Experimental Assessment of Skull Aberration and Transmission Loss at 270 kHz for Focused Ultrasound Stimulation of the Primary Visual Cortex

This data was collected in order to assess acoustic field aberrations and transmission loss induced by human skulls in the context of focused ultrasound stimulation of the primary visual cortex (V1) region of the brain.

A 2 element spherically focusing annular array ultrasound transducer (H115, driven at 270 kHz, Sonic Concepts) was used to generate an acoustic field. Measurements were performed with a 0.2 mm PVDF needle hydrophone (Precision Acoustics) with right angle connector to reduce its length so it could be accommodated within the skull cavity. The transducer was driven under quasi continuous wave conditions at low drive level to produce a linear field. The transducer was held in a fixed position, the skull was positioned to obtain the correct focal alignment and the hydrophone was held in a 3D printed mount with manual alignment in the axial direction and automated scanning in the lateral directions.

Measurements were performed inside 3 human skulls which had previously had the superior section of the parietal and frontal bones removed. Measurements were made with the transducer positioned at two locations for each skull corresponding to the focal region intersecting with the positions of the left and right V1 regions of the brain, with a 1 cm separation between source and skull. For each position, the hydrophone was aligned with the focus inside the skull, then a planar scan was performed covering the largest possible area while avoiding collision of the hydrophone with the skull bone. The skull was then removed and a 2^nd scan was performed in water as a reference, the axial position was determined from time of flight in free field during these reference water scans.

The study consists of 6 datasets, each of which contains a planar scan made within the skull cavity, and a reference planar scan in water after the skull was removed, preserving the coordinates.

File 1: skull 2120, left V1

File 2: skull 2120, right V1

File 3: skull 2150, left V1

File 4: skull 2150, right V1

File 5: skull 2125, left V1

File 6: skull 2125, right V1