WO2015196852A1 - 一种ct图像的标定方法、装置和一种ct系统 - Google Patents

一种ct图像的标定方法、装置和一种ct系统 Download PDF

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Publication number
WO2015196852A1
WO2015196852A1 PCT/CN2015/077098 CN2015077098W WO2015196852A1 WO 2015196852 A1 WO2015196852 A1 WO 2015196852A1 CN 2015077098 W CN2015077098 W CN 2015077098W WO 2015196852 A1 WO2015196852 A1 WO 2015196852A1
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Prior art keywords
calibration
reconstructed image
image
fixed calibration
theoretical value
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PCT/CN2015/077098
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English (en)
French (fr)
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张丽
金鑫
黄清萍
孙运达
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清华大学
同方威视技术股份有限公司
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Publication of WO2015196852A1 publication Critical patent/WO2015196852A1/zh

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/003—Reconstruction from projections, e.g. tomography
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]
    • A61B6/032—Transmission computed tomography [CT]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
    • A61B6/5205—Devices using data or image processing specially adapted for radiation diagnosis involving processing of raw data to produce diagnostic data
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/58—Testing, adjusting or calibrating thereof
    • A61B6/582—Calibration
    • A61B6/583—Calibration using calibration phantoms
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • G01N23/046—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material using tomography, e.g. computed tomography [CT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • G01V5/224—Multiple energy techniques using one type of radiation, e.g. X-rays of different energies
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • G01V5/226—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays using tomography
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/10—Image acquisition modality
    • G06T2207/10072—Tomographic images
    • G06T2207/10081—Computed x-ray tomography [CT]

Definitions

  • the invention relates to the technical field of radiation imaging detection, in particular to a calibration method and device for CT images and a CT system.
  • CT technology plays an important role in safety inspections and the like because it can eliminate the influence of object overlap.
  • the conventional CT uses the slip ring device to obtain the projection data at different angles by the rotation of the X light source and the detector, and obtains the tomographic image by the reconstruction method, thereby obtaining the internal information of the detected luggage item.
  • Multi-spectral analysis refers to the use of a material to distinguish the X-ray absorption properties of different energies to distinguish the material.
  • CT technology combined with multi-energy spectrum analysis technology enables the current baggage inspection equipment to reconstruct the atomic number and electron density of any position inside the substance to be detected, to realize the identification of the substance type, and to play a role in the detection of explosives and drugs. Good results.
  • the reconstructed images of the same type of CT equipment will always have different values, and with the increase of working time, optical machine, detection
  • the aging of the device, even for the same CT device, the reconstructed image will drift in value, deviating from the factory.
  • the CT equipment will perform calibration work during the factory and regular maintenance. By scanning the workpiece of a specific material, the reconstructed image value is compared with the actual value of the workpiece, and the post-calibration parameters are determined to realize the post-calibration of the CT image.
  • the above-mentioned conventional post-calibration method has the following disadvantages: on the one hand, the aging of the CT equipment is a continuous process, and the calibration process can only be performed periodically, such as 1 or 2 times per year, which means that the post-calibration parameters are not available at all.
  • the time is optimal, and because the calibration process is technically strong, it must be implemented by after-sales engineers, the maintenance cost increases, and it may occupy the normal working time of the equipment; on the other hand, it is affected by the detector, belt, channel shape, reconstruction The difference between the reconstructed value and the ideal value is the same in the tomographic image.
  • the traditional calibration workpiece is usually placed in a medium or small volume toolbox and placed on the CT conveyor belt. It is sent to the scanning channel to achieve calibration, so this method is often only calibrated after the value of the area near the belt. Better, but other areas do not get the best correction.
  • the invention provides a CT image calibration method and device and a CT system, so as to solve the technical problem that the calibration of the prior art CT image is not timely and the accuracy is not high.
  • the present invention provides a calibration method for a CT image, including:
  • the actual reconstructed image is compared to the stored corresponding theoretical value to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • the fixed calibration component is one or more groups, and each set of calibration components is one or more.
  • the function also includes:
  • a linear and/or polynomial interpolation means is used to obtain a mapping function of different spatial positions in the maximum reconstruction area of the CT scanning device.
  • the actual reconstructed image of the fixed calibration component includes: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a density based on a specific element.
  • One or more reconstructed images in the distribution include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a density based on a specific element.
  • the theoretical values of the fixed calibration component include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a specific element-based material.
  • a high energy attenuation coefficient of a fixed calibration component a low energy attenuation coefficient
  • an attenuation coefficient under a specific X-ray energy an atomic number
  • an electron density and a specific element-based material.
  • One or more theoretical values in the density distribution include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a specific element-based material.
  • the method further includes:
  • the scan reconstructed image is corrected using the mapping function to obtain a corrected reconstructed image.
  • the present invention also provides a calibration apparatus for a CT image, comprising: a fixed calibration component, a storage unit, an acquisition unit, and a mapping unit, wherein:
  • the fixed calibration component is disposed outside the channel area of the CT scanning device and within the maximum reconstruction area;
  • the storage unit is configured to store a theoretical value of the fixed calibration piece
  • the collecting unit is configured to collect projection data of the fixed calibration piece to obtain an actual reconstructed image of the fixed calibration piece;
  • the mapping unit is configured to compare the actual reconstructed image with the stored corresponding theoretical value to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • the fixed calibration component is one or more groups, and each set of calibration components is one or more.
  • mapping unit is further configured to:
  • the plurality of fixed calibration pieces in the group are used as a reference to each other to establish actual reconstructed images and theoretical values in one or more forms of linear, polynomial, and index.
  • a mapping relationship between the maps is based on the mapping relationship to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • mapping unit is further configured to:
  • a linear and/or polynomial interpolation means is used to obtain a mapping function of different spatial positions in the maximum reconstruction area of the CT scanning device.
  • the actual reconstructed image of the fixed calibration component includes: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a density based on a specific element.
  • One or more reconstructed images in the distribution include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a density based on a specific element.
  • the theoretical values of the fixed calibration component include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a specific element-based material.
  • a high energy attenuation coefficient of a fixed calibration component a low energy attenuation coefficient
  • an attenuation coefficient under a specific X-ray energy an atomic number
  • an electron density and a specific element-based material.
  • One or more theoretical values in the density distribution include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, an electron density, and a specific element-based material.
  • the material of the fixed calibration piece is:
  • One or more of water, graphite, and aluminum are selected from one or more of water, graphite, and aluminum.
  • the fixed calibration member is disposed at one or more of the channel side of the CT scanning device, the top of the channel, and the lower portion of the belt.
  • the collecting unit is further configured to perform projection data acquisition and image reconstruction on the scanned object in the channel region of the CT scanning device to obtain a scanned reconstructed image of the scanned object;
  • the apparatus further includes a correction unit coupled to the acquisition unit and the mapping unit, respectively, for correcting the scan reconstructed image using the mapping function to obtain a corrected reconstructed image.
  • the present invention provides a CT system comprising the calibration device for a CT image according to any of the above.
  • the CT scanner can be calibrated in real time by using a fixed calibration component, which eliminates the need for regular calibration in the conventional calibration method of the CT scanner.
  • the calibration quality can be effectively improved, the image calibration effect can be improved, the reliability of the CT scanning device can be improved, and the maintenance cost can be saved. It has high practical application value; and, by the calibration method of the present invention, correction values of different parts in the maximum reconstruction area of the CT scanning device can be obtained, instead of being limited to the vicinity of the channel area, more fine image correction can be realized.
  • FIG. 1 is a schematic flow chart showing a basic calibration method of a CT image according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram showing the basic structure of a calibration apparatus for a CT image according to an embodiment of the present invention
  • FIG. 3 is a schematic diagram showing a practical application flow of a calibration apparatus for a CT image according to an embodiment of the present invention
  • FIG. 4 is a schematic diagram of a channel area and a maximum reconstruction area of a CT scanning device
  • FIG. 5 is a schematic view showing a position where a fixed calibration piece is placed in a calibration apparatus for a CT image according to an embodiment of the present invention
  • FIG. 6 is a schematic diagram of a calibration method for linear interpolation in a calibration apparatus for a CT image according to an embodiment of the present invention.
  • the embodiment of the present invention first provides a calibration method for a CT image.
  • the method includes:
  • Step 101 A fixed calibration component is disposed outside the channel region of the CT scanning device and in a maximum reconstruction region thereof, and the theoretical value of the fixed calibration component is stored;
  • Step 102 Collect projection data of the fixed calibration component to obtain an actual reconstructed image of the fixed calibration component.
  • Step 103 Compare the actual reconstructed image with the stored corresponding theoretical value to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • the CT scanning device can be calibrated in real time by using the fixed calibration component, thereby eliminating the need for regular post-calibration in the traditional calibration method of the CT scanning device.
  • the utility model can effectively improve the calibration quality, improve the image calibration effect, improve the reliability of the CT scanning device, save the maintenance cost, and has high practical application value.
  • the fixed calibration members may be one or more sets, and each set of calibration elements may also be one or more, depending on the type of reconstructed image to be measured.
  • the actual reconstructed image may be performed.
  • the actual reconstructed image is corrected to a mapping function of theoretical values.
  • the fixed calibration components when they are in multiple groups, they may be grouped first, and then the spatial positional relationship between the groups may be considered for integration.
  • the method may include:
  • a linear and/or polynomial interpolation means is used to obtain a mapping function of different spatial positions in the maximum reconstruction area of the CT scanning device.
  • the method of the embodiment of the invention can calibrate a plurality of CT reconstructed images, and specifically, can include: a high energy attenuation coefficient of a fixed calibration component, a low energy attenuation coefficient, an attenuation coefficient under a specific X-ray energy, an atomic number, and an electron.
  • Density, density distribution based on a specific element, etc., the specific elements herein may be elements such as carbon, water or aluminum.
  • the CT scan device may be subjected to scan reconstruction image correction according to the calibration method of the embodiment of the present invention.
  • the method may further include:
  • the scan reconstructed image is corrected using the mapping function to obtain a corrected reconstructed image.
  • An embodiment of the present invention further provides a calibration apparatus for a CT image.
  • the method includes:
  • the fixed calibration component 201 is disposed outside the channel region 1 of the CT scanning device and within the maximum reconstruction region 2;
  • a storage unit 202 configured to store a theoretical value of the fixed calibration component 201
  • the collecting unit 203 is configured to acquire projection data of the fixed calibration component 201 to obtain an actual reconstructed image of the fixed calibration component 201;
  • the mapping unit 204 is configured to compare the actual reconstructed image with the stored corresponding theoretical value to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • Fig. 2 3 is a radiation source, and 4 is a conveyor belt.
  • the fixed calibration members 201 may be one or more groups, and each group of calibration members may also be one or more.
  • the mapping unit 204 is further configured to: when the fixed calibration members 201 are a group and a plurality of, the plurality of fixed calibration members 201 in the group are used as a reference to each other to establish one of a linearity, a polynomial, and an index. Or a mapping relationship between the actual reconstructed image and the theoretical value of the plurality of forms, and a mapping function for correcting the actual reconstructed image to a theoretical value is established according to the mapping relationship.
  • mapping unit 204 can also be used to:
  • mapping relationship between the actual reconstructed image and the theoretical value of one or more forms of linear, polynomial, and index is established in the same group, and the mapping relationship is established according to the mapping relationship.
  • a linear and/or polynomial interpolation means is used to obtain a mapping function of different spatial positions in the maximum reconstruction area 2 of the CT scanning device.
  • the actual reconstructed image of the fixed calibration component 201 may include: a high energy attenuation coefficient of the fixed calibration component 201, a low energy attenuation coefficient, an attenuation coefficient under a certain X-ray energy, an atomic number, an electron density, and a specific element.
  • the theoretical value of the fixed calibration member 201 may also include: a high energy attenuation coefficient of the fixed calibration member 201, a low energy attenuation coefficient, and a specific X-ray energy.
  • One or more theoretical values of the attenuation coefficient, the atomic number, the electron density, and the density distribution of the specific element-based material, and the specific element herein may be an element such as carbon, water or aluminum.
  • the material of the fixed calibration component 201 may be: a calibration material such as water, graphite, aluminum, or the like.
  • the position of the fixed calibration member 201 can be on the channel side of the CT scanning device, at the top of the channel, under the belt, etc., to obtain correction values for different parts of the maximum reconstruction area 2 of the CT scanning device, instead of being limited to the channel region only. Near 1 can achieve more detailed image correction.
  • the collecting unit 203 is further configured to perform projection data acquisition and image reconstruction on the scanned object in the channel region 1 of the CT scanning device to obtain a scanned reconstructed image of the scanned object;
  • the apparatus may further include: a correction unit respectively connected to the acquisition unit 203 and the mapping unit 204 for correcting the scan reconstructed image using a mapping function to obtain a corrected reconstructed image.
  • Step 301 Place the fixed calibration component outside the channel area of the dual-energy security CT, within the maximum reconstruction area.
  • the effective area where the scanning channel can be placed is smaller than the theoretical maximum reconstructable area of the scanning device, as shown in Fig. 4. Therefore, a part of the outer area of the channel can be reconstructed, but there is no object outside the channel during actual working. Therefore, this part has not been reconstructed under normal circumstances.
  • the fixed calibration component can be placed outside the channel area of the dual-energy security CT and the maximum reconstruction area by using the above-mentioned area.
  • a total of six sets of fixed calibration components are used.
  • Each set of fixed calibration parts includes pure water column 5, graphite column 6 and aluminum column 7, as shown in Fig. 5, and stores the theoretical values of the above fixed calibration pieces.
  • the dual-energy security CT using the dual-energy CT reconstruction principle, it is possible to reconstruct four reconstruction images of high-energy attenuation coefficient, low-energy attenuation coefficient, attenuation coefficient under certain X-ray energy, atomic number and electron density, due to atomic number and electrons. Density reconstructed images have an important role in the identification of materials.
  • the atomic number and electron density reconstructed images are selected for calibration.
  • the theoretical values of the atomic number and electron density of the above three materials are known.
  • the atomic number and electron density theoretical values of water, graphite, and aluminum materials can be stored by using a memory cell.
  • Step 302 Collect projection data of 6 sets of fixed calibration pieces to obtain an actual reconstructed image of the fixed calibration piece.
  • the projection data of the above six sets of fixed calibration pieces of different materials are collected by the acquisition unit, and the actual reconstructed image is obtained.
  • Step 303 Compare the actual reconstructed image with the stored corresponding theoretical value to establish a mapping function that corrects the actual reconstructed image to a theoretical value.
  • mapping unit specifically:
  • each fixed calibration member is used as a reference to establish a polynomial mapping relationship between the actual reconstructed image and the corresponding theoretical value, and a group mapping function of each group is obtained; then, six linear interpolation methods are used.
  • the group mapping function at different locations establishes a mapping function for each location within the entire reconstruction range.
  • Figure 6 shows an implementation of linear interpolation by establishing a triangle.
  • the smallest triangle containing the D point is first found, consisting of three points A, B, and C, followed by A.
  • B, C three points of the actual reconstruction image of the three material blocks
  • the actual reconstruction image of the three material blocks of the D point is estimated, this process can be realized by bilinear interpolation, and then according to the calculated three materials of the D point
  • the actual reconstructed image, the mapping function of the D point is obtained, and the atomic number of the D point and the electron density are respectively corrected.
  • Step 304 Perform projection data acquisition and image reconstruction on the scanned object in the channel region of the CT scanning device to obtain a scanned reconstructed image of the scanned object; and correct the scanned reconstructed image by using the mapping function to obtain a corrected reconstructed image.
  • the projection data acquisition and image reconstruction of the scanned object in the channel region of the CT scanning device are first performed by the acquisition unit, and the actual scanned reconstructed image of the scanned object is obtained, and then the scanned reconstructed image is performed according to the previously established mapping function. Correction, mapping the scanned reconstructed image back to the theoretical value to obtain a corrected reconstructed image.
  • the storage unit, the collecting unit, the mapping unit and the correcting unit in the device of the embodiment of the present invention may be located in the data collecting and image reconstructing device of the CT scanning device, or may be connected to the CT scanning device, and may be integrated into one or more
  • the split configuration is as long as it has the above functional unit.
  • Those skilled in the art can implement the above functional units by using hardware, software, firmware or a combination of the three.
  • the embodiment of the invention further provides a CT system, comprising the calibration device for the CT image according to any one of the preceding claims.
  • the CT scanner can be calibrated in real time by using a fixed calibration component, which eliminates the need for regular calibration in the conventional calibration method of the CT scanner.
  • the post-manual calibration step can effectively improve the calibration quality, improve the image calibration effect, improve the reliability of the CT scanning device, save maintenance costs, and has high practical application value; and the calibration method of the embodiment of the present invention can be A correction value for each of the different portions of the maximum reconstruction area of the CT scanning device is obtained, instead of being limited to only the vicinity of the channel region, enabling finer image correction.

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Abstract

本发明提供一种CT图像的标定方法、装置和一种CT系统，包括：在CT扫描装置的通道区域外，且在其最大重建区域内设置固定式标定件，存储所述固定式标定件的理论值；采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。本发明可以有效提高标定质量，提升图像标定效果，提高了CT扫描装置的可靠性，节约了维护成本，具有很高的实际应用价值。

Description

一种CT图像的标定方法、装置和一种CT系统 技术领域
本发明涉及辐射成像检测技术领域，尤其涉及一种CT图像的标定方法、装置和一种CT系统。
背景技术
CT技术由于能够消除物体重叠的影响，在安全检查等场合中发挥了重要作用。传统的CT采用滑环装置通过X光源和探测器的旋转来获取不同角度上的投影数据，通过重建方法来获取断层图像，从而获得被检测行李物品的内部信息。多能谱分析是指利用某种材料对不同能量的X射线吸收性能上的差异来分辨该材料。CT技术配合多能谱分析技术，使得目前的行李物品检查设备可以对被检物质内部任意位置的原子序数和电子密度进行重建，实现物质种类的识别，在爆炸物、毒品等检测中起到了较好的效果。
然而，不论是传统CT还是多能谱CT，由于光机和探测器的不一致性，同一型号的CT设备的重建图像在数值上总会存在差异，而随着工作时间的增加、光机、探测器的老化，即使是同一台CT设备，重建图像在数值上也会存在漂移，偏离出厂时的情况。为了解决上述问题，CT设备在出厂和定期维护时，都会进行标定工作，通过扫描特定材料的工件，将重建图像数值和工件真实值进行比较，确定后标定参数，实现CT图像的后标定。
但是，上述传统的后标定方法有着如下的不足：一方面，CT设备的老化是个持续的过程，而标定流程只能定期进行，如每年1～2次，这意味着后标定参数并不能在所有时间内都是最优的，并且由于标定流程技术性较强，必须有售后工程师来实现，维护成本增加，而且有可能占用设备正常工作时间；另一方面，受探测器、皮带、通道形状、重建算法等因素的影响，重建数值和理想值之间的差异在断层图像上并非各个区域都相同，而传统的标定工件通常放置于一个中等体积或者较小体积的工具箱中，放于CT传送带上送入扫描通道，实现标定，因此这种方法下往往只有皮带附近区域的数值后标定的 较好，而其他区域并不能得到最佳的校正效果。
发明内容
本发明提供一种CT图像的标定方法、装置和一种CT系统，以解决现有技术CT图像的后标定技术中标定不够及时，准确性不高的技术问题。
为解决上述技术问题，本发明提供一种CT图像的标定方法，包括：
在CT扫描装置的通道区域外，且在其最大重建区域内设置固定式标定件，存储所述固定式标定件的理论值；
采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；
将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
进一步地，
所述固定式标定件为一组或多组，每组标定件为一个或多个。
进一步地，当所述固定式标定件为一组且为多个时，所述将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数还包括：
将组内多个固定式标定件互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
进一步地，当所述固定式标定件为多组时，所述将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数还包括：
在同一组内建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域内不同空间位置的映射函数。
进一步地，
所述固定式标定件的实际重建图像包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种重建图像；
相应地，所述固定式标定件的理论值包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种理论值。
进一步地，所述方法还包括：
对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；
使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
另一方面，本发明还提供一种CT图像的标定装置，包括：固定式标定件、存储单元、采集单元和映射单元，其中：
所述固定式标定件设置在CT扫描装置的通道区域外，最大重建区域内；
所述存储单元用于存储所述固定式标定件的理论值；
所述采集单元用于采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；
所述映射单元用于将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
进一步地，
所述固定式标定件为一组或多组，每组标定件为一个或多个。
进一步地，所述映射单元还用于：
当所述固定式标定件为一组且为多个时，将组内多个固定式标定件互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
进一步地，所述映射单元还用于：
当所述固定式标定件为多组时，在同一组内建立线性、多项式、指数中 的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域内不同空间位置的映射函数。
进一步地，
所述固定式标定件的实际重建图像包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种重建图像；
相应地，所述固定式标定件的理论值包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种理论值。
进一步地，所述固定式标定件的材料为：
水、石墨、铝中的一种或多种。
进一步地，
所述固定式标定件的设置在CT扫描装置的通道侧面、通道顶部、皮带下方中的一个或多个位置。
进一步地，
所述采集单元还用于对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；
所述装置还包括：校正单元，与所述采集单元和映射单元分别相连，用于使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
再一方面，本发明还提供一种CT系统，包括如上任一项所述的CT图像的标定装置。
可见，在本发明所提供的CT图像的标定方法、装置和一种CT系统中，能够利用固定式标定件对CT扫描装置进行实时标定，免去了CT扫描装置的传统标定方法中需要定期进行人工后标定的环节，可以有效提高标定质量，提升图像标定效果，提高了CT扫描装置的可靠性，节约了维护成本，具有 很高的实际应用价值；并且，通过本发明的标定方法可以得到CT扫描装置最大重建区域内各个不同部分的校正值，而不是仅仅局限于通道区域附近，能够实现更为精细的图像校正。
附图说明
图1是本发明实施例CT图像的标定方法基本流程示意图；
图2是本发明实施例CT图像的标定装置基本结构示意图；
图3是本发明实施例CT图像的标定装置的实际应用流程示意图；
图4是CT扫描装置的通道区域和最大重建区域示意图；
图5是本发明实施例CT图像的标定装置中固定式标定件放置位置示意图；
图6是本发明实施例CT图像的标定装置中线性插值的标定方法示意图。
具体实施方式
以下，参照附图详细对本发明进行说明。
本发明实施例首先提供一种CT图像的标定方法，参见图1，包括：
步骤101：在CT扫描装置的通道区域外，且在其最大重建区域内设置固定式标定件，存储所述固定式标定件的理论值；
步骤102：采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；
步骤103：将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
可见，在本发明实施例所提供的CT图像的标定方法中，能够利用固定式标定件对CT扫描装置进行实时标定，免去了CT扫描装置的传统标定方法中需要定期进行人工后标定的环节，可以有效提高标定质量，提升图像标定效果，提高了CT扫描装置的可靠性，节约了维护成本，具有很高的实际应用价值。
优选地，固定式标定件可以为一组或多组，每组标定件也可以为一个或多个，取决于所需测量的重建图像类型。
优选地，当固定式标定件为一组且为多个时，可以对实际重建图像进行 如下处理：将组内多个固定式标定件互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
优选地，当固定式标定件为多组时，可以首先对其进行分组处理，然后再考虑各组之间的空间位置关系进行整合，具体地，可以包括：
在同一组内建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域内不同空间位置的映射函数。
本发明实施例的方法可以对多种CT重建图像进行标定，具体地，可以包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布等各项数据，此处的特定元素可以为碳、水或铝等元素。
优选地，可以根据本发明实施例的标定方法对CT扫描装置进行扫描重建图像校正，具体地，方法还可以包括：
对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；
使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
本发明实施例还提供一种CT图像的标定装置，参见图2，包括：
固定式标定件201，设置在CT扫描装置的通道区域1外，最大重建区域2内；
存储单元202，用于存储所述固定式标定件201的理论值；
采集单元203，用于采集所述固定式标定件201的投影数据，得到所述固定式标定件201的实际重建图像；
映射单元204，用于将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
图2中，3为射线源，4为传送带。
优选地，固定式标定件201可以为一组或多组，每组标定件也可以为一个或多个。
优选地，映射单元204还可以用于：当固定式标定件201为一组且为多个时，将组内多个固定式标定件201互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
优选地，映射单元204还可以用于：
当固定式标定件201为多组时，在同一组内建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域2内不同空间位置的映射函数。
优选地，固定式标定件201的实际重建图像可以包括：固定式标定件201的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种重建图像；相应地，固定式标定件201的理论值也可以包括：固定式标定件201的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种理论值，此处的特定元素可以为碳、水或铝等元素。
优选地，固定式标定件201的材料可以为：水、石墨、铝等标定材料。
优选地，固定式标定件201的位置可以在CT扫描装置的通道侧面、通道顶部、皮带下方等，以得到CT扫描装置最大重建区域2内各个不同部分的校正值，而不是仅仅局限于通道区域1附近，能够实现更为精细的图像校正。
优选地，采集单元203还可以用于对CT扫描装置的通道区域1内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像； 相应地，装置还可以包括：校正单元，与采集单元203和映射单元204分别相连，用于使用映射函数对所述扫描重建图像进行校正，得到校正重建图像。
下面以在双能安检CT中对本发明实施例的CT图像的标定装置的实际应用流程为例，来详细说明本发明实施例的具体实现过程，参加图3：
步骤301：将固定式标定件置于双能安检CT的通道区域外，最大重建区域内。
通常扫描通道可以放置物体的有效区域都会小于扫描装置理论上最大可以重建的区域，如图4所示，因此通道外区域有一部分是可以进行重建的，但是在实际工作时通道外不可能有物体，因此这一部分一般情况下并没有重建出来。
本发明实施例中，即可利用上述区域，将固定式标定件置于双能安检CT的通道区域外，最大重建区域内，其中，本实施例中，共使用了6组固定式标定件，每组固定式标定件均包括纯水柱5、石墨柱6和铝柱7三种，见图5，并存储上述固定式标定件的各项理论值。在双能安检CT中，利用双能CT重建原理，可以重建高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数以及电子密度四种重建图像，由于原子序数以及电子密度重建图像对于材料的识别有着重要的作用，因此本实施例中，将选择原子序数和电子密度重建图像进行标定。上述三种材料的原子序数和电子密度的理论值均为已知，本实施例中，可以利用存储单元将水、石墨和铝材料的原子序数和电子密度理论值进行存储。
步骤302：采集6组固定式标定件的投影数据，得到固定式标定件的实际重建图像。
本实施例中，通过采集单元采集上述6组不同材料的固定式标定件的投影数据，得到其实际重建图像。
步骤303：将实际重建图像与所存储的相应的理论值比较，建立将实际重建图像校正为理论值的映射函数。
本步骤中，通过映射单元来将采集单元采集到的实际重建图像和存储单元所存储的水、石墨和铝材料的相应理论值分别进行比较，具体地：
可以首先在同一组内，将各固定式标定件互相作为参考，建立实际重建图像和相应的理论值之间的多项式映射关系，得到每一组的分组映射函数；然后通过线性插值方法由6个不同位置的分组映射函数建立整个重建范围内各位置的映射函数。
或者直接根据6组不同位置的固定式标定件的空间位置直接建立整个重建范围内各位置的映射函数。图6中给出了一种通过建立三角形的方法进行线性插值的实现手段，对于给定任一位置D，首先找到包含D点的最小三角形，由A、B、C三点构成，之后由A、B、C三点三种材料块的实际重建图像，估计D点的三种材料块的实际重建图像，这一过程可以通过双线性插值实现，之后根据推算出来的D点的三种材料的实际重建图像，得到D点的映射函数，分别实现D点的原子序数以及电子密度的校正。
步骤304：对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
本步骤中，首先通过采集单元对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到扫描对象的实际的扫描重建图像，然后再根据之前建立的映射函数对扫描重建图像进行校正，将扫描重建图像映射回理论值，得到校正重建图像。
至此，则完成了本发明实施例CT图像的标定装置的实际应用流程的全过程。
本发明实施例装置中的存储单元、采集单元、映射单元和校正单元可以位于CT扫描装置的数据采集和图像重建装置内，也可以与CT扫描装置相连，可以成为一个整体，也可以由多个分体构成，只要具有上述功能单元即可。本领域技术人员可以采用硬件、软件、固件或三者的结合来实现上述功能单元。
本发明实施例还提供一种CT系统，包括如上任一项所述的CT图像的标定装置。
可见，本发明实施例至少具有如下有益效果：
在本发明实施例所提供的CT图像的标定方法、装置和一种CT系统中，能够利用固定式标定件对CT扫描装置进行实时标定，免去了CT扫描装置的传统标定方法中需要定期进行人工后标定的环节，可以有效提高标定质量，提升图像标定效果，提高了CT扫描装置的可靠性，节约了维护成本，具有很高的实际应用价值；并且，通过本发明实施例的标定方法可以得到CT扫描装置最大重建区域内各个不同部分的校正值，而不是仅仅局限于通道区域附近，能够实现更为精细的图像校正。
如上所述，对本申请发明进行了说明，但是并不限于此，应该理解为能够在本发明宗旨的范围内进行各种变更。

Claims (15)

  1. 一种CT图像的标定方法，其特征在于，包括：
    在CT扫描装置的通道区域外，且在其最大重建区域内设置固定式标定件，存储所述固定式标定件的理论值；
    采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；
    将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
  2. 根据权利要求1所述的CT图像的标定方法，其特征在于：
    所述固定式标定件为一组或多组，每组标定件为一个或多个。
  3. 根据权利要求2所述的CT图像的标定方法，其特征在于，当所述固定式标定件为一组且为多个时，所述将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数还包括：
    将组内多个固定式标定件互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
  4. 根据权利要求2所述的CT图像的标定方法，其特征在于，当所述固定式标定件为多组时，所述将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数还包括：
    在同一组内建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
    根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域内不同空间位置的映射函数。
  5. 根据权利要求1所述的CT图像的标定方法，其特征在于：
    所述固定式标定件的实际重建图像包括：固定式标定件的高能衰减系数、 低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种重建图像；
    相应地，所述固定式标定件的理论值包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种理论值。
  6. 根据权利要求1至5中任一项所述的CT图像的标定方法，其特征在于，所述方法还包括：
    对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；
    使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
  7. 一种CT图像的标定装置，其特征在于，包括：固定式标定件、存储单元、采集单元和映射单元，其中：
    所述固定式标定件设置在CT扫描装置的通道区域外，最大重建区域内；
    所述存储单元用于存储所述固定式标定件的理论值；
    所述采集单元用于采集所述固定式标定件的投影数据，得到所述固定式标定件的实际重建图像；
    所述映射单元用于将所述实际重建图像与所存储的相应的理论值比较，建立将所述实际重建图像校正为理论值的映射函数。
  8. 根据权利要求7所述的CT图像的标定装置，其特征在于：
    所述固定式标定件为一组或多组，每组标定件为一个或多个。
  9. 根据权利要求8所述的CT图像的标定装置，其特征在于，所述映射单元还用于：
    当所述固定式标定件为一组且为多个时，将组内多个固定式标定件互相作为参考，建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的映射函数。
  10. 根据权利要求8所述的CT图像的标定装置，其特征在于，所述映射单元还用于：
    当所述固定式标定件为多组时，在同一组内建立线性、多项式、指数中的一种或多种形式的实际重建图像和理论值之间的映射关系，根据所述映射关系建立将所述实际重建图像校正为理论值的分组映射函数；
    根据每一组的分组映射函数和各组之间的空间位置关系，使用线性和/或多项式插值手段，得到CT扫描装置的最大重建区域内不同空间位置的映射函数。
  11. 根据权利要求7所述的CT图像的标定装置，其特征在于：
    所述固定式标定件的实际重建图像包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种重建图像；
    相应地，所述固定式标定件的理论值包括：固定式标定件的高能衰减系数、低能衰减系数、某一特定X射线能量下的衰减系数、原子序数、电子密度、以特定元素为基材料的密度分布中的一种或多种理论值。
  12. 根据权利要求7所述的CT图像的标定装置，其特征在于，所述固定式标定件的材料为：
    水、石墨、铝中的一种或多种。
  13. 根据权利要求7所述的CT图像的标定装置，其特征在于：
    所述固定式标定件的设置在CT扫描装置的通道侧面、通道顶部、皮带下方中的一个或多个位置。
  14. 根据权利要求7所述的CT图像的标定装置，其特征在于：
    所述采集单元还用于对CT扫描装置的通道区域内的扫描对象进行投影数据采集和图像重建，得到所述扫描对象的扫描重建图像；
    所述装置还包括：校正单元，与所述采集单元和映射单元分别相连，用于使用所述映射函数对所述扫描重建图像进行校正，得到校正重建图像。
  15. 一种CT系统，其特征在于，包括如权利要求7至14中任一项所述的CT图像的标定装置。
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