Electromagnetic Tracking for Thermal Ablation and Biopsy Guidance: Clinical Evaluation of Spatial Accuracy

Abstract

PURPOSE-To evaluate the spatial accuracy of electromagnetic needle tracking and demonstrate the feasibility of ultrasonography (US)-computed tomography (CT) fusion during CT-and USguided biopsy and radiofrequency ablation procedures. MATERIALS AND METHODS-The authors performed a 20-patient clinical trial to investigate electromagnetic needle tracking during interventional procedures. The study was approved by the institutional investigational review board, and written informed consent was obtained from all patients. Needles were positioned by using CT and US guidance. A commercial electromagnetic tracking device was used in combination with prototype internally tracked needles and custom software to record needle positions relative to previously obtained CT scans. Position tracking data were acquired to evaluate the tracking error, defined as the difference between tracked needle position and reference standard needle position on verification CT scans. Registration between tracking space and image space was obtained by using reference markers attached to the skin ("fiducials"), and different registration methods were compared. The US transducer was tracked to demonstrate the potential use of real-time US-CT fusion for imaging guidance. RESULTS-One patient was excluded from analysis because he was unable to follow breathing instructions during the acquisition of CT scans. Nineteen of the 20 patients were evaluable, demonstrating a basic tracking error of 5.8 mm ± 2.6, which improved to 3.5 mm ± 1.9 with use of nonrigid registrations that used previous internal needle positions as additional fiducials. Fusion of tracked US with CT was successful. Patient motion and distortion of the tracking system by the CT table and gantry were identified as sources of error. CONCLUSIONS-The demonstrated spatial tracking accuracy is sufficient to display clinically relevant preprocedural imaging information during needle-based procedures. Virtual needles displayed within preprocedural images may be helpful for clandestine targets such as arterial phase enhancing liver lesions or during thermal ablations when obscuring gas is released. Electromagnetic tracking may help improve imaging guidance for interventional procedures and warrants further investigation, especially for procedures in which the outcomes are dependent on accuracy. Minimally invasive imaging-guided procedures such as radiofrequency ablation (RFA) have received increasing attention in recent years (1-15).

Real-time FDG PET Guidance during Biopsies and Radiofrequency Ablation Using Multimodality Fusion with Electromagnetic Navigation

“…Basic tracking error was calculated for 14 procedures and was defi ned as the distance between the "virtual" needle position computed by using the tracking data and the "reference standard" actual needle position extracted from the verifi cation CT scan ( 15 ). Basic tracking error was calculated for procedures in which a CT scan was obtained to confi rm the needle position for biopsy and tracking data were recorded just prior to the acquisition of the confi rmation CT scan.…”

“…Results of earlier clinical trials by members of our group suggest good spatial accuracy and feasibility of electromagnetic needle tracking ( 15 ). Particular benefi t has been noted when virtual needles are displayed on preprocedural images that include transiently apparent targets, such as arterial phase enhancing liver lesions, or during thermal ablations when obscuring gas is released during therapy ( 12 ).…”

“…Many image types may be coregistered, with multiplanar multimodality images providing real-time spatial information on device location in patient anatomy during a biopsy or immediately prior to radiofrequency (RF) ablation ( 12,13 ). This is analogous to a miniaturized global positioning system for medical instruments ( 14,15 ). Limited data exist concerning feasibility of overlaying a PET scan on an intraprocedural CT scan for biopsy and ablation.…”

A navigation system for percutaneous needle interventions based on PET/CT images: Design, workflow and error analysis of soft tissue and bone punctures

“…In the area of needle guidance applications, many navigation systems have been developed to solve specific clinical problems, such as liver puncture [7,8] and vertebroplasty procedures [9], as well as for general biopsy procedures [10,11]. While some groups [9][10][11] rely on well established rigid approaches for registering the patient to the image and are therefore limited to targeting static anatomical regions, other groups have investigated nonrigid methods to gate breathing [7] or to model deformation [8] in order to target organs that can deform considerably during the procedure. A recent review by Cleary and Peters [12] shows that even though non-rigid methods are making progress for interventions in the thorax and abdomen, most current work is still based on the rigid approach.…”

Comparison of Two Electromagnetic Navigation Systems For CT-Guided Punctures: A Phantom Study

“…Appelbaum et al used a similar electromagnetic deviation device for accuracy analysis in a phantom study, showing deviations of 2.6 ± 1.1 mm up to 4 ± 1 mm in 117 punctures using planning data sets with 1 mm slice thickness [24]. Krücker et al described the use of an electromagnetic navigation device for planning of sonographically guided radiofrequency ablation of liver lesions in 20 patients [25]. The mean deviation between the registered position of the needle and the actual position is given as 5.8 ± 2.6 mm.…”