Ultrasound Axicon: Systematic Approach to Optimize Focusing Resolution through Human Skull Bone

Abstract

The use of axicon lenses is useful in many high-resolution-focused ultrasound applications, such as mapping, detection, and have recently been extended to ultrasonic brain therapies. However, in order to achieve high spatial resolution with an axicon lens, it is necessary to adjust the separation, called stand-off (δ), between a conventional transducer and the lens attached to it. Comprehensive ultrasound simulations, using the open-source k-Wave toolbox, were performed for an axicon lens attached to a piezo-disc type transducer with a radius of 14 mm, and a frequency of about 0.5 MHz, that is within the range of optimal frequencies for transcranial transmission. The materials properties were measured, and the lens geometry was modelled. Hydrophone measurements were performed through a human skull phantom. We obtained an initial easygoing design model for the lens angle and optimal stand-off using relatively simple formulas. The skull is not an obstacle for focusing of ultrasound with optimized axicon lenses that achieve an identical resolution to spherical transducers, but with the advantage that the focusing distance is shortened. An adequate stand-off improves the lateral resolution of the acoustic beam by approximately 50%. The approach proposed provides an effective way of designing polydimethylsiloxane (PDMS)-based axicon lenses equipped transducers.

Factors Associated with Energy Efficiency of Focused Ultrasound Through the Skull: A Study of 3D-Printed Skull Phantoms and Its Comparison with Clinical Experiences

“…Biocompatible MED 610 is used in medical and dental applications where precise visualization and patient contact are required, and is a suitable material for simulating detailed structures with 3D printers. A study using a skull phantom made of MED 610 has been reported, and the acoustic properties of this material do not deviate significantly from the actual skull (Acquaticci et al, 2019) (Robertson et al, 2017). Phantoms were made by spraying liquid material and hardening and laminating through ultraviolet.…”

Ultrasound for Material Characterization and Processing

“…Acquaticci et al [ 7 ] in the paper entitled “ Ultrasound Axicon: systematic approach to optimize focusing resolution through human skull bone ” propose a numerical approach for designing axicon lenses for many high-resolution applications, such as mapping or detection. The aim is to generate a focused ultrasound field by plane transducer using axicon lens, which can be suitable for focused ultrasound through human skull bone.…”