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Transcranial focused ultrasound phase correction using the hybrid angular spectrum method | Scientific Reports

nature.com · 8,358 words · saved by 1 readers

The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52 ± 21% normalized target intensity (normalized to hydrophone), 76 ± 17% normalized peak intensity, and 0.72 ± 0.47 mm positioning error. The HAS method achieved 74 ± 9% normalized target intensity, 81 ± 9% normalized peak intensity, and 0.35 ± 0.09 mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use.

Introduction Transcranial focused ultrasound is a therapeutic modality that can be used to non-invasively induce thermal or biomechanical effects in the brain. Ultrasound is focused through the skull to achieve transient or permanent changes in brain tissue, and the durability of these changes depend on the parameters used during treatment. The most common applications include ablation1,2,3,4 as an alternative to open brain surgery, neuromodulation5,6,7 to probe the circuitry of the brain, and blood brain barrier opening8,9,10,11 to improve drug delivery into the brain. The intact skull…

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