JPH0677574B2 - 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. Generates light, photoelectrically reads the resulting stimulated emission light to obtain an image signal, and based on this image signal, a radiation image of the subject as a visible image on a recording device such as a photographic light-sensitive material or a display device such as a CRT. A radiation image information recording / reproducing system for outputting has already been proposed by the present applicant.

(JP-A-55-12429, JP-A-56-11395, etc.) This system is a practical system capable of recording an image over a very 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 is obtained by converting it into an electrical signal and using this electrical signal to output a radiation image as a visible image on a recording material such as a photographic photosensitive material or a display device such as a CRT. 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 part of the subject such as the abdomen, a recording pattern determined by an imaging method such as simple imaging or contrast imaging (hereinafter, these are collectively referred to as “accumulated recording information”) 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 Application Laid-Open No. 58-67240 is known as a method of grasping the accumulated and recorded information of the radiation image before outputting the visible image. This method uses excitation light of a lower level than the excitation light to be emitted during a reading operation for obtaining a visible image for observation / interpretation (hereinafter referred to as “main reading”), in advance of 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 vertebra K overlaps with the lung field P through which radiation easily penetrates. Therefore, in the stimulable phosphor sheet, the thoracic vertebra portion has a high accumulated radiation dose, and this portion becomes a high light emission amount portion. The maximum value Smax and the minimum value Smin of the image signal read from the stimulable phosphor sheet are used both in the case of frontal photography and in the case of lateral photography.
Since it does not change much, the reading condition and / or the image processing condition determined based on the maximum value Smax and the minimum value Smin as conventionally performed are almost 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 imaged 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. , The distribution along the predetermined direction across the human body in the image is obtained, the signal values forming this distribution are sequentially accumulated along the above direction, and the cumulative value at each point along the direction is calculated. The rate of change in the substantially central portion along the predetermined direction is obtained, and the photographing position of the image is determined based on the value of the rate of change.

(Operation) For example, considering a radiographic image of the chest of a human body,
The signal value (density) distribution in the left-right direction of the image, which is shown by the straight line L in FIGS. 2A and 2B, that is, the signal value distribution in the direction perpendicular to the body axis, is roughly as shown in FIG. 3A in the front view image. On the other hand, in the side face photographed image, it is roughly as shown in FIG. 3B. That is, in the front photographed image (see FIG. 2A), the thoracic spine K and the mediastinum where radiation is difficult to pass through are located in the central portion in the left-right direction, while in the lateral photographed image (see FIG. 2B), The lung field P where radiation is satisfactorily transmitted is located in this region, and it is difficult for radiation to pass through the vicinity of both ends.
Is located, the distribution is as described above. The signal value distribution in the left-right direction of the image is as shown in FIG.
The signal value distribution of the pixel columns along the straight line L in FIG. 2B may be considered, or the distribution of the signal total value or average value of each pixel column in the direction substantially orthogonal to the straight line L may be considered.

When the above signal value distribution is as shown in FIG. 3A and FIG. 3B, the above-mentioned accumulated values are as shown in FIG. 4A and FIG. 4B in the front image and the side image, respectively. Become.
Looking at the rate of change of this cumulative value near the center of the image in the left-right direction, the cumulative value pattern in FIG.
On the other hand, it can be seen that the cumulative value pattern in FIG. 4B is considerably large. Therefore, in this chest image, it is possible to discriminate a front image when the change rate is relatively small and a side image when the change rate is relatively large.

(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 pre-reading laser source 201 in the pre-reading reading unit 30 is a filter 203 that cuts the wavelength region of the stimulated emission light emitted from the stimulable phosphor sheet 103 by the excitation of the laser light 202. After passing through, the light is deflected linearly 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 phytomultiplier.
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 211.
Is digitized by 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, based on the accumulated record information indicated by the preread image signal Sp, for example, by histogram analysis,
The reading gain setting value a, the recording scale factor setting value b, and the reproduced image processing condition setting value c are determined.

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 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 10 is transferred.
The entire surface of 3 is irradiated with laser light. When the laser light 302 is thus irradiated, the stimulable phosphor sheet 103 emits stimulated emission light in an amount corresponding to the radiation energy stored and recorded therein, and this emission light is incident on the main reading light guide 309. To do. The stimulated emission light guided by repeating the total reflection in the main reading light guide 309 is emitted from its emission surface and received by a photodetector 310 such as a phytomultiplier. 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 the signal processing circuit 31.
Entered in 3. 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 recording laser light source
The laser light 403 from 402 is modulated by the optical modulator 401 based on the main reading image signal So input from the signal processing circuit 313, deflected by the scanning mirror 404, and scanned on the photosensitive material 405 such as photographic film. . And photosensitive material 4
Reference numeral 05 is transferred 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 onto the photosensitive material 405. As a method for reproducing the 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 input to the main reading control circuit 314 as described above and also to the imaging position determining circuit 500. FIG. 5 shows in detail the configuration of the photographing body position determination circuit 500, which will be described below with reference to FIG.
The signal extraction / addition unit 511 of the photographing body position determination circuit 500 receives the pre-read image signal Sp, and extends from the image signal Sp in the vertical direction of the image (direction orthogonal to the straight line L) in each pixel row G ₁ , G ₂ , G ₃ ... …
Signals are extracted in units of Gn (see FIG. 6), and these signals are added for each pixel column. The n addition signals H ₁ , H ₂ , H _3, ... Hn thus obtained each show the density total value of each pixel column, and show the density distribution in the horizontal direction of the image as a whole. The average value of the extracted signals for each pixel column may be used instead of this addition signal. That is, this average value also shows the density distribution in the left-right direction of the image as in the above. When the image recorded on the stimulable phosphor sheet 103 is a chest image, the signal value (density) distribution in the left-right direction of the image is 3A for the front image and the side image as described above.
As shown in FIG. 3B. Hereinafter, this chest image will be described as an example. The above n addition signals H =
H ₁ , H ₂ , H ₃ ... Hn are sent to the signal accumulator 512. The signal accumulating unit 512 sequentially accumulates the addition signals H ₁ , H ₂ , H _3, ... Hn from the addition signal on the left end side of the image to each pixel column position. That is, first, the cumulative value up to the pixel row G ₁ is H ₁ , next is the cumulative value up to the image row G ₂ (H ₁ + H ₂ ), and next is the cumulative value up to the pixel row G ₃ (H ₁ + H ₂ + H ₃ ) ... And finally, the cumulative value up to the pixel row Gn (H ₁ + H ₂ + H ₃ + ...
+ Hn) is required. The pattern of the signal cumulative value (which indicates the cumulative density value) obtained in this way is 4A for the front photographed image and the side photographed image as described above.
As shown in FIG. 4B. The information Ha indicating the accumulated value is sent to the change rate calculation unit 513. The change rate calculation unit 513 obtains a change rate r of the cumulative value indicated by the information Ha in the predetermined area I near the central portion in the left-right direction of the image (fourth A,
(See Figure 4B). The rate of change r may be defined as a value of (β-α) where α and β are the signal accumulated values at both ends of the predetermined region I, for example. The predetermined region I is, for example, a region between the points at the position of 40% and the point at the position of 60% of the image width, but is not limited to this and is appropriately determined according to the target image. Just do it. In addition, this area may be a certain point.

Information indicating the rate of change r is sent to the determination unit 514. The determination unit 514 determines the reference value Th sent from the reference value setting unit 515.
And the rate of change r are compared, and if r> Th, it is determined that the image carried by the prefetch image signal Sp is a side face captured image, and the correction signal T is output. When it is determined that there is, the correction signal T is not output. This 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 the value of the change rate r is relatively large as described above, that is, when the reading gain is reduced when reading the side face image, the main reading image signal So becomes a low level as a whole, and the reproduction radiation recorded on the photosensitive material 405 is reproduced. Image density is low overall.
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. Note that the proper correction amount for the reading gain is
It can be determined based on experiments or experience.

Further, in the above-described embodiment, the added value of each pixel column of the image signal Sp is obtained, but the image signal Sp of each pixel is compared with a predetermined threshold value in advance to be binarized, and the binarized data For the above, the same processing as described above may be performed.

The signal value distribution in the direction along the straight line L in FIGS. 2A and 2B is obtained by calculating the image signal total value or average value for each of the pixel rows G ₁ , G ₂ , G ₃ ... Gn described above. Besides, as shown in FIG. 7, each pixel F ₁ , F ₂ , F _{3 of} the pixel row along the straight line L ..
Since the signal value for Fn shows the distribution as it is, it may be obtained by extracting these signals.

In the above example, the front view image is read with the read gain determined by the main reading control circuit 314 as it is, and the read gain is corrected to a low value when reading the side view image. The captured 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 captured image is read. In addition, in order to adjust the density of the reproduced image, in addition to changing the reading gain as described above,
The condition of the recording scale factor in the A / D converter 312 may be changed, or the condition of the gradation processing in the signal processing circuit 313 may be changed. 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 differ in an image of a certain common region, the rate of change of the cumulative values for the images of the respective imaged body positions often greatly differ in the approximately central portion in the accumulation direction. The position can be correctly determined.

Further, in the above embodiments, the pre-reading image signal Sp is used to determine the photographing position, but the pre-reading as described above is not performed, and the signal processing circuit 31 is based on the main reading image signal So.
When the image processing condition in 3 is set, the photographing position may be determined by 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 this 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 imaged posture 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 an example of the density distribution in a predetermined direction of a radiographic image taken by changing the imaging position of the subject, and FIGS. 4A and 4B are cumulative density values in the density distribution. FIG. 5 is a block diagram showing an example of an apparatus for carrying out the method of the present invention, and FIGS. 6 and 7 are explanatory views for explaining signal extraction for obtaining the density distribution according to the present invention. It is a figure. 20 ... Radiation image photographing unit, 30 ... Pre-reading reading unit 40 ... Main-reading reading unit, 100 ... Radiation source 101 ... Subject, 102 ... Radiation 103 ... Accumulable phosphor sheet 201 ... Pre-reading laser light source 202 ... Pre-reading laser light 204 ... Pre-reading light deflector 208 ... Pre-reading light detector 210 ... Pre-reading sheet transport means 301 ... Main reading laser light source 302 ... Main reading laser light 305 ... Main reading optical deflector 310 ... Main reading optical detector 311 ... Amplifier 312 ... A / D converter, 313 ... Signal processing circuit 314 ... Control circuit 320 ... Main reading sheet transfer means 500 ... Imaging position determining circuit 507 ... Reading gain correction circuit 511 ... Signal extraction / addition unit, 512 ... Signal accumulation unit 513 ... change rate arithmetic unit, 514 ... each of the determination section 515 ... reference value setting unit a ... read gain setting value b ... From the scale factor setting value c ... image processing condition setting value F ₁ to Fn ... predetermined direction parallel to the pixel columns Pixels G _{1 to} Gn ... Images in a direction orthogonal to the predetermined direction Element sequence Ha ... Density accumulated value information r ... Change rate of density accumulated value Sp ... Pre-read image signal, So ... Main read image signal T ... Correction signal, Th ... Reference value

Claims (3)

[Claims] 1. A distribution of an image signal for carrying a transparent image of a human body along a predetermined direction across the human body in the image is obtained, and signal values forming the distribution are sequentially accumulated along the direction to obtain the direction. The cumulative value at each point along is determined, the rate of change of the cumulative value in the substantially central portion along the predetermined direction is determined, and the photographing position of the image is determined based on the value of this rate of change. The method for determining the position of a medical image. 2. The distribution of the signal values is a distribution of a total value or an average value of the signal values in each of the pixel rows in a direction substantially orthogonal to the predetermined direction, and the distribution of the signal values is used. Method for determining the postural position of medical images. 3. The medical image capturing posture determining method 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 signal values.