Feasibility of noninvasive transesophageal cardiac thermal ablation using an ultrasound phased array

Current, minimally invasive, treatments for cardiac arrhythmia use a transvenous radio-frequency (RF) catheter to ablate the malfunctioning cardiac muscle regions. The paper proposes a noninvasive transesophageal cardiac thermal ablation using focused ultrasound. A planar phased array (1 MHz, 60×10 mm², 0.525 mm element center-to-center distance, 2280 elements) was put in the esophagus. Using electronic beam steering, a matrix of 5×3×5 foci in the cardiac muscle was defined in three planes parallel to the transducer surface at short, medium and long (20, 40 and 60 mm) radial ranges and different steering angles. The transmitted ultrasound pressure distribution in a volume of 20×20×20 mm³ centered at each focus was calculated using a multilayer acoustic wave transmission model. The thermal lesions due to the acoustic energy absorption in cardiac muscle were simulated using the bioheat transfer equation. For short, medium and long (1-, 10- and 20-second) sonications, the acoustic powers needed to achieve 60°C and 70°C peak temperatures in the cardiac muscle were 89-725, 25-125, 20-86 W and 128-1040, 36-179, 28-123 W, respectively. The simulated tissue lesion (thermal dose >240 min at 43°C) lengths at these foci were 2-10, 5-12, 6-14 mm and 3-13, 7-15, 9-17 mm, respectively. The lesion widths were 2-8, 3-10, 4-11 mm and 3-11, 4-12, 5-13 mm, respectively. The simulations show that noninvasive transesophageal cardiac ablation with a planar phased ultrasound array is feasible.