Radiology: Mini-GPS fusion technique enables challenging biopsies

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Cervical biopsy facilitated by electromagnetic needle navigation and multimodality image fusion in a 71-year-old man with history of B-cell chronic lymphocytic leukemia with FDG-avid focus. Multiplanar display of intraprocedural CT scans fused to preacquired PET scans. Tracked biopsy of abnormal FDG avidity (arrow), facilitated by electromagnetic device tracking. Source: Radiology.

Researchers successfully fused real-time ultrasound to coregistered CT and FDG PET studies and combined the datasets with electromagnetic device tracking to perform percutaneous and intraoperative biopsies and radiofrequency ablation, according to a study published in the September issue of Radiology.

Although FDG PET/CT has demonstrated its utility in oncologic staging, it has not yet been deployed to guide interventions. Accurately diagnosing FDG abnormalities is critical as they may represent nonmalignant infections or inflammatory processes, rather than a malignancy.

However, interventional radiologists require anatomic images to biopsy or ablate FDG-detected abnormalities, explained Aradhana M. Venkatesan, MD, of the center for interventional oncology, radiology and imaging sciences at the National Institutes of Health in Bethesda, Md., and colleagues. In some technically challenging cases, PET datasets do not provide sufficient anatomic visualization for interventional procedures.

Venkatesan and colleagues sought to assess the feasibility of combining advanced integration visualization software image fusion and electromagnetic tracking of percutaneous devices during interventional procedures.

The prospective study cohort included 25 patients who underwent 33 percutaneous and three intraoperative biopsies of 36 FDG-avid targets between November 2007 and August 2010. Targets were not well visualized via conventional imaging or demonstrated heterogeneous FDG uptake.

Imaging datasets included PET/CT studies, a navigation CT performed with the patient in the interventional position and ultrasound images registered to the CT and PET/CT images.

During the procedure, images were transferred to an image fusion software platform for multimodality coregistration and display. Prior CT and PET/CT studies were imported, and the intraprocedural CT and ultrasound images were aligned and tracked via registration to skin fiducials or skin patches.

The real-time ultrasound images were successfully fused to the coregistered CT and PET/CT studies in all cases.

Mean registration time of PET to the navigation CT was 2.4 minutes. Electromagnetic tracking to CT registration ranged from two to five minutes. Mean PET/CT registration error was 1.14 mm; mean fiducial registration error was 1.73 mm. Mean procedure time for percutaneous biopsies and radiofrequency ablation was 1.62 hours.

“Overall mean procedural room time (1.62 hours) was reasonable for complex biopsies that might not otherwise be possible in the absence of FDG PET guidance,” wrote Venkatesan.

Procedure results were diagnostic in 31 of the 36 biopsies, and physicians initiated treatment in 11 of the 14 patients diagnosed with malignancies.

The researchers noted several limitations to the study, including: short clinical and imaging follow-up (mean 12.7 months) and inherent alignment uncertainties between PET and CT due to respiration and patient motion.

Although this study was not randomized, Venkatesan noted that a randomized multicenter trial comparing electromagnetic device tracking and image fusion with conventional guidance is planned. Future studies should address specific clinical benefits in terms of time, radiation dose and accuracy, the authors said.

Venkatesan and colleagues emphasized the feasibility and utility of the approach, concluding, “With an increasing trend toward minimally invasive body interventions, the role of advanced, integrated navigation platforms is expected to gain importance, particularly for the inconspicuous or technically challenging biopsy target.”