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Endoluminal high-intensity ultrasound offers spatially-precise thermal ablation of tissues adjacent to body lumens, but is constrained in treatment volume and penetration depth by the effective aperture of integrated transducers, which are limited in size to enable delivery through anatomical passages, endoscopic instrumentation, or laparoscopic ports. This study introduced and investigated three distinct endoluminal ultrasound applicator designs that can be delivered in a compact state then deployed or expanded at the target luminal site to increase the effective therapeutic aperture. The first design incorporated an array of planar transducers which could be unfolded at specific angles of convergence between the transducers. Two alternative designs consisted of fixed transducer sources surrounded by an expandable multicompartment balloon that contained acoustic reflector and dynamically-adjustable fluid lenses compartments. Parametric studies of acoustic output were performed across device design parameters via the rectangular radiator and secondary sources methods. Biothermal models were used to simulate resulting temperature distributions in three-dimensional heterogeneous tissue models. Simulations indicate that a deployable transducer array can increase volumetric coverage and penetration depth by ~80% and ~20%, respectively, while permitting more conformal thermal lesion shapes based on the degree of convergence between the transducers. The applicator designs incorporating reflector and fluid lenses demonstrated enhanced focal gain and penetration depth that increased with the diameter of the expanded reflector-lens balloon. Thermal simulations of assemblies with ~12 mm compact profiles and ~50 mm expanded balloon diameters demonstrated generation of localized thermal lesions at depths up to ~10 cm in liver tissue.
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