Reconstructing image

1. A method of reconstructing images, comprising:

acquiring data of a response line, the data including a respective actual energy parameter of each of photons in a photon pair, the actual energy parameters of the photons in the photon pair being detected by a crystal pair in a detector, the response line corresponding to the crystal pair, each of the actual energy parameters being within a preset energy range;

determining an energy factor of the response line according to the respective actual energy parameter of each of the photons in the photon pair and a theoretical energy parameter of the photon, the energy factor indicating a degree that the actual energy parameter of each of the photons in the photon pair is close to the theoretical energy parameter;

obtaining a system parameter according to the energy factor, the system parameter including an element indicating a probability that the photon pair generated in a region of a subject is detected by the detector, the region of the subject corresponding to an image voxel of an image;

constructing a system response model with the system parameter; and

reconstructing the image based on the system response model.

2. The method according to claim 1 , wherein the preset energy range is expressed by

[E m −n % E m , E m +n % E m ],

where E m is the theoretical energy parameter and n % is a crystal energy resolution.

3. The method according to claim 1 , wherein determining the energy factor comprises:

obtaining a first difference value between the theoretical energy parameter and the actual energy parameter of a first photon of the photon pair;

obtaining a second difference value between the theoretical energy parameter and the actual energy parameter of a second photon of the photon pair; and

determining the energy factor according to the first difference value and the second difference value, wherein the energy factor is negatively correlated with the first difference value and the second difference value.

4. The method according to claim 3 , wherein the energy factor is expressed by:

p

energy

=

1

n

evt

⁢

∑

i

evt

=

1

n

evt

⁢

⁢

exp

⁡

[

-

[

E

m

-

E

0

⁡

(

i

evt

)

]

2

+

[

E

m

-

E

1

⁡

(

i

evt

)

]

2

σ

2

]

where p energy represents the energy factor of the response line,

n evt is a number of coincidence events corresponding to the response line,

i evt represents an i th coincidence event corresponding to the response line,

E 0 (i evt ) is the actual energy parameter of the first photon,

E 1 (i evt ) is the actual energy parameter of the second photon,

E m is the theoretical energy parameter, and

σ is an empirical value positively correlated with an energy resolution.

5. The method according to claim 1 , wherein the data of the response line further comprises:

a crystal normalization coefficient that is a correction value for efficiency consistency of the detector;

a crystal blurring factor for correcting blur of image;

an attenuation coefficient for correcting attenuation of each of the photons in the photon pair during a propagation process; and

a geometric coefficient representing a spatial geometric relationship between the image voxel and the crystal pair corresponding to the response line, and

wherein obtaining the system parameter according to the energy factor comprises:

obtaining the system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient, the geometric coefficient and the energy factor.

6. The method according to claim 5 , further comprising:

obtaining an initial system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient and the geometric coefficient,

wherein constructing the system response model with the system parameter comprises:

constructing the system response model with the initial system parameter and the system parameter.

7. The method according to claim 6 , wherein the system response model is constructed by determining an expectation maximization based on a Poisson probability model.

8. A system for reconstructing an image, comprising:

one or more processors; and

a non-transitory machine readable storage medium storing machine executable instructions, the processors are caused by the machine executable instructions to:

acquire data of a response line, the data including a respective actual energy parameter of each of photons in a photon pair corresponding to the response line, the respective actual energy parameter being detected by a detector and within a preset energy range;

determine an energy factor of the response line according to the actual energy parameter of each of the photons in the photon pair and a theoretical energy parameter of the photon, wherein the energy factor reflects a degree that the actual energy parameter of each of the photons in the photon pair is close to the theoretical energy parameter;

obtain a system parameter according to the energy factor, wherein the system parameter comprises an element indicating a probability that a photon pair generated in a region of a subject corresponding to an image voxel is received by the detector;

construct a system response model with the system parameter; and

reconstruct an image based on the system response model.

9. The system according to claim 8 , wherein the preset energy range is expressed by

[E m −n % E m , E m +n % E m ],

where E m is the theoretical energy parameter and n % is a crystal energy resolution.

10. The system according to claim 8 , wherein the processors are caused by the machine executable instructions to:

obtain a first difference value between the theoretical energy parameter and the actual energy parameter of a first photon of the photon pair;

obtain a second difference value between the theoretical energy parameter and the actual energy parameter of a second photon of the photon pair; and

determine the energy factor according to the first difference value and the second difference value, wherein the energy factor is negatively correlated with the first difference value and the second difference value.

11. The system according to claim 10 , wherein the energy factor is expressed by

p

energy

=

1

n

evt

⁢

∑

i

evt

=

1

n

evt

⁢

⁢

exp

⁡

[

-

[

E

m

-

E

0

⁡

(

i

evt

)

]

2

+

[

E

m

-

E

1

⁡

(

i

evt

)

]

2

σ

2

]

where p energy represents the energy factor of the response line,

n evt is a number of coincidence events corresponding to the response line,

i evt represents an i th coincidence event corresponding to the response line,

E 0 (i evt ) is the actual energy parameter of the first photon,

E 1 (i evt ) is the actual energy parameter of the second photon,

E m is the theoretical energy parameter, and

σ is an empirical value positively correlated with an energy resolution.

12. The system according to claim 8 , wherein the data of the response line further comprises:

a crystal normalization coefficient that is a correction value for efficiency consistency of the detector;

a crystal blurring factor to correct blur of image;

an attenuation coefficient to correct attenuation of each of the photons in the photon pair during a propagation process; and

a geometric coefficient to represent a spatial geometric relationship between the image voxel and a crystal pair that is in the detector and corresponds to the response line;

when obtaining the system parameter according to the energy factor, the processors are caused by the machine executable instructions to:

obtain the system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient, the geometric coefficient and the energy factor.

13. The system according to claim 12 , wherein the processors are further caused by the machine executable instructions to:

obtain an initial system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient and the geometric coefficient; and

when constructing the system response model with the system parameter, the processors are further caused by the machine executable instructions to:

construct the system response model with the initial system parameter and the system parameter.

14. The system according to claim 13 , wherein the system response model is constructed by determining an expectation maximization based on a Poisson probability model.

15. A non-transitory machine-readable storage medium storing instructions executable by one or more processors and upon such execution cause the one or more processors to perform operations comprising:

acquiring data of a response line, wherein the data of the response line comprises an actual energy parameter of each of photons in a photon pair corresponding to the response line, and the actual energy parameter is detected by the detector and within a preset energy range;

determining an energy factor of the response line according to the actual energy parameter of each of the photons in the photon pair and a theoretical energy parameter of the photon, wherein the energy factor reflects a degree that the actual energy parameter of each of the photons in the photon pair is close to the theoretical energy parameter;

obtaining a system parameter according to the energy factor, wherein the system parameter comprises an element indicating a probability that a photon pair generated in a region of a subject corresponding to an image voxel is received by the detector;

constructing a system response model with the system parameter; and

reconstructing an image based on the system response model.

16. The storage medium according to claim 15 , wherein the preset energy range is expressed by

[E m −n % E m , E m +n % E m ],

where E m is a theoretical energy parameter and n % is a crystal energy resolution.

17. The storage medium according to claim 15 , wherein the operations further comprise:

obtaining a first difference value between the theoretical energy parameter and the actual energy parameter of a first photon of the photon pair;

obtaining a second difference value between the theoretical energy parameter and the actual energy parameter of a second photon of the photon pair; and

determining the energy factor according to the first difference value and the second difference value, wherein the energy factor is negatively correlated with the first difference value and the second difference value.

18. The storage medium according to claim 17 , wherein the energy factor is expressed by

p

energy

=

1

n

evt

⁢

∑

i

evt

=

1

n

evt

⁢

⁢

exp

⁡

[

-

[

E

m

-

E

0

⁡

(

i

evt

)

]

2

+

[

E

m

-

E

1

⁡

(

i

evt

)

]

2

σ

2

]

wherein p energy represents the energy factor of the response line,

n evt is a number of coincidence events corresponding to the response line,

i evt represents an i th coincidence event corresponding to the response line,

E 0 (i evt ) is the actual energy parameter of the first photon,

E 1 (i evt ) is the actual energy parameter of the second photon,

E m is the theoretical energy parameter,

σ is an empirical value positively correlated with an energy resolution.

19. The storage medium according to claim 15 , wherein the data of the response line further comprises:

a crystal normalization coefficient that is a correction value for efficiency consistency of the detector;

a crystal blurring factor for correcting blur of image;

an attenuation coefficient for correcting attenuation of each of the photons in the photon pair during a propagation process; and

a geometric coefficient representing a spatial geometric relationship between the image voxel and a crystal pair that is in the detector and corresponds to the response line;

wherein obtaining the system parameter according to the energy factor comprises:

obtaining the system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient, the geometric coefficient and the energy factor.

20. The storage medium according to claim 19 , wherein the operations further comprise:

obtaining an initial system parameter corresponding to the response line according to a product of the crystal normalization coefficient, the crystal blurring factor, the attenuation coefficient and the geometric coefficient; and

wherein constructing the system response model with the system parameter comprises:

constructing the system response model with the initial system parameter and the system parameter.