Patent Number: 
Section: claims

1. A system comprising:a radiation source comprising a plurality of focal spots located at different positions;a detector comprising a plurality of detector cells;a first grid located between the radiation source and the detector cells, the first grid comprising a plurality of radiation transmitting sections and a plurality of radiation absorbing sections; anda shielding device configured for adjustably blocking the radiation source, the shielding device being movably attached to a side of at least one of the plurality of radiation absorbing sections at a connecting point and being swinging around the connecting point by an angle;whereinat least one of the plurality of detector cells comprises an active area receiving radiation from the radiation source that passes through at least one of the plurality of radiation transmitting sections of the first grid,the radiation source, the first grid, the shielding device, and the detector cells are operatively coupled for detecting an object, andthe active area is adjustable by adjusting at least one of the first grid, the shielding device, or a position of at least one of the plurality of focal spots of the radiation source. 2. The system according to claim 1, wherein the active area is adjustable by adjusting the position of the first grid or tilting the first grid by an angle. 3. The system according to claim 1, further comprising a second grid, the second grid being located between the first grid and the detector. 4. The system according to claim 3, the second grid comprising a plurality of radiation transmitting portions, and at least one of the plurality of radiation transmitting portions being coupled with the active area. 5. The system according to claim 4, the first grid and the second grid being moveable relative to each other. 6. The system according to claim 4, the active area being at least partially determined by the at least one of the plurality of radiation transmitting sections of the first grid and at least one of the plurality of radiation transmitting portions of the second grid. 7. The system according to claim 3, at least one of the plurality of radiation transmitting sections extending in a first direction. 8. The system according to claim 7, the first grid being moveable in a second direction perpendicular to the first direction. 9. The system according to claim 7, the second grid being moveable in the first direction. 10. The system according to claim 1, the detecting the object comprising scanning the object with radiation from at least two different focal spots of the radiation source. 11. The system according to claim 1, wherein the shielding device comprises one or more plates. 12. A method comprising:locating a first grid and a shielding device between a radiation source and a detector, the radiation source comprising a plurality of focal spots located at different positions, the detector comprising a plurality of detector cells, the first grid comprising a plurality of radiation transmitting sections and a plurality of radiation absorbing sections, the shielding device being movably attached to a side of at least one of the plurality of radiation absorbing sections at a connecting point and being swinging around the connecting point by an angle;emitting radiation from the radiation source toward the first grid; andreceiving, on an active area of at least one of the plurality of detector cells, the radiation that passes through at least one of the plurality of radiation transmitting sections of the first grid;whereinthe active area is adjustable by adjusting at least one of the first grid, the shielding device, or a position of at least one of the plurality of focal spots of the radiation source, andthe radiation source, the first grid, the shielding device, and the detector cells are operatively coupled for detecting an object. 13. The method according to claim 12, wherein the active area is adjustable by adjusting the position of the first grid or tilting the first grid by an angle. 14. The method according to claim 12, further comprising locating a second grid between the first grid and the detector. 15. The method according to claim 14, the second grid comprising a plurality of radiation transmitting portions, and at least one of the plurality of radiation transmitting portions being coupled with the active area, wherein the active area is at least partially determined by the at least one of the plurality of radiation transmitting sections of the first grid and the at least one of the plurality of radiation transmitting portions of the second grid. 16. The method according to claim 15, the first grid and the second grid being moveable relative to each other. 17. The method according to claim 12, the at least one of the plurality of radiation transmitting sections extending in a first direction. 18. The method according to claim 17, further comprising moving the first grid in a second direction perpendicular to the first direction. 19. The method according to claim 17, further comprising moving the second grid in the first direction. 20. The method according to claim 12, wherein the shielding device comprises one or more plates.