## 4 Design of the Bendable Endoscope, Surgical Tool and Phantom Design  
### Design of Bendable Endoscope and Surgical Tool  
In contrast to previously developed devices [4; 5; 6; 7; 8; 9; 10; 11], we developed a bendable device for pituitary surgery which did not use motors, instead employing a passive, hand-held mechanism incorporating an end-effector designed to be bent through \(90^{\circ}\) by turning a lever. The bendable device pulls two wires through a pulley to cause bending and as shown Figure 17, a worm wheel was installed in the middle of the rotary shaft of the pulley, with a worm gear installed on the same axis as the lever.  
We had previously [4] conducted a workspace analysis for TSA surgery. In the TSA, preprocessing was performed to remove some tissue and bone, thereby opening a pathway to the pituitary gland, as shown in Figure 18. Based on 3-D patient model, we have conducted to analyze the bendable device motion, as shown in Figure 19.  
Figure 17: Mechanism of proposed passive, hand-held bendable device.  
Figure 18: Patient 3-D model, showing: (**a**) reconstruction of a patient model created using CT imagery; (**b**) blind spots which occur when using a rigid endoscope.  
The position of the lever was decided by considering the surgeon's posture when grasping the endoscope, as shown Figure 20. The reason for developing a hand-held type was that an endoscope needs to be frequently washed during surgery. To remove blood from the endoscope lens, the endoscope is taken out of the patient's body and wiped with alcohol cotton or gauze--this is more easily done with a hand-held instrument.  
The bending motion of the endoscope was achieved by turning the lever, as shown in Figure 21. A camera, with a 3.8 mm external diameter, capable of achieving high-definition (HD, 1080 \(\times\) 720 pixels) image quality, was installed at the distal end of the mechanism. To achieve bending, a spring backbone was employed and the radius of curvature, bending angle, radius of cylinder and the length of the continuum module were designed according to the task-dependent requirements of TSA surgery. In our design, we fixed cylinder length at 1.1 mm and after analyzing the anatomical structure of the pathway from the nostril to the pituitary gland, the radius of curvature and bending angle were settled as 9.5 mm and 90\({}^{\circ}\), respectively. Then, taking the geometry of the pathway and the diameter of the HD camera into account, the bendable device diameter was fixed at 5 mm. The length of the continuum mechanism was then obtained from the radius of curvature and bending angle.  
Figure 21: Proposed passive, hand-held type, bendable endoscope end-effector.  
Figure 19: Simulation used to determine bendable end-effector design parameters.  
Then, for these given values, the number of nodes and the length of the spring were determined by using the design parameter determining method [6]. Figure 22 shows the flexible device structure, which was created by connecting several hollow cylinders, a spring backbone and wires inserted into the cylinders. The design parameters for the bendable endoscope are presented in Table 2 and the process used to measure the bending angle and radius of curvature have been depicted in Figure 23.  
The tool used in transsphenoidal pituitary tumor removal surgery is called a \"curette.\" The proposed bendable surgical tool was built with a bending motion of 90\({}^{\circ}\), as shown in Figure 24 and employed a ring curette as its end-effector. An optical marker was attached to the bendable surgical tool to enable real-time surgical tool tracking by the navigation system.