Development of a Telesurgical Robotic System

In 1994, a group at the Imperial College in London investigated a robotic system to assist the urologist with intraoperative percutaneous renal access [7]. They employed a passive, encoded, 5 degrees of freedom (DOF) manipulator equipped with electromagnetic brakes mounted on the operating table. The access needle was manually positioned as prescribed by a computer that triangulated the calyx location from multiple C-arm images [8]. In vitro experiments evaluating system performance demonstrated a targeting accuracy of less than 1.5 mm. Nevertheless, no human trials have been performed with this system to date.

A similar system was developed at the Johns Hopkins University, which differed from the Imperial College system in that it employed an active robot (LARS) and biplanar fluoroscopy [9]. In this system, the surgeon selects the target calyx on two images, and the robot proceeds to insert the needle into the desired location. Although accuracy studies documented a margin of error of less than 1 mm, in live porcine percutaneous renal access experimentation the success rate at first attempt was only 50% [10]. Problems contributing to this included the mobility and deformability of the kidney, problems with needle deflection, and rib interference. This system, however, did prove the feasibility of performing fully automated needle placement in soft tissues. In addition, it represented another step in the evolution towards that goal in clinical practice.

The Hopkins URobotics group has developed a system for image-guided percutaneous access [11].This system was developed on the basis that a robot should be able to reduce tremor and position the needle exactly at the required location, thus increasing safety, speed, and accuracy, while reducing radiation exposure [12]. This new system was designed to mimic the standard percutaneous renal access technique, thus providing an easy-to-use, surgeon-friendly device. The system is based on an active and radiolucent needle driver, PAKY (percutaneous access to the kidney) [13]. PAKY utilizes an axial-loaded rotational-to-translational friction transmission principle to grasp, stabilize, and advance an 18-gauge access needle into the kidney percutaneously (Fig. 1).The trocar needle used for percutaneous procedures is secured by the needle driver along its barrel near the tip in order to minimize deflection or bowing of the unsupported length

Fig. 1. PAKY stand-alone (bottom) and PAKY-RCM (top) systems

of the needle during passage through various tissue planes [14]. The needle driver is constructed with radiolucent material and thus provides an unobstructed X-ray image of the anatomical target. An electrical motor integrated into the driver's fixture makes it inexpensive to produce and permits it to be employed as a sterile disposable part [15].

Another development allowed automation of the needle orientation procedure by adding a remote center of motion (RCM) module [16]. The RCM is a compact robot adapted for surgical use [17]. It consists of a fulcrum point that is located distal to the mechanism itself, typically at the skin entry point [18]. This allows the RCM to precisely orientate a surgical instrument/needle in space while maintaining the needle tip at the skin entry point (or another specified location).

In contrast to the earlier LARS robot, the RCM employs a chain transmission rather than a parallel linkage. This permits unrestricted rotations about the RCM point and uniform rigidity of the mechanism, and eliminates singular points. The RCM can accommodate different end-effectors via an adjustment to the location of the RCM point, thus allowing the rotation to be nonorthogonal. The robot is small (171 x 69 x 52mm box) and weighs only 1.6kg [16], facilitating its placement within the imaging device (Fig. 2).

The needle is initially placed into the PAKY so that its tip is located at the remote center of motion. To confirm the position, the PAKY is equipped with a visible laser diode whose ray intersects the needle at the RCM point. The robot permits two motorized DOF about the RCM point (R1 and R2 on the schematic diagram) and is supported by a 7 DOF passive arm, which may be locked at the desired position by depressing a lever. A custom rigid rail allows the system to be mounted to the operating table to provide the fixed reference frame required to maintain the needle trajectory under the insertion force. Thus, the combined

Fig. 2. PAKY-RCM in percutaneous renal access procedure at Johns Hopkins

Fig. 2. PAKY-RCM in percutaneous renal access procedure at Johns Hopkins

RCM-PAKY allows the needle tip to pivot about a fixed point on the skin. This allows the urologist to properly align the needle at the skin level along a selected trajectory path during fluoroscopic imaging, all by remote control, thus minimizing radiation exposure to his or her hands. The robot is therefore ideal for use in situations requiring a single entry point, such as PCNL.

An electrical impedance sensor, the "smart needle," was incorporated in the procedure needle for confirming percutaneous access through bioimpedance measurements [19].This has been evaluated in ex vivo porcine kidneys distended with water using an 18-gauge needle, where a sharp drop in resistivity was noted from 1.9 to 1.1 ohm-m when the needle entered the collecting system [20]. The smart needle can be combined with the PAKY-RCM to detect successful entry into the renal collecting system or other percutaneous procedures via a change of resistivity.

The most recent system, AcuBot [21], augments a cartesian positioning stage and an integrated passive arm for initial positioning (Fig. 3).

These systems, in their evolving stages, have had proven feasibility, safety, accuracy, and efficacy in limited clinical trials. A more extensive trial by Su et al. validated these results [22]. In this trial, 23 patients undergoing access by the robot were compared with a contemporaneous cohort of patients undergoing access by standard techniques.The robotic system was successful in gaining access 87% of the time, with the number of attempts and time to access comparable to those with the standard technique. Furthermore, the system has been used successfully to biopsy and ablate targets in kidneys and spine and to gain percutaneous renal access in international telesurgical cases [12,23] (see over). Although its use in humans has been limited to date, this system demonstrates great promise and has the potential to provide a mechanical platform for a completely automated percutaneous renal access.

Fig. 3. The AcuBot Robot

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