The fabrication and characterization of forward-looking active catheter actuated by titanium-nickel (Ti-Ni) shape memory alloy (SMA) springs are described. The catheter has been designed for wide-range observation of an affected area inside a blood vessel when the blood vessel is occluded. The developed active catheter consists of eight Ti-Ni SMA spring actuators for actuation of catheter tip, an ultrasonic transducer for forward-looking, a guide wire, a polyurethane tube for coating, and spiral wirings for realization of various flexure motions of catheter tip using Ti-Ni SMA actuators. The size of the catheter is 3.5？mm in diameter and 60？mm in length of the sum of transducer and actuator sections. Ti-Ni SMA springs were fabricated from a Ti-50.9at.%Ni sheet by electrochemical etching with a mixed solution of ethanol and lithium chloride. The catheter was assembled by hand under a stereomicroscope. The tip of the produced catheter was able to move in parallel toward at least eight directions by controlling an applied current to Ti-Ni SMA springs. We have confirmed that the active catheter was able to observe an object settled in the front. 1. Introduction In the medical field, the catheter is a promising tool and can be widely used for minimally invasive treatment. To date, many kinds of catheter have come into practical use to remedy inside the blood vessel. To accurately treat a diseased area inside a blood vessel using a catheter, doctors must examine the exact condition of the area. It is, however, difficult to do that because doctors have to control a catheter from the outside of patient body. At present, doctors need to manipulate the catheter with their sense and experience when a blood vessel is completely occluded. So, there is some risk for catheter remedy that doctors may harm a nondiseased area accidentally. To address this issue, several devices have been developed for observing the inside of blood vessel [1–6]. For instance, intravascular ultrasound (IVUS) having a number of transducers around the catheter tube is able to obtain the cross sectional image of a blood vessel [6]. However, the device is hard to be used if the blood vessel is blocked up by a thrombus. Furthermore, even if the thrombus in front of the catheter is observed, there is no much obtainable information. Thus, a novel technique for examining a thrombus in front of the catheter should be developed for more definitive treatment. The purpose of this study is to develop a forward-looking active catheter for observing a diseased area, such as thrombus, inside a blood
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