KR20180046597A - Method for calibrating ct images, apparatus, and recording medium thereof - Google Patents

Abstract

The present invention relates to a method for correcting a CT image, an apparatus therefor, and a recording medium recording the same. According to the present invention, since a CT coefficient is corrected by applying a correction formula measured based on a reference region extracted from a CT image, an error of the CT coefficient can be reduced, and the accuracy in treatment planning and disease diagnosing through the CT image in various medical fields can be effectively improved.

Description

Technical Field [0001] The present invention relates to a CT image correction method, an apparatus therefor, and a recording medium on which the CT image correction method,

The present invention relates to a CT (Computed Tomography) image correction method, an apparatus therefor, and a recording medium on which the CT image correction method is performed. More particularly, the present invention relates to a CT image correction method for adjusting a CT number And a recording medium recording the same.

Compared to MDCT (Multi-detector CT), which is generally used in medical field, CBCT (Cone-beam CT) can provide accurate craniofacial region skeleton images with a relatively low radiation dose, And is widely used in the field of oral and maxillofacial surgery.

Since it is important to place the implant at a position having sufficient bone density at the time of implant treatment to replace the teeth, the bone density is determined using the CT image and the implant placement position is determined based on the bone density. The bone density can be determined on the basis of the CT coefficient. The CT coefficient means the attenuation coefficient of each pixel in the CT apparatus. The water is 0 HU (Hounsfield Unit), the air is -1000 HU And the bones vary by equipment, but generally high-density bone has a value of more than 1000 HU.

In general CT equipment, the quality of image characteristics is periodically managed by Phantom for CT performance evaluation at the medical image quality management center, so that the consistency and reproducibility of CT coefficients are maintained per equipment. On the other hand, for CBCT equipment, there is known a method of correcting the equipment itself by photographing the phantom of which the CT coefficient is known in advance. However, a consistent quality control standard has not been established yet, and a method of reducing the artifact Because of the artificial adjustment of the CT coefficient for the purpose, even if the same model equipment of the same company, the variation of the CT coefficient is very large according to the set value.

As an example of the classification for bone mineral density assessment, Misch has classified the most dense bone with more than 1250 HU, D2 between 850 and 1250 HU, D3 between 350 and 850 HU, D4 between 150 and 350 HU, and D5 less than 150 HU , Implant placement is done near the bone density of D2 or D3.

However, this classification is based on general CT equipment. If the CT coefficient of CBCT equipment, which has a large CT coefficient error, is used as it is and if the above classification criteria is applied, the bone density can be mistakenly recognized and the success rate of the implant procedure may be significantly lowered have.

In addition, since the use range of CBCT such as diagnosis of oral cancer as well as bone mineral density evaluation is gradually increasing recently, there is a need for a method of correcting the error of CT coefficient in CBCT.

The present invention has been made in order to solve the problems of the prior art which had difficulty in establishing accurate diagnosis and treatment plan due to errors of CT coefficients appearing in CT images including CBCT images, An apparatus for the same, and a recording medium storing the same.

According to an aspect of the present invention, there is provided a method of correcting CT images performed through a computer, the method comprising: extracting at least one reference region in a CT image; Obtaining a CT coefficient of the reference region; Calculating a correction formula for matching the CT coefficient obtained based on the obtained CT coefficient and the standard value of the CT coefficient with respect to the reference area to the standard value; And correcting the CT coefficient of the CT image by applying the correction formula.

At this time, in the step of calculating at least one reference region in the CT image, the reference region may include at least one region of the airway and the tooth region.

According to another aspect of the present invention, there is provided a CT image correction apparatus comprising: a reference region extraction unit for extracting at least one reference region from a CT image; A correction formula calculating unit for calculating a correction formula for making the CT coefficient obtained based on the standard value of the CT coefficient of the reference area and the standard value of the CT coefficient of the reference area correspond to the standard value; And an image correction unit for correcting the CT coefficient of the CT image by applying the correction formula.

The apparatus of claim 1, further comprising a CT coefficient re-scale unit for re-scaling the CT coefficient of the CT image so that the CT coefficient of the CT image is within a predetermined range, The correction formula can be calculated on the basis of the formula.

The apparatus may further include a user interface unit for visually dividing and displaying the CT images corrected through the image correction unit according to the level of the CT coefficients.

In addition, the CT apparatus may further include a correction storage unit for storing the correction formula for each CT apparatus.

As described above, according to the present invention, it is possible to effectively improve the accuracy of the diagnosis of various diseases and the evaluation of the bone density through the CT image in various fields including the dentistry by correcting the error of the CT coefficient appearing in the CT image.

In addition, according to the present invention, since a separate tool such as a phantom is not required, it can be conveniently used.

1 is a block diagram illustrating a configuration of a CT image correction apparatus according to an embodiment of the present invention;
2 is a flowchart of a CT image correction method according to the present invention; And
3 is an example of a screen visually displayed according to the level of the CT coefficient.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, detailed description of well-known functions or constructions that may obscure the subject matter of the present invention will be omitted. It should be noted that the same constituent elements are denoted by the same reference numerals as possible throughout the drawings.

The terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings and the inventor is not limited to the concept of terminology for describing his or her invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention, and not all of the technical ideas of the present invention are described. Therefore, It is to be understood that equivalents and modifications are possible.

For reference, the CT image described in the present specification includes CBCT image and MDCT image, and includes all CT images, including spiral CT (Helical CT), and the like, It means.

1 is a block diagram showing a configuration of a CT image correction apparatus according to an embodiment of the present invention. Referring to FIG. 1, a CT image correction apparatus 100 according to an embodiment of the present invention includes a user interface unit 10, a CT coefficient reset unit 20, a reference region extraction unit 30, a correction calculation unit 40, an image correction unit 50, and a correction type storage unit 60.

The user interface unit 10 receives necessary information from a user and displays various information including an input means for inputting information such as a mouse, a keyboard, a button, and a keypad, an input menu, a processing result, A touch screen for providing input and output through a single device, and the like.

The CT coefficient rescue part 20 performs a rescaling on the CT coefficient of the voxel shown in the loaded CT image.

The CT coefficient rescue part 20 searches the volume of the CT image to grasp the distribution of the CT coefficients of the voxels constituting the volume and measures the CT coefficients of the voxels so that the CT coefficients of the entire voxels are within a predetermined range. do. Here, the rescale not only involves adjusting the CT coefficients proportionally so that the range in which the CT coefficients are distributed is expanded / contracted, but also includes a process of adjusting the CT coefficients such that the range of the CT coefficients is simply shifted.

For example, when the CT coefficients of the CT images are distributed from -2000 HU to 2000 HU, considering that the air CT coefficient is approximately -1000 HU and the high density bone is +1000 HU, the CT coefficient is in the vicinity of -1000 HU to 1000 HU The CT coefficient can be reduced so as to be included in the range up to the limit. On the other hand, when the CT coefficient is distributed from -1500 HU to 500 HU, the CT coefficient can be shifted to be included in the range of -1000 HU to 1000 HU.

For this, the CT coefficient rescue part 20 can calculate an index capable of grasping the dispersion of the CT coefficient of the voxel, and can totally rescan the CT coefficient of the voxel based on the index. For example, the CT coefficient rescue section 20 may generate a histogram representing the distribution of CT coefficients and rescale the CT coefficients by expanding, contracting, or moving the histogram so that the histogram is defined within a predetermined range. It is needless to say that various indexes such as the standard deviation value in addition to the histogram or the maximum value and the minimum value among the CT coefficient values can be used. When the maximum value and the minimum value of the CT coefficient are used, the minimum value and the maximum value are detected through the volume search of the CT image, and the CT coefficient of the CT image is rescaled such that the minimum value and the maximum value fall within a predetermined range.

The reference area calculating unit 30 extracts at least one reference area from the volume indicated in the CT image. The extraction of the reference region may be based on user input through the user interface unit 10 or may be implemented to automatically detect the reference region by incorporating an image recognition algorithm.

The reference region is a region that serves as a reference for correcting the CT coefficient, such as an area including air and water, and an area having a CT coefficient usually set to a substantially constant value is set according to the subject. As the reference area, for example, all or a part of the airway area where the air exists, a tooth area, and the like can be utilized. In addition, statistical information according to sex, age, Can be set as a reference area. Therefore, the reference region is not limited to a specific region, but may be a region in which blood or fat exists, and various tissues and regions.

The correction formula calculating unit 40 obtains a CT coefficient for the reference region and calculates a correction formula for matching the CT coefficient obtained based on the obtained CT coefficient and the standard value of the CT coefficient for the reference region to the standard value. For this, the correction formula calculator 40 stores a standard value of the CT coefficient for each reference area. Here, the standard value is a CT coefficient having a substantially constant irrespective of the subject, Can be approximately -1000 HU, and the CT coefficient value of the corresponding reference region can be statistically applied as a standard value.

The correction formula calculator 40 converts or maps the CT coefficients obtained based on the standard values of the CT coefficients obtained for the extracted reference area and the CT coefficients for the reference area to a standard value, And calculates a function formula for correcting the CT coefficient. The order or type of the correction formula is not particularly limited and can be variously derived depending on the relationship between the obtained CT coefficient and the standard value.

At this time, when the CT coefficient of the CT image is primarily rescaled through the CT coefficient recall part 20, the correction type calculating part 40 will calculate the correction formula using the rescaled CT coefficient .

The image correcting unit 50 corrects the CT coefficient of the CT image by applying the correction formula calculated through the correction formula calculating unit 40. [ The correction of the CT coefficient is performed by transforming the CT coefficients of each voxel of the CT image volume to the CT coefficient values derived by the correction formula.

In this way, the rescaled information such as the rescale coefficient and the correction information such as the correction formula through the CT coefficient recall section 20 are stored in the DICOM tag or the like and used to provide a CT image corrected whenever necessary Or may store the image itself that has been corrected separately from the original image.

The user interface unit 10 displays the CT images whose CT coefficients are corrected through the image correction unit 50 by dividing the CT images into different colors according to the magnitude levels of the CT coefficients. In this way, the dentist can visually grasp the bone density, etc., and determine the position of the implant procedure, so that the user can establish an implant treatment plan based on this. In other medical fields, it is useful for diagnosing various diseases or determining the treatment direction Can be utilized.

In addition, the user interface unit 10 can provide a user with the option of confirming the corrected result, selecting whether or not to adopt the correction result, and providing a menu in which the user can manually adjust the CT coefficient . When the user manually adjusts the CT coefficients of the specific region, the image correcting unit 50 corrects the CT coefficients of the entire volume while maintaining the relative relationship between the CT coefficients of the respective voxels.

Meanwhile, the CT image correction apparatus 100 according to the present invention further includes a correction storage unit 60, and the correction formula calculated through the correction formula calculation unit 50 for each CT apparatus according to equipment manufacturer, Can be stored. This is due to the fact that the equations of CT coefficients are similar when the equipments are the same and the correction formula is calculated almost similar.

2 is a flowchart of a CT image correction method according to the present invention. Hereinafter, an organic operation of the configuration of the CT image correction apparatus 100 will be described with reference to FIG.

When the CT image is loaded, the CT coefficient rescue section 20 searches the CT coefficient for each voxel of the CT image, and rescales the CT coefficient so that the CT coefficient is included in the predetermined range (S10). The rescaling of CT coefficients is accomplished by expanding, reducing or shifting the CT coefficient range.

The reference region extracting unit 30 extracts a reference region from the CT image through a user input through the user interface unit 10 or an image recognition algorithm (S20). The reference region can be set as an area having a generally constant CT coefficient depending on the subject. For example, the airway region includes air, which is a substance that is naturally present in common to each person, so that the airway region has a substantially constant HU value when photographed by the same equipment, and thus can be set as a reference region. On the other hand, the teeth are hard tissue, and since the CT coefficient of the teeth is relatively large as compared with other tissues, the tooth can be used as a reference area without a metal-like material. In addition, the reference area can be set based on statistical information based on sex, age, and the like. The reference area may be set to one area or a plurality of areas.

When the reference area is extracted as described above, the correction formula calculating unit 40 obtains the CT coefficient for the reference area (S30).

The CT coefficient for the reference region may be obtained by applying the CT coefficient of the corresponding voxel when the reference region is composed of a single voxel and by using the average value, the maximum value, the minimum value, and the like of a plurality of voxels when the reference region is composed of a plurality of voxels A value representative of the CT coefficients of a plurality of voxels can be applied. At this time, the values that can represent CT coefficients can be applied differently depending on the reference region. For example, when the reference region is airway, a minimum value among CT coefficients of a plurality of voxels can be applied, and when the reference region is a tooth, a maximum value can be applied.

Next, a correction formula for matching the CT coefficient obtained based on the obtained CT coefficient and the standard value of the CT coefficient with respect to the reference area to the standard value is calculated (S40). The standard value can be determined experimentally considering the classification criteria, relative relationships between tissues, statistical information, etc., which are applied for the evaluation of bone mineral density based on -1000 HU and 0 HU of water having the lowest X-ray absorptivity.

On the other hand, the correction formula may be calculated so as to exactly match the standard value, but the correction formula may be calculated so that the CT coefficient obtained within a predetermined error range is converted to approximate to the standard value.

The image correcting unit 50 applies the calculated correction formula to the CT image to correct the CT coefficients of the respective voxels (S50). The corrected result can be displayed through the user interface unit 10 in a different color or symbol depending on the CT coefficient level.

3 is an example of a screen visually displayed according to the level of the CT coefficient.

FIG. 3 shows an example in which the colors are displayed in different levels according to five levels from D1 to D5 according to the Misch classification (301). By doing so, the user can visually grasp the bone density and utilize it to establish the implant plan.

On the other hand, the steps described above with reference to Fig. 2 can be appropriately modified or added as needed.

For example, if the correction formula is first calculated for a specific device, the correction formula is stored in the correction type storage unit 60 for each device, so that the photographing equipment can be identified from the tag value of the diCom header, If there is a correction formula corresponding to the device, the CT image can be corrected by using the stored correction formula without going through the correction calculation process.

On the other hand, the CT coefficient recall part 20 for rescaling the CT coefficient is selectively activated according to user input, so that the CT coefficient is not rescaled in step S10 but the reference area is extracted in step S20 without going through step S10 .

Therefore, the present invention is not necessarily limited to the order of the CT image correction method according to the present embodiment.

The CT image correction method according to an exemplary embodiment of the present invention may be embodied as a program that can be executed by a computer and may be implemented as a variety of recording media such as a magnetic storage medium, an optical reader, and a digital storage medium.

As described above, according to the CT image correcting apparatus 100 and method according to the present invention, the CT coefficients appearing differently according to the photographing equipment are corrected. Thus, in various medical fields including dentistry, The accuracy of diagnosis of various diseases can be improved. In addition, according to the present invention, since a separate tool such as a phantom is not required, it can be conveniently used.

Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or combinations thereof. Implementations may be implemented in a computer program product, such as an information carrier, e.g., a machine readable storage device, such as a computer readable storage medium, for example, for processing by a data processing apparatus, Apparatus (computer readable medium) or as a computer program tangibly embodied in a propagation signal. A computer program, such as the computer program (s) described above, may be written in any form of programming language, including compiled or interpreted languages, and may be stored as a stand-alone program or in a module, component, subroutine, As other units suitable for use in the present invention. A computer program may be deployed to be processed on one computer or multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

Processors suitable for processing a computer program include, by way of example, both general purpose and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer may include one or more mass storage devices for storing data, such as magnetic, magneto-optical disks, or optical disks, or may receive data from them, transmit data to them, . ≪ / RTI > Information carriers suitable for embodying computer program instructions and data include, for example, semiconductor memory devices, for example, magnetic media such as hard disks, floppy disks and magnetic tape, compact disk read only memory A magneto-optical medium such as a floppy disk, an optical disk such as a DVD (Digital Video Disk), a ROM (Read Only Memory), a RAM , Random Access Memory), a flash memory, an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), and the like. The processor and memory may be supplemented or included by special purpose logic circuitry.

While the specification contains a number of specific implementation details, it should be understood that they are not to be construed as limitations on the scope of any invention or claim, but rather on the description of features that may be specific to a particular embodiment of a particular invention Should be understood. Certain features described herein in the context of separate embodiments may be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments, either individually or in any suitable subcombination. Further, although the features may operate in a particular combination and may be initially described as so claimed, one or more features from the claimed combination may in some cases be excluded from the combination, Or a variant of a subcombination.

Likewise, although the operations are depicted in the drawings in a particular order, it should be understood that such operations must be performed in that particular order or sequential order shown to achieve the desired result, or that all illustrated operations should be performed. In certain cases, multitasking and parallel processing may be advantageous. Also, the separation of the various device components of the above-described embodiments should not be understood as requiring such separation in all embodiments, and the described program components and devices will generally be integrated together into a single software product or packaged into multiple software products It should be understood.

It should be noted that the embodiments of the present invention disclosed in the present specification and drawings are only illustrative of specific examples for the purpose of understanding and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

10: User interface part 20: CT coefficient rescue part
30: Reference area extracting unit 40: Correction calculating unit
50: Image correction unit 60: Correction type storage unit

Claims (7)

A method for correcting a CT image in which each step is performed through a computer,
Extracting at least one reference region from the CT image;
Obtaining a CT coefficient of the reference region;
Calculating a correction formula for matching the CT coefficient obtained based on the obtained CT coefficient and the standard value of the CT coefficient with respect to the reference area to the standard value; And
And correcting the CT coefficient of the CT image by applying the correction formula.
The method according to claim 1,
Wherein the reference region includes at least one of an airway region and a tooth region in the step of calculating at least one reference region in the CT image.
A computer-readable recording medium on which a program for executing the CT image correction method according to claim 1 or 2 is recorded.
A reference region extracting unit for extracting at least one reference region from the CT image;
A correction formula calculating unit for calculating a correction formula for making the CT coefficient obtained based on the standard value of the CT coefficient of the reference area and the standard value of the CT coefficient of the reference area correspond to the standard value; And
And an image correction unit for correcting the CT coefficient of the CT image by applying the correction formula.
5. The method of claim 4,
Further comprising a CT coefficient re-scale unit for rescaling the CT coefficient of the CT image so that the CT coefficient of the CT image is within a predetermined range,
Wherein the correction formula calculating unit calculates the correction formula based on the CT coefficient of the reference area that has been rescaled.
5. The method of claim 4,
Further comprising a user interface unit configured to visually distinguish and display the CT images corrected through the image correction unit according to the level of the CT coefficients.
5. The method of claim 4,
And a correction storage unit for storing the correction formula for each CT apparatus.

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