Generation of Induced Wavefront Focalization in the Human Temporal Bone Using a Standard Focused Ultrasound Single-Element Transducer

Purpose Focused ultrasound (FUS) has been studied extensively in the medical field for tissue ablation, neuromodulation, and medication administration. The present proposal investigates the influence of frequency and skull geometry on acoustic transmission through the human temporal fossa by using single-element immersion ultrasound transducers to verify the acoustic map pressure generated by the deformation of acoustic waves. Methods A needle-type hydrophone with a 1-mm tip attached to a computed guided 3D axis system was used to characterize the aberrations induced by a human skull in a water tank. A planar ultrasound transducer with a central frequency of 0.4 MHz and a focused transducer with a central frequency of 1.7 MHz, both targeting the beam through the human temporal bone, was used to create the acoustic pressure profile maps. Results The results show that by focusing acoustic waves in the temporal bone, a planar transducer can be focalized by passing through the skull, creating a maximum focal pressure of 236.1 kPa, and a focused ultrasound transducer with a higher central frequency than those reported in the literature for human neurostimulation protocols can generate an acoustic map with a maximum focal pressure of 24.1 kPa. Conclusion These experiments have demonstrated that the skull behaves as an acoustic lens, concentrating and attenuating the acoustic beam as it passes through. This study also proposes that a single-element focused ultrasound transducer with a center frequency of 1.7 MHz may be useful for non-invasive transcranial ultrasound applications. This finding could improve the effectiveness of transcranial ultrasound applications.