machine manipulation of string 40 within the window catheter 78 can be advanced into position followed by string first region 44 being advanced within the catheter or shaft using window 80 referring now to fig6 another catheter 90 having a shaft 91 is illustrated having a distal region 92 and a proximal region 94 string 40 has first region 44 intermediate region 48 and second region 46 as in fig5 but with the first and second regions not forming a loop at the catheter proximal end a string payout spool 96 holds enough string to allow beads 42 to reach catheter distal region 92 a string takeup spool 98 has sufficient room to hold the string paid out from payout spool 96 in one embodiment spools 96 and 98 are biased by springs such that if string 40 is released it tends to a first position having beads 42 located proximally in another embodiment payout spool 96 is spring biased to return beads 42 to a proximal position while a takeup spool 98 is motor driven in yet another embodiment both spools are motor driven in still another embodiment takeup spool 98 is located outside the vault for easy manipulation by the treating physician motor driven string spools allow quick advancement and retraction of beads 42 through the catheter minimizing exposure to tissue along the catheter path in the embodiment shown string 40 extends through vault wall 40 through two apertures 100 while catheter shaft 91 remains external to vault walls 34 catheter embodiment 90 illustrates how catheter proximal region 94 can remain unshielded at all times while string first region 44 is alternately shielded and unshielded catheter 91 can be inserted within the human body while string 40 requiring no contact with the human body need not be sterilized.