Scanning method and device with reduced scanning dosage

1. A computed tomography (CT) scanning method, comprising:

determining values for a first scanning dosage and a second scanning dosage used in a scanning process based on a trigger condition which varies regularly and attenuation fluctuations of an object to be scanned, wherein the first scanning dosage is higher than the second scanning dosage, and at least one of the first scanning dosage and the second scanning dosage has an inconstant value;

scanning a target position with dosages at the determined values;

during a transition process from the first scanning dosage stage to the second scanning dosage stage, implementing real-time calculation to obtain a time period for transition from a current scanning dosage to an initial scanning dosage in a third scanning dosage stage performed after the second scanning dosage stage;

implementing real-time comparison between the calculated time period and a preset time period; and

if the calculated time period is longer than or equal to the preset time period, terminating the transition process from the first scanning dosage stage to the second scanning dosage stage, terminating the second scanning dosage stage, and transitioning to the third scanning dosage stage from a current time point.

2. The method according to claim 1 , wherein when the first scanning dosage has an inconstant value, the second scanning dosage has a constant value which is determined according to the trigger condition which varies regularly.

3. The method according to claim 1 , wherein when the second scanning dosage has an inconstant value, the first scanning dosage has a constant value which is determined according to the trigger condition which varies regularly.

4. The method according to claim 1 , wherein when the second scanning dosage has an inconstant value, the step of determining values for a first scanning dosage and a second scanning dosage used in a scanning process based on a trigger condition which varies regularly and attenuation fluctuations of an object to be scanned comprises:

determining to use the inconstant second scanning dosage to scan the target position according to the trigger condition which varies regularly; and

adjusting the second scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence.

5. The method according to claim 1 , wherein when the first scanning dosage has an inconstant value, the step of determining values for a first scanning dosage and a second scanning dosage used in a scanning process based on a trigger condition which varies regularly and attenuation fluctuations of an object to be scanned comprises:

determining to use the inconstant first scanning dosage to scan the target position according to the trigger condition which varies regularly; and

adjusting the first scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence.

6. The method according to claim 4 , wherein the step of adjusting the second scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence comprises:

calculating a first set of dosage values for the second scanning dosage based on equation

N

j

=

DoseRightFactor

×

N

low

×

(

ⅇ

(

-

μ

water

*

D

ref

)

ⅇ

(

-

μ

water

*

D

j

)

)

adjCoef

,

wherein the first set of dosage values are used for scanning different target positions; and

calculating a second set of dosage values for the second scanning dosage based on equation

N

i

=

N

j

∑

i

=

1

V

⁢

A

max

,

i

*

A

max

,

i

,

wherein the second set of dosage values are used for scanning one target position from different scanning angles,

wherein N j is a scanning dosage on a j th target position, DoseRightFactor is an image noise coefficient, N low is the second scanning dosage, μ water is an attenuation coefficient of water, D ref is a referenced equivalent diameter of a water phantom, D j is an equivalent diameter of the water phantom on the j th target position, adjCoef is an exponent adjustment parameter of a current in a tube filament, N i is a scanning dosage of a i th scanning angle on the j th target position, A max,i is maximum attenuation of all channels of the i th scanning angle, and V is the total number of scanning angles in a round of scanning.

7. The method according to claim 5 , wherein the step of adjusting the first scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence comprises:

calculating a first set of dosage values for the first scanning dosage based on equation

N

j

=

DoseRightFactor

×

N

high

×

(

ⅇ

(

-

μ

water

*

D

ref

)

ⅇ

(

-

μ

water

*

D

j

)

)

adjCoef

,

wherein the first set of dosage values are used for scanning different target positions; and

calculating a second set of dosage values for the first scanning dosage based on equation

N

i

=

N

j

∑

i

=

1

V

⁢

A

max

,

i

*

A

max

,

i

,

wherein the second set of dosage values are used for scanning one target position from different scanning angles,

wherein N j is a scanning dosage on a j th target position, DoseRightFactor is an image noise coefficient, N high is the first scanning dosage, μ water is an attenuation coefficient of water, D ref is a referenced equivalent diameter of the water phantom, D j is an equivalent diameter of the water phantom on the j th target position, adjCoef is an exponent adjustment parameter of a current in a tube filament, N i is a scanning dosage of a i th scanning angle on the j th target position, A max,i is maximum attenuation of all channels of the i th scanning angle, and V is the total number of scanning angles in a round of scanning.

8. The method according to claim 1 , wherein when the target position is being scanned with the determined values, a current in a tube filament is under open-loop control.

9. The method according to claim 1 , wherein the initial scanning dosage in the third scanning dosage stage is predicted by following steps:

fitting an equivalent diameter of the water phantom on a target position where the initial scanning dosage is used based on equivalent diameters of the water phantom of a plurality of parts obtained in previous scannings;

calculating a ratio of the equivalent diameter of water phantom on the target position where the initial scanning dosage is used to an equivalent diameter of the water phantom on a target position where the current scanning dosage is used; and

calculating a product of the ratio and the current scanning dosage as the initial scanning dosage in the third scanning dosage stage.

10. A computed tomography (CT) scanning device, comprising:

a scanning dosage determination unit, adapted to determine values for a first scanning dosage and a second scanning dosage used in a scanning process based on a trigger condition which varies regularly and attenuation fluctuations of an object to be scanned, wherein the first scanning dosage is higher than the second scanning dosage, and at least one of the first scanning dosage and the second scanning dosage has an inconstant value;

a CT scanning unit, adapted to scan a target position with dosages at the determined values;

a real-time calculation unit, adapted to implement real-time calculation to obtain a time period for transition from a current scanning dosage to an initial scanning dosage in a third scanning dosage stage performed after the second scanning dosage stage, during a transition process from the first scanning dosage stage to the second scanning dosage stage;

a real-time comparison unit, adapted to implement real-time comparison between the calculated time period and a preset time period; and

a transition unit, adapted to terminate the transition process from the first scanning dosage stage to the second scanning dosage stage, terminate the second scanning dosage stage, and transition to the third scanning dosage stage from a current time point, if the calculated time period is longer than or equal to the preset time period.

11. The device according to claim 10 , wherein when the first scanning dosage has an inconstant value, the second scanning dosage has a constant value which is determined according to the trigger condition which varies regularly.

12. The device according to claim 10 , wherein when the second scanning dosage has an inconstant value, the first scanning dosage has a constant value which is determined according to the trigger condition which varies regularly.

13. The device according to claim 10 , wherein when the second scanning dosage has an inconstant value, the scanning dosage determination unit comprises:

a first scanning mode determination sub-unit, adapted to determine to use the inconstant second scanning dosage to scan the target position according to the trigger condition which varies regularly; and

a first scanning dosage adjustment sub-unit, adapted to adjust the second scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence.

14. The device according to claim 10 , wherein when the first scanning dosage has an inconstant value, the scanning dosage determination unit comprises:

a second scanning mode determination sub-unit, adapted to determine to use the inconstant first scanning dosage to scan the target position according to the trigger condition which varies regularly; and

a second scanning dosage adjustment sub-unit, adapted to adjust the first scanning dosage to be a dosage which varies with the target position or varies with the target position and a scanning angle based on a dosage adjustment mode to ensure image noise congruence.

15. The device according to claim 13 , wherein the first scanning dosage adjustment sub-unit comprises:

a first position scanning dosage calculation sub-unit, adapted to calculate a first set of dosage values for the second scanning dosage based on equation

N

j

=

DoseRightFactor

×

N

low

×

(

ⅇ

(

-

μ

water

*

D

ref

)

ⅇ

(

-

μ

water

*

D

j

)

)

adjCoef

,

wherein the first set of dosage values are used for scanning different target positions; and

a first angle scanning dosage calculation sub-unit, adapted to calculate a second set of dosage values for the second scanning dosage based on equation

N

i

=

N

j

∑

i

=

1

V

⁢

A

max

,

i

*

A

max

,

i

,

wherein the second set of dosage values are used for scanning one target position from different scanning angles,

wherein N j is a scanning dosage on a j th target position, DoseRightFactor is an image noise coefficient, N low is the second scanning dosage, μ water is an attenuation coefficient of water, D ref is a referenced equivalent diameter of a water phantom, D j is an equivalent diameter of the water phantom on the j th target position, adjCoef is an exponent adjustment parameter of a current in a tube filament, N i is a scanning dosage of a i th scanning angle on the j th target position, A max,i is maximum attenuation of all channels of the i th scanning angle, and V is the total number of scanning angles in a round of scanning.

16. The device according to claim 14 , wherein the second scanning dosage adjusting sub-unit comprises:

a second position scanning dosage calculation sub-unit, adapted to calculate a first set of dosage values for the first scanning dosage based on equation

N

j

=

DoseRightFactor

×

N

high

×

(

ⅇ

(

-

μ

water

*

D

ref

)

ⅇ

(

-

μ

water

*

D

j

)

)

adjCoef

,

wherein the first set of dosage values are used for scanning different target positions; and

a second angle scanning dosage calculation sub-unit, adapted to calculate a second set of dosage values for the first scanning dosage based on equation

N

i

=

N

j

∑

i

=

1

V

⁢

A

max

,

i

*

A

max

,

i

,

wherein the second set of dosage values are used for scanning one target position from different scanning angles,

wherein N j is a scanning dosage on a j th target position, DoseRightFactor is an image noise coefficient, N high is the first scanning dosage, μ water is an attenuation coefficient of water, D ref is a referenced equivalent diameter of the water phantom, D j is an equivalent diameter of the water phantom on the j th target position, adjCoef is an exponent adjustment parameter of a current in a tube filament, N i is a scanning dosage of a i th scanning angle on the j th target position, A max,i is maximum attenuation of all channels of the i th scanning angle, and V is the total number of scanning angles in a round of scanning.

17. The device according to claim 10 , wherein when the CT scanning unit scans the target position with the determined values, a current in a tube filament is under open-loop control.

18. The device according to claim 10 , wherein the real-time calculation unit comprises:

a fitting sub-unit, adapted to fit an equivalent diameter of the water phantom on a target position where the initial scanning dosage is used based on equivalent diameters of the water phantom of a plurality of parts obtained in previous scannings;

a ratio calculation sub-unit, adapted to calculate a ratio of the equivalent diameter of water phantom on the target position where the initial scanning dosage is used to an equivalent diameter of the water phantom on a target position where the current scanning dosage is used; and

an initial scanning dosage calculation sub-unit, adapted to calculate a product of the ratio and the current scanning dosage as the initial scanning dosage in the third scanning dosage stage.