JPH0642880B2 - Medical image capturing posture determination method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for automatically discriminating a photographing 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-ray, α-ray, β-ray, γ-ray, electron beam, ultraviolet ray, etc.), a part of this radiation energy is accumulated in the phosphor, It is known that when a phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated emission depending on the stored energy, and a phosphor having such a property is a stimulable phosphor (luminescent material). Exhaustible phosphor).

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on a stimulable phosphor sheet, and the stimulable phosphor sheet is scanned with excitation light such as laser light to stimulate emission. An image signal is obtained by photoelectrically reading the obtained stimulated emission light by generating light, and based on this image signal, a radiation image of the subject is visible 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 / reproducing system for outputting as. (JP-A-55-12429, JP-A-56-11395, etc.) This system is practical because it can record an image over an extremely wide radiation exposure area as compared with a conventional radiographic system using silver salt photography. Have advantages. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the radiation exposure amount over a very wide range,
Therefore, even if the radiation exposure amount fluctuates considerably due to various photographing conditions, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value. A radiation image that is not affected by fluctuations in radiation exposure amount is obtained by converting the radiation signal into a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT by converting the radiation signal into an electrical signal. be able to.

By the way, in the above system, in order to eliminate the influence of fluctuations in imaging conditions or to obtain a radiographic image with excellent observation and interpretation suitability, the recording state of the radiographic image information accumulated and recorded in the stimulable phosphor sheet, or the chest , A recording pattern (hereinafter referred to as “accumulated record information” when collectively referred to) which is determined by a region of the subject such as the abdomen, a photographing method such as simple photographing, construction photographing, or the like can be used for observation and interpretation. Grasping is performed prior to visual image output, the reading gain is adjusted to an appropriate value based on this accumulated recording information, and the recording scale factor is set so that the resolution is optimized according to the contrast of the recording pattern. When the image processing 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.

A method disclosed in Japanese Patent Laid-Open No. 58-67240 is known as a method of grasping the accumulated record information of the radiation image prior to the output of the visible image. This method uses excitation light of a lower level than the excitation light to be emitted during a reading operation (hereinafter, referred to as “main reading”) for obtaining a visible image for observation and photography, prior to the main reading. A reading operation (hereinafter referred to as "pre-reading") for grasping the accumulated record information of the radiation image accumulated and recorded on the stimulable phosphor sheet is performed, the outline of the accumulated record of the radiation image is grasped, and the main reading is performed. At this time, the read gain is appropriately adjusted based on the preread information, the recording scale factor is determined, or the image processing condition is determined.

According to the above method, since the recording state and recording pattern of the radiation image information accumulated and recorded on the stimulable phosphor sheet can be grasped in advance before the main reading, a reading system having a particularly wide dynamic range can be provided. Even if it is not used, the reading gain is adjusted appropriately based on this recorded information, the recording scale factor is determined, and the signal processing according to this recording pattern is performed on the electrical signal after reading, thereby making observation and interpretation. It is possible to obtain a radiation image with excellent suitability.

(Problems to be Solved by the Invention) However, when the reading condition and / or the image processing condition of the radiation image information is determined as described above, when the same subject is photographed in different photographing positions, the respective reproductions are performed. The density of the region of interest in the subject may change in the image. Hereinafter, this will be described in detail. For example, consider a case where the chest is photographed from the front as shown in FIG. 2A and a case where the chest is photographed from the side as shown in FIG. 2B in order to diagnose the thoracic spine. In the case of frontal imaging, the thoracic spine K, which is the region of interest, overlaps the mediastinum where it is difficult for radiation to pass therethrough. On the other hand, in lateral imaging, the thoracic spine K is a lung field P through which radiation easily penetrates.
Therefore, in the stimulable phosphor sheet, the accumulated radiation dose in the thoracic vertebra portion is high, and this portion becomes a high light emission amount portion.
The maximum value Smax and the minimum value Smin of the read image signal from the stimulable phosphor sheet do not change much in the case of both front and side photographing, so that the maximum value Smax, The reading condition and / or the image processing condition determined based on the minimum value Smin are substantially the same in both cases. Therefore, when an image is read under such a reading condition and / or an image processing condition to obtain a reproduced image, the thoracic vertebra part has a relatively low density in the front image, while it has a relatively low density in the lateral image. It becomes a high concentration.

Further, it is conceivable to appropriately set the image processing condition based on the read image signal obtained by the main reading without performing the pre-reading as described above, but in such a case, the above problem similarly occurs. .

In order to solve the above-mentioned problems, conventionally, when reading radiation image information from a stimulable phosphor sheet, it is necessary to determine in what position the subject is photographed on the sheet one by one. The reading conditions and / or the image processing conditions are input to the image processing apparatus, and the above-mentioned reading conditions and / or image processing conditions are set according to the input photographing body position information.

However, it is very troublesome to input the above-mentioned image-taking position information every time each stimulable phosphor sheet is read, and it is easy to mistakenly input the image-taking position information.

Therefore, it is an object of the present invention to provide a method capable of automatically discriminating a photographing position of a medical image recorded on the above-mentioned stimulable phosphor sheet or the like.

(Means for Solving Problems) A medical image capturing position determining method according to the present invention is an image signal obtained by a reading process from the above-mentioned stimulable phosphor sheet, that is, an image signal for transmitting a human body. A histogram is created, the degree of matching between the pattern of this histogram and each of a plurality of image signal reference histogram patterns defined in advance for each image-taking position of the image is determined, and the image-taking position of the image is determined according to the degree of matching. It is characterized by.

The degree of matching between the histogram pattern of the image signal and the reference histogram pattern can be checked by various conventionally known pattern matching methods.

(Operation) For example, the histogram of the image signal that carries the radiation image of the chest of the human body is approximately as shown in FIG. 3A in the front image, while it is approximately 3B in the side image.
It becomes something like the figure. Therefore, for example, such a pattern is stored in the storage means as the reference histogram pattern of the front chest photographed image and the reference histogram pattern of the side photographed image, respectively, and a front chest photographed image or a certain image signal of the chest side photographed image When the degree of matching between the histogram pattern and the two reference histogram patterns is examined, if the histogram pattern of the image signal matches the reference histogram pattern of FIG. 3A better than the reference histogram pattern of FIG. It is possible to determine that the image carried by the signal is a front imaged image, and in the opposite case, it is a side imaged 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 / reproducing system configured to determine the imaged posture of a human body by the method of the present invention. This radiation image information recording / reproducing system basically includes a radiation image capturing unit 20 and a read-ahead reading unit 3
0, a main reading reading unit 40, and an image reproducing unit 50. In the radiation image capturing unit 20, radiation 102 is emitted from a radiation source 100 such as an X-ray tube toward a subject (examinee) 101. At the position where the radiation 102 transmitted through the subject 101 is irradiated, the stimulable phosphor sheet 103 for accumulating the radiation energy is arranged as described above, and the transmitted radiation of the subject 101 is placed on the stimulable phosphor sheet 103. Image information is accumulated and recorded.

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 is recorded in this manner is sent to the prereading reading unit 30 by the sheet transfer means 110 such as a transfer roller. The laser light 202 emitted from the laser light source 201 for pre-reading in the pre-reading reading section 30 passes through the filter 203 that cuts the wavelength region of the stimulated emission light emitted from the stimulable phosphor sheet 103 by the excitation of this laser light 202. After that, it is linearly deflected by an optical deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a plane reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as the excitation light does not overlap with the wavelength range of the stimulated emission light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is transferred in the direction of arrow 206 by the sheet transfer means 210 such as a transfer roller and is sub-scanned, and as a result, the entire surface of the phosphor sheet 103 is irradiated with the laser beam 202. Here, the emission intensity of the laser light source 201, the beam diameter of the laser light 202, the scanning speed of the laser light 202, and the transfer speed of the stimulable phosphor sheet 103 are the energy of the pre-read excitation light (laser light 202), which will be described later. It is selected to be smaller than that of the main reading performed by the main reading reading unit 40.

When the laser light 202 is irradiated as described above, the stimulable phosphor sheet 103 emits stimulated emission light of a light amount corresponding to the radiation energy stored and recorded in the stimulable phosphor sheet 103. Incident on. The stimulated emission light is guided through the light guide 207, emitted from the emission surface, and received by a photodetector 208 such as a photomultiplier.
On the light receiving surface of the photodetector 208, a filter that transmits only light in the wavelength range of stimulated emission light and cuts light in the wavelength range of excitation light is attached, and detects only stimulated emission light. Is ready to go. The detected stimulated emission light is converted into an electric signal carrying the accumulated record information and amplified by the amplifier 209. The signal output from the amplifier 209 is the A / D converter 2
It is digitized by 11, and is input to the main reading control circuit 314 of the main reading reading unit 40 as the preread image signal Sp.
The main reading control circuit 314 determines the reading gain setting value a, the recording scale factor setting value b, and the reproduced image processing condition setting value c by, for example, histogram analysis or the like based on the accumulated recording information indicated by the preread image signal Sp.

The stimulable phosphor sheet that has been read ahead as described above
103 is transferred to the reading unit 40 for main reading. Book reader 4
The laser light 302 emitted from the main reading laser light source 301 at 0 passes through the filter 303 that cuts the wavelength region of the stimulated emission light emitted from the stimulable phosphor sheet 103 by the excitation of the laser light 302, and then the beam The beam diameter is strictly adjusted by the expander 304, is linearly deflected by the optical deflector 305 such as a galvanometer mirror, and the stimulable phosphor sheet 1 is passed through the plane reflecting mirror 306.
03 incident on. An fθ lens 307 is arranged between the light deflector 305 and the plane reflecting mirror 306 so that the beam diameter of the laser light 302 for scanning the stimulable phosphor sheet 103 becomes uniform. On the other hand, the stimulable phosphor sheet 103 is transferred in the direction of arrow 308 by the sheet transfer means 320 such as a transfer roller to be sub-scanned, and as a result, the stimulable phosphor sheet 103.
Is irradiated with laser light over the entire surface. When the laser light 302 is thus irradiated, the stimulable phosphor sheet 103 emits stimulated emission light of a light amount corresponding to the radiation energy stored and recorded in the stimulable phosphor sheet 103.
It is incident on 309. The stimulated emission light guided by repeating the total reflection in the main reading light guide 309 is emitted from the emission surface and is received by the photodetector 310 such as a photomultiplier. A filter that selectively transmits only the wavelength region of the stimulated emission light is attached to the light receiving surface of the photodetector 310,
The photodetector 310 is adapted to detect only stimulated emission light.

The output of the photodetector 310 that photoelectrically detects stimulated emission light indicating the radiation image recorded on the stimulable phosphor sheet 103 is the read gain based on the read gain set value a determined by the control circuit 314. Is amplified to an appropriate level electric signal by the amplifier 311 in which is set. The amplified electric signal is input to the A / D converter 312, converted into a digital signal with a recording scale factor suitable for the signal fluctuation width based on the recording scale factor setting value b, and input to the signal processing circuit 313. . In 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 set value c so that a radiographic image excellent in observation and interpretation suitability is obtained, and output. To be done.

The read image signal (main read image signal) So output from the signal processing circuit 313 is input to the optical modulator 401 of the image reproducing unit 50. In the image reproducing section 50, the laser light 403 from the recording laser light source 402 is modulated by the optical modulator 401 based on the main reading image signal So input from the signal processing circuit 313, and is deflected by the scanning mirror 404. The photosensitive material 405 such as a photographic film is scanned over. Then, the photosensitive material 405 is transported in a direction (arrow 406 direction) orthogonal to the scanning direction in synchronization with the scanning, and a radiation image based on the main reading image signal So is output on the photosensitive material 405. As a method for reproducing a radiation image, various methods such as the above-described CRT display can be adopted in addition to such a method.

Next, the method of the present invention for automatically discriminating the photographing position of the subject 101 will be described. The pre-reading image signal Sp output from the A / D converter 211 is the main reading control circuit as described above.
It is input to 314 and also to the imaging position determination circuit 500. FIG. 4 is a detailed explanation of the configuration of the photographing position determining circuit 500, which will be described below with reference to FIG. Histogram creation unit 511 of the photographing position determination circuit 500
Receives the pre-read image signal Sp and creates a histogram of the image signal Sp. If the histogram thus created is represented by a rough pattern, the stimulable phosphor sheet 103
When the image recorded in 1 is a chest image, the front and side images are as shown in FIGS. 3A and 3B, respectively, as described above. Hereinafter, this chest image will be described as an example.

The histogram creating unit 511 creates histograms of the pre-reading image signals Sp for some typical frontal chest imaged images and side imaged images in advance in the general histogram patterns as shown in FIGS. 3A and 3B. , These histograms are sent to the function determination unit 512, and can be obtained by averaging or smoothing them. Then, the function determination unit 512 obtains the functions g ₁ (i) and g ₂ (i) that approximate the representative histogram pattern obtained as described above (i is an image signal value). Such a function, for example, by using the multiple regression analysis method,
It can be obtained as a function composed of high-order polynomials.
These functions g ₁ (i) and g ₂ (i) are stored in the storage means 515 as the reference histogram patterns for the front side image and the side side image, respectively.

When discriminating the radiographic image capturing position of each radiographic image, a histogram of the preread image signal Sp that carries the radiographic image is created one by one in the histogram creating unit 511. The actual histogram for each image is as shown in FIG. 3C, for example, and can be defined as the function f (i) of the image signal i. The information F indicating the function f (i) is sent to the mismatch measure calculation unit 513. The mismatch measure calculator 513
A mismatch measure between the histogram pattern of the prefetch image signal Sp created for each image and the two reference histogram patterns is obtained. That is, the calculation unit 513
Receives the information F and the information G ₁ and G ₂ indicating the functions g ₁ (i) and g ₂ (i) from the storage means 515, and receives each mismatch measure. Ask for. The mismatch measures S ₁ and S thus obtained
_The information indicating ₂ is sent to the determination unit 514.

If S ₁ > S ₂ , the discrimination unit 514 determines that the prefetch image signal S
It is determined that the image carried by p is a side-captured image, and the correction signal T is output. Conversely, if S ₁ <S ₂ , it is determined that the image is a front-captured image, and the correction signal T is not output. Referring to this determination in detail, for example, _S 1 <mismatch measure of _{S 2} if a function f (i) and the function g ₁ (i) is from a mismatch measure of the function f (i) and the function g ₂ (i) Is smaller, that is, the function f (i) is better matched (matched) to the function g (i) than the function g ₂ (i). Therefore, the histogram pattern of the prefetch image signal Sp is the reference histogram pattern of FIG. 3B. Instead, it can be determined that it is better matched to the reference histogram pattern of FIG. 3A. If S ₁ > S ₂ , then vice versa.

The correction signal T is sent to the gain correction circuit 507 shown in FIG. Upon receiving the correction signal T, the correction circuit 507 corrects the read gain setting value a determined by the main read control circuit 314 as described above so as to reduce the read gain. As described above, when the image reading condition and the image processing condition are constant, the density of the portion of the thoracic vertebra K in the reproduced image of the lateral chest image becomes higher than that in the front image. Therefore, when S ₁ > S ₂ as described above, that is, when the reading gain is lowered during reading of the side face photographed image, the main reading image signal So becomes a low level as a whole, and the photosensitive material
The density of the reconstructed radiation image recorded on 405 is generally low. As a result, the density of the portion of the thoracic vertebra K in the reproduced image of the side surface of the chest becomes equal to the density of the thoracic vertebra in the reproduced image of frontal photography. The proper correction amount of the reading gain can be obtained based on experiments or experience.

Further, in creating the histogram, histograms of all the pre-read image signals Sp may be created, or a signal not directly related to the subject, that is, an image signal of a radiation direct irradiation area (so-called blank portion) or the like. Alternatively, histograms for other image signals may be created, or histograms of all the prefetch image signals Sp may be created once, and then the histogram area corresponding to the image signal such as the above-mentioned blank portion is removed. You may do it. That is, the histogram created by the method of the present invention may be for all of the image signals or for some of them.

Moreover, as the mismatch measure, in addition to the above-mentioned ones, for example, Value of f (1) -g (1), f (2) -g
(2), ... May be specified by the maximum value or the like of f (N) -g (N).

In the above example, the reading gain determined by the main reading control circuit 314 is read as it is with respect to the front side photographed image, and the reading gain is corrected to be low when the side side photographed image is read. The side view image may be read with the read gain determined by the main reading control circuit 314 as it is, and the read gain may be corrected to be high when the front view image is read. To adjust the density of the reproduced image, the reading gain is changed as described above, the condition of the recording scale factor in the A / D converter 312 is changed, and the condition of the gradation process in the signal processing circuit 313 is changed. You may do the same. Further, these concentration adjusting methods may be used together.

Although the embodiment for discriminating between the front photographed image and the side photographed image of the chest has been described above, the present invention can be applied to discriminate other regions, and further other photographing positions. That is, if the imaged body postures in the image of a certain common region are different, the histogram patterns of the image signals for the images of the respective photographed body positions often take different basic patterns from each other. The degree of matching with the actual histogram pattern of the image signal can be obtained, and the photographing position can be correctly determined according to the degree of matching.

Further, in the above embodiments, the pre-read image signal Sp is used to determine the photographing position, but the pre-read as described above is not performed, and the image processing conditions in the signal processing circuit 313 are set based on the main read image signal So. If you want to set
The photographing position may be determined using the main reading image signal So. Further, in the above-mentioned embodiment, the density of the reproduced image is corrected according to the discriminated photographing posture, but the present invention is of course applicable to discriminating the photographing posture for other purposes. .

Furthermore, in the above embodiment, the stimulable phosphor sheet 103
However, the present invention is applied to determine not only the radiation image recorded on the stimulable phosphor sheet 103 but also other medical images. Of course, it is also possible.

(Effects of the Invention) As described in detail above, according to the method for discriminating the medical image capturing body position of the present invention, the medical image capturing body posture can be automatically and accurately determined. Therefore, if the present method is applied to the radiation image information recording / reproducing system as described above, the densities of the regions of interest in the reproduced image can be made uniform even if the imaging position of the subject is different. It is possible to greatly improve the diagnostic performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a radiation image information recording / reproducing system for discriminating an imaged body position by the method of the present invention, and FIGS. 2A and 2B are schematic diagrams showing examples of a radiation image in which an imaged body position of a subject is different, FIGS. 3A and 3B are graphs showing basic pattern examples of the histogram of the read image signal from the stimulable phosphor sheet which is photographed by changing the photographing position of the subject, and FIG. 3C is the graph of the actual image signal. A graph showing an example of a histogram, and FIG. 4 is a block diagram showing an example of an apparatus for carrying out the method of the present invention. 20: Radiation image capturing unit, 30: Pre-reading reading unit 40: Main reading reading unit, 100: Radiation source 101: Subject, 102: Radiation 103: Accumulative phosphor sheet 201: Pre-reading Laser light source 202 …… Pre-reading laser light 204 …… Pre-reading light deflector 208 …… Pre-reading light detector 210 …… Main reading sheet transfer means 301 …… Main reading laser light source 302 …… Main reading laser light 305 …… Main reading light deflector 310 …… Main reading light detector, 311 …… Amplifier 312 …… A / D converter, 313 …… Signal processing circuit 314 …… Control circuit 320 …… Main reading sheet transfer means 500 …… Shooting Posture discriminating circuit 507 …… Reading gain correction circuit 511 …… Histogram creating unit, 512 …… Function determining unit 513 …… Mismatch measure computing unit 514 …… Discriminating unit, 515 …… Storage means a …… Reading gain set value b …… … Recording scale factor setting value c …… Image processing condition setting F ...... information G 1 indicating the function of the histogram _{pattern, G} 2 _...... reference histogram pattern information Sp ...... prefetching image signal indicating the functions, So ...... real reading image signals T ...... correction signal

Claims (1)

[Claims] 1. A histogram of an image signal that carries a transparent image of a human body is created, and a matching degree between the pattern of this histogram and each of a plurality of image signal reference histogram patterns defined in advance for each imaged body position of the image is calculated, A method for discriminating a photographing position of a medical image, characterized by discriminating a photographing position of the image according to the degree of matching.