An efficient and accurate parallel hybrid acoustic signal correction method for transcranial ultrasound

A rapid element pressure field simulation method for transcranial phase correction in focused ultrasound therapy

Transcranial focused ultrasound ablation has emerged as a promising technique for treating neurological disorders. The clinical system exclusively employed the ray tracing method to compute phase aberrations induced by the human skull, taking into account computational time constraints. However, this method compromises slightly on accuracy compared to simulation-based methods. This study evaluates a fast simulation method that simulates the time-harmonic pressure field within the region of interest for effective phase correction. Experimental validation was carried out using a 512-element, 670 kHz hemispherical transducer for fourex vivoskulls. The ray tracing method achieved a restoration ratio of 64.81% ± 4.33% of acoustic intensity normalized to hydrophone measurements. In comparison, the rapid simulation method demonstrated improved results with a restoration ratio of 73.10% ± 7.46%, albeit slightly lower than the full-wave simulation which achieved a restoration ratio of 75.87% ± 5.40%. The rapid simulation methods exhibited computational times that were less than five minutes for parallel computation with 8 threads. The incident angle was calculated, and a maximum difference of 6.8 degrees was found when the fixed position of the skull was changed. Meanwhile, the restoration ratio of acoustic intensity was validated to be above 70% for different target positions away from the geometrical focus of the transducer. The favorable balance between time consumption and correction accuracy makes this method valuable for clinical treatment applications.

Binary acoustic metasurfaces for dynamic focusing of transcranial ultrasound

Transcranial focused ultrasound (tFUS) is a promising technique for non-invasive and spatially targeted neuromodulation and treatment of brain diseases. Acoustic lenses were designed to correct the skull-induced beam aberration, but these designs could only generate static focused ultrasound beams inside the brain. Here, we designed and 3D printed binary acoustic metasurfaces (BAMs) for skull aberration correction and dynamic ultrasound beam focusing. BAMs were designed by binarizing the phase distribution at the surface of the metasurfaces. The phase distribution was calculated based on time reversal to correct the skull-induced phase aberration. The binarization enabled the ultrasound beam to be dynamically steered along wave propagation direction by adjusting the operation frequency of the incident ultrasound wave. The designed BAMs were manufactured by 3D printing with two coding bits, a polylactic acid unit for bit "1" and a water unit for bit "0." BAMs for single- and multi-point focusing through the human skull were designed, 3D printed, and validated numerically and experimentally. The proposed BAMs with subwavelength scale in thickness are simple to design, easy to fabric, and capable of correcting skull aberration and achieving dynamic beam steering.

Airy Beam-enabled Binary Acoustic Metasurfaces for Underwater Ultrasound Beam Manipulation

Airy beams are peculiar beams that are non-diffracting, self-accelerating, and self-healing, and they have offered great opportunities for ultrasound beam manipulation. However, one critical barrier that limits the broad applications of Airy beams in ultrasound is the lack of simply built device to generate Airy beams in water. This work presents a family of Airy beam-enabled binary acoustic metasurfaces (AB-BAMs) to generate Airy beams for underwater ultrasound beam manipulation. AB-BAMs are designed and fabricated by 3D printing with two coding bits: a polylactic acid (which is the commonly used 3D printing material) unit acting as a bit "1" and a water unit acting as a bit "0". The distribution of the binary units on the metasurface is determined by the pattern of Airy beam. To showcase the wavefront engineering capability of the AB-BAMs, several examples of AB-BAMs are designed, 3D printed, and coupled with a planar single-element ultrasound transducer for experimental validation. We demonstrate the capability of AB-BAMs in flexibly tuning the focal region size and beam focusing in 3D space by changing the design of the AB-BAMs. The focal depth of AB-BAMs can be continuous and electronical tuned by adjusting the operating frequency of the planar transducer without replacing the AB-BAMs. The superimposing method is leveraged to enable the generation of complex acoustic fields, e.g., multi-foci and letter patterns (e.g., "W" and "U"). The more complex focal patterns are shown to be also continuously steerable by simply adjusting the operating frequency. Furthermore, the proposed 3D-printed AB-BAMs are simple to design, easy to fabricate, and low-cost to produce with the capabilities to achieve tunable focal size, flexible 3D beam focusing, arbitrary multipoint focusing, and continuous steerability, which creates unprecedented potential for ultrasound beam manipulation.

Suppressing Grating Lobes for Transcranial Focused Ultrasound System by Frequency-Modulated Excitation

Transcranial focused ultrasound is a novel noninvasive therapeutic modality for glioblastoma and other disorders of the brain. However, because the phase aberrations caused by the skull need to be corrected with computed tomography (CT) images, the transcranial transducer is tightly fixed on the patient's head to avoid any variation in the relative position, and the focus shifting relies mainly on the capacity for electronic beam steering. Due to the presence of grating lobes and the rapid degradation of the focus quality with increasing focus-shifting distance, transcranial focus-shifting sonication may damage healthy brain tissue unintentionally. To reduce the risks associated with transcranial focused ultrasound therapy, linear frequency-modulated (FM) excitation is proposed. The k-space corrected pseudospectral time domain (PSTD) and acoustic holography approach based on the Rayleigh integral are combined to calculate the distribution of the deposited acoustic power. The corresponding simulation was performed with axial/lateral focus shifting at different distances. The distributions of the deposited acoustic power show that linear FM excitation can effectively suppress undesired prefocal grating lobes without compromising focus quality.