catheter 14 is received within outer catheter inner lumen 16. When inner catheter 14 is at the predetermined position Pi, at least one sidewall opening 24A of the plurality of sidewall openings 24 remains positioned within outer catheter lumen 16 and at least one other sidewall opening 24B of the plurality of sidewall openings 24 is positioned distal to outer catheter distal opening 18. This predetermined position Pi may correspond to a configuration that allows both suction and continuous flow through inner catheter lumen 20. While only one predetermined position is shown, in some examples, aspiration catheter system 10 may include a variety of predetermined positions corresponding to various configurations of sidewall openings positioned within outer catheter distal opening 18 and distal to outer catheter distal opening 18. In these examples, alignment element 26 may include a plurality of alignment elements, each alignment element corresponding to a respective predetermined position of inner catheter 14 relative to outer catheter 12. 

[0077] In some examples, the predetermined position Pi may correspond to various flow paths of fluid from outer catheter lumen 16 to inner catheter lumen 20. For example, when inner catheter 14 is at the predetermined position Pi, aspiration catheter system 10 may define (1) a first flow path of fluid from outer catheter lumen 16 through outer catheter distal opening 18 and inner catheter distal opening 22 to inner catheter lumen 20; (2) a second flow path of fluid from outer catheter lumen 16 through outer catheter distal opening 18 and sidewall opening 24B to inner catheter lumen 20; and (3) a third flow path of fluid from outer catheter lumen 16 directly through sidewall opening 24A to inner catheter lumen 20. When inner catheter distal opening 22 may be at least partially blocked, aspiration catheter system 10 may be configured to deliver the fluid from outer catheter lumen 16 to inner catheter lumen 20 through at least one of the second flow path or the third flow path. 

[0078] Alignment element 26 can be positioned on inner catheter 14, on outer catheter 12, or on both inner catheter 14 and on outer catheter 12. As discussed in further detail below’,alignment element 26 may be a visible element, e.g., a visible marker on outer catheter 12 and/or inner catheter 14. In these examples, alignment element 26 may not protrude from a surface of the respective catheter 12, 14, and may be flush (e.g., printed on or embedded in) with the outer surface of the respective catheter 12, 14. In other examples, however, alignment element 26 may include a structure that protrudes from one or both catheters 12, 14, e.g., and engages the other catheter in order to indicate the predetermined position of inner catheter 14 relative to outer catheter 12. As shown in 

