An imaging system (10, 210) comprising: a first mask unit having a surface (16, 116) and a hollow cavity (14, 114, 214) surrounding a rotational axis; wherein the first mask unit has a first pattern (22, 112, 122, 212, 222) encoded on the surface (16, 116), the first pattern (22, 112, 122, 212, 222) defining a height along an axial direction (44, 244) parallel to the rotational axis; wherein the first pattern (22, 112, 122, 212, 222) includes a respective plurality of elements (24, 224) with at least one open element (26, 126, 226) in each of the axial direction (44, 244) and a circumferential direction (42, 242) and at least one blocking element (28, 228) in each of the axial direction (44, 244) and the circumferential direction (42, 242); a detector (30, 230, 231) configured to receive radiation data from at least one source such that one of the detector (30, 230, 231) and the at least one source is located inside the hollow cavity (14, 114, 214) and another of the detector (30, 230, 231) and the at least one source is located outside the hollow cavity (14, 114, 214); wherein the first mask (12, 212) unit is configured to move relative to the rotational axis in at least one of the axial direction (44, 244) and the circumferential direction (42, 242) until the first pattern (22, 112, 122, 212, 222) is at least partially recorded by the detector (30, 230, 231); a second mask unit concentric with and positioned surrounding the first mask (12, 212) unit, wherein the second mask unit defines a second surface, the second mask unit having a second pattern encoded on the second surface; wherein the second pattern includes the respective plurality of elements (24, 224) with another at least one open element (26, 126, 226) in each of the axial direction (44, 244) and the circumferential direction (42, 242) and another at least one blocking element (28, 128, 228) in each of the axial direction (44, 244) and the circumferential direction (42, 242); characterized in that the respective plurality of elements (24, 224) are arranged along a slope angle of positive alpha (α) in the first pattern (22, 112, 122, 212, 222) and along the slope angle of beta (β) in the second pattern, where β =α - (π/2); and wherein the first mask unit is configured to spin relative to the rotational axis at a first frequency and the second mask unit is configured to spin relative to the rotational axis at a second frequency. a first mask unit having a surface (16, 116) and a hollow cavity (14, 114, 214) surrounding a rotational axis; wherein the first mask unit has a first pattern (22, 112, 122, 212, 222) encoded on the surface (16, 116), the first pattern (22, 112, 122, 212, 222) defining a height along an axial direction (44, 244) parallel to the rotational axis; wherein the first pattern (22, 112, 122, 212, 222) includes a respective plurality of elements (24, 224) with at least one open element (26, 126, 226) in each of the axial direction (44, 244) and a circumferential direction (42, 242) and at least one blocking element (28, 228) in each of the axial direction (44, 244) and the circumferential direction (42, 242); a detector (30, 230, 231) configured to receive radiation data from at least one source such that one of the detector (30, 230, 231) and the at least one source is located inside the hollow cavity (14, 114, 214) and another of the detector (30, 230, 231) and the at least one source is located outside the hollow cavity (14, 114, 214); wherein the first mask (12, 212) unit is configured to move relative to the rotational axis in at least one of the axial direction (44, 244) and the circumferential direction (42, 242) until the first pattern (22, 112, 122, 212, 222) is at least partially recorded by the detector (30, 230, 231); a second mask unit concentric with and positioned surrounding the first mask (12, 212) unit, wherein the second mask unit defines a second surface, the second mask unit having a second pattern encoded on the second surface; wherein the second pattern includes the respective plurality of elements (24, 224) with another at least one open element (26, 126, 226) in each of the axial direction (44, 244) and the circumferential direction (42, 242) and another at least one blocking element (28, 128, 228) in each of the axial direction (44, 244) and the circumferential direction (42, 242); characterized in that the respective plurality of elements (24, 224) are arranged along a slope angle of positive alpha (α) in the first pattern (22, 112, 122, 212, 222) and along the slope angle of beta (β) in the second pattern, where β =α - (π/2); and wherein the first mask unit is configured to spin relative to the rotational axis at a first frequency and the second mask unit is configured to spin relative to the rotational axis at a second frequency.