Precision targeting of liver lesions using a novel electromagnetic navigation device in physiologic phantom and swine

Radiofrequency ablation of primary and metastatic liver tumors is becoming a potential alternative to surgical resection. We propose a novel system that uses real-time electromagnetic position sensing of the needle tip to help with precision guidance into a liver tumor. The purpose of this study was to evaluate this technology in phantom and animal models. Using an electromagnetic navigation device, instrumented 18 g needles were advanced into radioopaque tumor targets in a respiratory liver phantom. The phantom featured a moving liver target that simulated cranio-caudal liver motion due to respiration. Skin-to-target path planning and real-time needle guidance were provided by a custom-designed software interface based on pre-operative 1 mm CT data slices. Needle probes were advanced using only the electromagnetic navigation device and software display. No conventional real-time imaging was used to assist in advancing the needle to the target. Two experienced operators (interventional radiologists) and two inexperienced ones (residents) used the system. The same protocol was then also used in two anesthetized 45 kg Yorkshire swine where radioopaque agar nodules were injected into the liver to serve as targets. A total of 76 tumor targeting attempts were performed in the liver phantom, and 32 attempts were done in the swine. The average time for path planning was 30 s in the phantom, and 63 s in the swine. The median time for the actual needle puncture to reach the desired target was 33 s in the phantom, and 42 s in the swine. The average registration error between the CT coordinate system and electromagnetic coordinate system was 1.4 mm (SD 0.3 mm) in the phantom, and 1.9 mm (SD 0.4 mm) in the swine. The median distance from the final needle tip position to the center of the tumor was 6.4 mm (SD 3.3 mm, n=76) in the phantom, and 8.3 mm (SD 3.7 mm, n=32) in the swine. There was no statistical difference in the planning time, procedure time, or accuracy of needle placement between experienced and inexperienced operators. The novel electromagnetic navigation system allows probe delivery into hepatic tumors of a physiologic phantom and live anesthetized swine. The system allows less experienced operators to perform equally well as experienced radiologists in terms of procedure time and accuracy of needle probe delivery.