Multi-Operational Selective Computer-Assisted Targeting of hepatocellular carcinoma-Evaluation of a novel approach for navigated tumor ablation.

OBJECTIVE: To facilitate precise local ablation of hepatocellular carcinoma (HCC) in a setting of combined ablation and transarterial chemoembolization (TACE), we evaluated accuracy and efficiency of a novel technique for navigated positioning of ablation probes using intrahepatic tumor referencing and electromagnetic (EM) guidance, in a porcine model. METHODS: An angiographic wire with integrated EM reference sensor at its tip was inserted via a transarterial femoral access and positioned in the vicinity of artificial liver tumors. The resulting offset distance between the tumor center and the intrahepatic endovascular EM reference was calculated. Subsequently, EM tracked ablation probes were inserted percutaneously and navigated toward the tumor center, relying on continuous EM guidance via the intrahepatic reference. Targeting accuracy was assessed as the Euclidean distance between the tip of the ablation probe and the tumor center (Target Positioning Error, TPE). Procedural efficiency was assessed as time efforts for tumor referencing and tumor targeting. RESULTS: In 6 animals, 124 targeting measurements were performed with an offset distance < 30 mm (clinically most feasible position), resulting in a mean TPE of 2.9 ± 1.6 mm. No significant correlation between the TPE and different intrahepatic offset distances (range 21 to 61 mm, n = 365) was shown as long as the EM reference was placed within the liver. However, the mean TPE increased when placing the EM reference externally on the animal skin (p < 0.01). TPE was similar when targeting under continuous ventilation or in apnea (p = 0.50). Mean time for tumor referencing and navigated targeting was 6.5 ± 3.8 minutes and 14 ± 8 seconds, respectively. CONCLUSION: The proposed technique allows precise and efficient navigated positioning of ablation probes into liver tumors in the animal model. We introduce a simple approach suitable for combined ablation and TACE of HCC in a single treatment session.

Design and implementation of an electromagnetic ultrasound-based navigation technique for laparoscopic ablation of liver tumors.

BACKGROUND: Efficient laparoscopic ablation of liver tumors relies on precise tumor visualization and accurate positioning of ablation probes. This study evaluates positional accuracy and procedural efficiency of a dynamic navigation technique based on electromagnetic-tracked laparoscopic ultrasound (ELUS) for laparoscopic ablation of liver tumors. METHODS: The proposed navigation approach combines intraoperative 2D ELUS-based planning for navigated positioning of ablation probes, with immediate 3D ELUS-based validation of intrahepatic probe position. The environmental influence on electromagnetic-tracking stability was evaluated in the operation room. Accuracy of navigated ablation probe positioning assessed as the target-positioning error (TPE), and procedural efficiency defined as time efforts for target definition/navigated targeting and number of probe repositionings, were evaluated in a laparoscopic model and compared with conventional laparoscopic ultrasound (LUS) guidance. RESULTS: The operation-room environment showed interferences < 1 mm on the EM-tracking system. A total of 60 targeting attempts were conducted by three surgeons, with ten targeting attempts using ELUS and ten using conventional LUS each. Median TPE and time for targeting using ELUS and LUS were 4.2 mm (IQR 2.9-5.3 mm) versus 6 mm (IQR 4.7-7.5 mm), and 39 s (IQR 24-47 s) versus 76 s (IQR 47-121 s), respectively (p < 0.01 each). With ELUS, median time for target definition was 48.5 s, with 0 ablation probe repositionings compared to 17 when using LUS. The navigation technique was rated with a mean score of 85.5 on a Standard Usability Scale. CONCLUSIONS: The proposed ELUS-based navigation approach allows for accurate and efficient targeting of liver tumors in a laparoscopic model. Focusing on a dynamic and tumor-targeted navigation technique relying on intraoperative imaging, this avoids potential inaccuracies due to organ deformation and yields a user-friendly technique for efficient laparoscopic ablation of liver tumors.

A concept for electromagnetic navigated targeting of liver tumors using an angiographic approach.

BACKGROUND: The benefits of using navigation technology for percutaneous local ablation of selected hepatocellular carcinoma (HCC) have been shown. Due to additional efforts in the procedural workflow, barriers to introducing navigation systems on a broad clinical level remain high. In this work, initial steps toward a novel concept for simple and precise targeting of HCC are evaluated. MATERIAL AND METHODS: The proposed technique is based on an angiographic approach using an intrahepatic electromagnetic (EM) reference, for consecutive percutaneous navigated positioning of ablation probes. We evaluated the environmental influence of the angiography suite on EM tracking accuracy, the measurement of a 3 D offset from two 2 D fluoroscopy images, and the accuracy and efficiency of the proposed approach in a porcine liver model. RESULTS: The C-arm had a major influence on EM tracking accuracy, with an error up to 3.8 mm. The methodology applied for measurement of a 3 D offset from 2 D fluoroscopy images was confirmed to be feasible with a mean error of 0.76 mm. In the porcine liver model experiment, the overall target positioning error (TPE) was 2.0 mm and time for navigated targeting was 17.9 seconds, when using a tracked ablation probe. CONCLUSIONS: The initial methodology of the proposed technique was confirmed to be feasible, introducing a novel concept for simple and precise navigated targeting of HCC.

Feasibility of stereotactic MRI-based image guidance for the treatment of vascular malformations: a phantom study.

PURPOSE: Treatment of vascular malformations requires the placement of a needle within vessels which may be as small as 1 mm, with the current state of the art relying exclusively on two-dimensional fluoroscopy images for guidance. We hypothesize that the combination of stereotactic image guidance with existing targeting methods will result in faster and more reproducible needle placements, as well as reduced radiationexposure, when compared to standard methods based on fluoroscopy alone. METHODS: The proposed navigation approach was evaluated in a phantom experiment designed to allow direct comparison with the conventional method. An anatomical phantom of the left forearm was constructed, including an independent control mechanism to indicate the attainment of the target position. Three interventionalists (one inexperienced, two of them frequently practice the conventional fluoroscopic technique) performed 45 targeting attempts utilizing the combined and 45 targeting attempts utilizing the standard approaches. RESULTS: In all 45 attempts, the users were able to reach the target when utilizing the combined approach. In two cases, targeting was stopped after 15 min without reaching the target when utilizing only the C-arm. The inexperienced user was faster when utilizing the combined approach and applied significantly less radiation than when utilizing the conventional approach. Conversely, both experienced users were faster when using the conventional approach, in one case significantly so, with no significant difference in radiation dose when compared to the combined approach. CONCLUSIONS: This work presents an initial evaluation of a combined navigation fluoroscopy targeting technique in a phantom study. The results suggest that, especially for inexperienced interventionalists, navigation may help to reduce the time and the radiation dose. Future work will focus on the improvement and clinical evaluation of the proposed method.

A clinically applicable laser-based image-guided system for laparoscopic liver procedures.

PURPOSE: Laser range scanners (LRS) allow performing a surface scan without physical contact with the organ, yielding higher registration accuracy for image-guided surgery (IGS) systems. However, the use of LRS-based registration in laparoscopic liver surgery is still limited because current solutions are composed of expensive and bulky equipment which can hardly be integrated in a surgical scenario. METHODS: In this work, we present a novel LRS-based IGS system for laparoscopic liver procedures. A triangulation process is formulated to compute the 3D coordinates of laser points by using the existing IGS system tracking devices. This allows the use of a compact and cost-effective LRS and therefore facilitates the integration into the laparoscopic setup. The 3D laser points are then reconstructed into a surface to register to the preoperative liver model using a multi-level registration process. RESULTS: Experimental results show that the proposed system provides submillimeter scanning precision and accuracy comparable to those reported in the literature. Further quantitative analysis shows that the proposed system is able to achieve a patient-to-image registration accuracy, described as target registration error, of [Formula: see text]. CONCLUSIONS: We believe that the presented approach will lead to a faster integration of LRS-based registration techniques in the surgical environment. Further studies will focus on optimizing scanning time and on the respiratory motion compensation.