Abstract Details
| Presented By: | Vyas, Urvi |
| Affiliated with: | University of Utah, Bioengineering |
| Authors: | A. Payne, U. Vyas, J. de Bever, N. Todd, R. Roemer, D. Christensen, D. Parker |
| From: | Separate institution names with commas |
Title
Abstract
Objective: Show through simulation and experimental results that prefocal heating increases significantly when electronically steering a focal spot using a phased array transducer. This increase in prefocal energy deposition causes increased HIFU treatment times when there are critical tissues surrounding the treatment region.
Methods: The thermal response of several HIFU treatment strategies are generated using both simulation and experimental techniques. The power deposition of an existing 256-element phased array transducer is simulated using the hybrid angular spectrum (HAS) method. The resulting thermal response is simulated using a finite difference approximation of the Pennes' bioheat transfer equation. All experiments were conducted in a Siemens 3T MRI with a 256 element phased array focused ultrasound system (Image Guided Therapy, Inc.). The HIFU treatments were executed using a set scanning path trajectories using the electronic steering capabilities only. The same treatments were then done using the mechanical motion of the transducer, with the focal spot electronically manipulated in the z-direction only. Temperatures throughout the treatment region were monitored using a segmented EPI MR sequence with a spatial and temporal resolution of 2x2x3mm and 3.9 seconds.
Results: Electronically steering the ultrasound beam increases the grating lobe magnitude generated by the phased array transducer. These lobes increase the heating in the near-field, causing an increase of thermal dose when compared to the same treatment that was executed through mechanical movement only. In a single plane, nine position HIFU treatment (electronic steering of +/- 7mm in the x-y plane, -10mm in the z-direction, 150W electrical power input) there is a 563% more voxels had a thermal dose accumulation of 30 CEM or more 1.8cm from the focal spot center. This increase of thermal buildup, particularly for a large tumor next to a critical normal tissue region, causes an increase of total treatment time.
Conclusions: Electronically manipulating a focal zone trajectory increases the energy deposited in the prefocal region, necessitating longer interpulse cooling times within a HIFU treatment, increasing the total treatment time. The optimization of scanning path trajectories with both mechanical and electronic movements could offer significant gains in the reduction of treatment times.