A medical instrument includes a flexible catheter and a catheter accessory device. The catheter has a distal end insertable within a body lumen of a patient. The device is slidably engagable with the catheter. One of the catheter and the device includes magnetic material, and the other of the catheter and the device includes electrically-energizable windings. The catheter and the device are adapted to operate as a linear motor wherein controllably electrically energizing the windings while immobilizing one of the catheter and the device slidingly moves the other of the catheter and the device. A method for using the medical instrument, wherein the medical instrument also includes a controller operatively connected to the windings, includes inserting the distal end within the body lumen, immobilizing one of the catheter and the device, and activating the controller to advance the other of the catheter and the device within the body lumen.
