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Image-guided thermal interventions have been proposed for potential palliative and curative treatments of pancreatic
tumors. Catheter-based ultrasound devices offer the potential for temporal and 3D spatial control of the energy
deposition profile. The objective of this study was to apply theoretical and experimental techniques to investigate the
feasibility of endogastric, intraluminal and transgastric catheter-based ultrasound for MR guided thermal therapy of
pancreatic tumors. The transgastric approach involves insertion of a catheter-based ultrasound applicator (array of 1.5
mm OD x 10 mm transducers, 360° or sectored 180°, ~7 MHz frequency, 13-14G cooling catheter) directly into the
pancreas, either endoscopically or via image-guided percutaneous placement. An intraluminal applicator, of a more
flexible but similar construct, was considered for endoscopic insertion directly into the pancreatic or biliary duct. An
endoluminal approach was devised based on an ultrasound transducer assembly (tubular, planar, curvilinear) enclosed in
a cooling balloon which is endoscopically positioned within the stomach or duodenum, adjacent to pancreatic targets
from within the GI tract. A 3D acoustic bio-thermal model was implemented to calculate acoustic energy distributions
and used a FEM solver to determine the transient temperature and thermal dose profiles in tissue during heating. These
models were used to determine transducer parameters and delivery strategies and to study the feasibility of ablating 1-3
cm diameter tumors located 2-10 mm deep in the pancreas, while thermally sparing the stomach wall. Heterogeneous
acoustic and thermal properties were incorporated, including approximations for tumor desmoplasia and dynamic
changes during heating. A series of anatomic models based on imaging scans of representative patients were used to
investigate the three approaches. Proof of concept (POC) endogastric and transgastric applicators were fabricated and
experimentally evaluated in tissue mimicking phantoms, ex vivo tissue and in vivo canine model under multi-slice MR thermometry. RF micro-coils were evaluated to enable active catheter-tracking and prescription of thermometry slice
positions. Interstitial and intraluminal ultrasound applicators could be used to ablate (t43>240min) tumors measuring 2.3-3.4 cm in diameter when powered with 20-30 W/cm2 at 7 MHz for 5-10 min. Endoluminal applicators with planar and
curvilinear transducers operating at 3-4 MHz could be used to treat tumors up to 20-25 mm deep from the stomach wall
within 5 min. POC devices were fabricated and successfully integrated into the MRI environment with catheter tracking,
real-time thermometry and closed-loop feedback control.
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