Patent Number: 
Section: claims

1. A collimator for shaping a beam of energy emitted from a focal spot of a beam source, the collimator comprising: two elongated parallel plates arranged side by side to define an elongated collimating slit between the plates, wherein at least one of the plates is movably relative to the other plate for varying a width of the collimating slit; and  a movable cam operatively arranged with respect to the at least one movable plate such that movement of the cam in a first direction causes the width of the collimating slit to increase, and movement of the cam in a second direction causes the width of the collimating slit to decrease, wherein the at least one movable plate includes a follower contacting a cam surface of the cam, and wherein the cam surface includes steps. 2. A collimator according to  claim 1 , wherein the cam is rotatably movable. claim 1 3. A collimator according to  claim 2 , further including a motor having a rotatable shaft coupled to the cam. claim 2 4. A collimator according to  claim 1 , further including a motor for moving the cam. claim 1 5. A collimator according to  claim 4 , wherein the motor comprises a stepping motor, and the collimator also includes a motor controller having a counter for counting steps of the steping motor and a memory for saving the count. claim 4 6. A computed tomography scanner including a collimator according to  claim 1 , and further including: claim 1 an annular gantry rotatable about a rotation axis;  a beam source mounted within the gantry and having a focal spot for emitting an x-ray beam through the rotation axis; and  an array of x-ray detectors for receiving the x-ray beam from the focal spot;  wherein the collimator is mounted within the gantry between the focal spot and the detectors for collimating the x-ray beam. 7. A scanner according to  claim 6 , wherein the collimator is located between the rotation axis of the gantry and the detectors. claim 6 8. A scanner according to  claim 7 , wherein the plates of the collimator each have curved side profiles sharing a common axis of curvature intersecting the focal spot of the beam source. claim 7 9. A collimator according to  claim 1 , wherein both plates are movable. claim 1 10. A collimator according to  claim 1 , further including at least one spring biasing the movable plate towards the cam. claim 1 11. A collimator according to  claim 10 , wherein the spring biases the plates together and the cam is positioned between the plates. claim 10 12. A collimator according to  claim 10 , wherein the spring comprises a compression band of resilient material stretched between the plates. claim 10 13. A collimator according to  claim 1 , wherein the plates each have curved side profiles sharing a common axis of curvature. claim 1 14. A collimator according to  claim 1 , wherein the collimating slit has a predetermined minimum width. claim 1 15. A collimator for shaping a beam of energy emitted from a focal spot of a beam source, the collimator comprising: two elongated parallel plates arranged side by side to define an elongated collimating slit between the plates, wherein at least one of the plates is movably relative to the other plate for varying a width of the collimating slit; and  a movable cam operatively arranged with respect to the at least one movable plate such that movement of the cam in a first direction causes the width of the collimating slit to increase, and movement of the cam in a second direction causes the width of the collimating slit to decrease, wherein the at least one movable plate includes a follower contacting a cam surface of the cam, and wherein the follower is rotatable. 16. A collimator according to  claim 15 , wherein the cam surface is substantially smooth. claim 15 17. A collimator according to  claim 15 , wherein both plates are movable. claim 15 18. A computed tomography scanner including a collimator according to  claim 15 , and further including: claim 15 an annular gantry rotatable about a rotation axis;  a beam source mounted within the gantry and having a focal spot for emitting an x-ray beam through the rotation axis; and  an array of x-ray detectors for receiving the x-ray beam from the focal spot;  wherein the collimator is mounted within the gantry between the focal spot and the detectors for collimating the x-ray beam. 19. A scanner according to  claim 18 , wherein the collimator is located between the rotation axis of the gantry and the detectors. claim 18 20. A scanner according to  claim 19 , wherein the plates of the collimator each have curved side profiles sharing a common axis of curvature intersecting the focal spot of the beam source. claim 19 21. A collimator according to  claim 15 , wherein the cam is rotatably movable. claim 15 22. A collimator according to  claim 21 , further including a motor having a rotatable shaft coupled to the cam. claim 21 23. A collimator according to  claim 15 , further including a motor for moving the cam. claim 15 24. A collimator according to  claim 23 , wherein the motor comprises a stepping motor, and the collimator also includes a motor controller having a counter for counting steps of the stepping motor and a memory for saving the count. claim 23 25. A collimator according to  claim 15 , further including at least one spring biasing the movable plate towards the cam. together and the cam is positioned between the plates. claim 15 26. A collimator according to  claim 25 , wherein the spring biases the plates together and the cam is positioned between the plates. claim 25 27. A collimator according to  claim 25 , wherein the spring comprises a compression band of resilient material stretched between the plates. claim 25 28. A collimator according to  claim 15 , wherein the plates each have curved side profiles sharing a common axis of curvature. claim 15 29. A collimator according to  claim 15 ,wherein the collimating slit has a predetermined minimum width. claim 15 30. A collimator for shaping a beam of energy emitted from a focal spot of a beam source, the collimator comprising: two elongated parallel plates arranged side by side to define an elongated collimating slit between the plates, wherein at least one of the plates is movably relative to the other plate for varying a width of the collimating slit;  a movable cam operatively arranged with respect to the at least one movable plate such that movement of the cam in a first direction causes the width of the collimating slit to increase, and movement of the cam in a second direction causes the width of the collimating slit to decrease;  a rotatable shaft extending generally normal to the collimating slit, wherein the cam is mounted on the shaft for rotation therewith and the at least one movable plate is slidingly received on the shaft; and  a follower extends from the movable plate and contacts a cam surface of the cam;  whereby rotation of the shaft and the cam causes the movable plate to slide on the shaft. 31. A computed tomography scanner including a collimator according to  claim 14 , and further including: claim 14 an annular gantry rotatable about a rotation axis;  a beam source mounted within the gantry and having a focal spot for emitting an x-ray beam through the rotation axis; and  an array of x-ray detectors for receiving the x-ray beam from the focal spot;  wherein the collimator is mounted within the gantry between the focal spot and the detectors for collimating the x-ray beam. 32. A scanner according to  claim 31 , wherein the collimator is located between the rotation axis of the gantry and the detectors. claim 31 33. A scanner according to  claim 32 , wherein the plates of the collimator each have curved side profiles sharing a common axis of curvature intersecting the focal spot of the beam source. claim 32 34. A collimator according to  claim 30 , further including a motor for rotating the shaft. claim 30 35. A collimator according to  claim 34 , wherein the motor comprises a stepping motor, and the collimator also includes a motor controller having a counter for counting steps of the stepping motor and a memory for saving the count. claim 34 36. A collimator according to  claim 30 , further including at least one spring biasing the movable plate towards the cam. claim 30 37. A collimator according to  claim 36 , wherein the spring biases the plates together and the cam is positioned between the plates. claim 36 38. A collimator according to  claim 36 , wherein the spring comprises a compression band of resilient material stretched between the plates. claim 36 39. A collimator according to  claim 30 , wherein the plates each have curved side profiles sharing a common axis of curvature. claim 30 40. A collimator according to  claim 30 , wherein the collimating slit has a predetermined minimum width. claim 30 41. A collimator according to  claim 30 , wherein both plates are movable. claim 30 42. A collimator according to  claim 30 , further comprising a linear-rotary bearing supporting the plate on the shaft. claim 30