Design and development of adapters for electromagnetic trackers to perform navigated laparoscopic radiofrequency ablation
© Hildebrand et al; licensee BioMed Central Ltd. 2007
Received: 22 May 2007
Accepted: 31 October 2007
Published: 31 October 2007
Laparoscopic radiofrequency ablation (RFA) is an accepted approach to treat unresectable liver tumours distinguishing itself from other techniques by combining minimal invasiveness and the advantages of a surgical approach. The major task of laparoscopic RFA is the accurate needle placement to achieve complete tumour ablation. The use of an ultrasound-based, laparoscopic online-navigation system could increase the safety and accuracy of punctures. To connect such a system with the laparoscopic ultrasound (LUS) transducer or the RFA needle especially designed adapters are needed. In this article we present our first experiences and prototypes for different sterilizable adapters for an electromagnetic navigation system for laparoscopic RFA.
All adapters were constructed with the help of a standard 3D CAD software. The adapters were built from medical stainless steel alloys and polyetherketone (PEEK). Prototypes were built in aluminium and polyoxymethilen (POM). We have designed and developed several adapters for the connection of electromagnetical tracking systems with different RFA needles and a laparoscopic ultrasound transducers.
Based on earlier experiences of the initial version of the adapter, sterilisable adapters have been developed using biocompatible materials only. After short introduction, the adapters could be mounted to the laparoscopic ultrasound probe and the RFA needle under sterile conditions without any difficulties. Laboratory tests showed no disturbance of laparoscopic navigation system by the adapters. Anatomic landmarks in the liver could be safely reached. The adapters showed good feasibility, ergonomics, sterilizability and stability.
The development of usable adapters is the prerequisite for accurate tracking of a RFA needle for laparoscopic navigation purposes as well as 3D navigated ultrasound data acquisition. We designed, tested and used different adapters for the use of a laparoscopic navigation system for the improvement of laparoscopic RFA.
Laparoscopic Radiofrequency-ablation is a save and effective method for local tumour destruction and offers a combination of minimal invasive surgery and the advantages of laparotomy. However in contrary to the transcutaneously free-hand puncture application of the laparoscopic free-hand puncture is restricted because of the capnoperitoneum and the consecutive fixation of the needle on 2 different points. The use of a laparoscopic ultrasound probe with a canal for puncture can solve this problem and improve the precision of puncture. However, a stiff needle limits the necessary angulation that is needed to reach right-lateral and cranial liver metastases .
An ultrasound-based, laparoscopic online-navigation system, which allows guided out-of-plane needle placement, could significantly increase the accuracy of puncture. The system is aligned to help the surgeon to perform laparoscopic radiofrequency ablations using preoperative planning data and tracked laparoscopic ultrasound (LUS) as well as a tracked RFA needle . The tracking hardware for the prototype of the system consists of an electromagnetical tracking system. In order to connect the tracking system with the RFA needle and the LUS, different adapters have to be used. These adapters should provide a reproducible, sterilisable, easy to handle and save connection between the trackers and the RFA needle and the LUS respectively. Furthermore, the adapters need to be designed in a way that the electromagnetic tracking system is not influenced. In this article, we present our experiences and solutions with the development of electromagnetic adapters.
Adapter for laparoscopic ultrasound probe
Adapter for laparoscopic RFA needle
Newly developed adapters
All newly developed adapters were constructed using standard 3D CAD software (Solid Edge, UGS). The adapters were build from medical stainless steel alloys (1.4301 or 1.405) and Polyetherketone (PEEK). Prototypes were built in aluminium and polyoxymethilen (POM).
Furthermore, new electromagnetic tracking systems (NDI Canada, Type AURORA® and Ascension, Type 3D-Guidance®) with smaller electromagnetic trackers were used.
New adapters for laparoscopic ultrasound probe
New adapter for laparoscopic RFA needle
The first experiences with the development of adapters for electromagnetic trackers revealed the feasibility of the combination of an electromagnetic navigation system with a RFA needle and LUS [2–4, 6]. However, problems of sterilisation, size of the adapters and fixation of the adapters had to be solved. Using the experiences of the initial versions of the adapters, sterilizable adapters have been developed using biocompatible materials only. The new adapters could be sterilized repeatedly without any problems or surface variations. After a short introduction, a surgical nurse and a surgeon were able to mount the adapters to the LUS probe and the RFA needle under sterile conditions without any difficulties.
The adapters for the LUS can be used to acquire navigated three-dimensional ultrasound even from segments that are difficult to reach (right lateral and cranial segments), because the electromagnetic tracker was attached to the tip of the LUS probe, which allows free angulation of the ultrasound transducer without interference of the navigation system. Initial material testing for the ring adapter showed no detectable interferences of the navigation system . New laboratory tests could confirm that there is no influence of the ring adapter on the tracking system. However, the calibration of the ultrasound probe with the tracking system has to be performed after mounting of the ring adapter, which means under sterile conditions in the operating room. This procedure is time-consuming and is not effective for surgical procedures. The shoe-alike adapter prototype for the laparoscopic probe, which allows a reproducible positioning of the sensor, was designed to solve this problem. The shoe adapter, which consists only of POM has no influence on the tracking sensor, too. The most recently developed adapters for the LUS and laparoscopic RFA-needle have also been tested in organ models. They showed no disturbance of the tracking system as well as reproduceble calibration results due to their defined fixation and combined an ergonomic handling with a sufficient stability even after repeated sterilization.
The new developed adapter for the RFA probe showed neither influence on the NDI Aurora nor on the Ascension 3D-Guidance tracking system. Anatomic landmarks in the perfused porcine liver could be safely reached [6, 8]. Accurate measurements are still outstanding.
Overall, the newly developed adapter for the LUS and the RFA needle showed good feasibility, ergonomics, sterilizability and stability.
The laparoscopic approach for radiofrequency ablation, originally described by Siperstein et al. in 1997, offers a minimally invasive procedure in combination with the advantages of an open procedure . Above that laparoscopic RFA can be performed with the same exactness and effectiveness in comparison to the open approach in well-selected patients [10, 11]. Even carrying a higher access trauma laparoscopic RFA shows no significantly increased morbidity- or mortality-rates in comparison to the percutaneous probe application, which means a safe and mild treatment for the patient [10, 12]. Unfortunately today there are also limitations to the laparoscopic approach based on general contraindications for laparoscopic procedures and the limitations of laparoscopic needle application. Ultrasound-guided navigation tools for laparoscopic RFA offer a new technique for interventional liver therapy. The major advantage is the possibility of out-of-plane needle placement and the combination of flexibility of free-hand type procedures with the accuracy of a biopsy-transducer. This improves the safety and accuracy of punctures and leads to an improvement of quality of the intervention. However, in order to combine an electromagnetic navigation system with the LUS and the laparoscopic RFA needle, special designed adapters are needed to mount the trackers to the instruments. These adapters must be sterilizable and ergonomic, should provide reproducibility and need to be designed in a way that the navigation system is not disturbed.
Our evaluation shows the difficulties in designing adapters that combine all required qualifications. Ongoing development is needed to solve existing problems, guarantee steady progress and achieve acceptable results for clinical use. This study presents the feasibility and usability of special designed adapters for electromagnetic trackers to combine an electromagnetic navigation system with the LUS and laparoscopic RFA needle. This is the prerequisite for navigated laparoscopic RFA to improve the accuracy and results of laparoscopic liver interventions.
In the next steps we are planning to perform animal studies with the presented adapters. Furthermore, we are working on further miniaturization of the laparoscopic adapters to reduce the used trocar size. Besides that, adapters for hybrid tracking (optical and electromagnetical) of LUS and different RFA needles are already under evaluation, but can not be presented today for patent reasons.
The design and development of adapters for electromagnetic trackers is the prerequisite for an accurate tracking of the RFA needle for laparoscopic navigation purposes as well as 3D navigated ultrasound data acquisition. We designed, built, tested and used different adapters for the use of a laparoscopic navigation system for the improvement of laparoscopic RFA.
The authors would like to thank Prof. Dr. S. Klein and his staff from the Laboratory for Devices Engineering, University of Applied Sciences Lübeck and D. Theisen-Kunde and R. Schulz, from Institute for Biomedical Optics Lübeck, University of Lübeck for their support and good collaboration.
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