the outer catheter distal opening and the inner catheter distal opening to the inner catheter lumen, a second flow path of the fluid from the outer catheter lumen through the outer catheter distal opening and at least a first sidewall opening of the plurality of sidewall openings to the inner catheter lumen, and a third flow path of the fluid from the outer catheter lumen directly through at least a second sidewall opening of the plurality of sidewall openings to the inner catheter lumen. 

[0027] Clause 22: In some examples of the system of clause 21, the system further comprises an aspiration pump fluidically coupled to the outer catheter and the inner catheter, the aspiration pump configured to: deliver an aspiration fluid to the outer catheter lumen; generate a positive pressure on the outer catheter lumen; and generate a negative pressure on the inner catheter lumen. 

[0028] Clause 23: In some examples of the system of clause 22, when the inner catheter distal opening is at least partially blocked, the aspiration catheter system is configured to deliver the fluid from the outer catheter lumen to the inner catheter lumen through at least one of the second flow path or the third flow path. 

[0029] Clause 24: In some examples, an aspiration catheter system comprises: an outer catheter defining an outer catheter lumen and an outer catheter distal opening; an inner catheter configured to be positioned within the outer catheter lumen, the inner catheter defining an inner catheter lumen, an inner catheter distal opening, and at least one sidewall opening proximal to the inner catheter distal opening; and an alignment element configured to indicate a predetermined position of the inner catheter relative to the outer catheter when the inner catheter is received within the outer catheter distal opening, wherein when the inner catheter is at the predetermined position, the at least one sidewall opening is positioned distal to the outer catheter distal opening. 

[0030] Clause 25: In some examples, a method comprises introducing at least a portion of an outer catheter and an inner catheter of an aspiration catheter system into vasculature of a patient, the aspiration catheter system comprising: the outer catheter defining an outer catheter lumen and an outer catheter distal opening; the inner catheter defining an inner catheter lumen, an inner catheter distal opening, and at least one sidewall opening proximal to the inner catheter distal opening; and an alignment element configured to indicate a predetermined position of the inner catheter relative to the outer catheter when the inner catheter is received within the outer catheter distal opening. In some of these examples, the method further comprises positioning the inner catheter within the outer catheter lumen at the predetermined position such that the at least one 

