontium compound.

A second breast energy subtraction method according to the present invention is characterized in that, in the first breast energy subtraction method according to the present invention, the low energy transmission filter is a molybdenum filter.

Here, the molybdenum filter means not only a filter using only molybdenum but also a filter using a material containing molybdenum such as a molybdenum compound.

Further, a first breast energy subtraction imaging apparatus according to the present invention is a radiation source, a strontium filter arranged at a position for receiving radiation emitted from the radiation source, and the strontium filter arranged at the position. A low energy transmission filter which transmits a relatively large amount of radiation having a low energy component than the energy of the radiation transmitted through the switching means, switching means for switching between the strontium filter and the low energy transmission filter, and each of the filters switched by the switching means. Fixing means for fixing the breast to a position for receiving the radiation transmitted through the breast, and two pieces of high energy radiation image information and low energy radiation image information of the breast at the position for receiving the radiation transmitted through the breast. Accumulation and recording on each fluorescent phosphor sheet And it is characterized in that comprising a Mel recording means.

A second breast energy subtraction imaging apparatus according to the present invention is characterized in that, in the first breast energy subtraction imaging apparatus according to the present invention, the low energy transmission filter is a molybdenum filter. is there.

[0020]

The energy subtraction method and imaging apparatus for breasts according to the present invention comprises a strontium filter and
By using a low energy transmission filter that transmits a relatively large amount of radiation having a lower energy component than the radiation energy that has passed through this strontium filter, it is possible to separate the high energy component and the low energy component of the radiation irradiating the breast. did. Therefore, the radiation can be completely separated into the high energy component and the low energy component, and the image of the normal mammary gland can be prevented from remaining in the energy subtraction image of the breast.

If a molybdenum filter is used as the low energy transmission filter, the radiation energy can be separated even better.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an example of a breast energy subtraction imaging apparatus according to an embodiment of the present invention.

The breast energy subtraction imaging apparatus according to the embodiment of the present invention includes a radiation source housing 2 for housing a radiation source 1 therein, an imaging stand having IP magazines 6A and 6B and sheet switching means (not shown). 3 is connected by an arm 4 so as to face each other, and is attached to a base 5. In addition, the strontium filter 9 is used when photographing with high-energy radiation.
The molybdenum filter 10 is switched and used at the time of imaging with low energy radiation.

When radiographing the breast 7, the breast 7 is imaged on the imaging table 3
It is fixedly held by being pressed onto the holding plate 8 from above. When the breast 7 is fixedly held, first, the strontium filter 9 is used to image the breast 7 with high-energy radiation.
Is set, and the stimulable phosphor sheet 11A is taken out from the IP magazine 6A in synchronism therewith, and is set at a position where the radiation transmitted through the breast 7 inside the imaging table 3 is received.

The strontium filter 9 contains a strontium compound in a binder,
Examples of the strontium compound include strontium boride (SrB ₆ ), strontium bromide (SrBr ₂ ), strontium carbide (SrC ₂ ), strontium carbonate (SrCO ₃ ), strontium chloride (SrCl ₂ ),
Strontium fluoride (SrF ₂ ), strontium hydrogen phosphate (SrHPO ₄ ), strontium hydroxide (S
r (OH) ₂ ), strontium imide (SrNH),
Strontium iodide (SrI ₂ ), strontium nitrate (Sr (NO ₃ ) ₂ ), strontium oxalate (C
₂ O ₄ Sr.H ₂ O), strontium oxide (Sr
O), strontium perchlorate (Sr (Cl
O ₄ ) ₂ ), strontium peroxide (SrO ₂ · 8H ₂
O), strontium sulfate (SrSO ₄ ), strontium sulfide (SrS), or a strontium compound of strontium fluoride (SrFBr) may be used.

As described above, the strontium filter 9
When the stimulable phosphor sheet 11A is set, the radiation source 1 emits radiation 12 with the tube voltage of the radiation source 1 set to 40 keV, and irradiates the breast 7 through the strontium filter 9. The spectrum of the radiation 12 transmitted through the strontium filter 9 is as shown in FIG.
It has a peak at keV. The radiation 12 transmitted through the breast 7 is applied to the stimulable phosphor sheet 11A, and high energy radiation image information of the breast 7 is stored and recorded.

Next, the strontium filter 9 and the molybdenum filter 10 are exchanged, and in synchronization with this, the stimulable phosphor sheet 11A is formed by sheet switching means (not shown).
Is stored in the IP magazine 6A, the stimulable phosphor sheet 11B is taken out from the IP magazine 6B, and is set at a position where the radiation transmitted through the breast inside the imaging table 3 is received.

When the molybdenum filter 10 and the stimulable phosphor sheet 11B are set in this way, radiation 12 is emitted from the radiation source 1 with the tube voltage of the radiation source 1 being 30 keV, and passes through the molybdenum filter 10 to the breast 7. Is irradiated. The spectrum of the radiation 12 transmitted through the molybdenum filter 10 is as shown in Fig. 4, which is approximately 17keV and 19keV.
It has a peak in the part. The radiation 12 transmitted through the breast 7 is applied to the stimulable phosphor sheet 11B, so that the breast 7
The low energy radiation image information of is stored and recorded.

Here, the spectrum of the radiation 12 which has passed through the strontium filter 9 described above has a peak at a portion of approximately 38 keV as shown in FIG.
Comparing the spectra of FIG. 4 and FIG. 4, there is no portion where the spectra overlap. Therefore, two stimulable phosphor sheets 11A
The energy of the radiation images stored and recorded in 11B and 11B is completely separated, and an energy subtraction image with an improved S / N ratio can be obtained.

When the photographing of the stimulable phosphor sheets 11A and 11B is completed in this way, the radiation image information accumulated and recorded on the stimulable phosphor sheets 11A and 11B becomes
It is read by the radiation image information reading device shown in FIG.
A digital image signal representing the image is obtained.

First, while moving the stimulable phosphor sheet 11A in the direction of arrow Y for sub scanning, the laser light source 20
The laser light 21 from the main sheet is scanned in the X direction by the scanning mirror 22, and the accumulated radiation energy from the phosphor sheet A is diverged as stimulated emission light 23 according to the accumulated and recorded radiation image information. The stimulated emission light 23 is formed by molding a transparent acrylic plate from one end surface of the light collector 24.
The light enters the inside of 24, reaches the photomultiplier 25 while repeating total reflection inside, and the amount of emitted stimulated emission light 23 is output as an image signal S. The output image signal S is subjected to a logarithmic value (lo by a logarithmic converter 26 including an amplifier and an A / D converter.
g S) digital image signal log S _A. The digital image signal log S _A is stored in the storage medium 27 such as a magnetic disk, for example. Then, just like the other,
The recorded image of one stimulable phosphor sheet 11B is read out,
The digital image signal log S _B is stored similarly in the storage medium 27.

Next, the digital image signals log S _A , log
S _B is read from the memory 27 and input to the subtraction operation circuit 28.

The subtraction operation circuit 28 weights the two input image signals logS _A and logS _B appropriately and subtracts them for each corresponding pixel to obtain a digital difference signal Ssub = a · logS _A −. b · logS _B + c [a and b are weighting coefficients and c is a bias component]. The difference signal Ssub is subjected to image processing such as gradation processing and frequency processing in the image processing circuit 29, and then sent to the image reproducing device 30 to be used for reproducing a radiation image.

The reproducing device 30 may be a display means such as a CRT or a recording device for performing optical scanning recording on a photosensitive film, or for that purpose, an image signal is once transmitted to an image file such as an optical disk or a magnetic disk. May be replaced with a device for storing the data.

When the coefficients a and b are appropriately determined when performing the subtraction operation as described above, the obtained difference signal S
In sub, signals for parts other than the tumor (normal mammary gland and other soft tissues) in the breast are deleted. In addition, in the present embodiment, since the strontium filter and the molybdenum filter that do not overlap the radiation spectra are used, the tumor and the other parts are completely separated. Therefore, this difference signal S
If the image is reproduced based on sub, a radiation image in which only the tumor in the breast is extracted can be obtained.

In the above-mentioned embodiment, the molybdenum filter is used at the time of low-energy radiography of the breast, but any filter can be used as long as it transmits a radiation having a lower energy than the radiation energy transmitted through the strontium filter. May be.

[0038]

As described in detail above, the energy subtraction method and imaging apparatus for breasts according to the present invention is a strontium filter and a filter that transmits a relatively large amount of radiation having a low energy component than the radiation energy transmitted through the strontium filter. Was used to improve the separation performance between high energy radiation and low energy radiation during energy subtraction imaging of the breast. Therefore, when obtaining the energy subtraction image, it is possible to extract and emphasize only the tumor covered by the normal mammary gland in the breast, and further it is possible to accurately extract the spread of the cancer tissue, which improves the diagnostic efficiency and the breast cancer progress. It is possible to accurately grasp the range.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a breast energy subtraction imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a spectrum of radiation transmitted through strontium.

FIG. 3 is a schematic diagram showing a radiographic image information reader for obtaining an energy subtraction image of a breast.

FIG. 4 is a diagram showing a spectrum of radiation transmitted through molybdenum.

FIG. 5 is a diagram showing a spectrum of radiation transmitted through aluminum.

[Explanation of symbols]

 1 Radiation Source 3 Imaging Table 6A, 6B IP Magazine 7 Breast 9 Strontium Filter 10 Molybdenum Filter 11A, 11B Accumulable Phosphor Sheet 12 Radiation 20 Laser Light Source 21 Laser Light 22 Scanning Mirror 23 Photostimulated Emission Light 24 Optical Guide 25 Photomultiplier

Claims (4)

[Claims] 1. A breast is irradiated with radiation through a strontium filter, and the radiation that has passed through the breast through the strontium filter is irradiated onto a first stimulable phosphor sheet, and the first stimulable phosphor sheet. High-energy radiation image information of the breast is stored and recorded in the breast, and the breast is irradiated with radiation again through a low-energy transmission filter that transmits relatively more radiation of a low-energy component than the energy of the radiation transmitted through the strontium filter. Then, the second stimulable phosphor sheet different from the first stimulable phosphor sheet is irradiated with the radiation transmitted through the breast through the low energy transmission filter, and the second stimulable phosphor sheet is irradiated. Low-energy radiation image information of the breast is stored and recorded on the breast, and then the first and second storage phosphors are stored. The excitation light to the excited light to emit stimulated emission light, and the stimulated emission light is photoelectrically read to obtain first and second image signals, respectively, and to obtain the first and second image signals. On the other hand, an energy subtraction method for a breast, characterized in that the energy subtraction image of the breast is obtained by performing an operation between signals of corresponding pixels. 2. The breast energy subtraction method according to claim 1, wherein the low energy transmission filter is a molybdenum filter. 3. A radiation source, a strontium filter arranged at a position for receiving the radiation emitted from the radiation source, a radiation having an energy component lower than the energy of the radiation transmitted at the position and passing through the strontium filter. A low energy transmission filter that transmits a relatively large amount, a switching unit that switches between the strontium filter and the low energy transmission filter, and a fixing that fixes the breast at a position to receive the radiation transmitted through each of the filters switched by the switching unit. And means for recording the high-energy radiation image information and the low-energy radiation image information of the breast at a position where the radiation transmitted through the breast is received and recorded on two stimulable phosphor sheets, respectively. Breast energy subtraction characterized by ® emission imaging apparatus. 4. The energy subtraction imaging apparatus for breast according to claim 3, wherein the low energy transmission filter is a molybdenum filter.