An adjustable three-layer skull phantom with realistic ultrasound transmission properties

Transcranial ultrasound research has garnered significant attention due to its non-invasive nature, absence of ionizing radiation, and portability, making it advantageous for both imaging and therapy. A critical aspect of advancing transcranial research lies in understanding the ultrasound transmission performance of the human skull. However, inherent variations in skull shape, physical parameters, and age-related changes pose challenges for comparative studies. To address these challenges, we designed a three-layer structured skull (TSS) phantom that closely mimics the structural and ultrasound transmission properties of real skulls. The TSS substrate is composed of epoxy resin/Al₂O₃powders, with purple perilla seeds incorporated into the middle layer to replicate the porous structure found in real skulls. Both simulation and experimental results demonstrate that TSS phantom achieves acoustic transmission properties closely approximating those of human skull bone within the 1.25-1.75 MHz frequency range. Experimentally, the TSS phantom containing 27 wt% purple perilla seeds shows a sound pressure transmission coefficient ranging from 5.0% to 6.6%, closely matching the skull's transmission characteristics (4.2%-9.8%). This performance represents a significant improvement over conventional phantom materials, outperforming epoxy resin plate phantoms (42.6%-48.4%) and polyetheretherketone phantoms (64.5%-75.2%). Notably, the transmission performance of TSS can be adjusted by varying the mass fraction of purple perilla seeds, making it adaptable to diverse research needs. The TSS phantom holds significant potential as a valuable tool in transcranial research, offering a reliable and accessible alternative for comprehensive investigations into ultrasound applications in brain therapy.