JPH0281277A - Method for determining desired picture signal range - Google Patents

Abstract

PURPOSE:To accurately determine a desired picture signal range by extracting picture signals at points on the outline of a radiation shielding material to generate a histogram and determining the signal range on the higher density side than a specific signal value determined by the maximum frequency point of this histogram as the desired picture signal range bearing a part other than the radiation shielding material. CONSTITUTION:A radiation shielding material packed area K of a radiography has a density considerably lower than that of the other part. That is, since a considerable density difference is generated in an outline part E of the radiation shielding material, the absolute values of the differential value of points on the outline of the radiation shielding material normally take remarkably large values. In the histogram of picture signals related to points where absolute values of differential values exceed a prescribed threshold, the signal whose signal value is a maximum frequency point bears the density on the boundary. Thus, the range on the higher density side than this signal value is the signal range bearing the desired part.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides an image signal obtained by reading radiographic image information from a recording medium on which radiographic image information is recorded.
The present invention relates to a method for determining a range of an image signal that carries only a desired part, excluding parts such as a contrast agent-enriched area different from the object to be observed.

(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. It is called an exhaustible phosphor).

Using this stimulable phosphor, radiation image information of the human body, etc. is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence light. The resulting photostimulated light is photoelectrically read to obtain an image signal, and based on this image signal, a radiation image is output as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT. A radiation image information recording and reproducing system has already been proposed by the applicant. (Unexamined Japanese Patent Publication No. 55-124
No. 92, No. 56-11395, etc. ) In this system, in order to eliminate the influence of fluctuations in imaging conditions or to obtain radiographic images with excellent observation and interpretation suitability, it is necessary to Recording patterns (hereinafter collectively referred to as "accumulated recorded information") determined by the part of the subject such as the abdomen, the imaging method such as plain radiography or contrast radiography, etc. are visualized for observation and interpretation. It is determined before the image is output, and the reading gain is adjusted to an appropriate value based on the acquired recorded information, and the recording scale factor is determined so that the resolution is optimized according to the contrast of the recorded pattern. It is desirable to do so.

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 "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 signal processing conditions are determined based on this pre-read information.

Various methods have been considered for grasping the accumulated record information of a stimulable phosphor sheet from the pre-read image signal obtained by the above-mentioned pre-reading, and one such method is to create a histogram of the pre-read image signal. method is known. In other words, since it is possible to grasp the accumulated recording information from this histogram, for example, the signal maximum value, minimum value, signal value at the maximum frequency point, etc., the reading conditions such as the reading gain and recording scale factor can be determined based on this histogram. By determining the image processing conditions, it becomes possible to reproduce radiation images with excellent diagnostic suitability.

On the other hand, when recording radiation image information (photography), in order to avoid irradiating radiation to areas that are not necessary for diagnosis,
Photographing is often performed by placing a radiation shielding plate such as a lead plate on a part of the subject. Furthermore, in order to clearly photograph the area to be observed, imaging is often performed by injecting a contrast agent such as barium, which has high radiation absorption, into the organ. Although these contrast agents (more specifically, negative contrast agents) and the radiation shielding plate described above have completely different effects, they both have high radiation absorption properties, so they are particularly effective at low-density areas in reconstructed radiographic images. is played as.

(Problem to be Solved by the Invention) Therefore, when grasping the accumulated record information of stimulable phosphor cells as described above, it is necessary to use contrast agents or radiation shielding plates (substances with high radiation absorption such as both). , hereinafter collectively referred to as a radiation shield), there arises a problem in that the accumulated recorded information may be erroneously recognized. In other words, in the above case, the histogram is created including the image signals for the radiation shielding area, so the signal frequency in the low density area is high overall, and therefore The accumulated recorded information will be understood as if the part had a low density as a whole.

In order to eliminate the above-mentioned problem, a method has conventionally been considered in which the low-density range carrying the radiation shielding part is removed from the histogram of the pre-read image signal, and the accumulated recording information is determined from the remaining histogram. However, in the histogram of an image signal, the range taken by the image signal that carries the radiation shielding part changes depending on the part of the subject to be photographed, the photographing method, etc. In some cases, it may not be possible to accurately grasp the range of the image signal carrying the desired part (in other words, the range of the image signal carrying the desired part excluding the radiation shielding part).

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a method that can accurately determine the range of an image signal that carries a desired portion as described above.

(Means for Solving the Problems) A method for determining a desired image signal range according to the present invention includes an image signal obtained by performing a reading process on a recording medium on which a radiographic image of a subject is recorded together with a radiation shielding material such as the contrast agent.
Differential processing is performed along multiple lines on the recording medium, including lines that cross radiation shielding objects, and image signals are extracted at points on the recording medium where the absolute value of the resulting differential value exceeds a predetermined threshold. do,
A histogram of those image signals is created, and a signal range on the higher density side than a specific signal value determined from the maximum frequency point in this histogram is determined as the range of the image signal carrying the desired portion. That is.

(Effect) In radiographic images, radiation shielding materials such as contrast agents have a significantly lower density than other parts. In other words, a significant difference in density occurs at the contour of the radiation shield. Therefore, the absolute value of the above-mentioned differential value usually takes a particularly large value at a point on the contour of the radiation shield. Of course, the absolute value of this differential value may take a large value even at a point within the ground object (for example, the edge of a bone, etc.), but in general, it , there are significantly more points on the contour of the radiation shield as points that take a uniquely large value. Therefore, in the histogram of the image signal regarding the points where the absolute value of the differential value exceeds a predetermined threshold, the signal value at the maximum frequency point is a signal that carries the density on the contour. Therefore, the lower concentration side than the signal value that is the maximum frequency point is the signal range that covers the radiation shielding part.In other words, the higher concentration side than the signal value that is the maximum frequency point is the signal range that covers the aforementioned desired portion. It can be regarded as the signal range that is responsible.

Basically, as mentioned above, the higher concentration side than the signal value at the maximum frequency point can be considered to be the signal range responsible for other than radiation shielding (in other words, in this case, the above signal value determined from the maximum frequency point (The specific signal value is the signal value of the maximum frequency point itself.) To be more precise, the density of a point on the radiation shielding object contour may be slightly higher than that of the radiation shielding object itself. Therefore, in such a case, the signal value at the maximum frequency point may be the same as or greater than the value of the image signal responsible for the extremely low-density portion of the subject. In that case, if the image signal range is determined using the signal value of the maximum frequency point as the boundary as described above, the image signal actually responsible for the low-density portion of the subject will fall outside of this range. To prevent such problems from occurring, the specific signal value should not be set to the signal value at the maximum frequency point itself, but should be set to a signal value on the lower concentration side by a predetermined width than the signal value to be safe. Bye.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a radiation image information recording and reproducing system in which a desired image signal range is determined by the method of the present invention. This radiation image information recording and reproducing system basically includes a radiation image capturing section 20, a prefetch reading section 30,
It is composed of a reading section 40 for actual reading and an image reproduction section 50. In the radiation image capturing section 20, for example,
A subject (subject) 101 from a radiation source 100 such as a radiation tube
Radiation 102 is irradiated toward. This subject 10
A stimulable phosphor sheet 103 that accumulates radiation energy is placed at the position where the radiation 102 that has passed through the stimulable phosphor sheet 103 is irradiated, as described above. Information is accumulated and recorded.

The stimulable phosphor sheet I03 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. In the pre-reading reading section 30, the pre-reading laser light source 2
The laser beam 202 emitted from the laser beam 2
A filter 2 that cuts the wavelength range of stimulated luminescence light emitted from the stimulable phosphor sheet 103 by excitation of 02
03, the light is linearly deflected by a light deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a flat reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as excitation light does not overlap with the wavelength range of the stimulated luminescence light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is moved by a sheet transport means 21 such as a transport roller.
0, the phosphor sheet 103 is moved in the direction of the arrow 206 for sub-scanning, and as a result, the entire surface of the phosphor sheet 103 is irradiated with the laser light 202. Here, the emission intensity of the laser light source 201, the beam diameter of the laser light 202, the laser light 202
The scanning speed of the stimulable phosphor sheet 103 and the transport speed of the stimulable phosphor sheet 103 are as follows.
The energy of the excitation light (laser light 202) for pre-reading is selected to be smaller than that for main reading performed in the main reading reading unit 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 book reading control circuit 314 is
Based on the accumulated recording information indicated by the pre-read image signal Sp, the reading gain setting value a1 recording scale factor setting value b1
Determine reproduction image processing condition setting value C. Further, the above-mentioned pre-read image signal Sp is sent to an image signal range determining section 22 which will be described in detail later.
0 is also input.

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 luminescence light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light is emitted from the book reading light guide 3°9. incident on . 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. 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 is input to the A/D converter 312, and based on the recording scale factor setting value, it is converted into a digital signal with a recording scale factor suitable for the signal fluctuation width, and the digital signal is input to the signal processing circuit 313. . The above digital signal is
In this signal processing circuit 313, signal processing (image processing) is performed based on the reproduction image processing condition setting value C so that a radiographic image with excellent observation and interpretation suitability is obtained, and is 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 40B 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 the above methods, methods for reproducing radiographic images include the above-mentioned CRT
Various methods can be adopted, such as display by.

Here, the stimulable phosphor sheet 103 may record (photograph) an organ injected with a contrast agent such as barium, which has high radiation absorption. An example of such a recording state is shown in FIG. In the figure, E is the stomach wall, and K is the contrast agent filled area. Furthermore, radiographic imaging may be performed with a portion of the subject Lot covered with a radiation shielding plate. An example of such a recording state is shown in FIG. In the figure, J indicates a radiation shielding plate. These contrast agent-filled areas and the radiation shielding plate J are recorded as areas with extremely low density compared to the subject area used for diagnosis. Hereinafter, even when such a portion is recorded, the reading gain setting value a1 recording scale factor setting value b1 image processing condition setting value C
A mechanism for appropriately determining is explained with reference to FIG. As shown in FIG. 5, the control circuit 3
14 is a signal extraction unit 350 and a histogram analysis unit 351
, a reading section 352 and a storage section 353. The pre-read image signal Sp is input to the signal extracting section 350, and the signal extracting section 350 extracts the pre-read image signal Sp' only for a specified area as will be described later. The pre-read image signal Sp' outputted from the signal extraction section 350 is input to the histogram analysis section 351. The histogram analysis section 351 creates a histogram of the pre-read image signal Sp', finds its maximum value, minimum value, maximum frequency value, etc., and sends information Sr indicating these values to the reading section 351.
Send to 2. The storage unit 353 stores the optimum reading gain setting value a1 recording scale factor setting value and image processing condition setting value C corresponding to these maximum values, minimum values, etc., and the reading unit 352 stores the optimum reading gain setting value a1 corresponding to the minimum value, etc. The corresponding set value aSbSc is read from the storage section 353 and sent to the amplifier 311, A/D converter 312, and signal processing circuit 313, respectively, as described above.

Next, signal extraction in the signal extraction section 350 will be explained. The image signal range determining unit 220 includes a differential processing unit 221,
L threshold setting section 222, contour candidate point signal detection section 223
, a signal extraction section 224 and a histogram analysis section 225. In the look-ahead image signal Sp, the image signal range determining unit 220 includes a differential processing unit 221 and a signal extraction unit 224.
is input. The differential processing unit 221 first performs differential processing on this digitized pre-read image signal Sp along the line D1 shown in FIGS. 2 and 3, and then similarly on the lines D2, D3...Dn. Perform differential processing along . This method of differentiation may be one-dimensional first-order differentiation or higher-order differentiation, or two-dimensional first-order differentiation or higher-order differentiation. Furthermore, in the case of discretely sampled images, differentiation is equivalent to finding the difference between adjacent image data, and in this example, this difference is found. The plurality of lines D1 to Dn collectively form the stimulable phosphor sheet 1.
03, and at least some lines are set to cross the radiation shielding object such as the radiation shielding plate J. In this embodiment, these lines are parallel to one side of the sheet 103 and spaced apart from each other, but they may also be, for example, a plurality of lines extending radially from the center of the sheet 103.

By performing this differentiation process, the above difference is obtained. Information Sm indicating this difference is sent to the contour candidate point signal detection section 223. The contour candidate point signal detection section 223 detects contour candidate points that are considered to be in the contour portion of the radiation shielding object based on the information S11 indicating the difference and the information sth indicating the threshold Th outputted by the threshold setting section 222. seek. In other words, since the image signal level within the radiation shield is clearly lower overall than the image signal level in other areas, the pre-read image signal along the line that crosses the radiation shield The value of Sp has a distribution as shown in FIG. 4(a). Therefore, as shown in FIG. 4(b), the value of the above-mentioned difference specifically changes greatly in the contour portion of the radiation shield. Therefore, the contour candidate point signal detecting section 223 detects a point where the absolute value of this difference exceeds the predetermined threshold Th, and obtains a contour candidate point.

The contour candidate point signal detection unit 223 determines the pixel position of the contour candidate point determined as described above, and sends information Se indicating the pixel position to the signal extraction unit 224. Although most of the contour candidate points found as described above are located on the contour of the radiation shielding object, there are also places within the subject part of the radiation image where the density changes rapidly. Some points that are not actually on the contour are also detected as contour candidate points.

The signal extraction unit 224 extracts only the signal at the pixel position indicated by the information Se from the input prefetch image signal Sp,
This extracted pre-read image signal Sp is sent to the histogram analysis section 225. The histogram analysis unit 225 creates a histogram of the extracted pre-read image signal Sp, and determines the image signal value at the maximum frequency point in the histogram. This histogram is, for example, as shown in FIG. 6, and the image signal value at the maximum frequency point is indicated by Sc in the figure. The histogram analysis section 225 sends information St indicating the image signal value Sc obtained in this way to the signal extraction section 350 of the control circuit 314.

The signal extraction section 350 extracts only signals having a value equal to or greater than the signal value Sc from the pre-read image signal Sp outputted by the A/D converter 211, and sends the extracted pre-read image signal Sp' to the histogram analysis section 351. As mentioned earlier, the signal value Sc at the maximum frequency point is considered to be the signal value responsible for the contour of the radiation shielding object with extremely low concentration.
By performing the signal extraction as described above, the pre-read image signal Sp' sent to the histogram analysis section 351 is
The range is such that it supports only the portion other than the radiation shield. In other words, while the entire histogram of the pre-read image signal Sp is as shown by h in FIG. (part) is excluded. Therefore, this pre-read image signal Sp
If the above-mentioned setting values a, b, and C are determined based on the histogram of °, these setting values will be optimal for the radiation image information about the subject, eliminating the influence of the extremely low-density radiation shielding part. Becomes the property of If the reading conditions and image processing conditions are determined based on the set values aSb and C determined in this way, a radiation image with excellent diagnostic performance can be reproduced.

Note that the signal value used as a reference for signal extraction in the signal extraction section 350 is not only the signal value Sc as in the above embodiment, but also a signal value slightly lower in concentration than the signal value Sc as described above. I don't mind.

In addition, in the histogram of the pre-read image signal Sp",
The signal frequency in this histogram may be weighted by the absolute value of the differential value so that the image signal value that corresponds to the contour of the radiation shielding object becomes the maximum frequency point more reliably.

In addition, "pre-reading" as explained above is usually called "book-reading".
This is done on a coarser pixel basis than in . The above-mentioned differential processing may be performed on the image data itself obtained by such a relatively coarse reading operation, or the image data may be interpolated to obtain finer image data and then the images may be It may also be performed on data. Furthermore, the above differential processing may be performed on image data obtained by averaging image signals of a plurality of pixels.

Further, in the above embodiment, the desired image signal range is determined in the pre-read image signal Sp, but it is also possible to similarly determine the desired image signal range in the main read image signal SO. In this case, the determined desired image signal range can be used, for example, as a condition for appropriately determining the above-mentioned image processing condition setting value C.

In addition, the method of the present invention can be applied to correctly grasp accumulated recorded information regarding a subject and optimally set reading conditions and image processing conditions as in the above embodiments, and can also be used for radiation shielding and other purposes. Of course, the present invention can also be applied to the case where an image signal range carrying only a portion excluding an object is determined.

Furthermore, in the embodiments described above, a stimulable phosphor sheet is used as a recording medium for radiographic image information, but the method of the present invention is capable of producing radiation from conventionally known silver halide photographic film for X-ray photography. The same method can be used when reading an image to obtain an image signal.

(Effects of the Invention) As explained in detail above, in the desired image signal range determination method of the present invention, points considered to be on the contour of a radiation shielding object are detected in a radiation image, and image signals at these points are extracted. This is because a histogram is created, and the signal range on the higher density side than the specific signal value determined from the maximum frequency point in the histogram is determined as the desired image signal range that covers the portion excluding the radiation shielding object. , this desired image signal range can be accurately determined. Therefore, if this method is used to set the reading conditions and image processing conditions for radiographic image information, these conditions can be set optimally for recorded information excluding radiation shielding areas, and observation interpretation can be improved. It becomes possible to reproduce radiographic images with excellent suitability.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus that determines a desired image signal range and reads radiation image information using the method of the present invention. FIGS. An explanatory diagram showing the image information recording state, FIG. 4 is a graph showing the distribution state of the image signal and the distribution state of the image signal difference value according to the present invention, and FIG. 5 is a block diagram showing a part of the apparatus shown in FIG. 1 in detail. FIG. 6 is a schematic diagram showing a histogram of an extracted image signal according to the present invention, and FIG. 7 is a schematic diagram showing a histogram of a desired image signal according to the present invention. 20...Radiation image capturing unit 30...Reading unit for pre-reading 40...Reading unit for main reading 100...
Radiation source 101...Subject 102...
- Radiation, 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 220... Image signal range determining section 221... Differential processing section 222... Threshold setting section 223... Contour candidate point signal detection section 224... Signal extraction section 225. ... Histogram analysis unit 301 ... Laser light source for main reading 302 ... Laser light for main reading 305 ... Optical 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 a...Reading gain setting value b...Recording scale factor setting value C...Reproduction image processing conditions Setting values D1 to Dn...Differential processing line J...Radiation shielding plate K...Contrast medium filled region S
o...Actual reading image signal Sp...Pre-reading image signal Sp...Pre-reading image signal in the desired range 1 to 4

Claims (1)

[Claims] From an image signal obtained by performing a reading process on a recording medium in which a radiation image of a subject is recorded together with a radiation shield, an image signal range that carries almost only a desired portion other than the radiation shield is determined. The method comprises: differential processing the image signal along a plurality of lines on the recording medium including a line that crosses the radiation shield, and the absolute value of the differential value obtained thereby exceeds a predetermined threshold value. extracting the image signals at points on the recording medium exceeding the maximum frequency, creating a histogram of those image signals, and defining a signal range on the higher density side than a specific signal value determined from the maximum frequency point in this histogram as the image signal range; A method for determining a desired image signal range, comprising: determining a desired image signal range.