Patent Number: 
Section: claims

1. An x-ray collimator comprising:a first subassembly with a first plurality of adjacent apertures with each of said adjacent apertures corresponding to a single selected x-ray focal spot of a plurality of x-ray focal spots reducing leakage of x-ray radiation through apertures other than said aperture corresponding to said single selected x-ray focal spot; anda second subassembly positioned between said first subassembly and an imaging object reducing amount of said x-ray radiation striking outside an x-ray detector, said second subassembly with a second plurality of apertures corresponding to said first plurality of apertures and said plurality of x-ray focal spots wherein entrances of said second plurality of apertures is smaller than exits of said second plurality of apertures and wherein size of said second plurality of apertures linearly increase through thickness of said second subassembly from smallest at said entrances of said second plurality of apertures to largest at said exits of said second plurality of apertures. 2. The x-ray collimator of claim 1 wherein said first subassembly is made from a material with an atomic number of at least 39. 3. The x-ray collimator of claim 1 wherein said first subassembly is made from a material with a value of Young's modulus of at least 200 GPa. 4. The x-ray collimator of claim 1 wherein said first subassembly is made from tungsten. 5. The x-ray collimator of claim 1 wherein said first subassembly is made from lead. 6. The x-ray collimator of claim 1 wherein said first subassembly further comprises material sheets with thickness of at least 0.5 millimeters. 7. The x-ray collimator of claim 1 wherein thickness of said first subassembly is at least 1 millimeter. 8. The x-ray collimator of claim 1 wherein said second subassembly further comprises material sheets with thickness of at least 0.5 millimeters. 9. The x-ray collimator of claim 8 wherein said second subassembly further comprises an air gap of at least 0.5 millimeters between said material sheets. 10. The x-ray collimator of claim 1 wherein said second subassembly is made from a material with an atomic number greater than 10 and less than 39. 11. The x-ray collimator of claim 1 wherein said second subassembly is made from a material with relative magnetic permeability of at least 10,000. 12. The x-ray collimator of claim 1 wherein said second subassembly is made from mu-metal. 13. The x-ray collimator of claim 1 wherein said second subassembly is made from brass. 14. The x-ray collimator of claim 1 wherein said second subassembly is made from steel. 15. The x-ray collimator of claim 1 wherein thickness of said second subassembly is at least 5 millimeters. 16. The x-ray collimator of claim 1 further comprising:a third subassembly positioned between said first subassembly and an x-ray source, said third subassembly with a third plurality of apertures and a thickness of at least 0.5 millimeters and made from a material with an element having an atomic number of at least 39. 17. The x-ray collimator of claim 1 further comprising:a fourth subassembly positioned between said second subassembly and said x-ray detector, said fourth subassembly with a fourth plurality of apertures and a thickness of at least 1 millimeter and made from a material with an element having an atomic number of at least 39. 18. The x-ray collimator of claim 17 wherein said fourth subassembly is separated from said second subassembly by an air gap of at least 0.5 millimeters. 19. A x-ray collimator of claim 17 wherein entrances of said fourth plurality of apertures is smaller than exits of said fourth plurality of apertures. 20. The x-ray collimator of claim 1 further comprising:a fourth subassembly positioned between said second subassembly and said x-ray detector, said fourth subassembly with a fourth plurality of apertures and a thickness of at least 1 millimeter and made from a material with an element having an atomic number greater than 10 and less than 39.