JPS63262137A - 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 (Industrial Application Field) The present invention is directed to the IH1lii! Medical Ii such as i-en! This invention relates to a method for automatically determining the position of a human body in a statue.

(Prior art) 11M (X-rays, α-rays, β-rays, γ-rays,
For this reason, l) 111 m when irradiated with electron beam, ultraviolet ring, etc.
It is known that a part of the energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy.
A phosphor exhibiting such properties is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, the radial ring image of a subject such as a human body is recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is scanned with excitation light such as a laser beam to illuminate it. The generated stimulated luminescence light is photoelectrically read to obtain an image signal, and based on this image signal, the incident radiation of the subject is displayed on a recording material such as a photographic light-sensitive material or a display device such as a CRT.
The applicant has already proposed a radiation image information recording and reproducing system that outputs ir+- as a visible image.

(JP-A-55-12429, JP-A-56-11395, etc.) This system has practical advantages in that it can record images over an extremely wide radiation exposure range compared to conventional radiographic systems that use normal salt 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, and therefore the amount of radiation exposure varies depending on various imaging conditions. Even if the value varies considerably, the amount of stimulated luminescence light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value and converted into an electrical signal. Recording materials such as photographic materials, CRT
By outputting a radiation image as a visible image on a display device such as the above, 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 status of radiographic images and n-reports accumulated and recorded on the stimulable phosphor sheet, Alternatively, observation and interpretation of recording patterns (hereinafter collectively referred to as "accumulated recorded information") determined by the body part of the subject such as the chest or abdomen, or by the shading method such as plain radiography or contrast-enhanced shading, etc. The system determines the image quality before outputting a visible image, adjusts the reading gain to an appropriate value based on the accumulated recorded information, and optimizes the resolution according to the contrast of the recorded pattern. When the recording scale factor is 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 No. This method uses excitation light of a lower level than the excitation light that is irradiated during the reading operation (hereinafter referred to as "main reading") to obtain a visible image for observation and interpretation. Perform a reading operation (hereinafter referred to as "pre-reading") to understand the accumulated record information of the radiation image stored and recorded on the stimulable phosphor sheet, grasp the outline of the accumulated record of the radiation image, and perform the main reading. At this time, the reading gain is appropriately adjusted, the recording scale factor is determined, or the image processing conditions are determined based on this pre-read information.

According to the above method, the recording state and recording pattern of radiation image information accumulated and recorded on the stimulable phosphor sheet can be known in advance before the actual reading, so a reading system with an exceptionally wide dynamic range can be used. Even if you do not use it, 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 suitability for observation and interpretation.

(Problem to be Solved by the Invention) However, if 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 positions, In the reproduced image, the 81 degree angle 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 spine, which is the area of interest, is exposed to radiation! Since the 11th line overlaps with the mediastinum, which is difficult to pass through, the accumulated radiation dose in the thoracic vertebrae portion of the stimulable phosphor sheet is low, and this portion becomes a low luminescence amount portion. On the other hand, in the case of lateral radiation, the thoracic vertebrae overlap with the lung field P, which is transparent to radiation.
In the stimulable phosphor sheet, the accumulated radiation dose in the thoracic vertebrae portion is high, and this portion becomes a high luminescence amount portion. 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 5laX, and the minimum value is 3Ili.
Since n does not change much, the reading conditions and/or image processing conditions determined based on the maximum value 511ax and minimum value 5Ilin as conventionally done are almost the same in both cases. Therefore, when a reconstructed image is obtained by performing both readings under such reading conditions and/or image processing conditions, the thoracic vertebrae will have a relatively low density in the frontal shadow image, while in the side view image, the density will be relatively low. This results in a relatively high concentration.

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 even in such a case, the above problem still exists. arise.

In order to solve the above problems, conventionally, when reading radiation image information from a stimulable phosphor sheet, the reading device or the 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 incorrectly.

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) The method for determining the photographing body position of a medical image according to the present invention is based on an image signal obtained by reading processing from the above-mentioned stimulable phosphor sheet, that is, an image signal responsible for both transparent edges of the human body. , the distribution along a predetermined direction of the image is determined, and the degree of consistency between this signal value distribution pattern and a pattern corresponding to a plurality of standard signal values, which are predefined in advance in the image position negative, is determined, and this degree of consistency is calculated. The present invention is characterized in that the photographing body position of the image is determined according to the image.

The degree of matching between the signal value distribution pattern and the reference signal value distribution pattern can be checked by various conventionally known pattern matching techniques.

(Effect) For example, if we consider a radiographic image of the human chest,
The signal value (density) distribution in the horizontal direction of the image shown by the straight line 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, the side view image is approximately as shown in FIG. 3B. In other words, in the frontal photographed image (see Figure 2A), the mediastinal region is located in the thoracic vertebrae where radiation is difficult to penetrate in the center in the left and right direction, while in the lateral sectional image (see Figure 2B), The lung field P, through which radiation passes well, is located in the center, and the thoracic vertebrae, through which radiation does not easily pass, and the heart C are located near both ends, resulting in the above-mentioned distribution. Note that as the signal value distribution in the horizontal direction of the image, the signal value distribution of the pixel row along the straight line in FIGS. 2A and 2B may be considered, or the signal value distribution in the above-mentioned straight line! The distribution of the signal total value and average value of each pixel column in the direction substantially orthogonal to i1L may also be considered.

Therefore, for example, signal value distribution patterns such as those shown in Figures 3A and 3B of Section 1 may be stored in the storage means as a reference signal value distribution pattern for a front chest image and a reference signal value distribution pattern for a side view image, respectively. , when examining the degree of consistency between the distribution pattern of a certain image signal that is a frontal chest photographed image or a frontal chest photographed image and the two reference signal value distribution patterns, the distribution pattern of the image signal is found to be the standard shown in FIG. 3B. If it matches better with the reference signal value distribution pattern in Figure 3A than with the signal value distribution pattern, the image carried by the image signal can be determined to be a frontal photographed image, and in the opposite case, it can be determined that it is a side view image. can do.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings. - FIG. 1 shows an example of a radiation image information recording and reproducing system configured to determine the imaging position of a human body using the method of the present invention. This 9A line 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, a radiation a source 100 such as an Xa tube
74) Radiation 102 is irradiated toward 101. As mentioned earlier, the stimulable phosphor sheet 103 that accumulates radiation energy is placed at the position where the radiation 11) J-ray 102 transmitted through the subject 101 is irradiated, and this NV
Transmitted radiation image information of the subject 101 is accumulated and recorded on the tetrachromatic phosphor sheet 103.

The stimulable phosphor sheet 103 on which the ray image information of the subject 101 has been recorded in this way is sent to the pre-reading reading unit 30 by a 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 luminescent light emitted from the stimulable photoreceptor sheet 103 due to the excitation of 02
After passing through 03, the light is linearly deflected by an optical deflector 204 such as a galvanometer mirror, and enters the stimulable phosphor sheet 103 via a flat reflecting mirror 205 9A. 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 transported by a sheet transport means 2 such as a transport roller.
10 to perform sub-scanning in the direction of arrow 206, and as a result, the entire surface of phosphor sheet 103 is irradiated with laser light 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 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 irradiated with the laser beam 202 as described above, the stimulable phosphor sheet 103 emits stimulated luminescent light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the pre-reading light guide 207. incident on . 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 receives a pre-reading image signal S.

Based on the accumulated recording information indicated by , the reading gain setting value a, the recording scale factor setting value b, and the reproduction image processing condition setting value C are determined 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 stimulable phosphor sheet 103, the beam diameter is strictly adjusted by a beam expander 304, linearly deflected by an optical deflector 305 such as a galvanometer mirror, and passed through a flat reflecting mirror 306 to the stimulable phosphor sheet 103. incident on the top. There is a distance f between the optical deflector 305 and the plane reflecting mirror 306.
A θ lens 307 is arranged so that the beam diameter of the laser beam 302 scanning the stimulable phosphor sheet 103 is made uniform. On the other hand, the stimulable phosphor sheet 103 is transported in the direction of the arrow 308 by a sheet transport means 320 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the stimulable phosphor sheet 103 is irradiated with laser light. When irradiated with the laser beam 302 in this manner, the stimulable phosphor sheet 103 emits stimulated luminescent light with an amount of light corresponding to the radiation energy stored therein, and this luminescent light enters the main reading light guide 309. do. 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 type 310 such as a photomultiplier. Photodetector 3
A filter that selectively transmits only the wavelength range of the stimulated luminescent light is attached to the light receiving surface of the photodetector 310 so that the photodetector 310 detects only the stimulated luminescent 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 t is input to the A/DI converter 312, converted to a digital signal with a recording scale factor suitable for the signal fluctuation width based on the recording scale factor setting value, and input to the signal processing circuit 313. Ru. In this signal processing circuit 313, the above-mentioned digital signal is converted into radio-rMI!, which has excellent observation and interpretation aptitude. Image processing (signal processing) such as, for example, level w4 processing is performed based on the reproduced image processing condition setting value C so that J image is obtained, and the image is output.

The readout signal (actual reading 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 unit 50, a laser beam 403 from a recording laser light source 402 is transmitted to an optical modulator 40.
1, the main reading image signal SO&- inputted from the signal processing circuit 313 is modulated based on the scanning mirror 40.
A photosensitive material 405 such as photographic film is deflected by
Scan above. The photosensitive material 405 is then transported in a direction perpendicular to the scanning direction (arrow 40G direction) in synchronization with the scanning, and the actual reading image signal SO is transferred onto the photosensitive material 405.
A radiation 04-ray image based on is output. In addition to this method, the above-mentioned CR method can be used to reproduce radiographic images.
Various methods such as display by T can be adopted.

Next, a method of the present invention for automatically determining the photographing body position of the subject 101 will be described. The pre-read image signal Sp output from the A/D converter 211 is input to the main reading control circuit 314 as described above, and is also input to the photographing body position determination 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 stable shadow body position discrimination circuit 500 receives the above-mentioned pre-read image signal Sp, and from the image signal Sp, each pixel column Gl, Gz, G3, . . . ...Gn
(See FIG. 5) Signals are extracted at the middle level, and these signals are added for each pixel column. The n types of added signals H1, H2, H3, . . . , Hn obtained in this way each indicate the total density value of each pixel column, and the total indicates an S degree distribution in the left and right direction of the image. Note that the average value of the extracted signals for each pixel column may be used instead of this added signal.

In other words, this average value also indicates the density distribution in the horizontal direction of the image, similarly to the above. The signal value (density) distribution in the horizontal direction of this image can be roughly expressed as follows: If the image recorded on the stimulable phosphor sheet 103 is a chest image, it will be a frontal image, a lateral image, and a lateral image. The shadow images are as shown in FIGS. 3A and 3B, respectively. This chest image will be explained below as an example.

The approximate signal value distribution patterns as shown in FIGS. 3A and 3B are obtained by calculating the above-mentioned addition signal based on pre-read image signals Sp regarding several representative frontal chest images and side-view images, respectively. H1, Hz, H3...
Hn can be determined and sent to the function determining section 512 where it is averaged, smoothed, etc. The function determination unit 512 then determines a function g, (1
), gt(1) is determined (i indicates the horizontal position of the image). Such a function can be obtained as a function consisting of a high-order polynomial, for example, by using a total regression analysis method. These functions 01(i) and Qz(i> are stored in the storage means 515 as representing the reference signal value distribution patterns for the frontal shot and side view, respectively.

When determining the imaging position of each radiation image, the above-mentioned addition signals H1, Hz, H3...1-(n is the signal extraction addition unit 511. The actual distribution pattern of the added signals for each image, that is, the density distribution pattern, is as shown in FIG. 3C, for example, and can be defined as a function f (i) of the pixel position i. The information F indicating the interval number f (i) is obtained from the mismatch measure calculation unit 51
Sent to 3. The mismatch measure calculation unit 513 calculates the mismatch measure between the signal value distribution pattern indicated by this information F and the two reference signal value distribution patterns.

That is, the arithmetic unit 513 receives the information F and also stores the function (h(ri, CJ□(1
), and calculate each mismatch measure S1=Σ(f(i)-9,(i))21@1 G2-Σ(f(i)-92(i))21I+4. Mismatch measure S1, G obtained in this way
Information indicating 2 is sent to the determination unit 514.

If Sl>Sz, the determination unit 514 determines that the image carried by the look-ahead image signal So is a side view image and outputs a correction signal T; on the other hand, if Sz<Sz, it determines that the image is a front view image. Then, the correction signal T is not outputted. To explain this determination in detail, for example, if 81 < 82, the mismatch measure between function f (i) and function g + (! ) is smaller than any mismatch measure between function f (i) and function 9z (i > The number f (i> is a function Q,
(i), the signal value distribution pattern obtained sequentially based on the pre-read image signal Sp is better than the reference signal value distribution pattern in FIG. 3B. It can be determined that the pattern matches well with the reference signal value distribution pattern shown in FIG. 3A.

If 81<82, the opposite is of course true.

The correction signal T is supplied to the gain correction circuit 507 shown in FIG.
sent to. When this correction circuit 507 receives the correction signal T, it corrects the reading gain setting value a determined by the main reading control circuit 314 as described above so as 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 81 > 82 as described above, that is, if the reading gain is lowered when reading the side photographed image, the main reading image signal SO will be at a low level overall,
The overall m degree of the reproduced radiation image recorded on the photosensitive material 405 is lowered. As a result, the density of the thoracic vertebrae portion in the reproduced image of the thoracic side surface becomes equal to the density of the thoracic vertebrae portion in the reproduced image taken from the front. Note that an appropriate correction amount for the reading gain can be determined based on experiment or experience.

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

Furthermore, the signal value distribution in the direction along the direct ILL in FIGS. 2A and 2B is the pixel array G1, G2, G3, etc. mentioned above.
・In addition to calculating and calculating the total value or average value of the image signal for each Gn, as shown in FIG. Since the signal values for , directly indicate the distribution, it may be obtained by extracting these signals.

In addition to the above-mentioned mismatch measures, for example, the value of S=Σl f (i)-9<i) l is+, and furthermore, f (1)-cx (1), f (2
)-q(2), . . . f (N)-9<N), etc. may be specified.

In the above example, a frontal 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 a sideward photographed image. The captured image may be read with the reading gain determined by the main reading control circuit 314 as it is, and the reading gain may be corrected to be higher when reading the frontal captured image. In addition, to adjust the density of the reproduced image, in addition to changing the reading gain as described above, changing the recording scale factor conditions in the A/D converter 312 and changing the gradation processing conditions 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 frontal photographed image and a side photographed image of the chest has been described above, the present invention can also be applied to distinguish other body parts and other photographed body positions. In other words, if images of a common body part are captured in different body positions, the signal value distribution patterns for the images in each body position often take different basic patterns. The degree of consistency between the pattern and the actual image signal distribution pattern can be determined, and the photographing body position can be correctly determined based on the degree of consistency.

Further, in the embodiments described above, the photographing body position is determined using the pre-read image signal So, but the pre-read image signal So is not performed and the main read-out image signal S is used instead.

When setting the image processing conditions in the signal processing circuit 313 based on this, the actual reading image signal SO may be used to determine the photographing body position. Further, in the above embodiment, the density of the reproduced image is corrected according to the determined photographing position, but the present invention is of course applicable to determining the photographing position for other purposes. .

Furthermore, in the above embodiment, the stimulable phosphor sheet 10
However, the present invention is intended to determine the photographing position of not only the 01m image recorded on the stimulable phosphor sheet 103 but also other medical images. Of course, it is also possible to apply it to.

(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 the drawing]

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; FIGS. 2A and 2B are schematic diagrams showing examples of radiographic images in which the imaging position of the subject is different; Figures 3A and 3B are graphs showing basic pattern examples of density distribution in a predetermined direction of radiographic images taken while changing the imaging position of the subject, and Figure 3C is an example of an actual image density distribution pattern. 4 is a block diagram showing an example of an apparatus for carrying out the method of the present invention, and FIGS. 5 and 6 are explanatory diagrams each illustrating signal extraction for obtaining an 11 degree distribution according to the present invention. be. 20... Radiographic imaging 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 brightening section 512 ...Function determination unit 513...Mismatch measure computing unit 514...Discrimination unit 515...Storage means a...Reading gain setting value b...Recording scale factor setting value C...Image processing Condition setting value 01~Qn...Each pixel F in the pixel row parallel to the predetermined direction
・Information G1 to Gn indicating functions of concentration distribution pattern ・・
- Pixel rows Js, Jz in the direction orthogonal to the predetermined direction...
Information indicating the function of the reference density distribution pattern Sp...Pre-read image signal SO...Actual reading image signal T...Correction signal Fig. 2A Fig. 2B Fig. 3A Fig. 38

Claims (3)

[Claims] (1) Find the distribution of the image signal responsible for the transparent image of the human body along a predetermined image direction, and match this signal value distribution pattern with multiple reference signal value distribution patterns predefined for each image shooting position. 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 degree of consistency and determining 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.