Patent Number: 
Section: claims

1. A collimator having an aperture defined by the edges of four movable flexible shutters each shutter being movable independently of the other shutters. 2. The collimator of  claim 1  wherein the shutter is wound onto a drum. claim 1 3. The collimator of  claim 1  wherein one of the shutters is linked by at least one transmission member which is wound onto a drum. claim 1 4. The collimator of  claim 1  wherein one of the shutters is biased towards a facing shutter by resilient means. claim 1 5. The collimator of  claim 2  wherein one of the shutters is biased towards a facing shutter by resilient means. claim 2 6. The collimator of  claim 3  wherein one of the shutters is biased towards a facing shutter by resilient means. claim 3 7. The collimator of  claim 1  in which a stop member limits the displacement of a shutter moving away from a facing shutter. claim 1 8. The collimator of  claim 2  in which a stop member limits the displacement of a shutter moving away from a facing shutter. claim 2 9. The collimator of  claim 3  in which a stop member limits the displacement of a shutter moving away from a facing shutter. claim 3 10. The collimator of  claim 4  in which a stop member limits the displacement of a shutter moving away from a facing shutter. claim 4 11. The collimator of  claim 1  in which a shutter comprises of two layers one above the other. claim 1 12. The collimator of  claim 2  in which a shutter comprises of two layers one above the other. claim 2 13. The collimator of  claim 3  in which a shutter comprises of two layers one above the other. claim 3 14. The collimator of  claim 4  in which a shutter comprises of two layers one above the other. claim 4 15. The collimator of  claim 7  in which a shutter comprises of two layers one above the other. claim 7 16. The collimator of  claim 1  in which the edge of a shutter is provided with a metal part. claim 1 17. The collimator of  claim 2  in which the edge of a shutter is provided with a metal part. claim 2 18. The collimator of  claim 3  in which the edge of a shutter is provided with a metal part. claim 3 19. The collimator of  claim 4  in which the edge of a shutter is provided with a metal part. claim 4 20. The collimator of  claim 7  in which the edge of a shutter is provided with a metal part. claim 7 21. The collimator of  claim 11  in which the edge of a shutter is provided with a metal part. claim 11 22. An apparatus having a radiation source and a collimator according to  claim 1 . claim 1 23. A method for collimating radiation from a source comprising the steps of: providing a collimator having an aperture defined by the edges of four movable flexible shutters; and  moving each shutter independently of the other shutters to adjust collimation aperture. 24. The method of  claim 23  wherein the displacement step is preceded by a step in which a position of the collimator shutters is initialized, the initialization step comprising opening the shutters to a position where they encounter stop members. claim 23