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Numerous studies have demonstrated the efficacy of interstitial ablative approaches for the treatment of renal and hepatic
tumors. Despite these promising results, current systems remain highly dependent on operator skill, and cannot treat
many tumors because there is little control of the size and shape of the zone of necrosis, and no control over ablator
trajectory within tissue once insertion has taken place. Additionally, tissue deformation and target motion make it
extremely difficult to accurately place the ablator device into the target. Irregularly shaped target volumes typically
require multiple insertions and several sequential thermal ablation procedures. This study demonstrated feasibility of
spatially tracked image-guided conformal ultrasound (US) ablation for percutaneous directional ablation of diseased
tissue. Tissue was prepared by suturing the liver within a pig belly and 1mm BBs placed to serve as needle targets. The
image guided system used integrated electromagnetic tracking and cone-beam CT (CBCT) with conformable needlebased
high-intensity US ablation in the interventional suite. Tomographic images from cone beam CT were transferred
electronically to the image-guided tracking system (IGSTK). Paired-point registration was used to register the target
specimen to CT images and enable navigation. Path planning is done by selecting the target BB on the GUI of the realtime
tracking system and determining skin entry location until an optimal path is selected. Power was applied to create
the desired ablation extent within 7-10 minutes at a thermal dose (>300eqm43). The system was successfully used to
place the US ablator in planned target locations within ex-vivo kidney and liver through percutaneous access. Targeting
accuracy was 3-4 mm. Sectioned specimens demonstrated uniform ablation within the planned target zone. Subsequent
experiments were conducted for multiple ablator positions based upon treatment planning simulations. Ablation zones in
liver were 73cc, 84cc, and 140cc for 3, 4, and 5 placements, respectively. These experiments demonstrate the feasibility
of combining real-time spatially tracked image guidance with directional interstitial ultrasound ablation. Interstitial
ultrasound ablation delivered on multiple needles permit the size and shape of the ablation zone to be "sculpted" by
modifying the angle and intensity of the active US elements in the array. This paper summarizes the design and
development of the first system incorporating thermal treatment planning and integration of a novel interstitial acoustic
ablation device with integrated 3D electromagnetic tracking and guidance strategy.
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