Ultrasound Beam Research Articles

Electrowetting-driven liquid lens for ultrasound: Enabling controllable focal length and flexible beam steering

Focused ultrasound is an increasingly popular non-invasive treatment modality. Still, its fixed focal point requires an array ultrasound transducer or scanning system to cover different therapeutic scenarios. To address this limitation, we developed an electrically-controlled liquid lens that enables dynamic beam focusing and steering of the incident plane ultrasound beam. The lens was carefully optimized for low-energy attenuation and low-voltage driving. We evaluated the performance of the lens using a homemade 5.5-MHz planar transducer with a 7.5-mm aperture. Our results demonstrate that the planar ultrasound beam can be adjusted to a focused beam with a focal length from 27 mm to 32 mm within 1 s by increasing the electric input (0–60 V) to the lens. Additionally, the beam angle of the ultrasound is tunable from −5 to 5° by adjusting the charge distribution on the lens. Our design enables real-time, fast-response, on-demand changing of focal length and beam angle for a single-element planar transducer. Our study presents a promising technology for altering the ultrasound beam of a planar single-element transducer for different ultrasound applications. The development of this electrically-controlled liquid lens has the potential to enhance the efficacy of focused ultrasound treatment and improve patient outcomes.

Noninvasive measurement of local temperature using ultrasound-switchable fluorescence.

Measuring the local background temperature in diseased and inflamed tissues is highly desirable, especially in a non-invasive way. In this work, ultrasound-switchable fluorescence (USF) technique was utilized to estimate the local background temperature for the first time by analyzing the temperature dependence of fluorescence emission from USF contrast agents induced by a focused ultrasound (FU) beam. First, temperature-sensitive USF agents with distinct temperature switching-on thresholds were synthesized, and their thermal switching characteristics were quantified using an independent spectrometer system. Second, the USF contrast agent suspension was injected into a microtube that was embedded into a phantom and the dynamic USF signal was acquired using a camera-based USF system. The differential profile of the measured dynamic USF signal was computed and compared with the thermal switching characteristics. This allowed for the calculation of the local background temperature of the sample in the FU focal volume based on the estimation of heating speed. An infrared (IR) camera was used to acquire the surface temperature of the sample and further compare it with the USF system. The results showed that the difference between the temperatures acquired from the USF thermometry and the IR thermography was 0.64 ± 0.43 °C when operating at the physiological temperature range from 35.27 to 39.31 °C. These results indicated the potential use of the USF system for measuring the local temperature in diseased tissues non-invasively. The designed USF-based thermometry shows a broad application prospect in high spatial resolution temperature imaging with a tunable measurement range in deep tissue.

Acoustoelectric Time-Reversal for Ultrasound Phase-Aberration Correction.

Acoustoelectric imaging (AEI) is a technique that combines ultrasound (US) with radio frequency recording to detect and map local current source densities. This study demonstrates a new method called acoustoelectric time reversal (AETR), which uses AEI of a small current source to correct for phase aberrations through a skull or other US-aberrating layers with applications to brain imaging and therapy. Simulations conducted at three different US frequencies (0.5, 1.5, and 2.5 MHz) were performed through media layered with different sound speeds and geometries to induce aberrations of the US beam. Time delays of the acoustoelectric (AE) signal from a monopole within the medium were calculated for each element to enable corrections using AETR. Uncorrected aberrated beam profiles were compared with those after applying AETR corrections, which demonstrated a strong recovery (29%-100%) of lateral resolution and increases in focal pressure up to 283%. To further demonstrate the practical feasibility of AETR, we further conducted bench-top experiments using a 2.5 MHz linear US array to perform AETR through 3-D-printed aberrating objects. These experiments restored lost lateral restoration up to 100% for the different aberrators and increased focal pressure up to 230% after applying AETR corrections. Cumulatively, these results highlight AETR as a powerful tool for correcting focal aberrations in the presence of a local current source with applications to AEI, US imaging, neuromodulation, and therapy.

The Use of Focused Ultrasound Beams with Shocks to Suppress Diffusion Effects in Volumetric Thermal Ablation of Biological Tissue

The Use of Focused Ultrasound Beams with Shocks to Suppress Diffusion Effects in Volumetric Thermal Ablation of Biological Tissue

Ultrasound Speckle Decorrelation-Based Blood Flow Measurements.

Ultrasound imaging is the preferred noninvasive technique to measure blood flow to diagnose cardiovascular disease such as heart failure, carotid stenosis, and renal failure. Conventional ultrasound techniques such as Doppler ultrasound, ultrasound imaging velocimetry, vector Doppler and transverse oscillation beamforming have been used for blood flow velocity profile measurement. However, these techniques were limited to measuring blood flow velocities within the 2-D lateral (across the ultrasound beam) plane of a vessel, and the blood flow velocity profile was derived by assuming that blood vessels have a circular cross-section with axis symmetry. This assumption is incorrect because most vessels have complex geometries, such as tortuosity and branches, and an asymmetric flow profile in the presence of vascular plaque. Consequently, ultrasound speckle decorrelation has been proposed to measure blood flow from transverse views of blood vessels wherein the ultrasound beam is perpendicular to the vessel axis. In this review, we present a summary of recent progress in ultrasound speckle decorrelation-based blood flow measurement techniques.

The Use of Focused Ultrasound Beams with Shocks to Suppress Diffusion Effects in Volumetric Thermal Ablation of Biological Tissue

The article presents the results of numerical simulation of an experiment on irradiatingex vivobovine liver sample by the therapeutic array of the MR-HIFU clinical system (Sonalleve V1 3.0T, Profound Medical Corp., Canada). Continuous quasi-linear and pulsed shock-wave exposures with the same time-averaged power are compared. Volumetric thermal lesions were generated by moving the focus of the array in its focal plane along discrete trajectories consisting of two or four concentric circles with a maximum radius of 4 mm. The effect of using the criteria for controlling the thermal dose during treatment and ending the sonication on the shape, volume, and exposure time of generating thermal lesion were analyzed. The acoustic field in tissue was calculated using the Westervelt equation; the temperature field was simulated with the inhomogeneous heat conduction equation; and the lesion boundary was determined according to the thermal dose threshold. In the quasi-linear mode corresponding to the clinical one, thermal diffusion leads to elongation of the lesion by a factor of 2–3 along the beam axis compared to the transverse dimension of the trajectory. The use of pulsed shock-wave exposures with switching off the inner circles of the trajectory as they reach the threshold value of the thermal dose makes it possible to significantly suppress the thermal diffusion effects in the axial direction of the beam and obtain localized thermal lesion of a given shape with a thermal ablation rate comparable to the clinical case.

A volume-averaged model for acoustic streaming induced by focused ultrasound in soft porous media.

Equations describing acoustic streaming in soft, porous media driven by focused ultrasound are derived based on the assumption that acoustic waves pass through the porous material as if it were homogeneous. From these equations, a model that predicts the time-averaged flow on the macroscopic scale, as well as the advective transport of the trace components, is created. The model is used to perform simulations for different shapes of the focused ultrasound beam. For a given shape, and using the paraxial approximation for the ultrasound, the acoustic streaming is found to be linearly proportional to the applied ultrasound intensity, to the permeability of the porous material and to the attenuation coefficient, and inversely proportional to the liquid viscosity. Results from simulations are compared to a simplified expression stating that the dimensionless volumetric liquid flux is equal to the dimensionless acoustic radiation force. This approximation for the acoustic streaming is found to be reasonable near the beam axis for focused ultrasound beam shapes that are long in the axial direction, compared to their width. Finally, a comparison is made between the model and experimental results on acoustic streaming in a gel, and good agreement is found.

Measuring the alveolar bone level in adolescents: A comparison between ultrasound and cone beam computed tomography.

Cone beam computed tomography (CBCT) is an imaging modality, which is used routinely in orthodontic diagnosis and treatment planning but delivers much higher radiation than conventional dental radiographs. Ultrasound is a noninvasive imaging method that creates an image without ionizing radiation. To investigate the reliability of ultrasound and the agreement between ultrasound and CBCT in measuring the alveolar bone level (ABL) on the buccal/labial side of the incisors in adolescent orthodontic patients. One hundred and eighteen incisors from 30 orthodontic adolescent patients were scanned by CBCT with 0.3-mm voxel size and ultrasound at 20 MHz frequency. The ABL, distance from the cementoenamel junction (CEJ) to the alveolar bone crest (ABC), was measured twice to evaluate the agreement between ultrasound and CBCT. In addition, the intra- and inter-rater reliabilities in measuring the ABL by four raters were compared. The mean difference (MD) in the ABL between ultrasound and CBCT was -0.07 mm with 95% limit of agreement (LoA) from -0.47 to 0.32 mm for all teeth. For each jaw, the MDs between the ultrasound and CBCT were -0.18 mm (for mandible with 95% LoA from -0.53 to 0.18 mm) and 0.03 mm (for maxilla with 95% LoA from -0.28 to 0.35 mm). In comparison, ultrasound had higher intra-rater (ICC = 0.83-0.90) and inter-rater reliabilities (ICC = 0.97) in ABL measurement than CBCT (ICC = 0.56-0.78 for intra-rater and ICC = 0.69 for inter-rater reliabilities). CBCT parameters used in orthodontic diagnosis and treatment planning in adolescents may not be a reliable tool to assess the ABL for the mandibular incisors. On the contrary, ultrasound imaging, an ionizing radiation-free, inexpensive, and portable diagnostic tool, has potential to be a reliable diagnostic tool in assessing the ABL in adolescent patients.

Differences in ultrasound elevational beam width (slice thickness) between popular handheld devices

BackgroundHandheld ultrasound devices are increasingly used by medical professionals for bedside ultrasound-guided interventions. Especially for vascular access procedures, the width of the imaging plane, known as the slice thickness or elevational beam width is a prominent source for misinterpretation. A wide slice thickness can lead to the interpretation that 2 objects (i.e. needle and vessel) are on the same plane while in fact they are not and thereby negatively influencing the performance of in-plane ultrasound-guided interventions. Therefore, the beam profiles of three popular handheld US devices are tested and compared to a conventional US device. MethodsThe GE VScan, Philips Lumify and Butterfly IQ ​+ ​are tested using a slice phantom to determine the slice thickness. For comparison, a Philips Affiniti machine was investigated. Both linear and curved array settings were analyzed. In a slice phantom, a diffuse scattering plane at an angle of exactly 45° is scanned. For each imaging depth, the vertical height of the imaged rectangle corresponds to the slice thickness at that depth. Main resultsFor the linear array transducers, the focus depth ranges from 1.5 to 3.5 cm. At the focus depth, all transducers have a reasonable slice thickness of approximately 1 mm. More superficially, the slice thickness varies between 1 and 4 mm. The curved array probes have larger focus depths, ranging from 2.7 to 7.3 cm. The slice thickness at focus depth varies between 1.4 and 3.8 mm, but at 2 cm depth is even more than 5 mm. ConclusionsThe slice thickness of handheld ultrasound transducers varies between the different devices, and can be suboptimal for superficial in-plane ultrasound-guided interventions. The larger slice thickness of the curved array settings may complicate in-plane guidance. Handheld ultrasound users should be aware of the beam characteristics of their devices to optimize guidance for interventions.

Automated defect recognition (ADR) for monitoring industrial components using neural networks with phased array ultrasonic images

In this paper, we propose a framework to automate the process of defect characterizing for industrial structural component health monitoring by implementing automatic defect recognition (ADR) system. The ADR system consists of a convolutional neural network (CNN) and an edge detection algorithm medial axis transform (MAT). The CNN learns the defect feature space from the training dataset to detect and classify the defect. The MAT algorithm is used upon post-validation of the ADR, and the predicted feature’s edges are extracted to size them. The ADR is trained using the simulation-assisted finite element (FE) simulation datasets consisting of side drilled holes (SDH) and crack defects images. The training datasets are generated by introducing virtual array source aperture (VASA), which is a full matrix capture (FMC) scanning strategy by activating the group of elements in an active aperture with predefined focal laws to form a focused beam at a virtual source in the material. The VASA technique uses multiple virtual sources and active aperture positions in a given transducer, which are determined using the Poisson point process. The ultrasound beam is excited in sequence on each virtual source, and the reflected wave is recoded using all the transducers in the array to create FMC A-scans signals. The total focusing method (TFM) technique is a postprocessing algorithm implemented on the FMC signal to generate an image. A large quantity of training datasets is created for each defect by modeling various FE models with varying defect morphology. To create nearly close to experimental images, the experimental noise is introduced in the simulated images. The three separate ADR systems are trained with individual defects class and combined defects. The effectiveness of the trained ADR system is validated by conducting experiments on the plates with laboratory-made SDH and crack defects, the casting components, and weldments with unknown defect types and sizes. The mAP of ADR training is 82%, and the F1-score on testing image classification is 89%. The ADR system could detect and size the smallest defect is 0.219 mm, which is λ L /5.

Effects of high-intensity focused ultrasound combined with levonorgestrel-releasing intrauterine system on patients with adenomyosis

It is very important to treat adenomyosis which may cause infertility, menorrhagia, and dysmenorrhea for women at the reproductive age. High-intensity focused ultrasound (HIFU) is effective in destroying target tumor tissues without damaging the path of the ultrasound beam and surrounding normal tissues. The levonorgestrel-releasing intrauterine system (LN-IUS) is a medical system which is inserted into the uterine to provide medicinal treatment for temporary control of the symptoms caused by adenomyosis. This study was to investigate the effect of HIFU combined with the LN-IUS on adenomyosis. In the HIFU treatment, the parameters of the ultrasound were transmission frequency 0.8 MHz and input power 50–400 W (350 ± 30), and the temperature in the target tissue under these conditions would reach 60–100 °C (85 °C ± 6.3 °C). Size reduction and blood flow signal decrease were used to assess the effect of combined treatment. In this study, 131 patients with adenomyosis treated with HIFU combined with LN-IUS were retrospectively enrolled. The clinical and follow-up data were analyzed. After treatment, the volume of the uterine lesion was significantly decreased with an effective rate of 72.1%, and the adenomyosis blood flow signals were significantly reduced, with an effective rate of 71.3%. At six months, the menstrual cycle was significantly (P < 0.05) decreased from 31.4 ± 3.5 days before treatment to 28.6 ± 1.9 days, the menstrual period was significantly shortened from 7.9 ± 1.2 days before HIFU to 6.5 ± 1.3 days, and the menstrual volume was significantly (P < 0.05) decreased from 100 to 49% ± 13%. The serum hemoglobin significantly (P < 0.05) increased from 90.8 ± 6.2 g/L before treatment to 121.6 ± 10.8 g/L at six months for patients with anemia. Among seventy-two (92.3%) patients who finished the six-month follow-up, sixty-five (90.3%) patients had the dysmenorrhea completely relieved, and the other seven (9.7%) patients had only slight dysmenorrhea which did not affect their daily life. Adverse events occurred in 24 (18.3%) patients without causing severe consequences, including skin burns in two (1.5%) patients, skin swelling in four (3.1%), mild lower abdominal pain and low fever in 15 (11.5%), and subcutaneous induration in three (2.3%). Six months after treatment, no other serious side effects occurred in any patients with follow-up. In conclusions, the use of high-intensity focused ultrasound combined with the levonorgestrel-releasing intrauterine system for the treatment of adenomyosis is safe and effective even though the long-term effect remains to be confirmed.

Beyond Solvothermal: Alternative Synthetic Methods for Covalent Organic Frameworks

AbstractCovalent organic frameworks (COFs) are crystalline porous organic materials that hold a wealth of potential applications across various fields. The development of COFs, however, is significantly impeded by the dearth of efficient synthetic methods. The traditional solvothermal approach, while prevalent, is fraught with challenges such as complicated processes, excessive energy consumption, long reaction times, and limited scalability, rendering it unsuitable for practical applications. The quest for simpler, quicker, more energy‐efficient, and environmentally benign synthetic strategies is thus paramount for bridging the gap between academic COF chemistry and industrial application. This Review provides an overview of the recent advances in alternative COF synthetic methods, with a particular emphasis on energy input. We discuss representative examples of COF synthesis facilitated by microwave, ultrasound, mechanic force, light, plasma, electric field, and electron beam. Perspectives on the advantages and limitations of these methods against the traditional solvothermal approach are highlighted.

Beyond Solvothermal: Alternative Synthetic Methods for Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are crystalline porous organic materials that hold a wealth of potential applications across various fields. The development of COFs, however, is significantly impeded by the dearth of efficient synthetic methods. The traditional solvothermal approach, while prevalent, is fraught with challenges such as complicated processes, excessive energy consumption, long reaction times, and limited scalability, rendering it unsuitable for practical applications. The quest for simpler, quicker, more energy-efficient, and environmentally benign synthetic strategies is thus paramount for bridging the gap between academic COF chemistry and industrial application. This Review provides an overview of the recent advances in alternative COF synthetic methods, with a particular emphasis on energy input. We discuss representative examples of COF synthesis facilitated by microwave, ultrasound, mechanic force, light, plasma, electric field, and electron beam. Perspectives on the advantages and limitations of these methods against the traditional solvothermal approach are highlighted.

Global sonication of the human intracranial space via a jumbo planar transducer

Contrary to conditioning a Focused Ultrasound (FUS) beam to sonicate a localized region of the human brain, the goal of this investigation was to explore the prospect of distributing homogeneous ultrasound energy over the entire brain space with a large cranium-wide ultrasound beam. Recent ultrasound preclincal studies utilizing large or whole brain stimulation regions create a demand for expanding the treatment envelope of transcranial pulsed-low intensity ultrasound towards Global Brain Sonication (GBS) for potential human investigation. Here, we conduct ultrasound field characterizations when transmitting pulsed ultrasound through human skull specimens using a 1–3 piezocomposite planar transducer operating at 464 kHz with an active single-element surface of 30 × 30 cm. Through computational simulation and hydrophone scanning methodology, ultrasound wave behavior and dose homogeneity in the brain space were evaluated under various trajectories of sonication using the planar transducer. Clinically relevant pulse parameters used for transcranial therapeutic ultrasound applications were used in the experiments. Simulations and empirical testing revealed that dose homogeneity and acoustic intensity over the brain space are influenced by sonication trajectory, skull lens effects, and acoustic wave reflections. The transducer can emit a spatial peak pulse average intensity of 4.03 W/cm2 (0.24 MPa) measured in the free-field at 464 kHz with electrical power of 1 kW. The simulation showed that approximately 99 % of the cranial volume was exposed with <30 % of the maximum external acoustic intensity being transmitted into the skull. The transmission loss across all sonication trajectories is similar to previously reported FUS studies. A marker for GBS dose homogeneity is introduced to score the ultrasound pressure field uniformity in the intracranial space. Results of this study identify the initial challenges of exposing the entire human brain space with ultrasound using a large cranium-wide sonication beam intended for global brain therapeutic modulation.

A novel convex acoustic lens-attached ultrasound drug delivery system and its testing in a murine melanoma subcutaneous model

Target-specific drug release is indispensable to improve chemotherapeutic efficacy as it enhances drug uptake and penetration into tumors. Sono-responsive drug-loaded nano-/micro-particles are a promising solution for achieving target specificity by exposing them to ultrasound near tumors. However, the complicated synthetic processes and limited ultrasound (US) exposure conditions, such as limited control of ultrasound focal depth and acoustic power, prevent the practical application of this approach in clinical practice. Here, we propose a convex acoustic lens-attached US (CALUS) as a simple, economic, and efficient alternative of focused US for drug delivery system (DDS) application. The CALUS was characterized both numerically and experimentally using a hydrophone. In vitro, microbubbles (MBs) inside microfluidic channels were destroyed using the CALUS with various acoustic parameters (acoustic pressure [P], pulse repetition frequency [PRF], and duty cycle) and flow velocity. In vivo, tumor inhibition was evaluated using melanoma-bearing mice by characterizing tumor growth rate, animal weight, and intratumoral drug concentration with/without CALUS DDS. US beams were measured to be efficiently converged by CALUS, which was consistent with our simulation results. The acoustic parameters were optimized through the CALUS-induced MB destruction test (P = 2.34 MPa, PRF = 100 kHz, and duty cycle = 9%); this optimal parameter combination successfully induced MB destruction inside the microfluidic channel with an average flow velocity of up to 9.6 cm/s. The CALUS also enhanced the therapeutic effects of an antitumor drug (doxorubicin) in vivo in a murine melanoma model. The combination of the doxorubicin and the CALUS inhibited tumor growth by ∼ 55% more than doxorubicin alone, clearly indicating synergistic antitumor efficacy. Our tumor growth inhibition performance was better than other methods based on drug carriers, even without a time-consuming and complicated chemical synthesis process. This result suggests that our novel, simple, economic, and efficient target-specific DDS may offer a transition from preclinical research to clinical trials and a potential treatment approach for patient-centered healthcare.

Towards High-Resolution Ultrasound Neuromodulation With Crossed-Beam Phased Arrays.

Transcranial focused ultrasound stimulation (tFUS) has emerged as a potential noninvasive therapeutic technology. Due to skull attenuations at high ultrasound (US) frequencies, successful tFUS with sufficient penetration depth requires sub-MHz US waves, leading to relatively poor stimulation specificity particularly in the axial direction (perpendicular to the US transducer). This shortcoming can potentially be overcome by utilizing two individual US beams properly crossed in time and space. For large-scale tFUS, a phased array is also required to dynamically steer focused US beams at desired neural targets. This article presents the theoretical foundation and optimization (through a wave-propagation simulator) of crossed-beam formation using two US phased arrays. It also experimentally validates crossed-beam formation with two custom-made 32-element phased arrays (operating at 555.5 kHz) positioned relatively at different angles. In measurements, the sub-MHz crossed-beam phased arrays achieved 0.8/3.4 mm lateral/axial resolution at a focal distance of ∼ 46 mm, compared to the lateral/axial resolution of 3.4/26.8 mm of the individual phased array at 50 mm focal distance (∼ 28.4-fold improvement in reducing the main focal zone area). The crossed-beam formation in the presence of a rat skull and a tissue layer was also validated in the measurements.

ISUOG Practice Guidelines (updated): fetal cardiac screening.

ISUOG Practice Guidelines (updated): fetal cardiac screening.

Characterization of high intensity progressive ultrasound beams in air at 300 kHz.

The majority of reported measurements on high intensity ultrasound beams in air are below 40 kHz and performed on standing waves inside of a guide. Here, experimental characterization of high intensity progressive and divergent sound beams in air at 300 kHz are presented. Measurements in this frequency range are challenging. Accurate characterization of high intensity sound beams requires a measurement bandwidth at least ten times the beam's primary frequency, as high intensity soundwaves steepen and form shocks and, therefore, contain significant signal power at harmonic frequencies. Hence, a measurement bandwidth of at least 3 MHz is required. Calibrated measurement microphones are generally not available in this frequency range. This limitation has been overcome by using a hydrophone with a calibrated response from 250 kHz to 20 MHz. A narrowband piezoelectric transducer is used as the source in this study, and it is capable of generating tone burst waveforms centered at 300 kHz with 160 dB sound pressure level surface pressure. Cumulative wave steepening and shock formation are observed in on-axis measurements. The source's surface vibration profile is measured using a scanning laser Doppler vibrometer, and the vibration profile is imported into a numerical wide-angle Khokhlov-Zabolotskaya-Kuznetsov simulation for comparison against measured on-axis waveforms.

Influence of cerebrospinal fluid on power absorption during transcranial magnetic resonance-guided focused ultrasound treatment.

Ultrasound beam aberration correction is vital when focusing ultrasound through the skull bone in transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) applications. Current methods make transducer element phase adjustments to compensate for the variation in skull properties (shape, thickness, and acoustic properties), but do not account for variations in the internal brain anatomy. Our objective is to investigate the effect of cerebrospinal fluid (CSF) and brain anatomy on beam focusing in tcMRgFUS treatments. Simulations were conducted with imaging data from 20 patients previously treated with focused ultrasound for disabling tremor. The Hybrid Angular Spectrum (HAS) method was used to test the effect of including cerebral spinal fluid (CSF) and brain anatomy in determining the element phases used for aberration correction and beam focusing. Computer tomography (CT) and magnetic resonance imaging (MRI) images from patient treatments were used to construct a segmented model of each patient's head. The segmented model for treatment simulation consisted of water, skin, fat, brain, CSF, diploë, and cortical bone. Transducer element phases used for treatment simulation were determined using time reversal from the desired focus, generating a set of phases assuming a homogeneous brain in the intracranial volume, and a second set of phases assigning CSF acoustic properties to regions of CSF. In addition, for three patients, the relative effect of separately including CSF speed of sound values compared to CSF attenuation values was found. We found that including CSF acoustic properties (speed of sound and attenuation) during phase planning compared to phase correction without considering CSF increased the absorbed ultrasound power density ratios at the focus over a range of 1.06 to 1.29 (mean of 17%±6%) for 20 patients. Separately considering the CSF speed of sound and CSF attenuation showed that the increase was due almost entirely to including the CSF speed of sound; considering only the CSF attenuation had a negligible effect. Based on HAS simulations, treatment planning phase determination using morphologically realistic CSF and brain anatomy yielded an increase of up to 29% in the ultrasound focal absorbed power density. Future work will be required to validate the CSF simulations.

Eyebrow Lifting From High-Intensity, High-Frequency, Parallel Ultrasound Beams.

Wang, Jordan V. MD, MBE, MBA*; Bajaj, Shirin MD*; Kauvar, Arielle MD†,‡; Geronemus, Roy G. MD*,† Author Information