JPS63262131A - 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 imaging position of a human body in a medical image such as a radiographic image.

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

Using this stimulable phosphor, 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 luminescence. 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. The present applicant has already proposed a radiation image information recording and reproducing system that outputs as follows.

(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 using silver halide photography. It has 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. By outputting a radiation image as a visible image to a recording material such as a photographic material or a display device such as a CRT using the method, it is possible to obtain a radiation image that is not affected by fluctuations in the amount of radiation exposure.

By the way, in the above system, in order to eliminate the influence of fluctuations in imaging conditions or to obtain a radiation image with excellent observation and interpretation aptitude, the recording state of the radiation image information accumulated and recorded on the stimulable phosphor sheet, Alternatively, the recording pattern determined by the part of the subject such as the chest or abdomen, the imaging method such as plain imaging or contrast imaging, etc., is hereinafter collectively referred to as "accumulated recording information". ) is grasped before outputting a visible image for observation and interpretation, and the reading gain is adjusted to an appropriate value based on the accumulated recorded information, and the resolution is optimized according to the contrast of the recorded pattern. It is desirable to determine the recording scale factor so that the image data is read, and to optimally set the image processing conditions when image processing such as gradation processing is performed on the read image signal.

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 should be irradiated during the reading operation (hereinafter referred to as "single 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 don't 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 recorded pattern. Radiological images with excellent interpretation aptitude 1
It becomes possible to

(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 photographing positions, the reproduction of each image will be different. In an image, the density of a 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 portion of the stimulable phosphor sheet is low, and this region becomes a low luminescence amount portion. - In the case of right side imaging, the thoracic vertebrae overlaps with the lung field P through which radiation easily passes, so the thoracic vertebrae can be stored in the stimulable phosphor sheet! a The radiation dose is ^
This area is a high luminescence area. The maximum value of the read image signal from the stimulable phosphor sheet is 5laX and the minimum value is 31Ili in both the case of frontal photography and the case of side photography.
Since n does not change much, the reading conditions and/or image processing conditions determined based on the maximum finsIIax and minimum value 3m1n as conventionally done are as follows.
It is almost the same in both cases. Therefore, when images are read under such reading conditions and/or image processing conditions to obtain reconstructed images, the thoracic vertebrae will have a relatively low density in the frontal image, whereas it will be relatively low in density in the lateral image. This results in 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 the above problem also occurs in such a case. .

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 the image signal obtained by the above-mentioned reading process from the stimulable phosphor sheet, that is, the image signal responsible for the transparent image of the human body. After creating a histogram and finding a function that approximates the pattern of this histogram, finding the second derivative of this function,
Next, it is determined whether the value that this second derivative takes in a predetermined area is positive or negative, and the photographing body position of the image is determined according to the positive or negative angle.

(Function) For example, the histogram of an image signal that represents a radiographic image of the chest of a human body is roughly as shown in Figure 3A in a frontally photographed image, while it is approximately as shown in Figure 3B in a sidely photographed image.
It will look like the figure. If this histogram pattern is approximated to a function as described above, as is well known, Part 2
The second derivative takes a positive value in a region where the above function, that is, the histogram pattern is convex downward, and takes a negative value in a region where the histogram pattern is convex upward. If we pay attention to the pattern near the signal median value 3 mid in the histograms of Figures 3A and 3B, we see that the histogram of Figure 3A has a downward convexity, while the histogram of Figure 3B has an upward convexity. It is convex. Therefore, in this chest image, the value taken by the second derivative in the region near the signal median value 3 mid is examined, and if the value is positive, the frontal image is taken; It can be distinguished from a shadow image.

(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 by the method of the present invention. This radiation image information recording and reproducing system basically consists of a radiation image capturing section 20. It is composed of a pre-reading reading section 30, a main reading reading section 40°, and an image reproduction section 50. In the radiographic imaging unit 20, for example, a radiation source 100 such as an X-ray tube is
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 unit 30 by sheet transport means 110 such as a transport roller. A laser beam 202 emitted from a pre-reading laser light source 201 in the pre-reading reading unit 30 passes through a filter 203 that cuts the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 103 due to excitation of the laser beam 202. Thereafter, 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 plane reflecting mirror 205. Here, in the laser light source 201, the wavelength range of the laser light 202 as excitation light is the same as the wavelength range of the stimulated luminescence light emitted by the stimulable phosphor sheet 103! T! selected not to be viewed. On the other hand, the phosphor sheet 103 is transported in the direction of the arrow 20G by a sheet transport means 210 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the phosphor sheet 103 is irradiated with the laser beam 202. Here, laser light source 2
01, the beam diameter of the laser beam 202, the scanning speed of the laser beam 202, and the transport speed of the stimulable phosphor sheet 103. It has been selected to be smaller than that of the main reading conducted in .

When the laser beam 202 is irradiated as described above, the stimulable phosphor sheet 103 emits stimulated luminescence light corresponding to the radiation energy stored and recorded therein, and this luminescence light is transmitted to the pre-reading light guide. 207. The stimulated luminescence light is guided through the light guide 207, exits from the exit surface, and is received by a photodetector 20g 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 input as a pre-read image signal Sp to the main reading control circuit 314 of the main reading reader wS40.

This main reading control circuit 314 determines the reading gain setting value a, the recording scale factor setting mb, and the reproduction image processing condition setting value C by, for example, histogram analysis based on the accumulated recording information indicated by the preread image signal Sp.

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 unit 40, the main reading laser beam 'a30
The laser beam 302 emitted from the laser beam 30
A filter 30 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by the excitation of the stimulable phosphor sheet 103
3, 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 reflector 306 to a stimulable phosphor sheet. Enter on 103) 1. An fθ lens 307 is arranged between the optical deflector 305 and the plane reflecting mirror 306, and the M-stacked phosphor sheet 10
The beam diameter of the laser beam 302 that scans the area 3 is made uniform. On the other hand, the stimulable phosphor sheet 103 is moved by the arrow 30 by a sheet transport means 320 such as a transport roller.
The stimulable phosphor sheet 103 is moved in the direction 8 for 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 1o3 emits stimulated luminescence light with an amount corresponding to the radiation energy stored and recorded 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 310 such as a photomultiplier. A filter that selectively transmits only the wavelength range of the stimulated luminescence light is attached to the light receiving surface of the photodetector 310, so that the photodetector 310 detects only the 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 A/D converter 312, and based on the recording scale factor setting lb, it is converted into a digital signal '' with a recording scale factor suitable for the signal fluctuation range, and is input to the signal processing circuit 313. Ru. The digital signal is processed in the signal processing circuit 313 by image processing such as gradation processing based on the reproduction image processing condition setting value C so that a radiation image with excellent observation and interpretation suitability is obtained.
signal processing) 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 unit 50, a laser beam 403 from a recording laser light source 402 is transmitted to an optical modulator 40.
1, the reading image signal So input from the signal processing circuit 313 is modulated based on the scanning mirror 404.
The light beam is deflected by the light beam and scans over a photosensitive material 405 such as photographic film. The photosensitive material 405 is then transported in a direction perpendicular to the scanning direction (arrow 406 direction) in synchronization with the scanning, and a radiation image based on the actual reading image signal SO is output onto the photosensitive material 405. In addition to this method, various other methods can be used to reproduce the radiographic image, such as the above-mentioned CRT display.

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 Sρ outputted from the A/D converter 211 is input to the main reading control circuit 314 as described above, and is also input to the image position determining circuit 500. Figure 4 shows this forming body position discrimination circuit 5.
00 is shown in detail, and will be explained below with reference to FIG. 4. The histogram creation section 511 of the imaging body position determination circuit 500 receives the above-mentioned pre-read image signal Sp and creates a histogram of the image signal sp. When the image recorded on the stimulable phosphor sheet 103 is a chest image, the histograms created in this manner are shown in FIGS.
It will look like the one shown in the figure. This chest image will be explained below as an example. Information H indicating the histogram is sent to the function determining section 512.

The function determination unit 512 determines a function f (S) that approximates the histogram pattern indicated by the information H.

This function f (S) can be determined as a function consisting of a high-order polynomial by using, for example, multiple regression analysis. Information F indicating the function f(:S) obtained in this way
is sent to the calculation unit 513 for two or more machines.

The two-manufacturing unit 513 calculates the function f(S
) into two parts and find its second derivative f'' (S),
The determining unit 514 determines the information F'' indicating the second derivative f''(S).
send to

On the other hand, the area j determination unit 5 connected to this determination unit 514
The above-mentioned histogram information H is input to 15, and the area specifying unit 515 calculates the signal intermediate value 3II+id (see FIGS. 3A and 3B) of the histogram based on this information H. Information m indicating this intermediate jfi Sm1d is sent to the determination unit 514. Based on this information m, the determining unit 514 determines that the second derivative 1'(S) is the signal intermediate value 3 mid
The determination unit 514 determines that the image carried by the pre-read image signal Sp is a side view image if the value of f''<5aid) is a negative value. Outputs the correction signal T, f” (Sm
If the value of id ) is a positive value, it is determined that the image is a frontally photographed image, and the correction signal T is not output. This correction signal T is sent to a gain correction circuit 507 shown in FIG. 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 mentioned above, if the image reading conditions and image processing conditions are constant,
In the reproduced image of the thoracic lateral imaging, the m degree of the portion of the thoracic vertebrae is higher than that of the frontal imaging. Therefore, as mentioned above, if the value of f" (3aid) is a negative value, that is, if the reading gain is lowered when reading a side-view image, the actual reading image signal SO will be at a low level overall,
The overall density of the reproduced radiation image recorded on the photosensitive material 405 becomes lower. As a result, the density of the portion of the thoracic vertebrae in the reproduced image of the thoracic side surface becomes equal to the density of the thoracic vertebrae portion of the reproduced image of the frontal view. Note that an appropriate amount of correction of the reading gain can be determined based on experiments or experience.

Further, the value substituted for the second derivative f''(S) is not limited to the above-mentioned signal intermediate value Sm1d, but may be appropriately determined according to a typical histogram pattern of the target image signal.

Furthermore, when creating the above-mentioned histogram, it is possible to create a histogram for the entire pre-read image signal Sp, or for signals that are not directly related to the subject, such as the area directly irradiated with radiation (the so-called part that can be treated simply), etc. You can create histograms for other image signals other than the image signal, or you can create a histogram for the pre-read image signal Sp and then deal with the image signals such as the above-mentioned part. The histogram area may be excluded. That is, the histogram created in the method of the present invention may be for all of the image signal or for a portion thereof.

In the above example, the frontal shot image is read with the reading gain determined by the main reading control circuit 314, and when the side shot image is read, the reading gain is set to low (corrected), but this is the opposite. The side view image may be read with the read gain determined by the main reading control circuit 314, and the read gain may be corrected to be higher when reading the front view image.
In order to adjust the f1 degree, in addition to changing the reading gain as described above, changing the recording scale factor conditions in the A/D converter 312, changing the gradation processing conditions in the signal processing circuit 313, etc. Good too. Further, these concentration adjustment methods may be used in combination.

Although the embodiment for discriminating between a front view 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 and other body positions. In other words, if images of a common body part have different lunar positions, the histogram pattern of the image signal representing the image of each lunar position will often be convex downward in one part and convex upward in the other in a certain predetermined part. Therefore, the lunar shadow position can be correctly determined depending on the sign of the value that the second derivative takes in this predetermined portion.

Furthermore, in the embodiments described above, the imaging position is determined using the pre-read image signal Sp, but the image processing conditions in the signal processing circuit 313 are determined 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. Further, in the above embodiment, the density of the reproduced image is corrected according to the determined moon shadow body position, but the present invention is of course applicable to determining the photographing body position for other purposes. .

Furthermore, in the above embodiment, the stimulable phosphor sheet 10
3. Distinguishing the lunar shadow position of the recorded image, but the present invention is capable of determining the imaging position of not only radiographic images recorded on such a 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 drawings]

FIG. 1 is a schematic diagram showing an example of a radiation image information recording and reproducing system for determining the lunar position by the method of the present invention, and FIGS. 2A and 2B are schematic diagrams showing examples of radiographic images depending on the imaging position of the subject. , FIGS. 3A and 3B are graphs showing examples of histograms of image signals read from stimulable phosphor sheets photographed while changing the subject's photographic position, and FIG. 4 is a graph showing an example of a histogram of an image signal read from a stimulable phosphor sheet, and FIG. 4 is an apparatus for carrying out the method of the present invention. It is a block diagram showing an example. 20... Radiation image spiral portion 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...System (sum circuit 320...Main reading sheet transport means 500...Shooting body position discrimination circuit 507...Reading gain correction circuit 511...Histogram creation section 512 ...Function determination section 513...Two-several machine rendition section 514...Discrimination section 515...Area specification section a...Reading gain setting value b...Recording scale factor setting value C...・Image processing condition setting value F... Information indicating a function F''...Information indicating a second derivative H...Histogram information m...Information indicating an intermediate value Sp...Pre-read image signal SO・・・Main reading image signal T ・・Correction signal Figure 4 Section No. =・−

Claims (1)

[Claims] After creating a histogram of the image signal that represents the transparent image of the human body and finding a function that approximates the pattern of this histogram, finding the second derivative of this function, and then calculating the value that this second derivative takes in a predetermined area. 1. A method for determining the photographing body position of a medical image, characterized by determining whether the image is positive or negative, and determining the photographing body position of the image depending on whether the value is positive or negative.