Patent Application
20190150859
The present application relates to a technique of automatically estimating a bone region in a CT image.
Computed tomography (CT) is the technology of producing tomographic images of objects through the use of radiation. In general, X-rays are used to take tomographic images. CT is particularly used in the medical field, and is used to create tomographic images of skeletons and organs and create three-dimensional images of these.
Paragraph 0027 in Japanese Patent Application Laid-open No. 2013-088386 indicates that a CT image is binarized to obtain positional information on the femur.
CT images that have not been subjected to processing other than image reconstruction show bones, internal organs, and fat. To observe a specific bone, for example, it is therefore preferred to extract and display only pixels at which the bone appears. To reduce work burden on operators and prevent individual differences in extracted results, it is preferred to automatically perform the processing for extracting a bone region.
The present invention provides a technique for automatically estimating a bone region in a CT image, and includes: creating a histogram of pixel values based on the CT image; determining a soft region peak, which is a peak in a soft region in the histogram; and setting, based on the soft region peak, a threshold representing a lower limit of a bin value in a bone region in the histogram.
In some embodiments, the creating of a histogram may include: creating a reference image that is a binary image from which a bed portion is removed to leave only a human body portion in the CT image; and creating the histogram by using only pixels where data is present in corresponding pixels in the reference image among pixels in the CT image.
In some embodiments, the threshold may be a bin value that is larger than a bin value corresponding to the soft region peak and has a frequency value accounting for a predetermined proportion of a frequency value of the soft region peak.
An embodiment of the present invention provides a computer program including a program instruction configured to cause a device to implement the features described above when executed by processing means in the device. An embodiment of the present invention provides a method to be implemented by a device when processing means in the device executes a program instruction, the method including the features described above.
An embodiment of the present invention provides a device including processing means and memory means having a program instruction stored thereon, the program instruction being configured to cause the device to implement the features described above when executed by the processing means.
Referring to the accompanying drawings, exemplary embodiments of the technical concept disclosed in the present application are described below.
The mass storage device 106 stores therein an operating system (OS) 110 and a bone region automatic estimation program 120. The most basic functions of the system 100 are provided by the OS 110 executing the CPU 102. The bone region automatic estimation program 120 includes program instructions related to novel processing disclosed in the present application, and when at least a part of the instructions is executed by the CPU 102, the system 100 can implement the novel processing disclosed in the present application. The mass storage device 106 can also store therein CT images 130. Each of the CT images 130 is three-dimensional image data in which pixel values correspond to respective CT values, and is image data to be analyzed or operated by the program 120.
Other than the components illustrated in
Note that CT images 130 are not stored in the mass storage device 106 in many cases at the time of manufacture, sales, and initial start-up of the system 100. Each of the CT images 130 may be, for example, data transferred from an external device to the system 100 through the peripheral device interface 108 or the network interface 109. It should be understood that the scope of the invention disclosed herein is not limited whether CT image data is stored in a storage device.
Next, the procedure of automatic estimation processing 200 for a bone region in a CT image disclosed in the present application is described with reference to
Step 204 represents the start of processing. In Step 208, data to be processed by the bone region automatic estimation program 120 is read (loaded). Specifically, image data 130 is wholly or partially read from the mass storage device 106 and stored in the main storage device 104. The image data 130 may be directly fetched in the main storage device 104 from an external nuclear medical device through the network interface 109.
In a CT image 130 to be processed by the processing 200 in the present example, pixel values representing water are corrected to be zero in advance. Thus, the CT image 130 has some pixels having negative pixel values.
Next, the processing 200 creates a histogram of pixel values in the CT image 130 (Step 212). In some embodiments, a histogram may be created after a bed portion is removed from the CT image 130. Step 210 represents a step for creating a reference image used to remove the bed portion. Step 210 is performed as follows.
(Step 210A) First, the processing 200 creates a binary image obtained by binarizing the CT image 130. A threshold for the binarization may be a threshold with which a human body is highly likely to be extracted. For example, in the present example, the CT image 130 is corrected in advance such that pixel values representing water are zero as described above, and hence, for example, a binary image may be created by using −190 as a threshold.
(Step 210B) Next, the processing 200 searches a vertical slice in the body axis direction from the center of the created binary image for a location with data. Then, region growing processing is performed from the location to create a binary image from which the bed portion has been removed.
When region growing has failed, a binary image is created by removing a bed by 3D labeling processing. The largest label is regarded as a human body, and portions other than the human body are removed to extract only a human body portion.
(Step 210C) After the bed is removed, filling processing to fill hole portions in the body with values is performed, and opening processing of morphology operation is performed to remove a bed that has not be completely removed.
In Step 212, as described above, the processing 200 creates a histogram of pixel values in the CT image 130. In the present example, the histogram is created by using only pixels where data is present in corresponding pixels in the reference image created in Step 210 among pixels in the CT image 130.
In an embodiment in which Step 210 is not performed, a histogram may be created by using the entire CT image 130.
In Step 216, the processing 200 detects peaks of the created histogram. As illustrated in
A peak that is intended to be detected in Step 216 is a soft region peak. Hence, the peak detection processing is not required to be performed in the entire range of bin values, but only needs to be performed in the range of bin values with which it has been experientially known that a soft region peak is present. For example, in a CT image corrected and normalized such that pixel values corresponding to water are 0 and the range of pixel values is −1024 to +1024, the inventors of the present invention have confirmed that a soft region peak of the histogram is distributed in the range of bin values of 0 to 256 in most cases. Thus, the soft region peak detection processing in Step 216 may be performed in a range of bin values of 0 to 256.
In some embodiments, peak detection may be performed in the range of bin values that seem to include a fat region and a soft region. As described above in relation to
In some embodiments, the peak may be determined by subjecting a raw histogram to smoothing processing.
In Step 220, a threshold of a lower limit of a bin value in the bone region is automatically set based on the soft region peak determined in Step 216. The reason why the threshold is set based on the soft region peak is that pixels in a flat region on the right side of the soft region peak correspond to a bone as described above. Various specific setting processes may be used as long as the processes are based on the soft region peak.
In one example, the threshold may be defined as a bin value that is larger than a bin value corresponding to the soft region peak and has a frequency value accounting for a predetermined proportion of a frequency value of the soft region peak.
As the above-mentioned predetermined proportion, the inventors of the present invention have confirmed that 5%, for example, is one appropriate value. However, the proportion may be another value such as 10%. A proportion that is set in advance based on data on a plurality of subjects may be used. When the above-mentioned predetermined proportion was 5%, a threshold in the histogram illustrated in
Step 224 is an optional step. At this step, the processing 200 displays the CT image 130 by using only pixels that have pixel values equal to or larger than the threshold set in Step 220 (and pixels where data is present in corresponding pixels in the reference image). Thus, as illustrated in
Step 228 represents the end of processing.
The processing 200, which automatically estimates the lower limit value of pixel values in a bone region in a CT image, enables the bone region to be automatically extracted and reduces work burden on operators. Because the bone region extraction processing is automatically performed, bone region extraction results can be prevented from varying due to individual differences among operators.
It is preferred that the lower limit value (or upper limit value) of pixel values in a bone region be manually changeable by an operator in order for the operator to flexibly observe a CT image.
While the invention of the present application has been described above in detail by way of preferred examples, the above description and the appended drawings are not presented for the purpose of limiting the scope of the invention of the present application, but are presented in order to meet the legal requirements. The embodiments of the invention of the present application has various variations other than the ones introduced herein. For example, various kinds of numerical values indicated in the specification or the drawings are all illustrative, and these numerical values are not presented for the purpose of limiting the scope of the invention. Individual features included in various kinds of examples introduced in the specification or the drawings are not limited to usage with examples in which these features are explicitly described to be included, but may be used in combination with other examples described herein or various kinds of specific examples that are not described herein. In particular, the processing illustrated in the flowchart is not necessarily required to be executed in the order stated herein. According to the preference of an implementor or if necessary, the processing may be executed in another order or simultaneously in parallel, and a plurality of blocks may be implemented integrally or in a loop as appropriate. These variations are all included in the scope of the invention disclosed herein, and the scope of the invention is not limited by the embodiments of the processing. The described order of the processing defined in the claims is not necessarily required to specify the essential order of the processing. For example, an embodiment specifying a different order of the processing and an embodiment that executes the processing in a loop are also included in the scope of the invention as in the claims.
In addition, for example, embodiments of the bone region automatic estimation program 120 include an embodiment in which the bone region automatic estimation program 120 is a single computer program and an embodiment in which the bone region automatic estimation program 120 is a program group formed by a plurality of independent computer programs. As well known, there are various embodiments of computer programs, and these variations are all included in the scope of the invention disclosed herein.
It should be noted that the applicant claims the right to have a patent granted on all the embodiments not deviating from the spirit of the invention disclosed herein regardless of whether a patent is claimed in the current set of the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-080086 | Apr 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/001459 | 1/18/2017 | WO | 00 |
