X-ray imaging system with a combined filter and collimator positioning mechanism
A radiation therapy system includes an X-ray imaging system that is configured with a combined and simplified filter and collimator positioning mechanism. In addition, an X-ray imager of the RT system is only positioned at a few discrete locations within a plane that is a fixed distance from the imaging X-ray source when generating X-ray images. As a result, for each of these discrete imaging positions, the simplified filter and collimator positioning mechanism positions a specific collimator-filter combination in a specific location between the X-ray source and the imager.
1. An imaging system configured to rotate about a center point of rotation, the imaging system comprising:
an X-ray source configured to direct X-rays along an X-ray path that passes through the center point of rotation to an X-ray imager;
the X-ray imager, which is positioned at a fixed imaging distance along the X-ray path from the X-ray source and is configured to generate an X-ray image from the X-rays;
a first combined filter-collimator assembly that includes a first collimator configured with a first opening and a first compensating filter, wherein the first collimator and the first compensating filter are fixed in position relative to each other and the first opening is formed by two blades that oppose each other and are fixed in position relative to each other; and
a positioning mechanism that is configured to position the first combined filter-collimator assembly in the X-ray path so that:
the first collimator is in the X-ray path at a first fixed distance along the X-ray path from the X-ray source and the first opening defines a width of a first imaging field; and
the first compensating filter is in the first imaging field at a second fixed distance along the X-ray path from the first collimator so that a photon flux of X-rays on the X-ray imager is more balanced than when the first compensating filter is not positioned in the first imaging field at the second fixed distance from the first collimator.
2. The imaging system of claim 1 , further comprising a second combined filter-collimator assembly that includes a second collimator configured with a second opening and wherein the positioning mechanism is further configured to:
position the first collimator and the first compensating filter out of the X-ray path; and
position the second collimator in the X-ray path at a third fixed distance from the X-ray source along the X-ray path so that the second opening defines a width of a second imaging field.
3. The imaging system of claim 2 , wherein the positioning mechanism is configured to position the first collimator and the first compensating filter out of the X-ray path and position the second collimator in the X-ray path at the third fixed distance with a single mechanical operation.
4. The imaging system of claim 3 , wherein the single mechanical operation is one of a lateral sliding motion of the first collimator, the first compensating filter, and the second collimator; a longitudinal sliding motion of the first collimator, the first compensating filter, and the second collimator; and a planar rotational motion of the first collimator, the first compensating filter, and the second collimator.
5. The imaging system of claim 3 , wherein the single mechanical operation includes a motion of the first collimator, the first compensating filter, and the second collimator in a direction perpendicular to the X-ray path.
6. The imaging system of claim 2 , wherein the second combined filter-collimator assembly further includes a second compensating filter that is fixed in position relative to the second collimator and the positioning mechanism is further configured to position the second compensating filter in the second imaging field at a fourth fixed distance from the second collimator along the X-ray path so that a photon flux of X-rays on the X-ray imager is more balanced than when the second compensating filter is not positioned in the second imaging field at the fourth fixed distance from the second collimator.
7. The imaging system of claim 2 , wherein the X-ray imager is disposed at the fixed imaging distance along the X-ray path from the X-ray source when the first collimator is positioned in the X-ray path at the first fixed distance from the X-ray source and when the second collimator is positioned in the X-ray path at the third fixed distance from the X-ray source.
8. The imaging system of claim 2 , wherein the X-ray imager is disposed at a fixed rotational distance along the X-ray path from the center point of rotation when the first collimator is positioned in the X-ray path at the first fixed distance from the X-ray source and when the second collimator is positioned in the X-ray path at the third fixed distance from the X-ray source.
9. The imaging system of claim 1 , wherein the X-ray imager is configured to:
generate images in a first imaging position, in which a first portion of the X-ray imager is disposed at the fixed imaging distance along the X-ray path from the X-ray source; and
generate images in a second imaging position, in which a second portion of the X-ray imager is disposed at the fixed imaging distance along the X-ray path from the X-ray source and the X-ray imager is displaced from the first imaging position in a direction perpendicular to the X-ray path.
10. The imaging system of claim 9 , wherein the first portion of the X-ray imager comprises a center point of an X-ray detection surface of the X-ray imager and the second portion comprises an edge portion of the X-ray imager.
11. The imaging system of claim 1 , wherein the positioning mechanism is configured to position the first compensating filter in the first imaging field at the fixed distance from the first collimator along the X-ray path and not at any other distance from the first collimator when the first compensating filter is in the first imaging field.
12. The imaging system of claim 1 , wherein the positioning mechanism is configured to position the first compensating filter in the first imaging field at a fixed distance from the X-ray source along the X-ray path and not at any other distance from the X-ray source when the first compensating filter is in the first imaging field.
13. The imaging system of claim 1 , further comprising a second collimator that is disposed between the X-ray source and the X-ray imager and includes a second opening that defines a length of the first imaging field.
14. The imaging system of claim 13 , wherein the second collimator includes movable blades that modify the second opening.
15. The imaging system of claim 14 , wherein the movable blades are configured to change a width of the second opening.
16. The imaging system of claim 14 , wherein the movable blades are configured to move independently from each other.
17. The imaging system of claim 13 , wherein the movable blades are configured to change a longitudinal location of the second opening.
18. The imaging system of claim 2 , wherein the positioning mechanism is configured to simultaneously position the first combined filter-collimator assembly out of the X-ray path and position the second collimator of the second combined filter-collimator assembly in the X-ray path at the second fixed distance.
19. A method of generating an X-ray image in a system that includes an X-ray source and an X-ray imager, wherein the X-ray source is configured to direct X-rays along an X-ray path that passes through a center point of rotation of the system to the X-ray imager and the X-ray imager is configured to generate an X-ray image from the X-rays, the method comprising:
positioning in the X-ray path a combined filter-collimator assembly that includes a first collimator configured with a first opening that is formed by two blades that oppose each other and are fixed in position relative to each other and a first compensating filter, so that the first collimator is at a first fixed distance along the X-ray path from the X-ray source and defines a width of a first imaging field and the first compensating filter is at a second fixed distance along the X-ray path from the first collimator so that a photon flux of X-rays on the X-ray imager is more balanced than when the first compensating filter is not positioned in the first imaging field at the second fixed distance from the first collimator;
while the imager is positioned at a fixed imaging distance along the X-ray path from the X-ray source, the first collimator is positioned in the X-ray path at the first fixed distance along the X-ray path from the X-ray source, and the first compensating filter is positioned in the X-ray path at the second fixed distance along the X-ray path from the first collimator, rotating the X-ray source and the X-ray imager about the center point of rotation; and
while rotating the X-ray source and the X-ray imager about the center point of rotation, receiving the X-rays with the X-ray imager.
20. The method of claim 19 , wherein positioning the combined filter-collimator assembly so that the first collimator is in the X-ray path at the first fixed distance and the first compensating filter is in the X-ray path at the second fixed distance comprises positioning a second collimator out of the X-ray path.
21. The method of claim 19 , wherein positioning the first collimator in the X-ray path, positioning the first compensating filter in the X-ray path, and positioning second collimator out of the X-ray path is performed via a single mechanical operation.
22. The method of claim 19 , wherein the first collimator and the first compensating filter are fixed in position relative to each other in the combined filter-collimator assembly.
23. The method of claim 1 , wherein the two blades oppose each other in a lateral direction that is perpendicular to the X-ray path and are positioned to limit an extent of exposure to the X-rays in the lateral direction to no more than the width of the X-ray imager.