On the Evaluation of the Suitability of the Materials Used to 3D Print Holographic Acoustic Lenses to Correct Transcranial Focused Ultrasound Aberrations

Abstract

The correction of transcranial focused ultrasound aberrations is a relevant topic for enhancing various non-invasive medical treatments. Presently, the most widely accepted method to improve focusing is the emission through multi-element phased arrays; however, a new disruptive technology, based on 3D printed holographic acoustic lenses, has recently been proposed, overcoming the spatial limitations of phased arrays due to the submillimetric precision of the latest generation of 3D printers. This work aims to optimize this recent solution. Particularly, the preferred acoustic properties of the polymers used for printing the lenses are systematically analyzed, paying special attention to the effect of p-wave speed and its relationship to the achievable voxel size of 3D printers. Results from simulations and experiments clearly show that, given a particular voxel size, there are optimal ranges for lens thickness and p-wave speed, fairly independent of the emitted frequency, the transducer aperture, or the transducer-target distance.

Measurement of the ultrasound attenuation and dispersion in 3D-printed photopolymer materials from 1 to 3.5 MHz

“…This allows both for their behaviour to be accurately predicted and for their efficiency to be maximised for a particular application. 10 However, while a number of works have reported these parameters, 7,[11][12][13][14][15][16][17][18][19] these measurements have typically been made at a single frequency, reported only sound speed, and or been carried out on a single or limited range of materials. A more recent work carried out detailed measurements on the properties of 3D-printed thermoplastics.…”

Generating Bessel beams with broad depth-of-field by using phase-only acoustic holograms

“…Holographic lenses and fraxicons were 3D printed using stereo lithography (SLA) techniques with a Form 2 printer (Formlabs, USA), with a resolution of 50 μ m and 100 μ m in lateral and axial directions, respectively, and using a photosensitive resin (Standard Grey, Formlabs, USA). The acoustical properties of the material were obtained experimentally using a pulse-echo technique in a test cylinder, resulting in a measured sound speed of and a density of , and the absorption was set to α = 3.06 dB/cm at 1.112 MHz, matching the reported values of similar polymers 61,62 .…”

“…In this work, we present a simple method to generate zero-th and high-order Bessel beams of flat-intensity along their axis using phase-only acoustic holograms. These kind of lenses have recently been proposed to generate arbitrary acoustic fields and, simultaneously, to correct the strong aberrations during the propagation of transcranial ultrasound both with phase-and-amplitude encoding 59 or only with phase encoding 60,61 . Other applications of holographic phase-only lenses include particle manipulation applications 62 , multi-frequency focal generation 63 or photoacoustic generation of complex holographic fields 64 .…”

Ultrasound characterization of the viscoelastic properties of additively manufactured photopolymer materials

“…In particular, photopolymer-based AM has experienced a wide dissemination in engineering and science over the past years, and its versatility also has contributed to the field of acoustics (Naify et al, 2022). This concerns not only biomedical applications, such as the prototyping of tissue-mimicking phantoms for ultrasound imaging system assessment (Cloonan et al, 2014) or the conception of scaffolds intended for tissue engineering uses (Aliabouzar et al, 2018), but also the design of passive components for wave front shaping applications, including backing material, lenses and matching layers for piezoelectric transducers (Farinas et al, 2016), acoustic holograms to correct transcranial focused ultrasound aberrations (Ferri et al, 2019), and other metamaterials for wideband acoustic absorptions (Yang et al, 2020).…”