Patent Number: 
Section: claims

1. A collimator system comprising:a collimator comprising:at least one aperture configured to allow radiation to pass through;at least one outer annulus configured to reduce radiation passing through at an amount depending on the material and the thickness of said at least one outer annulus; andtwo carriages associated with said collimator, said carriages movable by at least one motor thereby moving said collimator in a 2-dimensional plane. 2. The collimator system of claim 1, wherein said collimator further comprises at least one inner annulus between said at least one aperture and said at least one outer annulus, said at least one inner annulus having changing thickness. 3. The collimator system of claim 2, wherein said thickness changes as a function of the distance from said at least one aperture, starting at a low thickness on the side of each one of said at least one apertures and ending at the thickness of said at least one outer annulus on the side of said at least one outer annulus. 4. The collimator system of claim 1, wherein said carriages movable by at least one motor along a track. 5. The collimator system of claim 4, wherein said tracks are perpendicular to each other. 6. The collimator system of claim 4, wherein said tracks are non-parallel. 7. The collimator system of claim 1, wherein said at least one motor is configured to rotate between an x-ray source's pulses and stop during said x-ray source's pulses. 8. A method of controlling a Region of Interest (ROI) in an image of an x-ray irradiated area, comprising:providing:a collimator comprising:at least one aperture configured to allow radiation to pass through;at least one outer annulus configured to reduce radiation passing through at an amount depending on the material and the thickness of said at least one outer annulus; andtwo carriages associated with said collimator, said carriages movable by at least one motor thereby moving said collimator in a 2-dimensional plane;determining a location on said image; andmoving said two carriages, thereby moving said collimator to place at least one of said at least one aperture according to said determined location. 9. The method of claim 8, further comprising:providing:a plurality of radiation attenuating plates, each one of said plates having an aperture;means for selecting a radiation attenuating plate; anda plate changing mechanism comprising:a body comprising on one face thereof said plurality of radiation attenuating plates;wherein said at least one aperture of said collimator comprises one aperture configured to receive any of said plurality of radiation attenuating plates; andmoving said body to bring a selected one of said plurality of radiation attenuating plates to said aperture of said collimator. 10. The method of claim 8, wherein said collimator further comprises at least one inner annulus, each said at least one inner annulus between a respective one of said at least one aperture and a respective one of said at least one outer annulus, each said at least one inner annulus having changing thickness. 11. The method of claim 10, wherein each said at least one inner annulus thickness changes as a function of the distance from an inner annulus respective aperture, starting at a low thickness on the side of said respective aperture and ending at the thickness of said inner annulus respective outer annulus on the side of said respective outer annulus. 12. The method of claim 8, wherein said two carriages are movable along a track. 13. The method of claim 8, wherein said two carriages are movable along two non-parallel tracks. 14. The method of claim 8, wherein said at least one motor is configured to rotate between an x-ray source's pulses and stop during said x-ray source's pulses. 15. The method of claim 9, wherein said body is highly transparent to radiation. 16. The method of claim 9, wherein said body has one of: a circular shape and an anchor like shape. 17. The method of claim 9, wherein said radiation attenuating plates are made of copper.