JPS63262136A - Method for discriminating photographing body posture of medical image - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for automatically determining the physical position of a human body in a medical image such as a radiographic image.

(Prior art) When a certain kind of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of the emitted t14Wa energy is accumulated in the phosphor. It is known that when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy. 1'l exhaustible phosphor).

Using this stimulable phosphor, ρ radiation image information of a subject such as a human body is recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to produce stimulated emission. Generate light, photoelectrically read the resulting stimulated luminescent light to obtain an image signal, and based on this image signal, a radiation image of the subject is displayed as a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT. A radiographic image information recording and reproducing system that outputs as

(JP-A-55-12429, JP-A-56-11395, etc.) This system records images over an extremely wide radiation exposure range compared to conventional radiographic systems using silver halide photography. It has many advantages. In other words, in stimulable phosphors, it is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range. Even if the light intensity fluctuates significantly, the amount of stimulated luminescence emitted from the stimulable phosphor sheet is read by the charging conversion means with the reading gain set to an appropriate value and converted into an electrical signal. Recording materials such as photographic materials and CRTs using signals
Can radiation images be displayed on other display devices? By outputting the image as a jA image, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure amount.

By the way, in the above-mentioned system, in order to eliminate the influence of fluctuations in imaging conditions or to obtain radiographic images that are suitable for observation and interpretation, the recording state of the radiographic image information accumulated and recorded on the stimulable phosphor sheet or the chest , recording patterns (hereinafter collectively referred to as ``accumulated recorded information'') determined by the subject's body parts such as the abdomen, imaging methods such as simple contrast imaging, and contrast imaging, etc., are used for observation and interpretation. It is determined before outputting the possible M image, and based on the acquired accumulated recording information, the reading gain is adjusted to an appropriate value <1, and the recording scale is adjusted so that the resolution is optimized according to the contrast of the recording pattern. When the factors are determined and further image processing such as gradation processing is performed on the read image signal, it is desirable to optimally set the image processing conditions.

As a method for grasping the accumulated record information of radiographic images before outputting visible images, Japanese Patent Laid-Open No. 58-67240
The method disclosed in @ is known. This method is worth watching!
During the reading operation (hereinafter referred to as "main reading") to obtain a visible image for the Ja shadow, excitation light of a lower level than the excitation light that should be irradiated is used to pre-introduce cumulative fluorescence prior to the main reading. A reading operation (hereinafter referred to as "pre-reading") for grasping the accumulated recording information of radiographic images accumulated and recorded on the body sheet.
That's what it means. 〉, to understand the outline of the radiological image accumulation record, and when performing the actual reading, to appropriately adjust the reading gain, determine the recording scale factor, or determine the image processing conditions based on this pre-read information. be.

According to the above method, the recording state and recording pattern of radiation images stored on the stimulable phosphor sheet and the recording pattern can be known in advance before actual reading, so a reading system with an exceptionally wide dynamic range can be obtained. Even if you do not use the recording pattern, you can adjust the reading gain appropriately based on this recorded information, determine the recording scale factor, and apply signal processing to the electrical signal after reading according to this recording pattern. It becomes possible to obtain radiographic images with excellent interpretation suitability.

(Problem to be Solved by the Invention) However, when the reading conditions and/or image processing conditions for radiation image information are determined as described above, when the same subject is photographed in different photographic positions, In the reproduced image, the 111 degrees of the region of interest in the subject may change.

This will be explained in detail below. For example, in order to diagnose the thoracic vertebrae, consider the case where the chest is photographed from the front as shown in FIG. 2A, and the case where the chest is photographed from the side as shown in FIG. 2B. In the case of frontal imaging, the thoracic vertebrae, which is the region of interest, overlaps with the mediastinum, which is difficult for radiation to pass through, so the accumulated radiation m in the thoracic vertebrae area is low in the stimulable phosphor sheet, and this area becomes one group of low source light. . On the other hand, in the case of lateral imaging, since the thoracic vertebrae overlaps with the lung field P through which radiation is transmitted, the accumulated radiation dose in the thoracic vertebrae region is high in the stimulable phosphor sheet, and this region becomes a highly luminescent region. In both the case of frontal photography and the case of side photography, the maximum value of the read image signal from the stimulable phosphor sheet is 1iaslaX S@minimum value 5w1n.
Since there is not much difference, the maximum 1IIIsI! The reading conditions and/or image processing conditions determined based on the 1ax1 minimum value Sm1n are almost the same in both cases. Therefore, when images are read and reproduced images are obtained under such reading conditions and/or image processing conditions, the thoracic vertebrae area will have a relatively low density in the frontal image, while it will have a relatively low density in the lateral image. The temperature will be high.

It is also possible to appropriately set the image processing conditions based on the read image signal obtained by main reading without performing the pre-reading described above, but the above problem also occurs in such a case. .

In order to solve the above-mentioned problems, conventionally, when reading radiation image information from a stimulable phosphor sheet, a V4 position was used to read the body position of the subject in the sheet one by one. Alternatively, the information is input to the image processing device, and the above-mentioned reading conditions and/or image processing conditions are set in accordance with the input imaging position information.

However, inputting the above-mentioned photographing position information one by one each time each stimulable phosphor sheet is read is very troublesome, and it is also easy to input the photographing position information by mistake.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method that can automatically determine the photographing position of a medical image recorded on the stimulable phosphor sheet or the like.

(Means for Solving the Problems) A medical image imaging body position determination method according to the present invention uses an image signal obtained by reading processing from the above-mentioned stimulable phosphor sheet, that is, an image that is a transparent image of a human body. The distribution of the signal along the predetermined direction of the image is determined, the average value near the center of the signal value distribution in the predetermined direction is determined, and the rectangular body position of the image is determined according to the magnitude of this average value. It is characterized by this.

(Effect) For example, if we consider a radiographic image of the human chest,
The signal i1m ('a degree) distribution in the left and right direction of the image, shown by the straight lines in Figures 2A and 2B, that is, the signal value distribution in the direction perpendicular to the body axis, is roughly as shown in Figure 3A in a frontal photographed image. On the other hand, in the lateral contrast image, it is approximately the third
It will look like figure B. In other words, the front photographed image (second A
(see figure), the thoracic vertebrae K and the mediastinum, which are difficult for radiation to pass through, are located in the center in the left-right direction, and the lateral imaging image (second
(see Figure B), the lung field P, through which radiation passes well, is located in the center, and the heart C is located in the thoracic vertebrae, where radiation is difficult to penetrate, near both ends, so the distribution as described above is achieved. It will become. Note that as the signal value distribution in the horizontal direction of the image, the signal value distribution of pixel rows along the straight line in FIGS. 2A and 2B may be considered, or the signal value distribution of each pixel in the direction approximately perpendicular to the straight line You may also consider the distribution of the total signal value or average value of the column.

When the above-mentioned signal value distribution is as shown in FIGS. 3A and 3B, the average signal value near the center of the image in the distribution is relatively low in the front-photographed image, while in the side-photographed image. is relatively high. Therefore, this chest image can be distinguished from a frontal image when the average signal value is relatively low, and from a side image when the average signal value is relatively high.

(Example) Hereinafter, the present invention will be described in detail with reference to the examples shown in the drawings.

FIG. 1 shows an example of a radiology information recording and reproducing system configured to determine the imaging position of a human body by the method of the present invention. This radiation image information recording and reproducing system basically includes a radiation image capturing section 20, a pre-reading reading section 30, a main reading reading section 40°, and an image reproducing section 50. In the radiographic imaging unit 20, for example, the radiation 8100 from an X-ray tube or the like
Radiation 102 is irradiated toward 101 . As described above, the stimulable phosphor sheet 103 that accumulates radiation energy is placed at the position where the radiation 102 that has passed through the subject 101 is irradiated. Image information is accumulated and recorded.

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 has been recorded in this manner is sent to the pre-reading reading section 30 by sheet transport means 110 such as a transport roller. In the pre-reading reading section 30, the pre-reading laser light source 2
The laser beam 202 emitted from the laser beam 2
A filter 2 that cuts the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 103 by excitation of 02
03, the light is linearly deflected by a light deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a flat reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as excitation light does not overlap with the wavelength range of the stimulated luminescence light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is moved by a sheet transport means 21 such as a transport roller.
0 in the direction of the arrow 206 for aj constant scanning, and as a result, the entire surface of the phosphor sheet 103 is irradiated with the laser beam 202. Here, the laser light source 201
The emission intensity of the laser beam 202, the beam diameter of the laser beam 202, the laser beam 20
2, the scanning speed of the stimulable phosphor sheet 103 and the transport speed of the stimulable phosphor sheet 103 are such that the energy of the pre-read excitation light (laser light 202) is
It is selected so that it is smaller than that of the book reading performed in the book reading reading section 40, which will be described later.

When the laser beam 202 is irradiated as described above, the stimulable phosphor sheet 103 emits stimulated luminescent light of the optical layer corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the pre-reading light guide. 201. The stimulated luminescence light is guided through the light guide 207, exits from the exit surface, and is received by a photodetector 208 such as a photomultiplier. A filter is attached to the light receiving surface of the photodetector 208, which transmits only light in the wavelength range of stimulated luminescence light and cuts light in the wavelength range of excitation light, and detects only stimulated luminescence light. It is now possible to do so. The detected stimulated luminescence light is converted into an electrical signal carrying accumulated recording information, and is sent to an amplifier 2.
09. The signal output from the amplifier 209 is digitized by the A/D converter 211 and inputted to the main reading control circuit 314 of the main reading reading section 40 as a pre-read image signal @Sp.

This main reading control circuit 314 determines the reading gain setting value a1 recording scale factor setting value b1 reproduction image processing condition setting value C by uncovering the accumulated recording information indicated by the pre-reading image signal Sp and by, for example, histogram analysis.

The stimulable phosphor sheet 103 whose pre-reading has been completed as described above is transferred to the reading section 40 for main reading.

In the main reading reading section 40, the main reading laser light source 301
The laser beam 302 emitted from this laser beam 302
A filter 303 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by excitation of the stimulable phosphor sheet 103.
After passing through the beam expander 304, the beam diameter is finely adjusted by the beam expander 304, and it is linearly deflected by the optical deflector 305 such as a galvanometer mirror, and is reflected in a plane! The light is incident on the stimulable phosphor sheet 103 via J1306. An fθ lens 307 is arranged between the optical deflector 305 and the plane reflecting mirror 306, and the stimulable phosphor sheet 1
The beam diameter of the laser beam 302 scanning the laser beam 303 is made uniform. On the other hand, the stimulable phosphor sheet 103
is moved by arrow 3 by a sheet transport means 320 such as a transport roller.
The stimulable phosphor sheet 103 is moved in the direction 08 and sub-scanned, and as a result, the entire surface of the stimulable phosphor sheet 103 is irradiated with laser light. When the laser beam 302 is irradiated in this way,
The stimulable phosphor sheet 103 emits stimulated luminescent light in an amount corresponding to the radiation energy stored and recorded therein,
This emitted light enters the main reading light guide 309. Stimulated luminescent light guided through the main reading light guide 309 while undergoing repeated total reflection is emitted from its exit surface and is received by a photodetector 310 such as a photomultiplier. A filter that selectively transmits only the wavelength range of stimulated luminescence light is attached to the light receiving surface of the photodetector 310.
is designed to detect only stimulated luminescence light.

The output of the photodetector 310 that photoelectrically detects the stimulated luminescent light representing the radiation image recorded on the stimulable phosphor sheet 103 has a read gain based on the read gain setting value a determined by the control circuit 314. The electric signal is amplified to an appropriate level by the amplifier 311 set to . The amplified electrical signal is input to the Δ/D converter 312, and based on the recording scale factor setting value, it is converted into a digital signal with a recording scale factor suitable for the signal fluctuation width, and is input to the signal processing circuit 313. . The digital signal is subjected to image processing (signal processing) such as gradation processing based on the reproduction image processing condition setting value C in order to obtain radiation (i! ) and output.

The read image signal (actual read image signal) So output from the signal processing circuit 313 is transmitted to the optical modulator 401 of the image reproducing unit 50.
is input. In this image reproducing section 50, a laser beam 403 from a recording laser beam 402 is transmitted to an optical modulator 4.
01, it is modulated based on the main reading image signal So input from the signal processing circuit 313, and is modulated by the scanning mirror 40.
A photosensitive material 405 such as photographic film is deflected by
Scan above. The photosensitive material 405 is transported in a direction perpendicular to the scanning direction (arrow 406 direction) in synchronization with the scanning, and the actual reading image signal So
A radiation image based on the image is output. In addition to this method, methods for reproducing radiographic images include the above-mentioned CRT.
Various methods can be adopted, such as display by.

Next, a method of the present invention for automatically determining the posture of the subject 101 will be described. The pre-read image signal Sp output from the Δ/D converter 211 is input to the main reading control circuit 314 as described above, and is also input to the photographing body position discriminating circuit 5.
00 is input. FIG. 4 shows this photographing position discrimination circuit 50.
The configuration of 0 is shown in detail, and will be explained below with reference to FIG. 4. The signal extraction and addition section 511 of the imaging body position determination circuit 500 receives the above-mentioned pre-read image signal Sp, and from the image signal Sp, each pixel column Gs, G2, G3, etc. extending in the image vertical direction (direction perpendicular to the straight line) is generated.・Gn
(See Figure 5) Signals are extracted in units of pixels, and these signals are added for each pixel column. It shows the density 1 product value of the pixel row, and the overall density distribution in the horizontal direction of the image is shown.Instead of this added signal, the average value of the extracted signal for each pixel row may be used.

In other words, this average value also shows an a distribution in the horizontal direction of the image as described above. When the image recorded on the stimulable phosphor sheet 103 is a chest image, the signal ff1 (1 degree) distribution in the left and right direction of the image is as shown in FIG. The result will be as shown in Figure 3B.

This chest image will be explained below as an example. The above n types of addition signals H=Ht, H2, H3...)(n
is sent to the cumulative value addition section 512. This cumulative value addition unit 512 receives an addition area designation signal m sent from an area designation unit 513, and receives an addition signal 1 for a predetermined area (see FIGS. 3A and 3B) at the center of the image in the horizontal direction indicated by the signal m.
Add. That is, if the area 141 is designated as between pixel rows Gm and GM, the cumulative value addition unit 512 calculates r-1-1, +HmH+...+HM-1+
Addition called HM is performed. This added value r indicates the average density of the radiographic image in the central area, and information indicating the added value r is sent to the determination unit 514. Note that the above-mentioned predetermined area I is, for example, an area between a point at a position of 40% of the image width and a point at a position of 60% of the image width, but is not limited to this, and may be determined as appropriate depending on the target image. Just set it.

The determination unit 514 compares the reference value Th sent from the reference value setting unit 515 and the additional value r, and if r>Th, determines that the image carried by the pre-reading image @ bond issue Sp is a side view image. If r≦Th, it is determined that the image is a frontally photographed image, and the correction signal T is not output. This correction signal T is applied to the gain correction circuit 50 shown in FIG.
Sent to 7. When this correction circuit 501 receives the correction signal, the main reading control circuit 314 sets the reading gain determined as described above! 1iHa is corrected to lower the reading gain. As described above, if the image reading conditions and image processing conditions are constant, the density of the thoracic vertebrae portion in the reproduced image of the lateral chest radiography will be higher than that in the case of the frontal radiography. Therefore, if the value of the addition mr is relatively large as described above, that is, if the reading gain is lowered when reading the side photographed image, the actual reading image signal So will be at a low level overall, and the reproduced radiation image recorded on the photosensitive material 405 will be reduced. 'a degree is lowered overall. As a result, the density of the portion of the thoracic vertebrae in the reproduced image of the side of the chest becomes equal to the temperature of the thoracic vertebrae portion of the reproduced image of the frontal image. Note that an appropriate correction amount for the reading gain can be determined based on experiment or experience.

Furthermore, in the embodiment described above, the sum value for each pixel column of the image signal Sp is calculated, but the image signal Sp for each pixel is calculated in advance.
may be compared with a predetermined threshold value and converted into 2 (2), and the same processing as described above may be performed on this binarized data.

Furthermore, the signal value distribution in the direction along the straight line in FIGS. 2A and 2B is the pixel columns G+, Gz, G3...
・In addition to calculating and calculating the total value or average value of the image signal for each Qn, as shown in FIG. Since the signal values directly indicate the distribution, it may be obtained by extracting these signals.

In the above example, the front photographed image is read with the reading gain determined by the main reading control circuit 314, and the reading gain is corrected to a lower value when reading the side b1 shadow image. The side view image may be read with the reading gain determined by the main reading control circuit 314, and the reading gain may be corrected to be higher when reading the front photographed image. Furthermore, in order to adjust the density of the reproduced image, in addition to changing the reading gain as described above, changing the conditions of the recording scale factor in the A/D converter 312, and changing the conditions of gradation processing in the signal processing circuit 313. may be equal. Further, these concentration adjustment methods may be used in combination.

Although the embodiment for discriminating between a frontally photographed image and a side view image of the chest has been described above, the present invention can also be applied to distinguish other body parts or other photographed body positions. In other words, if images of a common body part are captured in different body positions, the average values near the center of the signal value distribution for the images in each body position will often differ greatly. The imaging position can be correctly determined based on the size.

Furthermore, in the embodiments described above, the photographing body position is determined using the pre-read image signal Sp, but the image processing tea scoop in the signal processing circuit 313 is performed based on the main read image signal SO without performing the pre-reading as described above. In such a case, the actual reading image signal SO may be used to determine the photographing body position. Furthermore, in the above embodiment, the degree of m of the reproduced image is corrected according to the determined photographing position, but the present invention can of course be applied to determining the photographing position for other purposes. be.

Furthermore, in the above embodiment, the stimulable phosphor sheet 10
However, the present invention is applicable not only to radiation images recorded on the stimulable phosphor sheet 103, but also to other medical images. ff! Of course, it is also possible to apply it to the entire body position.

(Effects of the Invention) As described above in detail, according to the medical image photographing body position determination method of the present invention, the photographing body position of a medical image can be automatically and accurately determined. Therefore, if this method is applied to the radiation image information recording and reproducing system as described above, even if the imaging position of the subject is different, the density of the region of interest in the reproduced image can be made constant, and therefore the density of the region of interest in the reproduced image can be kept constant. It becomes possible to greatly improve diagnostic performance.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a radiation image information recording and reproducing system that determines the imaging position by the method of the present invention, and FIGS. 2A and 2B show ll1tAS! A schematic diagram showing an example of an iI image, FIGS. 3A and 3B are graphs showing an example of density distribution in a predetermined direction of a radiographic image taken while changing the imaging position of the subject, and FIG. 5 and 6 are explanatory diagrams each illustrating signal extraction for determining the concentration distribution according to the present invention. 20... Radiographic image presentation section 30... Reading section for pre-reading 40... Reading section for main reading 100...
Radiation source 101...Subject 102...
- Radiation 103...Stormative phosphor sheet 201...Laser light source for pre-reading 202...Laser light for pre-reading 204...Light deflector for pre-reading 208...Photodetector for pre-reading 210...Pre-reading Sheet transport means 301...Laser light source for main reading 302...Laser light for main reading 305...Light deflector for main reading 310...Photodetector for main reading 311...Amplifier 312...A/D Converter 313...Signal processing circuit 314...Control circuit 320...Main reading sheet transport means 500...Shooting body position discrimination circuit 507...Reading gain correction circuit 511...Signal extraction addition unit 512.・W4i
IA value numbing section 513... (a area specifying section 51
4...Discrimination section 515...Reference value setting section a...Reading gain setting value b...Recording scale factor setting value C...Image processing condition setting value F1 to Fn...Parallel to predetermined direction Each pixel 01 of the pixel row
~Gn... Pixel row H in the direction perpendicular to the predetermined direction...
Addition signal r...Additional value Sp...Pre-read image signal SO...Actual reading image signal lower...Correction signal Th...Reference value Fig. 28
Figure 2B Figure 38 Figure 38 Figure 4 Figure 5 Figure 6

Claims (3)

[Claims] (1) Find the distribution of the image signal responsible for the transmitted image of the human body along a predetermined image direction, find the average value near the center of the predetermined direction in this signal value distribution, and calculate the magnitude of this average value. 1. A method for determining the photographing position of a medical image, characterized in that the photographing position of the image is determined according to the photographing position of the image. (2) The medical image according to claim 1, characterized in that, as the distribution of the signal values, a total value or an average value of signal values in each pixel row in a direction substantially orthogonal to the predetermined direction is used. Method for determining shooting position. (3) The method for determining the photographing body position of a medical image according to claim 1, wherein a distribution of signal values in a pixel row parallel to the predetermined direction is used as the distribution of the signal values.