A needle-tract assistant (100, 200) for establishing a needle tract of a predetermined length, comprising: a needle thruster (110, 210) including: a cradle (112, 212); a carriage (114, 214) within the cradle (112, 212), the carriage (114, 214) configured to move between a proximal-end portion and a distal-end portion of the cradle (112, 212); and a plunger (116, 216) coupled to the carriage (114, 214), the plunger (116, 216) configured to move the carriage (114, 214) within the cradle (112, 212) and allow a user to set the predetermined length of the needle tract before establishing the needle tract; and a needle-in-catheter assembly (130, 230) including: a hub (132, 232); a catheter tube (134, 234) extending from a distal-end portion of the hub (132, 232); and a needle (137, 237) disposed within the catheter tube (134, 234), wherein the needle-in-catheter assembly (130, 230) is removably loaded in the carriage (114, 214) of the needle thruster (110, 210), the plunger (116, 216) being so arranged that, when the needle-in-catheter assembly (130, 230) is loaded in the carriage (114, 214), thrusting the plunger (116, 216) toward a distal end of the needle thruster (110, 210) causes thrusting the needle (137, 237) and the catheter tube (134, 234) in the same direction. a needle thruster (110, 210) including: a cradle (112, 212); a carriage (114, 214) within the cradle (112, 212), the carriage (114, 214) configured to move between a proximal-end portion and a distal-end portion of the cradle (112, 212); and a plunger (116, 216) coupled to the carriage (114, 214), the plunger (116, 216) configured to move the carriage (114, 214) within the cradle (112, 212) and allow a user to set the predetermined length of the needle tract before establishing the needle tract; and a cradle (112, 212); a carriage (114, 214) within the cradle (112, 212), the carriage (114, 214) configured to move between a proximal-end portion and a distal-end portion of the cradle (112, 212); and a plunger (116, 216) coupled to the carriage (114, 214), the plunger (116, 216) configured to move the carriage (114, 214) within the cradle (112, 212) and allow a user to set the predetermined length of the needle tract before establishing the needle tract; and a needle-in-catheter assembly (130, 230) including: a hub (132, 232); a catheter tube (134, 234) extending from a distal-end portion of the hub (132, 232); and a needle (137, 237) disposed within the catheter tube (134, 234), wherein the needle-in-catheter assembly (130, 230) is removably loaded in the carriage (114, 214) of the needle thruster (110, 210), the plunger (116, 216) being so arranged that, when the needle-in-catheter assembly (130, 230) is loaded in the carriage (114, 214), thrusting the plunger (116, 216) toward a distal end of the needle thruster (110, 210) causes thrusting the needle (137, 237) and the catheter tube (134, 234) in the same direction. a hub (132, 232); a catheter tube (134, 234) extending from a distal-end portion of the hub (132, 232); and a needle (137, 237) disposed within the catheter tube (134, 234), wherein the needle-in-catheter assembly (130, 230) is removably loaded in the carriage (114, 214) of the needle thruster (110, 210), the plunger (116, 216) being so arranged that, when the needle-in-catheter assembly (130, 230) is loaded in the carriage (114, 214), thrusting the plunger (116, 216) toward a distal end of the needle thruster (110, 210) causes thrusting the needle (137, 237) and the catheter tube (134, 234) in the same direction.