Embolic filters having multiple layers and controlled pore size

1. A device for filtering emboli from blood flowing through a lumen defined by the walls of a vessel in a patient's body, comprising:

a filter element being expandable from a collapsed configuration when the filter element is restrained to an expanded configuration when the filter element is unrestrained, wherein when the filter element is in the expanded configuration, the average pore size is from 30 to 300 microns and the standard deviation of the pore size is less than 20 percent of the average pore size, and wherein the filter element comprises two or more filtering layers, each filtering layer comprising pores, each filtering layer being adjacent to at least one other filtering layer, and at least one of the filtering layers being made of a self-expanding material.

2. A device of claim 1 , wherein each filtering layer is made of a self-expanding material.

3. A device of claim 1 , wherein when the filter element is in the expanded configuration, the average pore size is from 30 to 150 microns.

4. A device of claim 1 , wherein when the filter element is in the expanded configuration, the average pore size is from 100 to 140 microns.

5. A device of claim 1 , wherein when the filter element is in the expanded configuration, the average pore size is from 40 to 70 microns.

6. A device of claim 1 , wherein when the filter element is in the expanded configuration, the standard deviation of the pore size is less than 15 percent of the average pore size.

7. A device of claim 1 , wherein when the filter element is in the expanded configuration, the standard deviation of the pore size is less than 10 percent of the average pore size.

8. A device of claim 1 , wherein when the filter element is in the expanded configuration, the standard deviation of the pore size is less than 5 percent of the average pore size.

9. A device of claim 1 , wherein when the filter element is in the expanded configuration, the standard deviation of the pore size is less than 2 percent of the average pore size.

10. A device of claim 1 , wherein when the filter element is in the expanded configuration, the filter element has a percent open area greater than 50 percent.

11. A device of claim 1 , wherein when the filter element is in the expanded configuration, the filter element has a percent open area greater than 60 percent.

12. A device of claim 1 , wherein when the filter element is in the expanded configuration, the filter element has a percent open area greater than 70 percent.

13. A device of claim 1 , wherein when the filter element is in the expanded configuration, the filter element has a percent open area greater than 80 percent.

14. A device of claim 1 , wherein the self-expanding material has a tensile strength greater than 70,000 psi.

15. A device of claim 1 , wherein the the self-expanding material has a tensile strength greater than 100,000 psi.

16. A device of claim 1 , wherein the self-expanding material has a tensile strength greater than 200,000 psi.

17. A device of claim 1 , wherein the self-expanding material is made of metal.

18. A device of claim 1 , wherein the self-expanding material is made of nitinol.

19. A device of claim 1 , further comprising an elongate support member and wherein the filter element is carried on a portion of the elongate support member.

20. A device of claim 1 , wherein the filter element has proximal and distal portions and a central portion, the filter element having a shape in the expanded configuration which defines a cavity having a proximal facing opening.

21. A device of claim 20 , wherein the self-expanding material comprises wires braided to form diamond-shaped pores.

22. A device of claim 1 , wherein the self-expanding material comprises a single mesh rolled back on itself to form two filtering layers.

23. A device of claim 22 , wherein the filter element has proximal and distal portions and a central portion, the filter element having a shape in the expanded configuration which defines a cavity having a proximal facing opening.

24. A device of claim 23 , wherein the filter element comprises a drawstring tether at the proximal facing opening of the filter element.

25. A device of claim 23 , wherein the self-expanding material comprises wires braided to form diamond-shaped pores.

26. A device of claim 1 , wherein the filter element comprises two separate filtering layers.

27. A device of claim 26 , wherein the filter element has proximal and distal portions and a central portion, the filter element having a shape in the expanded configuration which defines a cavity having a proximal facing opening.

28. A device of claim 26 , wherein the self-expanding material comprises wires braided to form diamond-shaped pores.

29. A device of claim 26 , wherein the two separate filtering layers have different average pore sizes.

30. A device of claim 26 , wherein the two separate filtering layers are not attached to each other.

31. A device of claim 26 , wherein the two separate filtering layers are attached to each other.

32. A device of claim 31 , wherein the two separate filtering layers are attached to each other by a fixed element.

33. A device of claim 31 , wherein the two separate filtering layers are attached to each other by a sliding element.

34. A device of claim 31 , wherein the two separate filtering layers are attached to each other by a tether.

35. A device of claim 26 , wherein a first filtering layer comprises wires braided to from diamond-shaped pores, and the second filtering layer comprises a coiled wire.

36. A device for filtering emboli from blood flowing through a lumen defined by the walls of a vessel in a patient's body, comprising:

a filter element having pores, said filter element being expandable from a collapsed configuration when the filter element is restrained to an expanded configuration when the filter element is unrestrained, wherein the filter element comprises a single mesh rolled back on itself to form two filtering layers, wherein the filter element has proximal and distal portions and a central portion, the filter element having a shape in the expanded configuration which defines a cavity having a proximal facing opening, and wherein the filter element comprises a drawstring tether at the proximal facing opening of the filter element.

37. A device of claim 36 , wherein the filter element comprises wires braided to form diamond-shaped pores.

38. A device of claim 36 , wherein the filter element is self-expanding.

39. A device for filtering emboli from blood flowing through a lumen defined by the walls of a vessel in a patient's body, comprising:

a filter element having pores, said filter element being expandable from a collapsed configuration when the filter element is restrained to an expanded configuration when the filter element is unrestrained, wherein the filter element comprises a single mesh rolled back on itself to form two filtering layers, a first one of the filtering layers forming an inner filter portion and a second one of the filtering layers forming an outer filter portion, wherein the inner filter portion is wrapped with a third filtering layer, and wherein the third filtering layer is not contiguous with the outer filter portion.

40. A device of claim 39 , wherein the third filtering layer is made of a material selected from the group consisting of polymer filaments, braided wire, or a polymer sheet having pores.

41. A device of claim 39 , wherein the filtering element is self-expanding.

42. A device of claim 39 , wherein the filter element has proximal and distal portions and a central portion, the filter element having a shape in the expanded configuration which defines a cavity having a proximal facing opening.

43. A device of claim 42 , wherein the filter element comprises a drawstring tether at the proximal facing opening of the filter element.