CN106473761B - A kind of reconstruction of medicine dual intensity CT electron density image and numerical value calibration method - Google Patents
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Abstract
Description
技术领域technical field
本发明涉及一种医学双能CT电子密度图像的重建与数值校准方法，属于医学双能CT的技术领域。The invention relates to a reconstruction and numerical calibration method of a medical dual-energy CT electron density image, which belongs to the technical field of medical dual-energy CT.
背景技术Background technique
放射治疗(Radiation Therapy)是利用放射线治疗肿瘤的一种局部治疗方法，是治疗恶性肿瘤的主要手段之一。其中，病变部位人体组织的电子密度图像重建和数值校准直接关系到放射治疗计划系统(Radiation Therapy Planning System)靶区定位的精度和照射剂量计算的准确性。所以，现代肿瘤放射治疗需要对病变部位人体组织的电子密度及其分布进行测定。目前，临床上普遍采用CT(Computed Tomography；计算机断层成像)扫描模体的方法获得病变部位人体组织的电子密度及其分布。即，用已知电子密度的人体组织替代物制作模体，并对模体进行CT扫描得到所谓的“CT数-电子密度转换曲线”(这里，CT数的单位为Hounsfield Unit,HU)，进而获得病变部位人体组织的电子密度图像。但是，上述方法模体制作(或购买)成本高、实施过程繁琐、所测电子密度数值不准确。Radiation therapy is a local treatment method using radiation to treat tumors, and it is one of the main methods for the treatment of malignant tumors. Among them, the electron density image reconstruction and numerical calibration of the human tissue in the diseased part are directly related to the accuracy of target area positioning and the accuracy of irradiation dose calculation in the Radiation Therapy Planning System. Therefore, modern tumor radiation therapy needs to measure the electron density and distribution of the human tissue at the lesion site. At present, CT (Computed Tomography; computed tomography) scanning phantom is commonly used clinically to obtain the electron density and distribution of human tissue at the lesion site. That is, a phantom is made from a human tissue substitute with a known electron density, and a CT scan is performed on the phantom to obtain a so-called "CT number-electron density conversion curve" (here, the unit of CT number is Hounsfield Unit, HU), and then Obtain electron density images of human tissue at the lesion site. However, the above-mentioned method has high cost to manufacture (or purchase) the phantom, cumbersome implementation process, and inaccurate measured electron density values.
另外，双能CT(Dual-energy CT,DECT)能够精确测定不同能量水平下的X-射线线性衰减系数分布，且理论上也能够重建扫描对象的电子密度和有效原子序数图像，是近年X-射线医学成像领域的重大技术进展。但是，目前国内外主流的大型数字医疗设备生产厂商的DECT产品都不直接提供电子密度图像(包括GE、Siemens、Philips、Toshiba等公司的DECT产品)。这里的主要原因是：迄今为止，尚无工程实用、数值准确的人体组织电子密度CT/DECT图像重建和数值校准方法。In addition, dual-energy CT (DECT) can accurately measure the distribution of X-ray linear attenuation coefficients at different energy levels, and theoretically can also reconstruct the electron density and effective atomic number images of the scanned object. Significant technological advances in the field of radiographic medical imaging. However, at present, the DECT products of the mainstream large-scale digital medical equipment manufacturers at home and abroad do not directly provide electron density images (including DECT products of GE, Siemens, Philips, Toshiba and other companies). The main reason here is: so far, there is no engineering practical and numerically accurate method for image reconstruction and numerical calibration of human tissue electron density CT/DECT.
现有技术中获取人体组织电子密度图像的模体的获取成本高、过程繁琐、数值不准确，且国内外主流的大型数字医疗设备生产厂商，由于缺乏实用、准确的电子密度CT/DECT图像重建和数值校准方法，迄今尚不在其DECT产品中直接提供电子密度图像。The acquisition cost of the phantom for obtaining electron density images of human tissue in the prior art is high, the process is cumbersome, and the values are inaccurate, and the mainstream large-scale digital medical equipment manufacturers at home and abroad lack practical and accurate electron density CT/DECT image reconstruction. and numerical calibration methods, and so far have not provided electron density images directly in their DECT products.
发明内容SUMMARY OF THE INVENTION
针对现有技术的不足，本发明提供一种医学双能CT电子密度图像的重建与数值校准方法。In view of the deficiencies of the prior art, the present invention provides a reconstruction and numerical calibration method of a medical dual-energy CT electron density image.
发明概述：Summary of the invention:
本发明基于基物质分解DECT成像的基本原理，以及高、低两种不同能量水平下的X-射线线性衰减系数之组合与电子密度理论值之间的线性关系，对医学DECT电子密度图像进行重建和数值校准。The invention reconstructs the medical DECT electron density image based on the basic principle of the base substance decomposition DECT imaging and the linear relationship between the combination of the X-ray linear attenuation coefficient and the theoretical value of the electron density under two different energy levels, high and low. and numerical calibration.
本发明的技术方案为：The technical scheme of the present invention is:
一种医学双能CT电子密度图像的重建与数值校准方法，包括步骤如下：A method for reconstruction and numerical calibration of a medical dual-energy CT electron density image, comprising the following steps:
S1)计算基物质分解系数图像b1,…,bn；S1) Calculate the base substance decomposition coefficient images b 1 ,...,b n ;
将基物质密度图像记作I1,…,In；根据以下公式计算基物质分解系数图像b1,…,bn；其中，ρi表示第i种基物质的物质密度；物质密度的单位为g/cm3；Denote the base substance density images as I 1 ,...,In ; calculate the base substance decomposition coefficient images b 1 ,...,b n according to the following formula ; Among them, ρ i represents the material density of the i-th base material; the unit of material density is g/cm 3 ;
S2)计算理论上的电子密度图像ρe和高、低两种不同能量水平下的单能图像；S2) Calculate the theoretical electron density image ρ e and the monoenergy image at two different energy levels, high and low;
理论上的电子密度图像其中，ρei＝2·ρi·Zi/Ai为第i种基物质的电子密度，Zi和Ai分别表示第i种基物质的原子序数和原子量；理论上的电子密度图像ρe的像素值为电子密度理论值；像素值的单位为g/cm3；Theoretical Electron Density Image Among them, ρ ei =2·ρ i ·Z i /A i is the electron density of the i-th base substance, Z i and A i represent the atomic number and atomic weight of the i-th base substance, respectively; the theoretical electron density image ρ The pixel value of e is the theoretical value of electron density; the unit of pixel value is g/cm 3 ;
根据公式分别计算EH、EL两种不同X-射线能量水平下的单能图像μH、μL，其中，μei(EH)、μei(EL)分别表示i种基物质分别在EH、EL两种不同X-射线能量水平下的X-射线线性衰减系数；EH、EL的单位均为keV；According to the formula The single-energy images μ H and μ L under two different X-ray energy levels, E H and E L , are calculated respectively, where μ ei (E H ) and μ ei (E L ) respectively represent the X-ray linear attenuation coefficients under two different X-ray energy levels, H and E L ; the units of E H and E L are keV;
S3)计算高、低两种不同能量水平下的单能图像组合；S3) Calculate the combination of monoenergy images under two different energy levels, high and low;
计算μH和μL的组合图像Δμk(k＝1,2,3,…)：Δμk＝(1+αk)μH-αkμL，其中，权系数αk∈(0,1)；在(0,1)区间上，每取定一个αk就可以计算得到一个组合图像Δμk；组合图像Δμk的像素值为EH和EL两种不同X-射线能量水平下的X-射线线性衰减系数之组合；Calculate the combined image Δμk ( k = 1,2,3,...) of μH and μL : Δμk = (1+αk)μH -αkμL , where the weight coefficient αk ∈(0, 1); in the (0,1) interval, a combined image Δμ k can be calculated for each α k ; the pixel value of the combined image Δμ k is at two different X-ray energy levels, E H and E L The combination of X-ray linear attenuation coefficients;
S4)将组合图像Δμk与电子密度理论值进行线性拟合并计算相应的拟合优度；S4) linearly fit the combined image Δμk and the theoretical value of the electron density and calculate the corresponding goodness of fit;
S4-1)将组合图像Δμk编号为(i,j)的像素的像素值记作将理论上的电子密度图像ρe编号为(i,j)的像素的像素值记作理论上的电子密度图像ρe像素值的平均值记作定义为M表示图像的行数或者列数，以为自变量取值、为因变量取值，采用模型Y＝AX+B进行线性拟合，得到拟合估计值fx，并计算拟合优度拟合优度的计算公式为：S4-1) Denote the pixel value of the pixel numbered (i, j ) in the combined image Δμk as Denote the pixel value of the pixel numbered (i, j) in the theoretical electron density image ρ e as The average value of the pixel values of the theoretical electron density image ρ e is denoted as defined as M represents the number of rows or columns of the image, with take the value of the independent variable, For the value of the dependent variable, use the model Y=AX+B to perform linear fitting to obtain the fitting estimate f x , and calculate the goodness of fit goodness of fit The calculation formula is:
其中，SSres表示电子密度理论值与拟合估计值fx的差的平方总和，SStot表示电子密度理论值与电子密度理论值的平均值的差的平方总和；Among them, SS res represents the sum of the squares of the difference between the theoretical value of the electron density and the fitted estimated value f x , and SS tot represents the sum of the squares of the difference between the theoretical value of the electron density and the average value of the theoretical value of the electron density;
S4-2)对每个组合图像Δμk(k＝1,2,3,…)分别进行步骤S4-1)中的系列运算；其中，的最大值为最佳拟合优度；S4-2) Perform the series of operations in step S4-1) for each combined image Δμk ( k =1, 2, 3, . . . ) respectively; wherein, The maximum value of is the best goodness of fit;
S5)由最佳拟合优度获得校准的电子密度重建图像；S5) obtaining a calibrated electron density reconstructed image from the best goodness of fit;
确定最佳拟合优度所对应的理论上的电子密度图像ρe的拟合估计值fx，理论上的电子密度图像ρe的拟合估计值fx构成电子密度重建图像，电子密度重建图像的像素值为校准的电子密度数值。Determine the fitting estimate f x of the theoretical electron density image ρ e corresponding to the best goodness of fit, and the fitting estimate f x of the theoretical electron density image ρ e constitutes an electron density reconstruction image, and the electron density reconstruction The pixel values of the image are calibrated electron density values.
优选的，n＝2或3。Preferably, n=2 or 3.
优选的，EH＞EL。Preferably, E H >E L .
优选的，所述基物质密度图像由DECT设备或DECT影像工作站获得。Preferably, the base substance density image is obtained by a DECT equipment or a DECT imaging workstation.
本发明的有益效果为：The beneficial effects of the present invention are:
1.本发明所述医学双能CT电子密度图像的重建与数值校准方法，是一种易于工程实现、数值准确的医学双能CT电子密度图像的重建和数值校准方法；1. The reconstruction and numerical calibration method of the medical dual-energy CT electron density image according to the present invention is a reconstruction and numerical calibration method of the medical dual-energy CT electron density image that is easy to implement in engineering and numerically accurate;
2.本发明所述医学双能CT电子密度图像的重建与数值校准方法，在肿瘤放射治疗领域的临床应用，能够提高放射治疗计划系统靶区定位的精度和照射剂量计算的准确性。2. The medical dual-energy CT electron density image reconstruction and numerical calibration method of the present invention is clinically applied in the field of tumor radiation therapy, which can improve the accuracy of target area positioning and radiation dose calculation in the radiation therapy planning system.
附图说明Description of drawings
图1为本发明所述医学双能CT电子密度图像的重建与数值校准方法的流程图；Fig. 1 is the flow chart of the reconstruction and numerical calibration method of the medical dual-energy CT electron density image of the present invention;
具体实施方式Detailed ways
下面结合实施例和说明书附图对本发明做进一步说明，但不限于此。The present invention will be further described below with reference to the embodiments and accompanying drawings of the specification, but is not limited thereto.
实施例1Example 1
如图1所示。As shown in Figure 1.
一种医学双能CT电子密度图像的重建与数值校准方法，包括步骤如下：A method for reconstruction and numerical calibration of a medical dual-energy CT electron density image, comprising the following steps:
S1)计算基物质分解系数图像b1,…,bn；S1) Calculate the base substance decomposition coefficient images b 1 ,...,b n ;
DECT设备获得基物质密度图像，将基物质密度图像记作I1,…,In；根据以下公式计算基物质分解系数图像b1,…,bn；其中，ρi表示第i种基物质的物质密度；物质密度的单位为g/cm3；n＝3；The DECT equipment obtains the density image of the base substance, and denote the density image of the base substance as I 1 ,...,In ; calculate the base substance decomposition coefficient images b 1 ,...,b n according to the following formula; Wherein, ρ i represents the material density of the i-th base material; the unit of material density is g/cm 3 ; n=3;
S2)计算理论上的电子密度图像ρe和高、低两种不同能量水平下的单能图像；S2) Calculate the theoretical electron density image ρ e and the monoenergy image at two different energy levels, high and low;
理论上的电子密度图像其中，ρei＝2·ρi·Zi/Ai为第i种基物质的电子密度，Zi和Ai分别表示第i种基物质的原子序数和原子量；理论上的电子密度图像ρe的像素值为电子密度理论值；像素值的单位为g/cm3；Theoretical Electron Density Image Among them, ρ ei =2·ρ i ·Z i /A i is the electron density of the i-th base material, Z i and A i represent the atomic number and atomic weight of the i-th base material, respectively; the theoretical electron density image ρ The pixel value of e is the theoretical value of electron density; the unit of pixel value is g/cm 3 ;
根据公式分别计算EH、EL两种不同X-射线能量水平下的单能图像μH、μL，其中，μei(EH)、μei(EL)分别表示i种基物质分别在EH、EL两种不同X-射线能量水平下的X-射线线性衰减系数；EH、EL的单位均为keV；EH＞EL；According to the formula The single-energy images μ H and μ L under two different X-ray energy levels, E H and E L , are calculated respectively, where μ ei (E H ) and μ ei (E L ) respectively represent the X-ray linear attenuation coefficients under two different X-ray energy levels of H and E L ; the units of E H and E L are both keV; E H > E L ;
S3)计算高、低两种不同能量水平下的单能图像组合；S3) Calculate the combination of monoenergy images under two different energy levels, high and low;
计算μH和μL的组合图像Δμk(k＝1,2,3,…)：Δμk＝(1+αk)μH-αkμL，其中，权系数αk∈(0,1)；在(0,1)区间上，每取定一个αk就可以计算得到一个组合图像Δμk；组合图像Δμk的像素值为EH和EL两种不同X-射线能量水平下的X-射线线性衰减系数之组合；Calculate the combined image Δμk ( k = 1,2,3,...) of μH and μL : Δμk = (1+αk)μH -αkμL , where the weight coefficient αk ∈(0, 1); in the (0,1) interval, a combined image Δμ k can be calculated for each α k ; the pixel value of the combined image Δμ k is at two different X-ray energy levels, E H and E L The combination of X-ray linear attenuation coefficients;
S4)将组合图像Δμk与电子密度理论值进行线性拟合并计算相应的拟合优度；S4) linearly fit the combined image Δμk and the theoretical value of the electron density and calculate the corresponding goodness of fit;
S4-1)将组合图像Δμk编号为(i,j)的像素的像素值记作将理论上的电子密度图像ρe编号为(i,j)的像素的像素值记作理论上的电子密度图像ρe像素值的平均值记作定义为M表示图像的行数或者列数，以为自变量取值、为因变量取值，采用模型Y＝AX+B进行线性拟合，得到拟合估计值fx，并计算拟合优度拟合优度的计算公式为：S4-1) Denote the pixel value of the pixel numbered (i, j ) in the combined image Δμk as Denote the pixel value of the pixel numbered (i, j) in the theoretical electron density image ρ e as The average value of the pixel values of the theoretical electron density image ρ e is denoted as defined as M represents the number of rows or columns of the image, with take the value of the independent variable, For the value of the dependent variable, use the model Y=AX+B to perform linear fitting to obtain the fitting estimate f x , and calculate the goodness of fit goodness of fit The calculation formula is:
其中，SSres表示电子密度理论值与拟合估计值fx的差的平方总和，SStot表示电子密度理论值与电子密度理论值的平均值的差的平方总和；Among them, SS res represents the sum of the squares of the difference between the theoretical value of the electron density and the fitted estimated value f x , and SS tot represents the sum of the squares of the difference between the theoretical value of the electron density and the average value of the theoretical value of the electron density;
S4-2)对每个组合图像Δμk(k＝1,2,3,…)分别进行步骤S4-1)中的系列运算；其中，的最大值为最佳拟合优度；S4-2) Perform the series of operations in step S4-1) for each combined image Δμk ( k =1, 2, 3, . . . ) respectively; wherein, The maximum value of is the best goodness of fit;
S5)由最佳拟合优度获得校准的电子密度重建图像；S5) obtaining a calibrated electron density reconstructed image from the best goodness of fit;
确定最佳拟合优度所对应的理论上的电子密度图像ρe的拟合估计值fx，理论上的电子密度图像ρe的拟合估计值fx构成电子密度重建图像，电子密度重建图像的像素值为校准的电子密度数值。Determine the fitting estimate f x of the theoretical electron density image ρ e corresponding to the best goodness of fit, and the fitting estimate f x of the theoretical electron density image ρ e constitutes an electron density reconstruction image, and the electron density reconstruction The pixel values of the image are calibrated electron density values.
实施例2Example 2
如实施例1所述的医学双能CT电子密度图像的重建与数值校准方法，所不同的是，所述基物质密度图像由DECT影像工作站获得。The method for reconstruction and numerical calibration of a medical dual-energy CT electron density image is as described in Embodiment 1, except that the base substance density image is obtained by a DECT imaging workstation.
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| CN106473761A (en) | 2017-03-08 |
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