CN103064047A - Correcting method and correcting system for elastic rebuilding of magnetic resonance elastography (MRE) - Google Patents

Abstract

The invention relates to a correcting method and correcting system for elastic rebuilding of magnetic resonance elastography (MRE). The method comprises the following steps: acquiring a shear wave generated by an imaging object; comparing the size of the imaging object with the wavelength of the shear wave, and when the size of the imaging object and the wavelength of the shear wave are of an identical order of magnitude, the shear wave is introduced into a higher order term to correct an equation of motion and then obtain an objective function through calculation, wherein according to the objective function, gamma is the correction factor, mu is the lame constant, rho is the medium density, omega is the angular frequency of an incentive, and U is the displacement vector of a medium. According to the correcting method and correcting system for the elastic rebuilding of the MRE, through acquisition of the shear wave generated by the imaging object, comparison of the wavelength of the shear wave with the size of the imaging object and then adoption of an algorithm of the objective function, the elastic rebuilding can be relatively accurately achieved.

Description

The elasticity of magnetic resonance elastography is rebuild modification method and system

Technical field

The present invention relates to magnetic resonance elastography (Magnetic Resonance Elastography, MRE) technology, the elasticity that particularly relates to magnetic resonance elastography is rebuild modification method and system.

Background technology

The elasticity reconstruction algorithm is a most important link in magnetic resonance elastography (MRE) process, has determined spatial resolution and the elasticity measurement accuracy of MRE image.

At present, the research of MRE elasticity reconstruction algorithm mainly launches around finding the solution the Helmholtz algorithm.Suppose that shearing wave propagates in isotropic Infinite medium, and ignore the impact of compressional wave, then Particles Moving satisfies the Helmholtz equation

Wherein U is particle displacement, and ρ is Media density, and ω is the angular frequency of excitation, μ modulus of shearing.

Also have simultaneously some other methods, local frequency estimation method (local frequency estimation for example, LFE), method (the Directly Inversion that directly inverts, DI), matched filter method (Matched Filter, MF), phase gradient method (Phase Gradient, PG), finite element iterative method (FEM) etc., yet all there is a problem in above-mentioned MRE elasticity reconstruction algorithm: suppose all in the algorithm that shearing wave propagates in Infinite medium.But in fact, owing to be subjected to edge effect, reflection and refraction appear in shearing wave, that MRE captures is the result who has been mingled with a plurality of ripple stacks such as reflection wave and reflection wave, this and assumed condition are runed counter to, especially approach or during less than the shearing wave wavelength, the elasticity number that LFE, DI and PG method calculate can be significantly less than actual value, has error when the Spatial Dimension of imaging object.

Summary of the invention

Based on this, be necessary for the problems referred to above, provide the elasticity of the higher magnetic resonance elastography of a kind of accuracy to rebuild modification method.

In addition, also rebuild update the system with the necessary elasticity of the higher magnetic resonance elastography of a kind of accuracy that provides.

A kind of elasticity of magnetic resonance elastography is rebuild modification method, comprises the steps: to obtain the shearing wave that imaging object produces; The wavelength of described imaging object and described shearing wave compares, when the wavelength of described imaging object and described shearing wave during at an order of magnitude, revise described shearing wave introducing higher order term and to the equation of motion, calculate objective function, described objective function is:

Wherein γ is correction factor, and μ is Lame's constant, and ρ is Media density, and ω is the angular frequency of excitation, and U is the dielectric displacement vector.

Among embodiment, also comprise therein: described imaging object is during greater than the wavelength of three times of described shearing waves, and described shearing wave includes ejected wave and reflection wave:

Described incident wave equation is: $\stackrel{\→}{r}\left(t\right)={\stackrel{\→}{r}}_0+{\stackrel{\→}{\mathrm{\ξ}}}_0\exp \left(j(\stackrel{\→}{k}\·\stackrel{\→}{r}-\mathrm{\ωt})\right),$

Described reflection wave equation is: ${\stackrel{\→}{r}}^{\′}\left(t\right)={{\stackrel{\→}{r}}_0}^{\′}+{{\stackrel{\→}{\mathrm{\ξ}}}_0}^{\′}\exp \left(j({\stackrel{\→}{k}}^{\′}\·{\stackrel{\→}{r}}^{\′}-\mathrm{\ωt})\right),$

Wherein

Be respectively the incident wave of r and k direction,

With incident wave

The reflection wave that is the Mirror Symmetry relation take the border as axis,

Be respectively the particle equilibrium position of incident wave and reflection wave, Be respectively incident wave and reflection wave amplitude, ω is the angular frequency of excitation, and t is the time;

Carry out filtering by wave filter, the filtering of described wave filter is defined as:

Q(ω)＝R(ω)D _k(ω)， $R\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{1+{(\mathrm{\ω}/{\mathrm{\ω}}_c)}^{2n}}},$

Wherein Q (ω) is anisotropic filter, and R (ω) is the frequency response function of wave filter, D _k(ω) be the directional response function of wave filter, ω is angular frequency, ω _cBe filter cutoff frequency, n is filter order,

Be filter direction,

Be self-defining direction vector.

Among embodiment, the direction of described wave filter is described reflection wave line of propagation therein, described wave filter filtering be described reflection wave.

Among embodiment, parameter is carried out in the filtering definition of described wave filter select therein, described parameter is R (ω) and D _k(ω), described parameter selects to adopt the linear search method to be: wherein a parameter is on the impact of reconstruction quality in investigation, and wherein a parameter is for adjusting parameter in selection, and fixing another parameter is preset parameter; The curve that the drawing image quality changes with described adjustment parameter; The described adjustment parameter of selection and goldstandard error minimum is as only parameter; Described goldstandard is to set in advance the accurate reference value of obtaining.

Among embodiment, described parameter selects to adopt the linear search method also to comprise therein: be described adjustment setting parameter new preset parameter, described preset parameter is set as new adjustment parameter; Return described drawing image quality with the step of the curve of described adjustment parameter variation.

In addition, also be necessary to provide a kind of elasticity of magnetic resonance elastography to rebuild update the system, comprising: the shearing wave acquisition module is used for obtaining the shearing wave that imaging object produces; Comparison module is used for the wavelength of described imaging object and described shearing wave is compared; First selects module, when the wavelength of described imaging object and described shearing wave during at an order of magnitude, revises described shearing wave introducing higher order term and to the equation of motion, calculates objective function.

Among embodiment, also comprise therein: second selects module, and when described imaging object during greater than the wavelength of three times of described shearing waves, described shearing wave includes ejected wave and reflection wave; Wave filter is used for described shearing wave is carried out filtering.

Among embodiment, the direction of described wave filter is described reflection wave line of propagation therein, described wave filter filtering be described reflection wave.

Among embodiment, described wave filter comprises therein: parameter selection unit, be used for investigating wherein a parameter to the impact of reconstruction quality, and select that wherein a parameter is for adjusting parameter, fixing another parameter is preset parameter; The Image Rendering unit is used for the curve that the drawing image quality changes with described adjustment parameter; Comparing unit is used for the described adjustment parameter of selection and goldstandard error minimum as only parameter; Described goldstandard is to set in advance the accurate reference value of obtaining.

Among embodiment, described wave filter also comprises: exchange unit is described adjustment setting parameter new preset parameter, and described preset parameter is set as new adjustment parameter therein; Return the unit, return described Image Rendering unit.

Adopt the elasticity of the application's magnetic resonance elastography to rebuild modification method and system, the shearing wave that produces by obtaining imaging object, the size of the wavelength of this shearing wave and imaging object is compared, then adopt the objective function algorithm, can carry out more accurately elasticity and rebuild.

Description of drawings

Fig. 1 is the process flow diagram that the elasticity of a magnetic resonance elastography among the embodiment is rebuild modification method;

Fig. 2 is the process flow diagram that the elasticity of the magnetic resonance elastography among another embodiment is rebuild modification method;

Fig. 3 is the process flow diagram that a parameter among the embodiment selects to adopt the linear search method;

Fig. 4 is the process flow diagram that the parameter among another embodiment selects to adopt the linear search method;

Fig. 5 is the logic diagram that the elasticity of a magnetic resonance elastography among the embodiment is rebuild update the system;

Fig. 6 is the logic diagram that the elasticity of the magnetic resonance elastography among another embodiment is rebuild update the system;

Fig. 7 is the logic diagram of a wave filter among the embodiment;

Fig. 8 is the logic diagram of the wave filter among another embodiment.

Embodiment

In reconstruction algorithm, imaging object receives that extraneous excitation produces shearing wave, yet can produce reflection wave etc. on the border of imaging object, and what collect is the stack result such as shearing wave, transmitted wave.Usually, there are three kinds of situations on the border of imaging object, is respectively: rigid boundary, free boundary and elastic restraint border.In the rigid boundary condition: reflection does not have the variation of waveform, and the shearing wave of incident (compressional wave) only produces the shearing wave (compressional wave) of a reflection; In free boundary condition: reflection wave is relevant with the Poisson ratio of incident angle; At the elastic restraint boundary condition: reflection wave is relevant with incident angle, also depends on the rigidity on border and the wavelength of incident wave.

As shown in Figure 1, in one embodiment, rebuild in the modification method in the elasticity of the application's magnetic resonance elastography, comprise the steps:

Step S10: obtain the shearing wave that imaging object produces.In the process of elastogram, by exciting bank imaging object or body surface are produced shearing wave, this shearing wave frequency, wavelength can be adjusted by exciting bank.At this moment, the imaging object of excited target produces shearing wave, and the shearing wave frequency that this imaging object produces, wavelength etc. are different and different according to the hardness of imaging object etc., and the information of this shearing wave can reflect the elastic information of imaging object.For imaging object, can be the organs such as liver, heart.

Step S20: the wavelength of imaging object and shearing wave compares, and when the wavelength of imaging object and shearing wave during at an order of magnitude, shearing wave is introduced higher order term and the equation of motion is revised, and calculates objective function.Particularly, for imaging object, the size of imaging object is suitable with the wavelength of shearing wave, and namely the border for imaging object can be considered as not producing reflection wave, then can adopt this objective function to calculate.

Objective function is: $\min {\left|\right|\mathrm{\μ}{\▿}^{2}U+\mathrm{\γ\μ}{\mathrm{\Δ}}^{2}U+\mathrm{\ρ}{\mathrm{\ω}}^{2}U\left|\right|}_2^2$

Wherein γ is correction factor, and μ is Lame's constant, and ρ is Media density, and ω is the angular frequency of excitation, and U is the dielectric displacement vector.

The shearing wave that produces by obtaining imaging object compares the size of the wavelength of this shearing wave and imaging object, adopts the objective function algorithm of this programme, can carry out more accurately elasticity and rebuild.

In one embodiment, consult accompanying drawing 2, the elasticity of magnetic resonance elastography is rebuild modification method and also comprised: step S30: imaging object is during greater than the wavelength of three times of shearing waves, when the size of imaging object is much larger than the wavelength of shearing wave in other words, the shearing wave that imaging object produces mainly includes ejected wave and reflection wave, at this moment:

The incident wave equation is: $\stackrel{\→}{r}\left(t\right)={\stackrel{\→}{r}}_0+{\stackrel{\→}{\mathrm{\ξ}}}_0\exp \left(j(\stackrel{\→}{k}\·\stackrel{\→}{r}-\mathrm{\ωt})\right),$

The reflection wave equation is: ${\stackrel{\→}{r}}^{\′}\left(t\right)={{\stackrel{\→}{r}}_0}^{\′}+{{\stackrel{\→}{\mathrm{\ξ}}}_0}^{\′}\exp \left(j({\stackrel{\→}{k}}^{\′}\·{\stackrel{\→}{r}}^{\′}-\mathrm{\ωt})\right),$

Wherein

Be respectively the incident wave of r and k direction,

With incident wave The reflection wave that is the Mirror Symmetry relation take the border as axis,

Be respectively the particle equilibrium position of incident wave and reflection wave,

Be respectively incident wave and reflection wave amplitude, ω is the angular frequency of excitation, and t is the time.

Step S40: carry out filtering by wave filter, the filtering of wave filter is defined as:

Q(ω)＝R(ω)D _k(ω)， $R\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{1+{(\mathrm{\ω}/{\mathrm{\ω}}_c)}^{2n}}},$

Wherein Q (ω) is anisotropic filter, and R (ω) is the frequency response function of wave filter, D _k(ω) be the directional response function of wave filter, ω is angular frequency, ω _cBe filter cutoff frequency, n is filter order,

Be filter direction,

Be self-defining direction vector.

For wave filter, this wave filter is anisotropic filter.Because the directivity of reflection wave is very strong, and the direction of wave filter is the reflection wave line of propagation, so by anisotropic filter filtering reflection wave, can further reduce reconstruction error.

By reference to the accompanying drawings 3, further, to carry out parameter for the filtering definition of wave filter and select, this parameter is R (ω) and D _k(ω), parameter is selected to adopt the linear search method, is specially:

S41: wherein a parameter is on the impact of reconstruction quality in investigation, and wherein a parameter is for adjusting parameter in selection, and fixing another parameter is preset parameter.Particularly, can select parameters R (ω) or D _k(ω) parameter is adjusted at one of them seat, then fixing another one.

S42: the drawing image quality is with the curve of adjusting the parameter variation.Particularly, constantly linear change is adjusted parameter, and obtains to adjust the curve that parameter changes.

S43: the adjustment parameter of selection and goldstandard error minimum is as only parameter; Goldstandard is to set in advance the accurate reference value of obtaining.Particularly, preset reference value, this reference value is real value, is goldstandard.The comparison of curve map and goldstandard by picture quality, the error minimum be best adjustment parameter value.

In addition, by reference to the accompanying drawings 4, parameter selects to adopt the linear search method also to comprise:

S44: be new preset parameter adjusting setting parameter, preset parameter is set as new adjustment parameter.Particularly, exchanging former adjustment parameter and preset parameter is new adjustment parameter and preset parameter, and wherein new preset parameter is determined optimal adjusting parameters among the step S43, then with the new adjustment parameter of this new preset parameter adjustment.

S45: return the drawing image quality with the step of the curve of adjusting the parameter variation, namely return step S42, adopt above-mentioned identical method to determine new adjustment parameter.

Rebuild modification method based on the elasticity of above-mentioned magnetic resonance elastography, by reference to the accompanying drawings 5, in one embodiment, provide the elasticity of magnetic resonance elastography to rebuild the modification method system, comprising:

Shearing wave acquisition module 10 is used for obtaining the shearing wave that imaging object produces.Concrete, the shearing wave that the imaging object of excited target produces, this shearing wave is sheared ripple acquisition module 10 and gets access to.

Comparison module 20 is used for the wavelength of imaging object and shearing wave is compared.

First selects module 30, when the wavelength of imaging object and shearing wave during at an order of magnitude, revises shearing wave introducing higher order term and to the equation of motion, calculates objective function.Particularly, for imaging object, the size of imaging object is suitable with the wavelength of shearing wave, and namely the border for imaging object can be considered as not producing reflection wave, then can adopt this objective function to calculate.

Objective function is: $\min {\left|\right|\mathrm{\μ}{\▿}^{2}U+\mathrm{\γ\μ}{\mathrm{\Δ}}^{2}U+\mathrm{\ρ}{\mathrm{\ω}}^{2}U\left|\right|}_2^2$

Wherein γ is correction factor, and μ is Lame's constant, and ρ is Media density, and ω is the angular frequency of excitation, and U is the dielectric displacement vector.

The shearing wave that produces by obtaining imaging object compares the size of the wavelength of this shearing wave and imaging object, adopts the objective function algorithm of this programme, can carry out more accurately elasticity and rebuild.

By reference to the accompanying drawings 6, in one embodiment, the elasticity of magnetic resonance elastography is rebuild the modification method system, also comprises:

Second selects module 40, and when imaging object during greater than the wavelength of three times of shearing waves, shearing wave includes ejected wave and reflection wave.Particularly, during much larger than the wavelength of shearing wave, the shearing wave that imaging object produces mainly includes ejected wave and reflection wave for the size of imaging object, at this moment:

The incident wave equation is: $\stackrel{\→}{r}\left(t\right)={\stackrel{\→}{r}}_0+{\stackrel{\→}{\mathrm{\ξ}}}_0\exp \left(j(\stackrel{\→}{k}\·\stackrel{\→}{r}-\mathrm{\ωt})\right),$

The reflection wave equation is: ${\stackrel{\→}{r}}^{\′}\left(t\right)={{\stackrel{\→}{r}}_0}^{\′}+{{\stackrel{\→}{\mathrm{\ξ}}}_0}^{\′}\exp \left(j({\stackrel{\→}{k}}^{\′}\·{\stackrel{\→}{r}}^{\′}-\mathrm{\ωt})\right),$

Wherein Be respectively the incident wave of r and k direction,

With incident wave

The reflection wave that is the Mirror Symmetry relation take the border as axis,

Be respectively the particle equilibrium position of incident wave and reflection wave,

Be respectively incident wave and reflection wave amplitude, ω is the angular frequency of excitation, and t is the time.

Wave filter 50 is used for shearing wave is carried out filtering.The filtering of wave filter 50 is defined as:

Q(ω)＝R(ω)D _k(ω)， $R\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{1+{(\mathrm{\ω}/{\mathrm{\ω}}_c)}^{2n}}},$

Wherein Q (ω) is anisotropic filter, and R (ω) is the frequency response function of wave filter, D _k(ω) be the directional response function of wave filter, ω is angular frequency, ω _cBe filter cutoff frequency, n is filter order,

Be filter direction,

Be self-defining direction vector.

For wave filter, this wave filter is anisotropic filter.Because the directivity of reflection wave is very strong, and the direction of wave filter is the reflection wave line of propagation, so by anisotropic filter filtering reflection wave, can further reduce reconstruction error.

By reference to the accompanying drawings 7, further, to carry out parameter for the filtering definition of wave filter 50 and select, this parameter is R (ω) and D _k(ω), wave filter 50 comprises:

Parameter selection unit 51, wherein a parameter is on the impact of reconstruction quality to be used for investigation, and wherein a parameter is for adjusting parameter in selection, and fixing another parameter is preset parameter.Particularly, can select parameters R (ω) or D _k(ω) parameter is adjusted at one of them seat, then fixing another one.

Image Rendering unit 52 is used for the drawing image quality with the curve of adjusting the parameter variation.Particularly, constantly linear change is adjusted parameter, and obtains to adjust the curve that parameter changes.

Comparing unit 53 is used for the adjustment parameter of selection and goldstandard error minimum as only parameter; Goldstandard is to set in advance the accurate reference value of obtaining.Particularly, preset reference value, this reference value is real value, is goldstandard.The comparison of curve map and goldstandard by picture quality, the error minimum be best adjustment parameter value.

In addition, by reference to the accompanying drawings 8, wave filter 50 also comprises:

Exchange unit 54 is new preset parameter adjusting setting parameter, and preset parameter is set as new adjustment parameter.Particularly, exchanging former adjustment parameter and preset parameter is new adjustment parameter and preset parameter, and wherein new preset parameter is determined optimal adjusting parameters in the comparing unit 53, then with the new adjustment parameter of this new preset parameter adjustment.

Return unit 55, return Image Rendering unit 52.

The above embodiment has only expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to claim of the present invention.Should be pointed out that for the person of ordinary skill of the art without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with claims.

Claims (10)

1. the elasticity of a magnetic resonance elastography is rebuild modification method, comprises the steps:

Obtain the shearing wave that imaging object produces;

The wavelength of described imaging object and described shearing wave compares, when the wavelength of described imaging object and described shearing wave during at an order of magnitude, revise described shearing wave introducing higher order term and to the equation of motion, calculate objective function, described objective function is:

Wherein γ is correction factor, and μ is Lame's constant, and ρ is Media density, and ω is the angular frequency of excitation, and U is the dielectric displacement vector.

2. the elasticity of magnetic resonance elastography according to claim 1 is rebuild modification method, it is characterized in that, also comprises: described imaging object is during greater than the wavelength of three times of described shearing waves, and the described shearing wave of catching includes ejected wave and reflection wave:

Described incident wave equation is: $\stackrel{\→}{r}\left(t\right)={\stackrel{\→}{r}}_0+{\stackrel{\→}{\mathrm{\ξ}}}_0\exp \left(j(\stackrel{\→}{k}\·\stackrel{\→}{r}-\mathrm{\ωt})\right),$

Described reflection wave equation is: ${\stackrel{\→}{r}}^{\′}\left(t\right)={{\stackrel{\→}{r}}_0}^{\′}+{{\stackrel{\→}{\mathrm{\ξ}}}_0}^{\′}\exp \left(j({\stackrel{\→}{k}}^{\′}\·{\stackrel{\→}{r}}^{\′}-\mathrm{\ωt})\right),$

Wherein

Be respectively the incident wave of r and k direction,

With incident wave

The reflection wave that is the Mirror Symmetry relation take the border as axis, Be respectively the particle equilibrium position of incident wave and reflection wave,

Be respectively incident wave and reflection wave amplitude, ω is the angular frequency of excitation, and t is the time;

Carry out filtering by wave filter, the filtering of described wave filter is defined as:

Q(ω)＝R(ω)D _k(ω)， $R\left(\mathrm{\ω}\right)=\frac{1}{\sqrt{1+{(\mathrm{\ω}/{\mathrm{\ω}}_c)}^{2n}}},$

Wherein Q (ω) is anisotropic filter, and R (ω) is the frequency response function of wave filter, D _k(ω) be the directional response function of wave filter, ω is angular frequency, ω _cBe filter cutoff frequency, n is filter order,

Be filter direction,

Be self-defining direction vector.

3. the elasticity of magnetic resonance elastography according to claim 2 is rebuild modification method, it is characterized in that the direction of described wave filter is described reflection wave line of propagation, described wave filter filtering be described reflection wave.

4. the elasticity of magnetic resonance elastography according to claim 3 is rebuild modification method, it is characterized in that, parameter is carried out in the filtering definition of described wave filter select, and described parameter is R (ω) and D _k(ω), described parameter selects to adopt the linear search method to be:

Wherein a parameter is on the impact of reconstruction quality in investigation, and wherein a parameter is for adjusting parameter in selection, and fixing another parameter is preset parameter;

The curve that the drawing image quality changes with described adjustment parameter;

The described adjustment parameter of selection and goldstandard error minimum is as only parameter; Described goldstandard is to set in advance the accurate reference value of obtaining.

5. the elasticity of magnetic resonance elastography according to claim 4 is rebuild modification method, it is characterized in that, described parameter selects to adopt the linear search method also to comprise:

Be described adjustment setting parameter new preset parameter, described preset parameter is set as new adjustment parameter;

Return described drawing image quality with the step of the curve of described adjustment parameter variation.

6. the elasticity of a magnetic resonance elastography is rebuild update the system, it is characterized in that, comprising:

The shearing wave acquisition module is used for obtaining the shearing wave that imaging object produces;

Comparison module is used for the wavelength of described imaging object and described shearing wave is compared;

First selects module, when the wavelength of described imaging object and described shearing wave during at an order of magnitude, revises described shearing wave introducing higher order term and to the equation of motion, calculates objective function.

7. the elasticity of magnetic resonance elastography according to claim 6 is rebuild modification method, it is characterized in that, also comprise: second selects module, and when described imaging object during greater than the wavelength of three times of described shearing waves, the described shearing wave of catching includes ejected wave and reflection wave;

Wave filter is used for described shearing wave is carried out filtering.

8. the elasticity of magnetic resonance elastography according to claim 7 is rebuild modification method, it is characterized in that the direction of described wave filter is described reflection wave line of propagation, described wave filter filtering be described reflection wave.

9. the elasticity of magnetic resonance elastography according to claim 8 is rebuild modification method, it is characterized in that described wave filter comprises:

Parameter selection unit, wherein a parameter is on the impact of reconstruction quality to be used for investigation, and wherein a parameter is for adjusting parameter in selection, and fixing another parameter is preset parameter;

The Image Rendering unit is used for the curve that the drawing image quality changes with described adjustment parameter;

Comparing unit is used for the described adjustment parameter of selection and goldstandard error minimum as only parameter; Described goldstandard is to set in advance the accurate reference value of obtaining.

10. the elasticity of magnetic resonance elastography according to claim 9 is rebuild modification method, it is characterized in that described wave filter also comprises:

Exchange unit is described adjustment setting parameter new preset parameter, and described preset parameter is set as new adjustment parameter;

Return the unit, return described Image Rendering unit.

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