Ultrasound-based tumor movement compensation during navigated laparoscopic liver interventions.

BACKGROUND: Image-guided navigation aims to provide better orientation and accuracy in laparoscopic interventions. However, the ability of the navigation system to reflect anatomical changes and maintain high accuracy during the procedure is crucial. This is particularly challenging in soft organs such as the liver, where surgical manipulation causes significant tumor movements. We propose a fast approach to obtain an accurate estimation of the tumor position throughout the procedure. METHODS: Initially, a three-dimensional (3D) ultrasound image is reconstructed and the tumor is segmented. During surgery, the position of the tumor is updated based on newly acquired tracked ultrasound images. The initial segmentation of the tumor is used to automatically detect the tumor and update its position in the navigation system. Two experiments were conducted. First, a controlled phantom motion using a robot was performed to validate the tracking accuracy. Second, a needle navigation scenario based on pseudotumors injected into ex vivo porcine liver was studied. RESULT: In the robot-based evaluation, the approach estimated the target location with an accuracy of 0.4 ± 0.3 mm. The mean navigation error in the needle experiment was 1.2 ± 0.6 mm, and the algorithm compensated for tumor shifts up to 38 mm in an average time of 1 s. CONCLUSION: We demonstrated a navigation approach based on tracked laparoscopic ultrasound (LUS), and focused on the neighborhood of the tumor. Our experimental results indicate that this approach can be used to quickly and accurately compensate for tumor movements caused by surgical manipulation during laparoscopic interventions. The proposed approach has the advantage of being based on the routinely used LUS; however, it upgrades its functionality to estimate the tumor position in 3D. Hence, the approach is repeatable throughout surgery, and enables high navigation accuracy to be maintained.

Laparoscopic navigated liver resection: technical aspects and clinical practice in benign liver tumors.

Laparoscopic liver resection has been performed mostly in centers with an extended expertise in both hepatobiliary and laparoscopic surgery and only in highly selected patients. In order to overcome the obstacles of this technique through improved intraoperative visualization we developed a laparoscopic navigation system (LapAssistent) to register pre-operatively reconstructed three-dimensional CT or MRI scans within the intra-operative field. After experimental development of the navigation system, we commenced with the clinical use of navigation-assisted laparoscopic liver surgery in January 2010. In this paper we report the technical aspects of the navigation system and the clinical use in one patient with a large benign adenoma. Preoperative planning data were calculated by Fraunhofer MeVis Bremen, Germany. After calibration of the system including camera, laparoscopic instruments, and the intraoperative ultrasound scanner we registered the surface of the liver. Applying the navigated ultrasound the preoperatively planned resection plane was then overlain with the patient's liver. The laparoscopic navigation system could be used under sterile conditions and it was possible to register and visualize the preoperatively planned resection plane. These first results now have to be validated and certified in a larger patient collective. A nationwide prospective multicenter study (ProNavic I) has been conducted and launched.

Correlating chest surface motion to motion of the liver using epsilon-SVR--a porcine study.

In robotic radiosurgery, the compensation of motion of internal organs is vital. This is currently done in two phases: an external surrogate signal (usually active optical markers placed on the patient's chest) is recorded and subsequently correlated to an internal motion signal obtained using stereoscopic X-ray imaging. This internal signal is sampled very infrequently to minimise the patient's exposure to radiation. We have investigated the correlation of the external signal to the motion of the liver in a porcine study using epsilon-support vector regression. IR LEDs were placed on the swines' chest. Gold fiducials were placed in the swines' livers and were recorded using a two-plane X-ray system. The results show that a very good correlation model can be built using epsilon-SVR, in this test clearly outperforming traditional polynomial models by at least 45 and as much as 74%. Using multiple markers simultaneously can increase the new model's accuracy.

Design and development of adapters for electromagnetic trackers to perform navigated laparoscopic radiofrequency ablation.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Evaluation of an online navigation system for laparoscopic interventions in a perfused ex vivo artificial tumor model of the liver.

BACKGROUND: Laparoscopic radiofrequency ablation (RFA) is a safe and effective method for tumor destruction in patients with unresectable liver tumors. However, accurate probe placement using laparoscopic ultrasound guidance is required to achieve complete tumor ablation. After evaluation of an ultrasound navigation system for transcutaneous and open RFA, we now intend to transfer this technique to laparoscopic liver surgery. This study aimed to evaluate an electromagnetic navigation system for laparoscopic interventions using a perfusable ex vivo artificial tumor model. MATERIALS AND METHODS: First a special adapter was developed to attach the ultrasound and electromagnetic tracking-based navigation system to a laparoscopic ultrasound probe. The laparoscopic online navigation system was studied in a laparoscopic artificial tumor model using perfused porcine livers. Artificial tumors were created by injection of a mixture of 3% agarose, 3% cellulose, and 7% glycerol, creating hyperechoic lesions in ultrasound. RESULTS: This study showed that laparoscopic ultrasound-guided navigation is technically feasible. Even in cases of angulation of the ultrasound probe no disturbances of the navigation system could be detected. Artificial tumors were clearly visible on laparoscopic ultrasound and not felt during placement of the RFA probe. Anatomic landmarks and simulated 'tumors' in the liver could be reached safely. DISCUSSION: Laparoscopic RFA requires advanced laparoscopic ultrasound skills for accurate placement of the RFA probe. The use of an ultrasound-based, laparoscopic online navigation system offers the possibility of out-of-plane needle placement and could increase the safety and accuracy of punctures. The perfused artificial tumor model presented a realistic model for the evaluation of this new technique.