JP4650114B2 - Image processing method, image processing apparatus, and image processing program - Google Patents

Description

  The present invention relates to an image processing method, an image processing apparatus, and an image processing program for processing a radiographic image, and more specifically, an image processing method, an image processing apparatus, and an image processing program capable of obtaining a radiographic image suitable for diagnosis and the like. About.

  In recent years, an apparatus capable of directly capturing a radiographic image as a digital image has been developed. For example, as a device for detecting a radiation dose applied to a subject and obtaining a radiographic image formed in accordance with the detected dose as an electrical signal, a method using a detector using a stimulable phosphor is disclosed in JP Many publications such as 55-12429 and JP 63-189853 are disclosed.

  In such an apparatus, a stimulable phosphor is applied to a sheet-like substrate or fixed to the detector by vapor deposition or the like, and once irradiated with radiation transmitted through the subject, the stimulable phosphor absorbs the radiation.

  Thereafter, the stimulable phosphor is excited by light or heat energy, and the stimulating phosphor emits radiation energy accumulated by the absorption as fluorescence, and the fluorescence is photoelectrically converted. An image signal is obtained.

  On the other hand, a charge corresponding to the intensity of irradiated radiation is generated in the photoconductive layer, the generated charge is accumulated in a plurality of capacitors arranged two-dimensionally, and the accumulated charges are taken out. A radiation image detection apparatus has been proposed.

  Such a radiation image detection apparatus uses what is called a flat panel detector (FPD). As described in JP-A-9-90048, this type of FPD includes a phosphor that emits fluorescence corresponding to the intensity of irradiated radiation, and fluorescence emitted from the phosphor directly or through a reduction optical system. Known is a combination of a photodiode that receives light and performs photoelectric conversion, or a combination of photoelectric conversion elements such as a CCD.

In addition, as described in Japanese Patent Laid-Open No. 6-342098, there is also known one that directly converts irradiated radiation into electric charges.
In these radiological image detection apparatuses, various types of image processing such as gradation conversion processing and edge enhancement processing are generally performed on an acquired image so as to be an image suitable for diagnosis.

  In addition, when a radiographic image based on the image data obtained in this way is displayed or output, image processing is performed so that the radiographic image is easy to see without being subjected to fluctuations in imaging conditions.

  By the way, in the past, when performing image processing such as gradation processing and frequency processing on a radiographic image, a target human body structure such as a bone tissue or a soft tissue, and further a part structure thereof is deterministic. And image processing has been performed so that they have a desired density or a desired edge enhancement degree.

As such image processing, a method for detecting a part structure and performing image processing using morphological calculation processing is disclosed in JP-A-6-348818 (Patent Document 1) and JP-A-2002-99896 (Patent Document 2). Shown in
JP-A-6-348818 (first page, FIG. 1) JP 2002-99896 (first page, FIG. 1)

  Here, in the technique described in Japanese Patent Application Laid-Open No. 6-348818, a morphological operation process is used for an edge detection unit for distinguishing a foreground and a background in an image. This is because the morphological operation processing is less susceptible to noise. However, in the subsequent processing, the foreground and the background are discriminated by using the case detection and the threshold value by using the edge detection result. However, when performing deterministic image processing based on case classification and threshold values as described above, there is a problem that the processing result greatly deviates from the user needs when the determination is not suitable.

  Further, in the technique described in Japanese Patent Application Laid-Open No. 2002-99896, a morphological calculation process is used for the shape-dependent filter and a specific shape called a calcified image of a breast image is recognized. This can be done by preparing a filter in advance. However, when a plurality of filters are prepared in this way, there is a problem that the processing result greatly deviates from the user needs when the prepared filter or the selected filter is not suitable.

  However, in such deterministic detection, the target human body structure must be limited to a very narrow range, and the image when the detection fails cannot be flexibly answered to the needs of the user to diagnose. There was a problem that the deviation of processing results from user needs was very large.

  Morphological calculation processing has been used for detecting lesions and the like at specific sites because of its morphological structure detection capability. In many cases, noise removal processing is performed before morphological calculation processing, because noise is not simultaneously detected by morphological calculation processing when a minute structure is detected. However, in many cases, noise cannot be completely removed by this pre-processing alone, and after performing the morphological operation processing, in most cases, determination processing for determining the target structure and noise is performed. Since the judgment process is performed by comparing the strength of the extracted edges, etc., if the judgment process is wrong, the failure is large, or the subtle edges are not detected regardless of the subtlety It was creating a state that would exist. As a result, the advantage of the morphological operation processing of local structure detection by global filter processing is impaired.

  The present invention has been made in view of the problems as described above, and is a flexible image processing result that becomes a diagnosable image even when detection of a human body structure intended for diagnosis and accurate detection are not performed. An object is to realize an image processing method, an image processing apparatus, and an image processing program.

That is, the above-described problems can be solved by the inventions listed below.
When performing image processing for obtaining an image suitable for diagnosis on a radiographic image having a signal corresponding to an irradiation dose of radiation that has passed through the subject, the present invention performs top hat conversion as morphological operation processing on the radiographic image. processing performed based on said morphology operation processed result to detect the bone tissue that is included in the radiographic image, wherein determining the weights based on the results of the bone tissue detected, determined by the weight determining the Image processing is performed on the radiation image with a parameter corresponding to the weight.

In addition, it is desirable that the morphological operation process performs a skeleton process on the result of the top hat conversion process or performs a skeleton process in parallel with the top hat conversion process.
As the image processing, it is desirable that at least one of gradation processing and frequency enhancement processing is performed on the radiation image.
In the morphological operation, it is preferable that at least one of a top hat conversion process and a skeleton process is performed on the radiation image.

  In the structure detection, it is desirable to detect a bone tissue included in the radiation image as the structure. Alternatively, in the structure detection step, it is desirable to detect a soft tissue included in the radiation image as the structure.

The image processing is preferably performed on the original radiographic image.
Alternatively, it is desirable that the image processing is performed on a thinned image obtained by thinning an original radiation image.

  The present invention relates to a human body that is a diagnostic object by using morphological processing when performing image processing for obtaining an image suitable for diagnosis on a radiographic image having a signal corresponding to an irradiation dose of radiation transmitted through a subject. Image processing that flexibly meets user needs is provided by detecting the shape and performing image processing by weighting based on the detected area.

  In this way, even when the user does not detect and accurately detect the human body structure for the purpose of diagnosis, the user is provided with a flexible image processing result that can be diagnosed. It becomes possible.

  In addition, since human body structures are detected using morphological calculation processing, weighting is performed based on the detected human body structures, and at least one of gradation processing and frequency processing is performed. A suitable image can be provided.

Further, since the human body structure is detected by the top hat conversion or the skeleton process, it becomes possible to detect a fine human body structure.
Further, since the bone structure is detected in the human body structure detection step, it is possible to detect a bone part important for diagnosis and perform image processing flexibly.

Further, since soft tissue is detected in the human body structure detection step, it is possible to detect soft parts important for diagnosis and perform image processing flexibly.
In addition, since the previous image processing is performed on the original image, it is possible to detect a fine human body structure and perform flexible image processing.

  In addition, since the previous image processing is performed on the thinned image, it is possible to flexibly detect the overview of the structure and perform flexible image processing.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an image processing method, an image processing apparatus, and an image processing program of the best mode for carrying out the present invention will be described. Note that the present invention is not limited thereby.

  Note that each means of the embodiment of the present embodiment can be configured by hardware, firmware, or software. For this reason, FIG. 1 is shown as a functional block diagram in accordance with the processing procedure of each step of the image processing method, each means of the image processing apparatus, and each routine of the image processing program.

  Hereinafter, the configuration and operation of the present embodiment will be described in detail with reference to the block diagram of FIG. 1, the flowchart of FIG. 2, and other explanatory diagrams. The units and units in FIG. 1 indicate not only the units and units of the image forming apparatus but also the steps of the image processing method and the routines of the image processing program.

<Overall configuration and processing flow>
Overall system configuration:
The radiation generating device 30, the radiation image reader 40, and the image processing device 100 are configured as shown in FIG.

  Further, inside the image processing apparatus 100, a control unit 101 that constitutes a control means, an image data generation unit 110 that generates image data, a noise removal unit 120 that removes noise included in the image data, and a morphological operation process on the image data Morphological operation unit (morphological operation means) 130 for performing the structure, structure detection unit (structure detection means) 140 for detecting a structure included in the image data based on the result of the morphological operation processing, based on the structure detection result A weight determination unit (weight determination unit) 150 that determines a weight (image processing condition) of an area or pixel of image data, and an image processing unit (image processing unit) 190 that executes image processing based on the weight (image processing condition). As shown in FIG.

  In FIG. 1, the noise removing unit 120 includes a median filter unit 120a and a wavelet processing unit 120b. Further, in FIG. 1, the morphological operation unit 130 includes a top hat conversion processing unit 130a and a skeleton processing unit 130b.

Outline of processing:
In the following description of the process, a case where the process is advanced based on the bone as an important region will be described as a specific example.
The control unit 101 controls radiographic image capturing / reading and various processes associated with the image processing of the present embodiment.
The radiation from the radiation generator 30 passes through the subject 5, and the radiation that has passed through the subject 5 is read by the radiation image reader 40.
The signal read by the radiation image reader 40 is converted into image data by the image data generation unit 110 (S1 in FIG. 2).
The median filter processing unit 120a removes pulse noise components included in the image data by processing using the median filter (S2 in FIG. 2).
The wavelet processing unit 120b removes noise components included in the image data after the median filter processing by wavelet transform processing (S3 in FIG. 2).
The top hat conversion processing unit 130a detects a depression in the concave direction of the pixel value distribution of the image (S4 in FIG. 2). This method is suitable because the bone edge is an edge component having a distribution in the concave direction.
The skeleton processing unit 130b detects bones and the like by detecting the concave portions as a series using the skeleton processing with respect to the result of the top hat conversion processing (S5 in FIG. 2).
The structure detection unit 140 detects a structure included in the radiation image based on the result of the morphological calculation process, and generates structure data (S6 in FIG. 2).
The weight determination unit 150 determines a weight (image processing condition) so that a predetermined processing result is obtained for the structure included in the image data (S7 in FIG. 2).
The image processing unit 160 performs image processing on the image data based on the determined weight (image processing condition) (S8 in FIG. 2).

<Details of each means, each step, each routine>
Hereinafter, detailed processing procedures and contents in each means, each step, and each routine will be described.

(1) Imaging and radiation image input:
In the control unit 101, first, information such as an imaging region or an imaging direction is acquired from a user interface or the like. Such information is performed by the user specifying an imaging region or the like. For example, it is input from a user interface (not shown) of the image processing apparatus 100 having both a display unit and a touch panel by pressing a button displaying an imaging region. In addition, a magnetic card, bar code, HIS (hospital information system: network-based information management), etc. are used.

  The radiation generating apparatus 30 exchanges various data with the control unit 101 in the image processing apparatus 100. There are cases where the radiation generation apparatus 30 is controlled by the control unit 101 and cases where a control unit (not shown) in the radiation generation apparatus 30 and the control unit 101 in the image processing apparatus 100 communicate with each other.

  The radiation emitted from the radiation generator 30 is irradiated through the subject 5 onto the imaging panel mounted on the front surface of the radiation image reader 40. The radiation image reader 40 detects the radiation transmitted through the subject 5 and acquires it as an image signal.

  Specific examples of the configuration include those described in JP-A-11-142998 and JP-A-2002-156716 as using a stimulable phosphor plate. For those using a flat panel detector (FPD) as an input device, those described in Japanese Patent Laid-Open No. 6-342098 that directly convert detected X-rays into charges and obtain them as image signals, There is an indirect system described in Japanese Patent Laid-Open No. 9-90048 in which detected X-rays are once converted into light and then received and converted into electric charges.

  The radiation image reader 40 irradiates the silver salt film on which the radiation image is recorded with light from a light source such as a laser or a fluorescent lamp, and photoelectrically converts the transmitted light of the silver salt film to generate image data. Also good. Moreover, the structure which converts radiation energy directly into an electrical signal using a radiation quantum counting type detector, and produces | generates image data may be sufficient.

  When obtaining a radiographic image of the subject 5, the subject 5 is assumed to be positioned between the radiation generating device 30 and the imaging panel of the radiographic image reader 40, and the radiation emitted from the radiation generating device 30 is applied to the subject 5. Irradiation and radiation transmitted through the subject 5 are incident on the imaging panel.

  Then, the image signal read by the radiation image reader 40 is sent to the image data generation unit 110, and is converted into image data having a predetermined number of pixels and gradation bits by the image data generation unit 110 (S1 in FIG. 2).

(2) Noise removal:
Before performing a morphological operation process to be described later, a noise removal process is executed as a preprocess. As this noise removal processing, it is possible to employ smoothing by linear processing such as simple averaging filter processing or pulse noise removal processing by nonlinear filter processing such as median filter processing.

Noise removal processing using wavelet transform processing is also effective for removing Gaussian noise.
In this embodiment, first, median filter processing is performed by the median filter processing unit 120a to remove pulse noise (S2 in FIG. 2), and then wavelet transformation processing is performed by the wavelet processing unit 120b to remove Gaussian noise. The most desirable method is to remove noise by the combination. Note that noise outside the irradiation field is also effectively removed by such noise removal processing.

  Here, since the pulse noise is first removed and then the Gaussian noise is removed after the two-stage noise processing as described above, it is possible to effectively remove noises of different properties included in the image. Become. As a result, the determination process becomes unnecessary after the morphological process described later. Therefore, the advantage of the morphological treatment is not impaired.

(3) Morphological operations:
When the important region is a bone portion, the morphological operation unit 130 performs a bone edge included in the image data by various image processings such as top hat processing (FIG. 2S4) and skeleton processing (FIG. 2S5). The bone part is detected as an important region by the above.

  Here, the morphological operation processing is executed by combining logical set operation processing. It is desirable to use a structural element having a target structure from the characteristics of a two-dimensional image. In the present embodiment, a top hat conversion process or a skeleton process, preferably a top hat conversion process and a skeleton process, are used for detecting a bone part.

  Here, the top hat conversion processing unit 130a detects the depression in the concave direction of the pixel value distribution of the image (S4 in FIG. 2). This method is suitable because the bone edge is an edge component having a distribution in the concave direction. For detection of the bone edge, it is preferable that the structural element B has a 3 × 3 target structure and a hemispherical function distribution for a thinned image with a pixel size of 1.4 mm.

  Thereby, it is possible to detect details of the bone edge, and it is also possible to detect a thin bone edge such as a finger bone. At this time, there is a characteristic that an edge having an edge direction in a specific direction such as an irradiation field edge or an artificial bone edge is not detected from the concave detection characteristic of the top hat conversion process.

  Then, the skeleton processing unit 130b detects the bone part by detecting the concave part as a series using the skeleton process with respect to the result (the concave part detection result) obtained by the top hat conversion process by the top hat conversion processing part 130a. (S5 in FIG. 2).

  That is, although the bone part can be detected by the top hat conversion process, noise that cannot be removed by the noise removal process may be detected in the same manner as the bone part. Even in such a case, since the detected concave portion is detected as a series in the skeleton processing, the bone part having the series is detected, but it has a characteristic of not detecting unnecessary noise.

  When detecting a soft part region as an important region, first, the bone part edge is removed by subtracting the bone part detection result from the pre-processing image, and then a large or small structural element is applied multiple times. Can be detected. At this time, it is desirable to repeat the structure having a large size about 11 × 11 and the small structure element about 5 times. Through various image processes as described above, the soft part included in the image data is detected as an important region.

(4) Structure detection and weight determination:
The structure detection unit 140 detects the structure included in the radiographic image based on the result of the morphological calculation process performed by the morphological calculation unit 130, that is, the detected bone part, and generates the structure data (see FIG. 2S6).

  Then, the weight determination unit 150 performs binarization processing on the structure data generated from the result of the morphological operation processing, and sets a predetermined signal value, for example, 1 for the bone pixel, Weighted image data with a value of 0 is generated at the pixel (S7 in FIG. 2).

  Alternatively, it is possible to perform top-hat transform conversion and skeleton processing in parallel, and perform weighting from the sum of both results. Since the area detected by both the top hat conversion result and the skeleton processing result has high reliability as the bone part area, the weight becomes high. Since the detection of only one of them has a slightly low reliability, the weight is reduced.

  Here, FIG. 3A shows the original radiation image, and FIG. 3B shows the weight determination unit 150 for the image data in which the bone part is detected as a structure by the morphology operation unit 130 and the structure detection unit 140. Shows a state in which weighted image data having a value of 1 for the bone portion pixels and a value of 0 for the pixels other than the bone portion is generated by the binarization processing.

  If soft tissue is detected as a structure, the structure detection unit 140 performs binarization processing or the like on the structure data generated from the result of the morphological operation processing, and subsequently the weight determination unit 150 The structure data is generated with a predetermined signal value, for example, a value of 1 for a soft part pixel and a value of 0 for a pixel other than the soft part.

  Here, for convenience, the structure detection unit 140 and the weight determination unit 150 are described separately. However, as the structure detection / weight determination unit, a structure detection step (structure detection routine) and a weight determination step ( (Weight determination routine) may be executed simultaneously or in parallel.

(5) Image processing:
The image processing unit 160 converts the original image data from the image data generation unit 110 or the thinned image data thinned out at a predetermined ratio into the weighted image data determined by the weight determination unit 150 as described above. Therefore, image processing is executed (S8 in FIG. 2).

<Effect obtained by embodiment>
In this embodiment, when performing image processing for obtaining an image suitable for diagnosis on a radiographic image having a signal corresponding to the radiation dose transmitted through the subject, a morphological process is used for diagnostic purposes. By detecting the human body shape, weighting based on the detected area and performing image processing, image processing that flexibly meets user needs is provided. In this way, even when the user does not detect and accurately detect the human body structure for the purpose of diagnosis, the user is provided with a flexible image processing result that can be diagnosed. It becomes possible.

  It should be noted that in the conventional methods that have determined the image processing method according to each shooting and subject and performed the deterministic image processing, it is assumed in advance that the processing target exists in the image, and the target structure It is determined whether or not the object is actually the object by the correctness determination after the recognition process.

However, since the position of the structure or the like is used as information when performing the determination in this way, there is a risk that the determination will largely fail if the image is not in a general state.
In this embodiment, first, a structure, in this example, a bone part is detected by morphological processing. Here, since the filtering process is performed using the structural element, the structure does not need to exist at a specific position. Next, since weighting is applied to the detection result, a deterministic determination is not required, and the detection result is not completely lost.

  In addition, restrictions on weighting can be controlled by a weighting method, and in addition to a method that does not require position information and signal information completely as in the above-described method, there are some of these restrictions. It is also possible to increase the reliability of the weight by imposing restrictions.

  For example, regarding the position information, the weight of the structure located at the center of the image can be increased by using the centrality of the detected pixel. As for the signal value information, for example, the signal value is lower outside the irradiation field than the human body region, and the signal value distribution of the detection result can be reduced in weight for the low signal value.

  Simple X-ray imaging has various imaging methods such as divided imaging. In addition, there may be cases where it is not possible to achieve proper positioning due to poor positioning due to a lack of imaging experience of the photographer, or when the patient is in the condition of the patient or the patient is an infant. Even in such a case, it is possible to provide an image suitable for diagnosis without using a large image processing failure by using a weighted image.

It is a functional block diagram which shows functionally the whole structure of the example of 1 embodiment of this invention. It is a flowchart figure which shows the flow of the whole process of one embodiment of this invention. It is explanatory drawing which shows the mode of the process in the embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 Subject 30 Radiation generation apparatus 40 Radiation image reader 100 Image processing apparatus 101 Control part 110 Image data generation part 120 Morphology operation part 130 Structure detection part 140 Structure detection part 150 Weight determination part 160 Image processing part

Claims (15)

An image processing method for performing image processing for obtaining an image suitable for diagnosis on a radiation image having a signal corresponding to an irradiation dose of radiation transmitted through a subject,
Morphology calculation step for performing top hat conversion processing as morphological calculation processing on the radiation image,
A structure detection step for detecting bone tissue included in the radiographic image based on the result of the morphological calculation processing;
A weight determination step for determining a weight based on the result detected by the structure detection step;
An image processing step of performing image processing on the radiographic image according to a parameter according to the weight determined in the weight determination step;
An image processing method comprising: The morphological operation step performs a skeleton process on the result of the top hat conversion process, or performs a skeleton process in parallel with the top hat conversion process,
The image processing method according to claim 1. In the structure detection step, a soft tissue included in the radiation image is detected as the structure.
The image processing method according to claim 1, wherein the image processing method is an image processing method. The morphological calculation step is performed on the thinned image of the radiation image.
The image processing method according to claim 1, wherein: As the image processing step, at least one of gradation processing or frequency enhancement processing is performed on the radiation image.
The image processing method according to any one of claims 1 to 4 , wherein the image processing method is performed. An image processing apparatus that performs image processing for obtaining an image suitable for diagnosis on a radiation image having a signal corresponding to an irradiation dose of radiation transmitted through a subject,
Morphology calculation means for performing top hat conversion processing as morphological calculation processing on the radiation image,
A structure detection means for detecting bone tissue included in the radiographic image based on the result of the morphological calculation processing;
Weight determining means for determining a weight based on the result detected by the structure detecting means;
Image processing means for performing image processing on the radiographic image according to a parameter corresponding to the weight determined by the weight determination means;
An image processing apparatus comprising: The morphology operation means performs a skeleton process on the result of the top hat conversion process, or performs a skeleton process in parallel with the top hat conversion process,
The image processing apparatus according to claim 6. The structure detecting means detects soft tissue included in the radiation image as the structure.
The image processing apparatus according to claim 6, wherein the image processing apparatus is an image processing apparatus. The morphological operation means performs the morphological operation processing on the thinned image of the radiation image.
The image processing apparatus according to claim 6, wherein the image processing apparatus is an image processing apparatus. The image processing means executes at least one of gradation processing and frequency enhancement processing on the radiation image;
The image processing apparatus according to any one of claims 6 to 9, characterized in that. An image processing program for performing image processing for obtaining an image suitable for diagnosis on a radiographic image having a signal corresponding to an irradiation dose of radiation transmitted through a subject,
Morphology calculation routine for performing top hat conversion processing as morphological calculation processing on the radiation image,
A structure detection routine for detecting bone tissue included in the radiographic image based on the result of the morphological calculation processing;
A weight determination routine for determining a weight based on a result detected by the structure detection routine;
An image processing routine for performing image processing on the radiation image by a parameter according to the weight determined by the weight determination routine;
An image processing program comprising: The morphological operation routine performs a skeleton process on the result of the top hat conversion process, or performs a skeleton process in parallel with the top hat conversion process.
12. The image processing program according to claim 11, wherein The structure detection routine detects a soft tissue included in the radiation image as the structure.
The image processing program according to claim 11 or 12, The morphological operation routine is executed on the thinned image of the radiation image.
14. The image processing program according to claim 11, wherein the image processing program is any one of claims 11 to 13. The image processing routine executes at least one of gradation processing or frequency enhancement processing on the radiation image.
15. The image processing program according to claim 11, wherein the image processing program is any one of claims 11 to 14 .