CN103622717B - By single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method - Google Patents

Abstract

A kind of by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method: to be E to object at energy ₁x-ray under carry out single sweep operation, obtaining object at energy is E ₁x-ray under CT image; Bilinearity transfer algorithm is used to be E by this object obtained at energy ₁x-ray under the CT number conversion of CT image that scans for this object be E at energy ₂x-ray under linear attenuation coefficient; Use CT number defined formula that the linear attenuation coefficient obtained is converted to energy for E ₂x-ray under CT number, thus to obtain energy be E ₂x-ray under CT image; Be E to energy respectively ₁x-ray under CT image and energy be E ₂x-ray under CT Computer image genration digital image rebuilding image; To the digital image rebuilding image conbined usage logarithm dual energy subtraction algorithm generated, the weight factor required for selection, obtains the image of the unwanted material of cancellation.The present invention only carries out single source single sweep operation, just can obtain the CT image of two energy.

Description

By single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method

Technical field

The present invention relates to a kind of generation method of dual intensity X-ray CT image.Particularly relate to one by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT(hereinafter referred to as dual intensity CT) image method.

Background technology

Dual intensity CT removes at material after first being proposed in 1976 by Alvarez and Macovski, and the aspects such as contrast agent quantification and the resolution of organization material characteristic all achieve good effect.

" First performance evaluation of a dual-source CT (DSCT) system " of " European Radiology " 2006 Published in China Pharmacies and " the Dual energy CT:preliminary observations and potentialclinical applications in the abdomen " of 2009 Published in China Pharmacies assesses the picture quality of existing dual intensity CT.Dual intensity CT uses and is equipped with two bulb, and the system of double detector carries out two energy scan, is obtained the image expected by the method for dual intensity image procossing.But in such a system, the size of one of them detector is less, when causing scan volume larger object, the CT image reconstruction visual field (FOV) is not enough.This dual intensity CT has higher requirements to pendulum position during scanning in addition, adds the difficulty of scanning.

In radiation dose, " the Material differentiation by dualenergy CT:initial experience " of " European Radiology " 2007 Published in China Pharmacies shows: dual intensity CT total radiation dosage does not exceed maximal dose standard.But if dual intensity CT image effect can be simulated by means of only the scanning of single source single sweep operation, when being applied to medical inspection, be significantly for reduction patient irradiation dose.

Summary of the invention

Technical problem to be solved by this invention is, a kind of CT image by a certain energy is provided to be converted to CT image on another energy, dual energy subtraction technology are used to two energy CT images, thus obtain dual intensity CT image by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method.

The technical solution adopted in the present invention is: by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method, comprise the steps:

1) be E to object at energy ₁x-ray under carry out single sweep operation, obtaining object at energy is E ₁x-ray under CT image;

2) this object using bilinearity transfer algorithm step 1) to be obtained is E at energy ₁x-ray under the CT number conversion of CT image that scans for this object be E at energy ₂x-ray under linear attenuation coefficient;

3) CT number defined formula is used by step 2) to be converted to energy be E for the linear attenuation coefficient that obtains ₂x-ray under CT number, thus to obtain energy be E ₂x-ray under CT image;

4) be E to energy respectively ₁x-ray under CT image and energy be E ₂x-ray under CT Computer image genration digital image rebuilding image;

5) to the digital image rebuilding image conbined usage logarithm dual energy subtraction algorithm that step 4) generates, the weight factor required for selection, obtains the image of the unwanted material of cancellation.

Step 2) described in bilinearity transfer algorithm formula as follows:

${\mathrm{\μ}}_x\left(E_2\right)=\left\{\begin{array}{cc}[1+\frac{H{U}_x\left(E_1\right)}{1000}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}\≤0\\ [1+({\mathrm{\ρ}}_H\·R\left(E_2\right)-1)\·\frac{{\mathrm{HU}}_x\left(E_1\right)}{{\mathrm{HU}}_H\left(E_1\right)}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}>0\end{array}\right.---\left(1\right)$

Parameter declaration in formula is as follows:

μ _x(E ₂): need the material changed to be E at energy ₂x-ray under linear attenuation coefficient;

HU _x(E ₁): need the material of conversion at original scanning energy E ₁x-ray under CT number;

μ _w(E ₂): water is E at energy ₂x-ray under linear attenuation coefficient;

HU _h(E ₁): high z number material is E at energy ₁x-ray under CT number;

ρ _h: the density of high z number material;

R (E ₂): high z number material and water are E at energy ₂x-ray under the ratio of mass attentuation coefficient, obtained by following formula:

R(E ₂)=μ' _H(E ₂)/μ' _w(E ₂) （2）

Wherein μ ' _h(E ₂) for high z number material be E at energy ₂x-ray under mass attentuation coefficient; μ ' _w(E ₂) for water be E at energy ₂x-ray under mass attentuation coefficient.

CT number defined formula described in described step 3) is:

${\mathrm{HU}}_x\left(E_2\right)=\frac{{\mathrm{\μ}}_x\left(E_2\right)-{\mathrm{\μ}}_w\left(E_2\right)}{{\mathrm{\μ}}_w\left(E_2\right)}\·1000---\left(3\right)$

Namely the linear attenuation coefficient that bilinearity transfer algorithm formula obtains is substituted into above-mentioned CT number defined formula can be E by energy ₁x-ray under scan the CT image obtained CT number to obtain be E at energy ₂x-ray under the CT number of CT image, then by being E at energy ₂x-ray under the CT number of CT image to obtain energy be E ₂x-ray under CT image.

Of the present invention by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method, only carry out the single sweep operation scanning of single source, obtain the CT image of two energy, two width CT images do not need registration, method is simple, has easier form and the practical value of Geng Gao.When being applied to medical image, requiring low to the pendulum position of patient, and compared with traditional dual intensity CT, reducing its radiation dose to patient.

Accompanying drawing explanation

Fig. 1 (a) is 120kVp image;

Fig. 1 (b) is 80kVp image;

Fig. 1 (c) is subtraction image.

Detailed description of the invention

Be described in detail by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method of the present invention below in conjunction with embodiment and accompanying drawing.

Of the present invention by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method, use a kind of bilinearity transfer algorithm, the CT image of a certain energy is converted to the CT image on another energy, dual energy subtraction technology is used to two energy CT images, thus obtains dual intensity CT image.

Of the present invention by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method, comprise the steps:

1) be E to object at energy ₁x-ray under carry out single sweep operation, obtaining object at energy is E ₁x-ray under CT image;

2) this object using bilinearity transfer algorithm step 1) to be obtained is E at energy ₁x-ray under the CT number conversion of CT image that scans for this object be E at energy ₂x-ray under linear attenuation coefficient;

Material to the decay of X-ray kV level X-ray mainly photoelectric absorption and compton effect,scattering cause, but high atomic number and the decay of low atomic number material under different-energy X-ray be different.According to this physical characteristic, adopt bilinearity transfer algorithm can process respectively high z number material and low atomic number material to during CT number under another energy the CT number conversion obtained under an energy: when CT number is less than 0, think that now material is made up of water and air, when CT number is greater than 0, think that now material is made up of water and high z number material, two linear transformation factors be used to respectively CT number be greater than 0 material and CT number be less than the CT number conversion of the material of 0.So will the material x of conversion be needed in ENERGY E ₁under CT number conversion be that it is in ENERGY E ₂under linear attenuation coefficient, available bilinearity transfer algorithm formula,

Described bilinearity transfer algorithm formula is as follows:

${\mathrm{\μ}}_x\left(E_2\right)=\left\{\begin{array}{cc}[1+\frac{H{U}_x\left(E_1\right)}{1000}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}\≤0\\ [1+({\mathrm{\ρ}}_H\·R\left(E_2\right)-1)\·\frac{{\mathrm{HU}}_x\left(E_1\right)}{{\mathrm{HU}}_H\left(E_1\right)}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}>0\end{array}\right.---\left(1\right)$

Parameter declaration in formula is as follows:

μ _x(E ₂): need the material changed to be E at energy ₂x-ray under linear attenuation coefficient;

HU _x(E ₁): need the material of conversion at original scanning energy E ₁x-ray under CT number

μ _w(E ₂): water is E at energy ₂x-ray under linear attenuation coefficient;

HU _h(E ₁): high z number material is E at energy ₁x-ray under CT number;

ρ _h: the density of high z number material;

R (E ₂): high z number material and water are E at energy ₂x-ray under the ratio of mass attentuation coefficient, obtained by following formula:

R(E ₂)=μ' _H(E ₂)/μ' _w(E ₂) （2）

Wherein μ ' _h(E ₂) for high z number material be E at energy ₂x-ray under mass attentuation coefficient; μ ' _w(E ₂) for water be E at energy ₂x-ray under mass attentuation coefficient.Here high z number material is determined according to by the material composition scanned, and such as, when for during to body scans, high z number material is Compact bone, and its CT number can obtain by using imitative swept-volume to correct; Its linear attenuation coefficient and mass attentuation coefficient can be checked in by pertinent literature.Similarly, the linear attenuation coefficient of water under various energy X-ray and mass attentuation coefficient also check in by pertinent literature.

3) CT number defined formula is used to step 2) to be converted to energy be E for the linear attenuation coefficient that obtains ₂x-ray under CT number, thus to obtain energy be E ₂x-ray under CT image, wherein said CT number defined formula is as follows:

${\mathrm{HU}}_x\left(E_2\right)=\frac{{\mathrm{\μ}}_x\left(E_2\right)-{\mathrm{\μ}}_w\left(E_2\right)}{{\mathrm{\μ}}_w\left(E_2\right)}\·1000---\left(3\right)$

The linear attenuation coefficient obtained by bilinearity transfer algorithm formula substitutes into CT number defined formula (3), can be namely E by energy ₁x-ray under scan the CT image obtained CT number to obtain be E at energy ₂x-ray under the CT number of CT image, then by being E at energy ₂x-ray under the CT number of CT image to obtain energy be E ₂x-ray under CT image.

4) be E to energy respectively ₁x-ray under CT image and energy be E ₂x-ray under CT image use ray-tracing algorithm or Monte Carlo EGS4 method or other algorithms to generate digital image rebuilding image (DRR);

5) to the digital image rebuilding image conbined usage logarithm dual energy subtraction algorithm that step 4) generates, the weight factor required for selection, obtains the image of the unwanted material of cancellation.

As examples of implementation, give research the inventive method being applied to lung tumors case, after using bilinearity transfer algorithm to its CT data, on the digital image rebuilding image obtained, quantitative analysis uses the method to the raising degree of tumor resolution capability.

Below in conjunction with accompanying drawing 1, for the CT image of a patients with lung cancer, the inventive method is described further:

1, patient is carried out to the CT scan of 120kVp, 400mAs.CT image size in this embodiment is 512 × 512 pixels, and the gray value of pixel represents CT number during 120kVp.

2, use bilinearity transfer algorithm respectively to the gray value of each pixel of CT image, the CT image of 120kVp is converted to the linear attenuation coefficient scattergram of 80kVp, described bilinearity transfer algorithm formula is as follows:

${\mathrm{\μ}}_x\left(E_2\right)=\left\{\begin{array}{cc}[1+\frac{H{U}_x\left(E_1\right)}{1000}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}\≤0\\ [1+({\mathrm{\ρ}}_H\·R\left(E_2\right)-1)\·\frac{{\mathrm{HU}}_x\left(E_1\right)}{{\mathrm{HU}}_H\left(E_1\right)}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}>0\end{array}\right.---\left(1\right)$

The image size of the linear attenuation coefficient scattergram obtained of this embodiment is 512 × 512 pixels, and the gray value of pixel represents linear attenuation coefficient during 80kVp; Corresponding formula (1), high z number material is Compact bone structure, ρ _hget 1.53g/cm ², HU _h(E ₁) be the CT number 791.98HU of bone structure in 120kVpCT image.HU _x(E ₁) be the gray value of each pixel in 120kVpCT image.In this embodiment, CT x-ray source peak tube voltage is sent out in kVp representative, needs peak tube voltage to be converted to effective energy.At this, use CT to correct imitative body CIRS062 to electron density and scan at 80kVp, obtaining Compact bone at the CT number of 80kVp is 1116.98HU.Effective energy computing formula according to providing in this imitative volume data handbook: (keV) _eff=78387.86/ (HU)-35.71341+HU × 0.0369-HU × 7.3644 × 10 ^-2(HU is the CT number of Compact bone), the effective energy calculating 80kVp is 66.5keV, according to the data that National Institute of Standards and Technology (National Institute ofStandards and Technology, NIST) provides, μ _w(E ₂) for water is at the linear attenuation coefficient of 66.5keV, get 0.1987cm ^-1, μ ' _h(E ₂) for Compact bone is at the mass attentuation coefficient of 66.5keV, be 0.2849cm ²/ g, μ ' _w(E ₂) for water is at the mass attentuation coefficient of 66.5keV, 0.1987cm ²/ g, therefore by formula

R(E ₂)=μ' _H(E ₂)/μ' _w(E ₂) （2）

Obtain R (E ₂) be 1.43.Bring above-mentioned each parameter value into formula (1), calculate the linear attenuation coefficient under energy 80kVp.

3, each pixel of the linear attenuation coefficient figure that step 2 obtains is used respectively to the defined formula of CT number:

${\mathrm{HU}}_x\left(E_2\right)=\frac{{\mathrm{\μ}}_x\left(E_2\right)-{\mathrm{\μ}}_w\left(E_2\right)}{{\mathrm{\μ}}_w\left(E_2\right)}\·1000---\left(3\right)$

Linear attenuation coefficient under 80kVp is converted into the CT number of 80kVp, thus obtains the CT image of 80kVp.

4, ray-tracing algorithm is used to generate digital image rebuilding image, as shown in Fig. 1 (a), Fig. 1 (b) to the CT image of 120kVp and 80kVp respectively;

5, to the digital image rebuilding image conbined usage logarithm dual energy subtraction algorithm of 120kVp and 80kVp obtained, the subtraction image of cancellation skeletal tissue is obtained, as shown in Fig. 1 (c);

Log subtraction algorithm can be expressed as:

$I_{\mathrm{Bone}-\mathrm{canceled}}^{\mathrm{DE}}=\ln \left(I^H\right)-w_s\·\ln \left(I^L\right)$

The gray value of 120kVp digital image rebuilding image pixel is substituted into I ^h, the gray value of 80kVp digital image rebuilding image pixel substitutes into I ^l, w _schoose 0.6, the subtraction image of cancellation skeletal tissue can be obtained.

6, for subtracting shadow digital image rebuilding image, calculate the Contrast-to-noise ratio of relative its periphery background area of its tumor region, table 1 provide use the inventive method to obtain to other 10 patients with lung cancer subtraction image to the raising degree of tumor resolving ability.

Table 1

This embodiment is achieved by application the inventive method and uses single source single sweep operation X-ray CT scan to produce dual intensity CT image effect, and on digital image rebuilding image, demonstrate use the inventive method to the raising of tumor identification ability, compared with previous methods, there is easier form and the practical value of Geng Gao.

Below by reference to the accompanying drawings the specific embodiment of the present invention is described; but these explanations can not be understood to limit scope of the present invention; protection scope of the present invention is limited by the claims of enclosing, and any change on the claims in the present invention basis is all protection scope of the present invention.

Claims (1)

1., by single source single sweep operation X-ray CT Computer image genration dual intensity X-ray CT image method, it is characterized in that, comprise the steps:

1) be E to object at energy ₁x-ray under carry out single sweep operation, obtaining object at energy is E ₁x-ray under CT image;

2) bilinearity transfer algorithm is used by step 1) this object of obtaining is E at energy ₁x-ray under the CT number conversion of CT image that scans for this object be E at energy ₂x-ray under linear attenuation coefficient, described bilinearity transfer algorithm formula is as follows:

${\mathrm{\μ}}_x\left(E_2\right)=\left\{\begin{array}{cc}[1+\frac{{\mathrm{HU}}_x\left(E_1\right)}{1000}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}\≤0\\ [1+({\mathrm{\ρ}}_H\·R\left(E_2\right)-1)\·\frac{{\mathrm{HU}}_x\left(E_1\right)}{{\mathrm{HU}}_H\left(E_1\right)}]\·{\mathrm{\μ}}_w\left(E_2\right)& \mathrm{HU}>0\end{array}\right.---\left(1\right)$

Parameter declaration in formula is as follows:

μ _x(E ₂): need the material changed to be E at energy ₂x-ray under linear attenuation coefficient;

HU _x(E ₁): need the material of conversion at original scanning energy E ₁x-ray under CT number;

μ _w(E ₂): water is E at energy ₂x-ray under linear attenuation coefficient;

HU _h(E ₁): high z number material is E at energy ₁x-ray under CT number;

ρ _h: the density of high z number material;

R (E ₂): high z number material and water are E at energy ₂x-ray under the ratio of mass attentuation coefficient, obtained by following formula:

R(E ₂)＝μ' _H(E ₂)/μ' _w(E ₂) (2)

Wherein μ ' _h(E ₂) for high z number material be E at energy ₂x-ray under mass attentuation coefficient; μ ' _w(E ₂) for water be E at energy ₂x-ray under mass attentuation coefficient;

3) CT number defined formula is used by step 2) to be converted to energy be E for the linear attenuation coefficient that obtains ₂x-ray under CT number, thus to obtain energy be E ₂x-ray under CT image, described CT number defined formula is:

${\mathrm{HU}}_x\left(E_2\right)=\frac{{\mathrm{\μ}}_x\left(E_2\right)-{\mathrm{\μ}}_w\left(E_2\right)}{{\mathrm{\μ}}_w\left(E_2\right)}\·1000---\left(3\right)$

Namely the linear attenuation coefficient that bilinearity transfer algorithm formula obtains is substituted into above-mentioned CT number defined formula can be E by energy ₁x-ray under scan the CT image obtained CT number to obtain be E at energy ₂x-ray under the CT number of CT image, then by being E at energy ₂x-ray under the CT number of CT image to obtain energy be E ₂x-ray under CT image;

4) be E to energy respectively ₁x-ray under CT image and energy be E ₂x-ray under CT Computer image genration digital image rebuilding image;

5) to step 4) the digital image rebuilding image conbined usage logarithm dual energy subtraction algorithm that generates, the weight factor required for selection, obtains the image of the unwanted material of cancellation.