To provide a filter and a method for filtering blood inside a blood vessel effective for capturing a blood clot and preventing pulmonary embolism.

The filter 50 for capturing an embolus in a blood vessel in a patient's body has at least one helix 55 made of mesh material. The at least one helix has a plurality of turns 65 disposed spirally around an axis in the longitudinal direction. The mesh material has a plurality of pores 53 whose size is at least 120 μm (≥120 μm). The at least one helix also has a plurality of panels, which can move from the crushed state to the expanded state when disposed inside the blood vessel. In one embodiment, the mesh material is made of a self-expanding material, such as a nickel titanium alloy. In another embodiment, the filter has a double helix structure.

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